REGIONAL GROUNDWATER QUALITY AND SURFACE WATER …€¦ · 5. Nitrogen inputs to groundwater and...
Transcript of REGIONAL GROUNDWATER QUALITY AND SURFACE WATER …€¦ · 5. Nitrogen inputs to groundwater and...
REGIONAL GROUNDWATER QUALITY AND SURFACE WATER QUALITY
MODEL OF THE RUATANIWHA PLAINS
White, P.A. Institute of Geological and Nuclear Sciences, Private Bag 2000, Wairakei, Taupo.
Daughney, C. Institute of Geological and Nuclear Sciences, P O Box 30368, Lower Hutt.
HBRC Publication No. 4836Report No. SD16-08
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Contents
i List of Figures
ii List of Tables
1. Introduction
2. Review
3. Land use scenarios
4. Chemical conditions in groundwater
5. Nitrogen inputs to groundwater and landuse
6. Groundwater flow model
7. Groundwater quality and surface water quality model
7.1 Design
7.2 Model components
7.3 Nitrogen loading
7.4 Non-irrigated and irrigated models
7.5 Estimation of nitrogen concentrations – steady state
7.6 Checks on the mass balance equations
7.7 Transient calculations
7.8 Model calibration
7.8.1 Surface water
7.8.2 Groundwater
8. Nitrogen concentrations without irrigation
9. Nitrogen inputs and outputs
9.1 Current land use
9.2 Irrigated pasture
9.3 Irrigated crops and irrigated dairy
10. Nitrogen concentrations with irrigation
10.1 Irrigated pasture
10.2 Irrigated crops and irrigated dairy
11. Nitrogen concentrations in rivers over 20 years
11.1 River and stream flow means
11.2 Flows used in mixing calculations
11.2.1 Waipawa @ RD5, site 23235
11.2.2 Tukituki @ Tapairu Rd, site 23207
11.2.3 Kahahakuri @ Ongaonga, site 23248
11.3 Calculated nitrogen fluxes
11.4 Calculated surface water flows
11.5 Calculated river and stream nitrogen concentrations
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11.5.1 92 kgN/ha/yr irrigation
11.5.2 17 kgN/ha/yr irrigation
12. Ruataniwha Plains monitoring network
12.1 Surface-water monitoring
12.2 Groundwater monitoring
13. Conclusions
14. References
Appendix 1. Copy of contract
Appendix 2. Hydrological data used in this study
Appendix 3. Mean flow and mean water chemistry values
Appendix 4. Contents of Excel spreadsheets and worksheets.
A4.1 Excel spreadsheet Ruasteadystate.xls
A4.2 Excel spreadsheet Ruagwflux.xls
A4.3 Excel spreadsheet Ruagwqualtrans.xls
A4.4 Excel spreadsheet Ruasurfflowdist.xls
A4.5 Excel spreadsheet Ruawurfqualtrans.xls
A4.6 Excel spreadsheet Ruagwfluxirri.xls
A4.7 Excel spreadsheet Ruagwqualtransirri.xls
A4.8 Excel spreadsheet Ruasurfflowdistirri.xls
A4.9 Excel spreadsheet Ruasurfqualtransirri.xls
Appendix 5. Operation of the Excel spreadsheets
1.0 Nitrogen loading
1.1 Background nitrogen loading
1.2 „Irrigation‟ nitrogen
1.3 „Point source‟ nitrogen
2.0 Nitrogen balance
3.0 Surface water quality predictions
4.0 Groundwater quality predictions
5.0 Maintenance of spreadsheets
5.1 Changing groundwater flow velocities
5.2 Changing observed surface water and groundwater nitrogen concentrations
5.3 Adjusting the capture zones for surface water monitoring sites and groundwater
5.4 Adding new surface water or groundwater zones
5.5 Update seepage velocities in „transient‟ calculations
5.5.1 Groundwater travel times to monitoring wells
5.5.2 Travel times to surface water monitoring sites
5.5.3 Transient calculations
6.0 Assumptions
6.1 Surface water zones
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6.2 Groundwater capture
6.3 Mixing in surface water
6.4 Groundwater mixing ratio
6.5 Water balance
6.6 Chemistry balance
7.0 Spreadsheet security
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LIST OF FIGURES
Figure 1. Ruataniwha Plains and location of rivers, streams and roads
Figure 2. Ruataniwha Plains - 20 m contours
Figure 3. Regions of the Ruataniwha Plains where rivers and streams gain and lose flow
Figure 4. Rivers, streams and overall ranking (after Sarrazin, 2002)
Figure 5. Groundwater flow model grid of the Ruataniwha Plains with contours of predicted
groundwater level
Figure 6. Scatter plot of ammonium vs. nitrate concentrations in Ruataniwha groundwater
samples
Figure 7. Scatter plot of nitrate vs. total nitrogen concentration for Ruataniwha groundwater
samples with more than 0.1 mg/l nitrate
Figure 8. Scatter plot of ammonium vs. total nitrogen concentrations for Ruataniwha
groundwater samples with less than 0.1 mg/l nitrate
Figure 9. Scatter plot of nitrate concentration vs. well depth for Ruataniwha groundwater
samples
Figure 10. Location of surface-water zones
Figure 11. Location of surface-water monitoring sites
Figure 12. Location of groundwater capture zones
Figure 13. Location of groundwater monitoring sites
Figure 14. Estimated seepage velocity across the Ruataniwha Plains (m/day), non-irrigated
model
Figure 15. Estimated seepage velocity across the Ruataniwha Plains (m/day), irrigated model
Figure 16. Predicted weekly nitrogen concentration in the Waipawa River @ RD5 with a 92
kgN/ha/yr irrigation.
Figure 17. Predicted weekly nitrogen concentration in the Tukituki River @ Tapairu Rd with a
92 kgN/ha/yr irrigation.
Figure 18. Predicted weekly nitrogen concentration in the Kahahakuri @ Ongaonga with a 92
kgN/ha/yr irrigation.
Figure 19. Predicted weekly nitrogen concentration in the Waipawa River @ RDS with a
17 kgN/ha/yr irrigation.
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Figure 20. Predicted weekly nitrogen concentration in the Tukituki River @ Tapairu Rd with a
17 kgN/ha/yr irrigation.
Figure 21. Predicted weekly nitrogen concentration in the Kahahakuri @ Ongaonga with a
17 kgN/ha/yr irrigation.
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LIST OF TABLES
Table 1. Proxy variable to use for total nitrogen concentration.
Table 2. Zone loads and predicted surface water quality, steady-state.
Table 3. River N concentrations used in the model.
Table 4. Zone loads and predicted groundwater quality assuming full mixing.
Table 5. Zone loads and predicted groundwater quality assuming partial mixing.
Table 6. Nitrogen leaching for various land uses (HortResearch pers. comm.)
Table 7. Surface water quality with a nitrogen loading of 16 kgN/ha/yr to Ruataniwha Plains
irrigable area
Table 8. Surface water quality with a nitrogen loading of 43 kgN/ha/yr to Ruataniwha Plains
irrigable area
Table 9. Surface water quality with a nitrogen loading of 98 kgN/ha/yr to Ruataniwha Plains
irrigable area
Table 10. Surface water quality with a nitrogen loading of 176 kgN/ha/yr to Ruataniwha Plains
irrigable area
Table 11. Groundwater quality with a nitrogen loading of 176 kgN/ha/yr to all irrigable cells
Table 12. Mean nitrogen concentrations in streams over 50 years due to N loading of
16 kgN/ha/yr to all irrigable cells
Table 13. Mean nitrogen concentrations in streams over 50 years due to N loading of
43 kgN/ha/yr to all irrigable cells
Table 14. Mean nitrogen concentrations in streams over 50 years due to N loading of
98 kgN/ha/yr to all irrigable cells
Table 15. Mean nitrogen concentrations in streams over 50 years due to N loading of
176 kgN/ha/yr to all irrigable cells
Table 16. Calculated nitrogen balance with existing land use
Table 17. Nitrogen balance with existing land use plus 17 kgN/ha/yr, equivalent to an irrigated
beef land use, over the irrigable area of the Ruataniwha Plains
Table 18. Nitrogen balance with existing land use plus 92 kgN/ha/yr, equivalent to irrigated
crops and irrigated dairy, over the irrigable area of the Ruataniwha Plains
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Table 19. Steady-state mean surface water nitrogen concentrations with a loading of
17 kgN/ha/yr and irrigation.
Table 20. Steady-state mean groundwater nitrogen concentrations with a loading of
17 kgN/ha/yr and irrigation and partial mixing.
Table 21. Nitrogen concentrations in surface water over 50 years, loading of 17 kgN/ha/yr and
irrigation.
Table 22. Nitrogen concentrations in groundwater over 50 years, loading of 17 kgN/ha/yr and
irrigation, assuming full mixing.
Table 23. Nitrogen concentrations in groundwater over 50 years, loading of 17 kgN/ha/yr and
irrigation, assuming partial mixing.
Table 24. Surface water nitrogen concentrations with a 92 kgN/ha/yr loading and irrigation.
Table 25. Groundwater nitrogen concentrations with a 92 kgN/ha/yr loading and irrigation and
partial mixing.
Table 26. Nitrogen concentrations in surface water over 50 years, 92 kgN/ha/yr loading and
irrigation.
Table 27. Nitrogen concentrations in groundwater over 50 years, 92 kgN/ha/yr loading and
irrigation and partial mixing.
Table 28. Nitrogen concentration in three rivers and streams over 20 years due to irrigation of
92 kgN/ha/yr.
Table 29. Nitrogen concentration in three rivers and streams over 20 years due to irrigation of
17 kg N/ha/yr.
Table 30. Surface water sub-zones and „unique‟ identification of land use effects.
Table 31. Surface water quality network that could allow the monitoring of land use in each
subzone.
Table 32. Monitoring network that allows measurement of nitrogen entering the Ruataniwha
Plains through rivers and streams.
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Appendix 2
Table A2.1 Surface water hydrological data in TIDEDA file Rpflow.mtd.
Table A2.2 Groundwater hydrological data in TIDEDA file RPGWMan.mtd.
Table A2.3 Groundwater hydrological data in TIDEDA file RPGWAuto.mtd.
Table A2.4 Water chemistry – groundwater sites.
Table A2.5 Water chemistry – surface water sites.
Appendix 3
Table A3.1 Mean flow from TIDEDA records.
Table A3.2 Mean flows estimated by Geoff Wood from available gaugings or correlations.
Table A3.3 Mean nitrogen concentrations in groundwater.
Table A3.4 Mean nitrogen concentrations in surface water.
Appendix 4
Table A4.1. Location of surface water zones.
Table A4.2. Hawkes Bay Regional Council surface water quality monitoring sites.
Table A4.3. Groundwater capture zones and monitoring wells.
Table A4.4. Summary of all nitrogen loadings to the Ruataniwha Plains.
Table A4.5. Nitrogen loadings to land in Zone 1.
Table A4.6. Nitrogen application from irrigation.
Table A4.7. Nitrogen applications used in Table 7.
Table A4.8. Site-by-site nitrogen summary on the N point worksheet.
Table A4.9. Stream number and stream name.
Table A5.1 Entering nitrogen loadings in surface water zones, Nbkg worksheet.
Table A5.2 Example of estimation of nitrogen concentration of surface water monitoring site 26,
„Nbkg‟ worksheet.
Table A5.3 Example of estimation of nitrogen concentration of groundwater at site 222, „Nbkg‟
worksheet.
Table A5.4 Example of land use loadings of zone 19, „Nirri‟ worksheet.
Table A5.5 Example of an error in entering the land use areas for zone 19, „Nirri‟ worksheet.
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Table A5.6 Example of nitrogen balance calculations, „Nsummary‟ worksheet.
Table A5.7 Example of stream nitrogen concentrations, „Nbkgrd‟ worksheet.
Table A5.8 Example of stream nitrogen concentrations, „Npoint‟ worksheet.
Table A5.9 Example of groundwater nitrogen concentrations „Nbkgrd‟ worksheet.
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1.0 INTRODUCTION
The Ruataniwha Plains, Hawkes Bay, New Zealand is an area of approximately 31000 ha
farmland. The area regularly suffers from agricultural drought in summer, in common with
other regions on the east coast of the North Island and South Island.
Development pressures in the area have led to investigations into water demand for irrigation,
and investigations into water availability from surface water and groundwater. These
pressures have also led the Hawkes Bay Regional Council to investigate the potential risks to
the environment of future developments.
This reports assesses the effects of land use on surface water and groundwater quality, in
particular nitrogen applications to land. One common effect of development is an increase in
nitrogen concentrations in surface water and groundwater from infiltration of surface
application of fertilisers, animal wastes, etc. to groundwater and then to surface water.
Residence time in groundwater systems can be relatively long (decades) so this lag in the
system needs to be considered when predicting the effects of land use on water quality.
These effects are modelled with a set of Excel spreadsheets that combine existing data
including: surface water quality, surface water quantity, aquifer geometry, groundwater
quantity, groundwater quality and land use. The model uses groundwater quantity predictions
from a groundwater flow model, irrigation recharge from an irrigation model, and predictions
of nitrogen discharge from a land use model. All these data are combined to predict surface
and groundwater nitrate-nitrogen concentrations for a number of potential sub-regional
development options. This model has been developed for evaluation of the effects of existing
land use, irrigation, and point sources on nitrogen levels in surface water and groundwater.
This report summarises the input data to the model, the model datasets, and predicts nitrogen
concentrations Ruataniwha Plains surface water and groundwater over time. The report also
outlines operation of the Excel spreadsheets and discusses some of the assumptions used in
designing the model.
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2.0 REVIEW
Hawkes Bay Regional Council (2000, page 21) reported 18 nitrate concentrations in the
Ruataniwha Plains groundwater. Fifteen of these had mean nitrate concentrations less than
1 mg L-1
. Two wells had concentrations between 1 and 3 mg L-1
; one well had a
concentration in the range 3 to 5 mg L-1
. Nitrate concentrations were tending to increase in 8
of the 18 wells, and tending to decrease in 9 of the 18 wells.
Hawkes Bay Regional Council (2001, page 39) report nitrate concentrations in 11 Ruataniwha
wells. Nine wells had groundwater with nitrate concentrations of 0-1.9 mg L-1
and two wells
had groundwater with nitrate concentrations of 3 to 6 mg L-1
. Four surface water quality
measurements are reported for the Ruataniwha Plains in 2000/2001 (Hawkes Bay Regional
Council 2001, page 25). One site had a median concentration in the range 0.1 to 0.15 mg L-1
,
one site had median concentrations of 0.1 to 0.5 mg L-1
and two sites had median
concentrations between 0.51 and 1.0 mg L-1
. Hawkes Bay Regional Council (1998, page
74ff) report nitrate concentrations at low flows. Mean nitrate-nitrogen concentrations were in
the range 0.54 to 1.72 mg L-1
in Mangaonuku Stream. In general, mean nitrate concentration
for Ruataniwha Plains rivers range from below detection limit (upper Waipawa River) to 3.6
mg/L (Porangahau Stream). Concentrations are typically higher in the south western area of
the plains, most likely due to a combination of land use and underlying geology.
Groundwater flow directions in the Ruataniwha Plains are broadly towards the south east
(Hawkes Bay Regional Council, 1999 and Luba, 2001) converging on the Waipawa River and
Tukituki River gorges. West of line running approximately from Tikokino to Takapau the
groundwater elevation tends to decline with increasing depth (Brookes pers. comm.)
indicating a vertical-downwards component of groundwater flow. Groundwater level
elevation tends to increase with depth east of a line approximately between Tikokino and
Takapau indicating a vertical-upwards component of groundwater flow (Hawkes Bay
Regional Council, 1999 and Luba, 2001). Low-flow gaugings in February 1973 (Hawkes Bay
Regional Council, 1999) and Wood (pers. comm. 2002) identify sections of the Mangaonuku,
Waipawa, Tukituki, Tukipo, and Makaretu rivers that gain and lose flow (Fig. 3). The
Waipawa and Tukituki rivers lose water for most of their riverbed across the Ruataniwha
Plains. These rivers both gain flow in the lower plains between each rivers‟ gorge and
approximately 3 km upstream. Other rivers also tend to gain water in the lower sections of
the Ruataniwha Plains. Loris (pers.comm.) identifies a section of the lower Kahahakuri
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Stream that consistently gains water. Sarrazin (2002) identifies the Ongaonga Stream gaining
water blow Ongaonga township.
Tertiary geological units are interpreted by Hawkes Bay Regional Council (2001) to occur
under the Ruataniwha Plains in a synclinal structure. Quaternary gravels (Hawkes Bay
Regional Council, 2001) are interpreted as in-filling the synclinal structure.
Sarrazin (2002) summarises river and stream-habitats in the Ruataniwha Plains (e.g. Fig. 4).
Rivers and streams are also identified as: „groundwater recharged‟, „groundwater and
catchment recharged‟, and „catchment recharged‟. Streams that are classified with some
component of groundwater recharge include: streams on the Mangaonuku Stream above the
confluence with the Waipawa River, Kahakuri, Ongaonga. Waipawamate, Black Stream,
Maharakeke, and small streams on the Tukipo above the confluence with the Makaretu River.
The potentially-irrigable land area in the Ruataniwha Plains is estimated at 35,100 ha (Lincoln
Ventures, 2002). It is estimated that a maximum irrigation rate of 0.21 L s-1
ha-1
is required
for grape production and a maximum irrigation rate of 0.49 L s-1
ha-1
is required for intensive
pastoral farming and cropping. Seasonal requirements for irrigation are between 450 mm
year-1
in the west to 660 mm year-1
in the drier eastern areas.
Annual drainage is predicted for five landuses (Lincoln Ventures, 2002). Extensive non-
irrigated pasture, irrigated cropping, mixed cropping, grapes and mixed cropping, and grapes
and irrigated pasture are associated with drainage between 200 mm year-1
and 1600 mm
year-1
.
Groundwater generally travels in a NW to SE direction across the plains (Fig. 5 shows
contours of groundwater level). All groundwater in the plains would discharge through the
Waipawa and Tukituki gorges with the (reasonable) assumption of an impermeable geological
base to the plains.
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4.0 CHEMICAL CONDITIONS IN GROUNDWATER
The form of nitrogen in groundwater is strongly dependent on microbial processes (Chapelle,
1993). Under aerobic conditions, nitrate (NO3) is the dominant form of nitrogen, typically
being produced by oxidation of more reduced forms of nitrogen. Under anaerobic conditions,
ammonium (NH4) is the dominant forms of nitrogen, being produced by reduction of nitrate.
In addition to nitrate and ammonium, groundwaters typically contain minor components of
organic nitrogen, which is present in biological materials such as proteins and nitrite which is
an intermediate in the oxidation of NH4 to NO3.
Because nitrogen can exist as nitrate, nitrite, ammonium or organic nitrogen, a model of
nitrogen transport in groundwater should consider the total concentration of nitrogen, rather
than just one of these species. Unfortunately, the total nitrogen concentration has not been
measured for most groundwater samples from the Ruataniwha Plains. Hence a proxy for total
nitrogen concentration is required for modelling purposes.
Analysis of groundwater samples from wells on the Ruataniwha Plains clearly show that the
majority of groundwaters are either strongly oxidising, and therefore contain almost
exclusively nitrate, or are strongly reducing, and thus contain almost exclusively ammonium
(Figure 6). This relationship can also be presented by comparing the concentrations of nitrate
and ammonium to the concentration of total nitrogen (note that total nitrogen has not been
analysed for every sample). For samples that contain more than 0.1 mg/l nitrate, there is a
very good correlation between nitrate and total nitrogen (r2 = 0.99, n = 75), indicating that
almost all nitrogen is present as nitrate (Figure 7). For this same set of samples (NO3 > 0.1
mg/l), there is a very poor correlation between ammonium and total nitrate (r2 = 0.1, n = 56),
implying that very little of the nitrogen exists as ammonium. Conversely, for all groundwater
samples with less than 0.1 mg/L nitrate, total nitrogen is well correlated to ammonium
concentration (r2 = 0.92, n = 35) (Figure 8), but poorly correlated to nitrate concentration (r
2 =
0.03, n = 36). The importance of organic nitrogen in the Ruataniwha groundwaters is not
clear, because for most samples it has not been analysed.
Thus for the purpose of water quality modelling, nitrate or ammonium concentration can be
used to proxy total nitrogen concentration. For samples with more than 0.1 mg/L nitrate, the
nitrate concentration is a good proxy for total nitrogen concentration. For samples with less
than 0.1 mg/L nitrate, ammonium is a better proxy for total nitrogen concentration. Table 1
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shows which of the two proxy variables should be employed for nitrogen transport modelling,
in cases where a total nitrogen concentration is not available.
Table 1. Proxy variable to use for total nitrogen concentration.
SiteID Depth Proxy
133 NO3
134 NO3
135 NO3
136 NO3
137 30 NO3
138 NO3
145 NO3
146 12.4 NO3
147 NO3
220 45.7 NO3
221 57.3 NO3
222 21.8 NO3
223 55.5 NO3
224 75 NH4
225 52 NO3
226 25.2 NH4
227 45 NH4
229 24.4 NH4
230 65.9 NH4
231 22.6 NO3
233 46.3 NO3
234 53 NH4
235 88.2 NH4
236 65.8 NO3
237 110 NH4
239 142 NH4
243 NH4
1365 ~30 NH4
1377 7 NO3
1385 2 NO3
1497 NO3
2224 5.3 NH4
2227 NO3
2229 NO3
2387 30 NO3
2597 NO3
2598 NO3
2599 NO3
Because the nitrate-ammonium conversion is controlled by the oxidation state of the
groundwater, it is logical that there should be a relationship between nitrate concentration and
the depth from which the groundwater was extracted. There is a greater probability of finding
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elevated nitrate concentrations in shallow wells than in deeper wells (Figure 9). Similarly,
there is a greater probability of elevated ammonium concentrations in deeper wells. Note that
these relationships are probabilistic, not deterministic, and so they have limited use in water
quality modelling. In other words, nitrate on its own is not a conservative indicator of total
nitrogen, even if well depth is taken into consideration.
Wells with the highest nitrate-nitrogen concentration (Table A3.3) have not been sampled for
a considerable period. For example:
well 133, mean 21.6 mg/L, last sampled 1992
well 135, mean 13.8 mg/L, last sampled 1992
well 136, mean 14.03 mg/L, last sampled 1995
well 138, mean 31.5 mg/L, last sampled 1995
well 223, mean 6.26 mg/L, last sampled 1997
well 1377, mean 22.6 mg/L, last sampled 1989
well 1385, mean 10.4 mg/L, last sampled 1995
It is recommended that these wells are re-sampled to identify current groundwater quality.
Well 1487, last sampled in 1987 could also be re-sampled.
6.0 GROUNDWATER FLOW MODEL
Murray (2002) describes the groundwater flow model (Fig. 5) of the Ruataniwha Plains:
“The model grid is a single layer with 80 rows and 100 columns. The grid interval is
500 m… Active cells cover all the Ruataniwha Plains underlain by gravels, and in the east,
the north and the south, extend to the watersheds of the Waipawa and Tukituki Rivers. In the
west the grid boundary extends beyond the limits of the gravels to exclude the hill and
mountain catchments of the Makaroro, Waipawa, Tukituki and Makaretu Rivers above Burnt
Bridge, Pendle Hill, Folgers, Rd, and Pagetts Rd stage recording sites respectively.”
“The active grid within these boundaries contains 3719 cells, equivalent to 92,975 ha” and
34,600 ha of this area is irrigated in the model simulating irrigation scenarios.
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“Elevation of the base of the gravel aquifer in the model ranges from 77 m below sea level in
the vicinity of Linburn Road between the Waipawa and Mangaonuku Rivers, and rises to
more than 260 m above sea level in the hill country in the north and west of the basin. In the
irrigable area of the plains, gravel thickness ranges from 45 m to more than 200 m.”
The model layer is treated as unconfined, although there is some evidence that confined
aquifers occur on the Ruataniwha Plains. Water is input to the model through rainfall
recharge and rivers. Rainfall recharge is estimated from daily „percolation below the root
zone from specific soil types and in annual rainfall zones‟. Stream-groundwater interaction is
determined from the relative heights of the stream and the groundwater system. The model
simulates interaction of groundwater with the Mangaonuku Stream, and four short-length
tributaries, the Waipawa River, Makaroro River, Kahahakuri Stream (lower reaches),
Tukituki River, Tukipo River (and two of its tributaries), Makaretu River, Porangahau
Stream, and the Maharakeke Stream. Water also enters the model across the western
boundary from flow in the Makaroro River, Waipawa River, Tukituki River and Makaretu
River.
Water is lost from the model through pumping and river discharge. All the discharge from the
groundwater system, and rivers, is modelled as discharging through the Waipawa River gorge
and Tukituki River gorge.
The groundwater flow model is calibrated to river loss using a series of gaugings on the
Waipawa, Tukituki, and Makaretu Rivers. Calibration uses aquifer hydraulic conductivity,
stream bed conductance, specific yield and zonal hydraulic conductivity distributions to
match the observed stream depletion and the range in groundwater levels.
7.0 GROUNDWATER QUALITY AND SURFACE WATER QUALITY MODEL
7.1 Design
The model uses datasets that represent the Ruataniwha Plains area, stream flow, groundwater
flow, stream quality, groundwater quality, and landuse. Microsoft Excel is used to link these
datasets to allow users flexibility in the assessment of land use effects on surface water and
groundwater.
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The datasets and spreadsheets that form the model are described in detail in Appendix 4.
Follows an outline of the key components of the model.
7.2 Model components
The Ruataniwha Plains and surrounds are represented in this model by a 40 km-by-50 km
model with a grid of 500 m-by-500 m cells. This model has the same extents, and cell size, as
the Ruataniwha Plains groundwater flow model (Fig. 5).
Three major surface-hydrology zones are defined on the Ruataniwha Plains based on the
pattern of river losses and gains (Fig. 3), water quality ranking of streams (Fig. 4) and
groundwater flow directions (Fig. 5). This aims to associate land-use areas in the plains with
surface water quality, and groundwater quality, monitoring sites.
Three „major‟ land-use zones are defined:
Zone 1: Land that drains through streams or groundwater, to the Waipawa River.
Zone 2: Land that drains, through streams or groundwater, to the Tukituki River,
excluding the Tukipo River.
Zone 3: Land that drains, through streams or groundwater, to the Tukipo River.
These zones are further sub-divided (Fig. 10) into zones where surface water monitoring sites
may reflect the land use in the zone.
Surface water monitoring sites are chosen from the HBRC monitoring network (Fig. 11).
Generally monitoring sites are chosen in sections of river that are gaining flow. This is
because sections of river that are gaining flow likely to represent, at least in part, the water
quality effects of land use in zone.
Groundwater capture zones (Fig. 12) are defined based on the groundwater flow directions
derived from groundwater levels predicted by the groundwater flow model (Fig. 5). The up-
gradient end of the capture zone is generally taken as a hydrogeological boundary, e.g.
impermeable boundary or river boundary.
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Groundwater monitoring sites are chosen from the HBRC monitoring network (Fig. 13). One
capture zone is assigned to each well.
Groundwater seepage residence time is a significant control on the long-term response of
surface water quality, and groundwater quality, to land use. Estimates of groundwater
seepage velocity (e.g. Fig. 14 and Fig. 15) are used to calculate the area of land that will
contribute to surface water, and groundwater quality on estimates of transient water trends.
7.3 Nitrogen loading
The model allows zones, or individual cells, to be loaded with nitrogen. Nitrogen application
rates to land are expressed as kgN/ha/yr. Nitrogen can also be loaded to rivers as a
„background‟ concentration (in mg/L) representing the mean concentration that each river
begins its crossing of the Ruataniwha Plains.
There are three methods to load nitrogen onto the cells: „background‟, „irrigation‟, or just
„point‟ source.
„Background‟ nitrogen concentrations aim to represent observed nitrogen concentrations in
surface water and groundwater. „Irrigated‟ nitrogen concentrations aim to predict the effects
of land use change in the Ruataniwha Plains on top of the „background‟ land use. Nitrogen is
„applied‟ to the sub zones (Fig. 10) in three land uses. The land area and nitrogen application
rates are selectable by the user. Nitrogen applications at „point‟ sources are through
individual cells in the model. The rates of nitrogen application and locations of cells are
selectable by the user in a worksheet representing the Ruataniwha Plains.
7.4 Non-irrigated and irrigated models
Groundwater flow model predictions of groundwater flow rates without irrigation (Fig. 14)
and with irrigation (Fig. 15) are used to identify the areas of land that are contributing
nitrogen to surface water and groundwater monitoring sites within defined time periods.
Estimates of groundwater flow volumes calculated by these models are used in the estimates
of groundwater nitrogen concentrations.
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7.5 Estimation of nitrogen concentrations – steady state
Mass balance equations are used to calculate nitrogen concentrations in rivers. Equations for
rivers crossing the Ruataniwha Plains take the form:
MS MU + ML
MS nitrogen mass passing the monitoring point (mass/time)
MU nitrogen mass in the river as the river enters the Ruataniwha Plains (=0 for
streams that rise in the plains) (mass/time)
ML nitrogen mass from land use. This is the net nitrogen mass passing out of the
soil (mass/time)
Masses are calculated from observed nitrogen concentrations and observed, or estimated,
river/stream flow rates. An aim in designing the sub-zones (Fig. 10) is that one stream water
flow monitoring site and one stream water quality monitoring sites (gaining streams) would
represent the effects of land use in that sub-zone. Unfortunately this could not be achieved as:
a number of sub-zones, where there is a case for landuse in a sub-zone having an influence on
surface water quality, do not have monitoring sites; and a number of surface water quantity
monitoring sites have no measurements of water quality and vice-versa.
The concentrations of nitrogen in surface water at the monitoring site is:
CS = MS/MSW
CS concentration of N in surface water
MSW mass of water passing the monitoring point (mass/time)
It is assumed that the nitrogen is fully mixed in the surface water.
The concentrations of nitrogen in groundwater is:
CG = MG/MW
CG concentration of N in groundwater
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MG mass of nitrogen loaded to groundwater within the capture zone (mass/time)
MW mass of water passing the cell representing the groundwater monitoring site
(mass/time)
Nitrogen in groundwater is commonly not fully mixed within the formation, for example
nitrogen concentrations generally decline with depth on the Ruataniwha Plains (Fig. 9). This
is investigated in Section 7.8.
7.6 Checks on the mass balance equations
Background, irrigated, and point source applications in the Ruataniwha Plains model are
summarised in a model worksheet:
NIn = NU + NB + NI + NP
NOut = NW + NT
All units are kgN/yr
NIn nitrogen inputs to the Ruataniwha Plains
NU nitrogen entering through upstream boundary
NB nitrogen from „background‟ land use
NI nitrogen from „irrigated‟ land use
NP nitrogen from point sources
NOut nitrogen output from the Ruataniwha Plains
NW nitrogen leaving the Ruataniwha Plains through the Waipawa River
NT nitrogen leaving the Ruataniwha Plains through the Tukituki River
The difference between NIn and NOut, calculated on the worksheet, should be less than 1%.
Differences between these two numbers should only arise due to rounding errors in the
spreadsheets.
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7.7 Transient calculations
The model allows the prediction of long-term response of nitrogen concentrations in surface
water and groundwater. It does this by determining the land-use cells that are within a
specified time. This is calculated from the groundwater seepage velocities in the Ruataniwha
Plains (non-irrigated and irrigated). The user can investigate longer-term trends in
groundwater quality in weekly (or longer time interval) time-steps. The calculations are of
transient stream concentrations considering land use to be constant. The „transient‟ look of
the calculated nitrate concentrations is because the stream flow diluting nitrogen inputs is
transient.
7.8 Model calibration
7.8.1 Surface water
The model is calibrated to existing mean surface water quality measurements (Appendix 3) at
14 sites.
The nitrogen loadings (as kg N/ha/yr) to sub-zones are adjusted manually to produce the best
comparison between predicted surface water nitrogen concentrations and observed surface
water nitrogen concentrations.
Some subzones are uniquely associated with one monitoring point and therefore nitrogen
loadings are uniquely associated with surface water quality. For example, surface water zone
16 is associated with monitoring site 273 and a loading of 4 kgN/ha/yr to subzone 16 is
associated with a nitrogen concentration of 1.08 mg/L at site 273 (Table 2). Other monitoring
sites are associated with a number of zones; for example monitoring site 26 combines the land
use of zones 16, 17, 18 and 19. Therefore the nitrogen concentration at site 26 is a
combination of loadings from the four subzones and the loadings for each subzone are not
uniquely identifiable.
One aim of the design of sub-regional boundaries is to relate land use and water quality in the
Ruataniwha Plains by a „tree structure‟ of sub-zones and monitoring sites. However, nitrogen
loadings could not be estimated uniquely because a number of sub-zones are not uniquely
associated with a monitoring site. Subzones with non-unique estimates of nitrogen loading
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are: 11, 12, 13, 14, 15, 17, 18, 19, 21, 23, 25, 31, 33, 36, 37, 38 and 39. A monitoring
network that could give unique estimates of nitrogen loadings is outlined in Section 12.
The process of model calibration is summarised for the catchment of the Waipawa River:
set nitrogen concentrations and river flows of rivers and streams (Mangamate,
Mangaonuku, Waipawa) based on observations
set nitrogen concentration and river flows at monitoring sites
set nitrogen loadings of „up-catchment‟, unmonitored sub-zones:
- sub zone 11 0.5 kg N/ha/yr
- sub zone 12 0.5 kg N/ha/yr
- sub zone 13 0.5 kg N/ha/yr
adjust loading on sub zone 14 and 15 to match observed water quality at monitoring site
287:
- sub zone 14 1 kg N/ha/yr
- sub zone 15 1 kg N/ha/yr
This gives a predicted nitrogen concentration at site 287 of 0.5 mg/L versus observed mean
nitrogen concentration of 0.53 mg/L (Table 2).
adjust loading on sub zone 16 to match observed water quality at monitoring site 273:
- sub zone 16 4 kg N/ha/yr
This gives a predicted nitrogen concentration at site 273 of 1.08 mg/L versus observed mean
nitrogen concentration of 1.08 mg/L.
adjust loading on sub zone 17 to match observed water quality of monitoring site 286:
- sub zone 17 28 kg N ha/yr
This gives a predicted nitrogen concentration at site 286 of 1.64 mg/L versus observed mean
concentration of 1.64 mg/L. Monitoring site 286 represents land use in sub-zones 11 + 12 +
13 + 14 + 15 + 16 + 17.
adjust loading on sub zone 18 to match observed water quality at monitoring site 284:
- sub zone 18 5 kg N/ha/yr
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This gives a predicted nitrogen concentration at site 284 of 1.67 mg/L versus observed mean
concentration of 1.66 mg/L. Monitoring site 284 represents land use in sub-zones 11 + 12 +
13 + 14 + 15 + 16 + 17 + 18.
adjust loading on sub zone 19 to match observed water quality at monitoring site 26:
- sub zone 19 130 kg N/ha/yr
This gives a predicted nitrogen concentration at site 26 of 0.63 mg/L versus observed mean
concentration of 0.63 mg/L. Monitoring site 284 represents land uses in sub-zones 11 to 19.
This method of calibration represents the cumulative process where surface water
progressively intersect nitrogen as water moves down the catchment. In the case of Waipawa
River catchment, the land use in sub zone 19 is estimated as 130 kg N/ha/yr to match the
observed nitrogen mass exported out from the Ruataniwha Plains through the Waipawa River.
This loading is much greater than the loadings likely from actual land use (Ironside pers.
comm.).
Combinations of nitrogen loadings can produce similar surface water nitrogen concentrations.
For example, a land use of 10 kg N/ha/yr in sub zone 18 and a land use of 10 kg N/ha/yr in
sub zone 19 gives an estimated mean nitrogen concentration of 2.34 mg/L at site 284 (versus
observed of 1.66) and 0.6 mg/L at site 26 (versus observed of 0.63). The estimated loading of
10 kgN/ha/yr for subzone 19 is significantly different from the 130 kgN/ha/yr estimated in the
calibration process (Table 2). This implies that, for some subzones, surface water nitrogen
concentrations are relatively insensitive to sub zonal nitrogen loading.
Table 2 lists the sub-zones, and sub zone applications, with calculated and observed nitrogen
concentrations at surface water monitoring sites for the calibrated model of the Ruataniwha
Plains.
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Table 2. Zone loads and predicted surface water quality, steady-state.
Surface water subzones
11 12 13 14 15 16 17 18 19 21 22
Load kgN/ha/yr 0.5 0.5 0.5 1 1 4 28 5 130 2 22
Surface water subzones
23 24 25 31 32 33 34 35 36 37 38 39
Load kgN/ha/yr 3 4 0 0 5 25 46 9 13 0 0 0
Monitoring
points:
Surface water
site
River/stream name Calculated N
at site
(mg/L)
Observed
N
(mg/L)
Difference
calc-obs
273 Mangamate@SH50 bridge 1.08 1.08 0
284 Mangaonuku @ Tikokino Rd 1.67 1.66 0.01
286 Mangaonuku @ Argyll Rd 1.64 1.64 0
287 Mangaonuku@SH50 0.5 0.53 -0.03
26 Waipawa@RDS 0.63 0.63 0
356 Tukituki @SH50 0.13 0.18 -0.05
20 Tukituki at Ongaonga Br 0.26 0.26 0
659 Kahahakuri@Plant. Rd Bridge 2.56 2.59 -0.03
410 Kahahakuri@Ongaonga Rd 2.91 2.91 0
144 Tukipo@SH50 0.94 0.85 0.09
279 Tukipo@Burnside 2.07 2.08 -0.01
21 Tukipo@Ashcott 1.6 1.1 0.5
398 Porangahau@Fraser 3.5 3.53 -0.03
397 Porangahau@Oruawharo 1.83 1.91 -0.08
405 Maharakeke@SH2 1.91 1.96 -0.05
23 Tukituki@Coughlin 1.1 0.99 0.11
The comparison between calculated nitrogen concentrations and observed mean nitrogen
concentrations is worst at sites 356 (Tukituki River) and 21 (Tukipo River).
Observed nitrogen concentrations in the Tukituki River and the Tukipo River decline across
the Ruataniwha Plains (Table 3). For example, a mean concentration of 0.8 at site 356
compares with a mean concentration of 0.26 at site 20. The Tukituki River loses flow
between these two sites (Wood, pers. comm.) and a significant decline in mean concentration
is difficult to explain. The increase in N concentration between Tukituki River @ Folgers, an
assumed 0.1 mg/L, and Tukituki River @ SH50 requires significant land use effects. Zone 24
is predicted to have a nitrogen output of 72 kgN/ha/yr to match the increase in nitrogen
concentrations, and this output makes it impossible to model the nitrogen concentrations in
the lower reaches. Also, the reach of the Tukituki River between Folgers and SH50 loses
flow - up to 3 m3/s (Wood, pers. comm.). The mean of all the nitrogen concentrations is
significantly biased by one measurement of 38.18 mg/L on the 18/11/94. Removing this
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number from the data set calculates a mean of 0.18 mg/L nitrate-nitrogen. Such outliers do
not appear in the data of the Tukituki River sites, or Tukipo River sites. The Tukipo River
gains flow (Wood, pers. comm.) so dilution may cause the decline in concentration.
Table 3. River N concentrations used in model.
Location Site
Number
Observed N
(mg/L)
Comment
Tukituki @ Folgers - 0.1 Assumed
Tukituki @ SH50 356 0.18 Mean of observations
Tukituki @ Ongaonga Bridge 20 0.26 Mean of observations
Tukituki @ Coughlin 23 0.99 Mean of observations
Tukipo @ SH50 144 0.85 Mean of observations
Tukipo @ Burnside 279 2.08 Mean of observations
Tukipo @ Ashcott 21 1.1 Mean of observations
7.8.2 Groundwater
The nitrogen loadings that match best the surface water quality tend to predict groundwater
quality values that are too low (Table 4). This is possibly because the calculation of
groundwater nitrogen concentrations assumes mixing with the full thickness of aquifer.
Generally nitrogen concentrations decrease with increasing depth in the aquifer (Figure 7).
For example, the shallowest well (Appendix 3, Table A3.3), well 1377, has the highest
observed nitrogen concentration (Table 4). Wells with predicted nitrogen concentrations less
than observed are increased by adjusting the ratio of the saturated thickness. Ratios less than
0.1 indicate that input nitrogen is mixing in less than about 20 m of aquifer as the aquifer is up
to around 200 m thick in the Ruataniwha Plains.
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Table 4. Zone loads and predicted groundwater quality assuming full mixing.
Surface water
subzones
11 12 13 14 15 16 17 18 19 21 22
Load
kgN/ha/yr
0.5 0.5 0.5 1 1 4 28 5 130 2 22
Surface water
subzones
23 24 25 31 32 33 34 35 36 37 38 39
Load
kgN/ha/yr
3 4 0 0 5 25 46 9 13 0 0 0
Monitoring points:
groundwater
site
Calculated N
at site
(mg/L)
Observed
N
(mg/L)
Difference
calc-obs
220 4.7 0.3 4.4
236 1 1 0
146 1.2 1 0.2
222 0.9 0.48 0.42
224 0.1 0.27 -0.17
223 0.2 6.26 -6.06
239 0.2 0.55 -0.35
2227 1.5 3.52 -2.02
233 0.1 0.42 -0.32
2229 0 0.05 -0.05
231 0 4.41 -4.41
229 3.44 0.55 2.89
1497 0.03 1.22 -1.19
1377 1.62 22.6 -20.98
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Table 5. Zone loads and predicted groundwater quality assuming partial mixing.
Surface water
subzones 11 12 13 14 15 16 17 18 19 21 22
Load
kgN/ha/yr 0.5 0.5 0.5 1 1 4 28 5 130 2 22
Surface water
subzones 23 24 25 31 32 33 34 35 36 37 38 39
Load
kgN/ha/yr 3 4 0 0 5 25 46 9 13 0 0 0
Monitoring
points:
groundwater
site
Calculated N
at site
(mg/L)
Observed
N
(mg/L)
Difference
calc-obs
Mixing
thickness
% of full
thickness
220 4.7 0.3 4.4 1
236 1 1 0 1
146 1.2 1 0.2 1
222 0.9 0.48 0.42 1
224 0.25 0.27 -0.02 0.4
223 6.67 6.26 0.41 0.03
239 0.5 0.55 -0.05 0.4
2227 3.75 3.52 0.23 0.4
233 0.4 0.42 -0.02 0.25
2229 0 0.05 -0.05 1
231 0 4.41 -4.41 1
229 3.44 0.55 2.89 1
1497 1.5 1.22 0.28 0.02
1377 23.14 22.6 0.54 0.07
8.0 NITROGEN CONCENTRATIONS WITHOUT IRRIGATION
The effects of N applications on surface and groundwater quality can be estimated for land
use systems (Table 6). These models use the seepage velocity calculations for the non-
irrigated MODFLOW model (Fig. 14). The „irrigable area‟ of the Ruataniwha Plains is
defined by Hawkes Bay Regional Council to include most of the flat land in the Plains.
Land use with a 16 kgN/ha/yr loading, equivalent to irrigated beef, over the irrigable area of
the Ruataniwha Plains is predicted to result in mean surface water quality that is generally a
little better than present (Table 7). This is because sub-zonal nitrogen loadings in Table 7 are
generally less than current land use as estimated by the „calibrated‟ model (Table 2).
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Table 6. Nitrogen leaching for various land uses (HortResearch pers. comm.).
Land use system Leaching (kg/N/ha/yr)
Takapau Tikokino
Apples 15 17
Grapes 41 42
Maize 4 4
Potatoes 94 102
Squash 173 179
Dairy 42 44
Dryland beef 7 7
Irrigated beef 16 17
Dryland sheep 6 6
Irrigated sheep 20 21
The effects of increasing nitrogen leaching in the irrigable area of the Ruataniwha Plains from
43 kgN/ha/yr (equivalent to dairy), Table 8, to 98 kg/N/ha/yr (equivalent to potatoes), Table
9, and to 176 kg/N/ha/yr (equivalent to squash), Table 10 causes predicted mean nitrogen
concentrations in surface water to increase. For example, the predicted mean nitrogen
concentration at site 410 (Kahahakuri Stream) increases from 2.91 mg/L currently observed to
6.68 mg/L (dairy on the irrigable area) to 27.35 mg/L (squash on the irrigable area).
These calculations assume that mean stream flow remains the same under irrigation. These
calculations represent a „worst case‟ prediction because irrigation may increase stream flows,
due to an increase in soil drainage recharging spring-fed streams, and would cause some
dilution.
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Table 7. Surface water quality with a nitrogen loading of 16 kgN/ha/yr (equivalent to
irrigated beef) to Ruataniwha Plains irrigable area*.
Surface water
subzones 11 12 13 14 15 16 17 18 19 21 22
Load kgN/ha/yr 0.5 0.5 0.5 1 1 2.3 3.1 6.5 11.5 10.8 5.1
Surface water
subzones 23 24 25 31 32 33 34 35 36 37 38 39
Load kgN/ha/yr 7.9 7.7 14.2 13.6 0.9 5.8 7.8 4.2 11.2 15.6 6.9 16
Monitoring
points:
Surface
water
site
River/stream name Calculated N
at site
(mg/L)
Observed
N
(mg/L)
Difference
calc-obs
273 Mangamate@SH50 bridge 0.7 1.08 -0.38
284 Mangaonuku @ Tikokino Rd 1.12 1.66 -0.54
286 Mangaonuku @ Argyll Rd 0.35 1.64 -1.29
287 Mangaonuku@SH50 0.5 0.53 -0.03
26 Waipawa@RDS 0.32 0.63 -0.31
356 Tukituki @SH50 0.17 0.18 -0.01
20 Tukituki at Ongaonga Br 0.5 0.26 0.24
659 Kahahakuri@Plant. Rd Bridge 0.6 2.59 -1.99
410 Kahahakuri@Ongaonga Rd 2.49 2.91 -0.42
144 Tukipo@SH50 0.16 0.85 -0.69
279 Tukipo@Burnside 0.45 2.08 -1.63
21 Tukipo@Ashcott 0.85 1.1 -0.25
398 Porangahau@Fraser 0.6 3.53 -2.93
397 Porangahau@Oruawharo 0.85 1.91 -1.06
405 Maharakeke@SH2 1.3 1.96 -0.66
23 Tukituki@Coughlin 0.8 0.99 -0.19
* Land use in zones 11, 12 and 13 is set to 0.5 kg N/ha/yr; land use in zones 14 and 15 is set
to 1 kg N/ha/yr; other land uses are set to 16 kg N/ha/yr in the irrigable area of each zone. In
all zones, except zone 39, the number of irrigable cells is less than the number of cells in the
zone; therefore the loadings in Table 7 are less than 16 kg N/ha/yr.
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Table 8. Surface water quality with nitrogen loading of 43 kgN/ha/yr (equivalent to
dairy) to Ruataniwha Plains irrigable area.
Surface water
subzones 11 12 13 14 15 16 17 18 19 21 22
Load
kgN/ha/yr 0.5 0.5 0.5 1 1 6 8.3 17.5 30.9 29.1 13.7
Surface water
subzones 23 24 25 31 32 33 34 35 36 37 38 39
Load
kgN/ha/yr 21.3 20.7 38 36.5 2.3 15.5 21.1 11.3 30.1 42 18.4 43
Monitoring
points:
Surface
water
site
River/stream name Calculated N
at site
(mg/L)
Observed
N
(mg/L)
Difference
calc-obs
273 Mangamate@SH50 bridge 1.52 1.08 0.44
284 Mangaonuku @ Tikokino Rd 2.86 1.66 1.2
286 Mangaonuku @ Argyll Rd 0.79 1.64 -0.85
287 Mangaonuku@SH50 0.5 0.53 -0.03
26 Waipawa@RDS 0.74 0.63 0.11
356 Tukituki @SH50 0.3 0.18 0.12
20 Tukituki at Ongaonga Br 1.19 0.26 0.93
659 Kahahakuri@Plant. Rd Bridge 1.6 2.59 -0.99
410 Kahahakuri@Ongaonga Rd 6.68 2.91 3.77
144 Tukipo@SH50 0.43 0.85 -0.42
279 Tukipo@Burnside 1.21 2.08 -0.87
21 Tukipo@Ashcott 2.28 1.1 1.18
398 Porangahau@Fraser 1.6 3.53 -1.93
397 Porangahau@Oruawharo 2.29 1.91 0.38
405 Maharakeke@SH2 3.48 1.96 1.52
23 Tukituki@Coughlin 2.11 0.99 1.12
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Table 9. Predictions of surface water quality with nitrogen loading of 98 kgN/ha/yr
(equivalent to potatoes) to Ruataniwha Plains irrigable area.
Surface water
subzones
11 12 13 14 15 16 17 18 19 21 22
Load
kgN/ha/yr
0.5 0.5 0.5 1 1 13.8 19 39.9 70.4 66.4 31.3
Surface water
subzones
23 24 25 31 32 33 34 35 36 37 38 39
Load
kgN/ha/yr
48.6 47.1 86.7 83.1 5.3 35.4 48 25.6 68.6 95.8 42 98
Monitoring
points:
Surface
water
site
River/stream name Calculated N
at site
(mg/L)
Observed
N
(mg/L)
Difference
calc-obs
273 Mangamate@SH50 bridge 3.19 1.08 2.11
284 Mangaonuku @ Tikokino Rd 6.42 1.66 4.76
286 Mangaonuku @ Argyll Rd 1.68 1.64 0.04
287 Mangaonuku@SH50 0.5 0.53 -0.03
26 Waipawa@RDS 1.6 0.63 0.97
356 Tukituki @SH50 0.56 0.18 0.38
20 Tukituki at Ongaonga Br 2.58 0.26 2.32
659 Kahahakuri@Plant. Rd Bridge 3.65 2.59 1.06
410 Kahahakuri@Ongaonga Rd 15.23 2.91 12.32
144 Tukipo@SH50 0.98 0.85 0.13
279 Tukipo@Burnside 2.75 2.08 0.67
21 Tukipo@Ashcott 5.21 1.1 4.11
398 Porangahau@Fraser 3.65 3.53 0.12
397 Porangahau@Oruawharo 5.22 1.91 3.31
405 Maharakeke@SH2 7.94 1.96 5.98
23 Tukituki@Coughlin 4.78 0.99 3.79
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Table 10. Surface water quality with nitrogen loading of 176 kgN/ha/yr (equivalent to
squash) to Ruataniwha Plains irrigable area.
Surface water
subzones 11 12 13 14 15 16 17 18 19 21 22
Load kgN/ha/yr
0.5 0.5 0.5 1 1 24.8 34.1 71.7 126.5 119.2 56.3
Surface water subzones 23 24 25 31 32 33 34 35 36 37 38 39
Load kgN/ha/yr
87.2 84.6 155.7 149.3 9.4 63.5 86.2 46 123.2 172.1 75.4 176
Monitoring
points:
Surface water
site
River/stream name Calculated N
at site
(mg/L)
Observed
N
(mg/L)
Difference
calc-obs
273 Mangamate@SH50 bridge 5.56 1.08 4.48
284 Mangaonuku @ Tikokino Rd 11.47 1.66 9.81
286 Mangaonuku @ Argyll Rd 2.94 1.64 1.3
287 Mangaonuku@SH50 0.5 0.53 -0.03
26 Waipawa@RDS 2.82 0.63 2.19
356 Tukituki @SH50 0.93 0.18 0.75
20 Tukituki at Ongaonga Br 4.56 0.26 4.3
659 Kahahakuri@Plant. Rd Bridge 6.56 2.59 3.97
410 Kahahakuri@Ongaonga Rd 27.35 2.91 24.44
144 Tukipo@SH50 1.77 0.85 0.92
279 Tukipo@Burnside 4.95 2.08 2.87
21 Tukipo@Ashcott 9.35 1.1 8.25
398 Porangahau@Fraser 6.56 3.53 3.03
397 Porangahau@Oruawharo 9.37 1.91 7.46
405 Maharakeke@SH2 14.25 1.96 12.29
23 Tukituki@Coughlin 8.55 0.99 7.56
Groundwater concentrations are predicted to increase with increased nitrogen applications.
This is most marked for the wells that are possibly mixed in a small cross-section of aquifer.
For example, the nitrogen concentration in well 223 is predicted to rise to 570 mg/L with a
176 kg/N/ha/yr (Table 11).
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Table 11. Groundwater quality with a nitrogen loading of 176 kg/N/ha/yr (equivalent to
squash) to all irrigable cells.
Surface water subzones 11 12 13 14 15 16 17 18 19 21 22
Load kgN/ha/yr
0.5 0.5 0.5 1 1 24.8 34.1 71.7 126.5 119.2 56.3
Surface water subzones 23 24 25 31 32 33 34 35 36 37 38 39
Load kgN/ha/yr
87.2 84.6 155.7 149.3 9.4 63.5 86.2 46 123.2 172.1 75.4 176
Monitoring points:
groundwater
site
Calculated N at site
(mg/L)
Observed
N
(mg/L)
Difference
calc-obs
Mixing
thickness
% of full
thickness
220 6.3 0.3 6 1
236 6.8 1 5.8 1
146 17.2 1 16.2 1
222 5.8 0.48 5.32 1
224 19.3 0.27 18.98 0.4
223 570 6.26 563.74 0.03
239 40.5 0.55 39.95 0.4
2227 17.3 3.52 13.73 0.4
233 16.4 0.42 15.98 0.25
2229 4.2 0.05 4.15 1
231 14.5 4.41 10.09 1
229 2.8 0.55 2.25 1
1497 415 1.22 413.78 0.02
1377 244 22.6 221.7 0.07
The previous calculations assume that all nitrogen is transported to the monitoring sites
instantaneously. This is not the case because residence time in the groundwater system results
in a lag between application of chemicals to the groundwater system and the arrival of those
chemicals at monitoring sites.
Cell-by-cell estimates of residence time in the groundwater system are used to predict the
response of surface water quality to nitrogen applications of 16 (Table 12), 43 (Table 13), 98
(Table 14) and 176 kg/N/ha/yr (Table 15) application to all irrigation cells. These predictions
are made with the non-irrigated flow velocity predictions. As such the predictions represent a
worst case prediction for concentration as the dilution given by the non-irrigated model is less
than the dilution given by the irrigated model. The Kahahakuri @ Ongaonga site is predicted
as the most impacted by nitrogen application. For example, a 43 kg/N/ha/yr application
(Table 13) is predicted to raise mean nitrogen concentrations from the present mean
2.91 mg/L to 9.01 mg/L. The time scale of predicted change is generally decadal. For
example, nitrogen concentrations at Kahahakuri @ Ongaonga are predicted to increase in
response to loading throughout the 50 year period of simulation. In contrast, the nitrogen
Y:\Science\Groundwater\Staff Files\Husam\old_work\Paul\Ruataniwha Plains - 09 Oct.doc 25
concentration in the Porangahau @ Oruawharo appears to have „stabilised‟ after five years of
simulation.
Table 12. Mean nitrogen concentrations in streams over 50 years due to N loading of
16 kg/N/ha/yr to all irrigable cells.
Surface
site
Site name Observed
N
(mg/L)
Calculated N (mg/L) with 16 kg/h/yr loading
Year
1 2 5 10 20 30 50
273 Mangamate@SH50 bridge 1.08 1.08 1.08 1.08 1.08 1.18 1.18 1.18
284 Mangaonuku @ Tikokino Rd 1.66 1.66 1.76 1.76 1.96 2.06 2.06 2.16
26 Waipawa@RDS 0.63 0.63 0.63 0.73 0.83 0.93 0.93 0.93
410 Kahahakuri@Ongaonga Rd 2.91 2.91 3.01 3.31 3.71 4.51 4.91 5.21
659 Kahahakuri@Plant. Rd Bridge 2.59 2.59 2.69 2.79 2.99 3.13 3.19 3.19
20 Tukituki at Ongaonga Br 0.26 0.26 0.26 0.26 0.26 0.36 0.36 0.36
356 Tukituki @SH50 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8
23 Tukituki@Coughlin 0.99 1.09 1.19 1.29 1.39 1.59 1.69 1.69
21 Tukipo@Ashcott 1.1 1.3 1.4 1.6 1.7 1.8 1.9 1.9
144 Tukipo@SH50 0.85 0.85 0.85 0.85 0.95 1.05 1.15 1.15
279 Tukipo@Burnside 2.08 2.08 2.18 2.38 2.68 2.98 3.08 3.08
398 Porangahau@Fraser 3.53 3.93 3.93 4.03 4.03 4.13 4.13 4.13
397 Porangahau@Oruawharo 1.91 1.91 1.91 2.01 2.01 2.11 2.11 2.21
405 Porangahau@Oruawharo 1.96 2.26 2.36 2.46 2.56 2.66 2.66 2.66
Table 13. Mean nitrogen concentrations in streams over 50 years due to N loading of
43 kg/N/ha/yr to all irrigable cells.
Surface
site
Site name Observed
N
(mg/L)
Calculated N (mg/L) with 43 kg/h/yr loading
Year
1 2 5 10 20 30 50
273 Mangamate@SH50 bridge 1.08 1.08 1.08 1.08 1.18 1.28 1.28 1.28
284 Mangaonuku @ Tikokino Rd 1.66 1.76 1.86 1.96 2.36 2.76 2.76 2.86
26 Waipawa@RDS 0.63 0.73 0.73 0.83 1.13 1.33 1.33 1.43
410 Kahahakuri@Ongaonga Rd 2.91 2.91 3.21 4.01 5.11 7.21 8.31 9.01
659 Kahahakuri@Plant. Rd Bridge 2.59 2.59 2.79 3.09 3.69 4.19 4.19 4.29
20 Tukituki at Ongaonga Br 0.26 0.26 0.26 0.26 0.36 0.56 0.56 0.56
356 Tukituki @SH50 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8
23 Tukituki@Coughlin 0.99 1.19 1.39 1.79 2.19 2.59 2.79 2.89
21 Tukipo@Ashcott 1.1 1.5 1.9 2.3 2.8 3.1 3.2 3.2
144 Tukipo@SH50 0.85 0.85 0.85 0.95 1.15 1.45 1.55 1.55
279 Tukipo@Burnside 2.08 2.08 2.38 2.98 3.68 4.48 4.78 4.78
398 Porangahau@Fraser 3.53 4.53 4.73 5.03 5.03 5.03 5.03 5.03
397 Porangahau@Oruawharo 1.91 1.91 2.01 2.11 2.21 2.51 2.61 2.61
405 Porangahau@Oruawharo 1.96 2.66 2.96 3.36 3.56 3.86 3.86 3.96
Y:\Science\Groundwater\Staff Files\Husam\old_work\Paul\Ruataniwha Plains - 09 Oct.doc 26
Table 14. Mean nitrogen concentrations in streams over 50 years due to N application of
98 kg/N/ha/yr to all irrigable cells.
Surface
site
Site name Observed
N
(mg/L)
Calculated N (mg/L) with 98 kg/h/yr loading
Year
1 2 5 10 20 30 50
273 Mangamate@SH50 bridge 1.08 1.08 1.08 1.08 1.38 1.48 1.58 1.58
284 Mangaonuku @ Tikokino Rd 1.66 1.86 1.96 2.46 3.26 4.06 4.26 4.46
26 Waipawa@RDS 0.63 0.73 0.83 1.13 1.73 2.23 2.33 2.43
410 Kahahakuri@Ongaonga Rd 2.91 2.91 3.51 5.31 8.01 12.61 15.31 16.91
659 Kahahakuri@Plant. Rd Bridge 2.59 2.59 3.09 3.79 4.99 6.19 6.29 6.39
20 Tukituki at Ongaonga Br 0.26 0.26 0.26 0.36 0.56 0.86 0.96 1.06
356 Tukituki @SH50 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8
23 Tukituki@Coughlin 0.99 1.49 1.99 2.79 3.69 4.69 4.99 5.29
21 Tukipo@Ashcott 1.1 2 2.9 3.9 4.9 5.6 5.8 5.9
144 Tukipo@SH50 0.85 0.85 0.95 1.05 1.65 2.25 2.45 2.55
279 Tukipo@Burnside 2.08 2.18 2.78 4.18 5.68 7.48 8.18 8.28
398 Porangahau@Fraser 3.53 5.73 6.23 6.83 6.83 6.93 6.93 6.93
397 Porangahau@Oruawharo 1.91 2.01 2.11 2.21 2.71 3.31 3.41 3.61
405 Porangahau@Oruawharo 1.96 3.56 4.16 5.06 5.56 6.26 6.36 6.46
Table 15. Mean nitrogen concentrations in streams over 50 years due to N application of
176 kg/N/ha/yr to all irrigable cells.
Surface
site
Site name Observed
N
(mg/L)
Calculated N (mg/L) with 176 kg/h/yr loading
Year
1 2 5 10 20 30 50
273 Mangamate@SH50 bridge 1.08 1.08 1.08 1.08 1.58 1.88 1.98 1.98
284 Mangaonuku @ Tikokino Rd 1.66 2.06 2.26 3.06 4.66 6.06 6.26 6.66
26 Waipawa@RDS 0.63 0.83 1.03 1.53 2.53 3.43 3.63 3.83
410 Kahahakuri@Ongaonga Rd 2.91 2.91 4.01 7.21 12.11 20.31 25.11 28.01
659 Kahahakuri@Plant. Rd Bridge 2.59 2.59 3.39 4.79 6.89 8.99 9.29 9.39
20 Tukituki at Ongaonga Br 0.26 0.26 0.26 0.46 0.76 1.36 1.56 1.66
356 Tukituki @SH50 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.9
23 Tukituki@Coughlin 0.99 1.89 2.79 4.19 5.89 7.69 8.29 8.69
21 Tukipo@Ashcott 1.1 2.8 4.3 6.2 7.9 9.3 9.5 9.7
144 Tukipo@SH50 0.85 0.85 0.95 1.25 2.25 3.35 3.65 3.85
279 Tukipo@Burnside 2.08 2.18 3.28 5.78 8.48 11.88 12.98 13.28
398 Porangahau@Fraser 3.53 7.43 8.43 9.53 9.53 9.63 9.63 9.63
397 Porangahau@Oruawharo 1.91 2.01 2.21 2.51 3.31 4.51 4.61 5.01
405 Porangahau@Oruawharo 1.96 4.76 5.96 7.66 8.36 9.66 9.76 10.16
Y:\Science\Groundwater\Staff Files\Husam\old_work\Paul\Ruataniwha Plains - 09 Oct.doc 27
9.0 NITROGEN INPUTS AND OUTPUTS
9.1 Current land use
The model predicts, for current land use, that approximately 47 tonnes/year of nitrogen is
entering the Ruataniwha Plains through rivers crossing the northern and western boundary
(Table 16). This is based on average nitrogen concentrations in surface water. The model of
existing land use (Table 2) predicts that a further approximately 795 tonnes/year of nitrogen is
entering groundwater and streams due to land use on the Plains. Approximately 321
tonnes/year of nitrogen is predicted to be leaving the Ruataniwha Plains through the Waipawa
River, and approximately 516 tonnes/year is predicted as leaving through the Tukituki River.
9.2 Irrigated pasture
With a scenario of an irrigated beef land use (Table 7) it is predicted that nitrogen output to
surface and groundwater will increase by 16-17 kgN/ha/yr. An extra 17 kgN/ha/yr leaching
through soils, in addition to the existing land use, for all irrigable cells on the Ruataniwha
Plains (equivalent to 31000 ha) predicts an additional nitrogen output of 527 tonnes/year for
the whole Ruataniwha Plains (Table 17). Approximately 456 tonnes/year of the total nitrogen
loading (existing land use plus irrigated beef) is predicted to be leaving the Ruataniwha Plains
through the Waipawa River. Approximately 908 tonnes/year of nitrogen (existing land use
plus irrigated beef) is predicted as leaving through the Tukituki River.
9.3 Irrigated crops and irrigated dairy
A mean nitrogen output for a mix of land uses potatoes (20% of Plains area), onion (20% of
Plains area), squash (20% of Plains area) and dairy (0.4 of Plains area) is estimated at 92
kgN/ha/yr. Nitrogen output from onions (not listed in Table 6) is assumed as the same as
potatoes.
The nitrogen application to all the irrigable cells by a mix of irrigated crops and irrigated
dairy in the Plains predicts a nitrogen loading of 2852 tonnes/year (Table 18). It is predicted
that 1050 tonnes N/yr will leave through the Waipawa River and 2639 tonnes N/yr will leave
through the Tukituki River.
Y:\Science\Groundwater\Staff Files\Husam\old_work\Paul\Ruataniwha Plains - 09 Oct.doc 28
Table 16. Calculated nitrogen balance with existing land use.
N inputs kgN/yr
Background land use 794763
Irrigation 0
Point sources 0
Sum land use 794763
Boundary streams/rivers: 46989
Total N inputs 841752
N outputs kgN/yr
Waipawa River
From river boundary 29644
From land use 291588
Sum 321232
Tukituki River
From river boundary 12614
From Zone 2 113700
From Zone 3 389475
Sum 515789
Other river boundaries 4730
Sum of N outputs: 841751
Balance (Out -In) -1
Percent difference 0
Y:\Science\Groundwater\Staff Files\Husam\old_work\Paul\Ruataniwha Plains - 09 Oct.doc 29
Table 17. Nitrogen balance with existing land use plus 17 kgN/ha/yr, equivalent to an
irrigated beef land use, over the irrigable area of the Ruataniwha Plains.
N inputs kgN/yr
Background land use 794763
Irrigation 527000
Point sources 0
Sum land use 1321763
Boundary streams/rivers: 46989
Total N inputs 1368752
N outputs kgN/yr
Waipawa River
From river boundary 29644
From land use 426313
Sum 455957
Tukituki River
From river boundary 12614
From Zone 2 283700
From Zone 3 611750
Sum 908064
Other river boundaries 4730
Sum of N outputs: 1368751
Balance (Out -In) -1
Percent difference 0
Y:\Science\Groundwater\Staff Files\Husam\old_work\Paul\Ruataniwha Plains - 09 Oct.doc 30
Table 18. Nitrogen balance with existing land use plus 92 kgN/ha/yr, equivalent to
irrigated crops and irrigated dairy, over the irrigable area of the Ruataniwha
Plains.
N inputs kgN/yr
Background land use 794763
Irrigation 2852000
Point sources 0
Sum land use 3646763
Boundary streams/rivers: 46989
Total N inputs 3693752
N outputs kgN/yr
Waipawa River
From river boundary 29644
From land use 1020688
Sum 1050332
Tukituki River
From river boundary 12614
From Zone 2 1033700
From Zone 3 1592375
Sum 2638689
Other river boundaries 4730
Sum of N outputs: 3693751
Balance (Out -In) -1
Percent difference 0
10.0 NITROGEN CONCENTRATIONS WITH IRRIGATION
Predictions of nitrogen concentrations are made for two land uses, assuming that irrigation is
occurring on all irrigable land the Ruataniwha Plains. Each of the two land uses, irrigated
pasture and irrigated crops with irrigated dairy, are applied on all irrigable land on the Plains.
The models use the groundwater seepage velocity estimates made by the MODFLOW model
that simulates irrigation (Fig. 15). These seepage velocities are higher than seepage velocities
estimated for the model without irrigation (Fig. 14). The two effects of higher seepage
velocities are:
greater dilution of nitrogen by excess irrigation water. Therefore, assuming the same land
use, nitrogen in groundwater with irrigation will be of lower concentration than nitrogen
in groundwater without irrigation.
Y:\Science\Groundwater\Staff Files\Husam\old_work\Paul\Ruataniwha Plains - 09 Oct.doc 31
nitrogen in streams will respond to land use changes more quickly when land is irrigated.
10.1 Irrigated pasture
It is predicted that irrigated pasture, with an estimated nitrogen leaching rate of 17 kgN/ha/yr,
will result in increased nitrogen concentrations at most surface water sites (Table 19) and
groundwater sites (Table 20).
For example, Kahahakuri @ Ongaonga Road is predicted to increase from a mean of 2.91
mg/L with the current land use to 5.55 mg/L with irrigated pasture in addition to the existing
land use.
Transient nitrogen concentrations in surface water (Table 21) are predicted to increase the
most at Kahahakuri @ Ongaonga. Generally, the surface water sites „impacted‟ the most by
irrigation are those where the largest increases occur. The sites not „impacted‟ by irrigation
(e.g. Tukituki @ SH50) show no increase in nitrogen levels.
Table 19. Steady-state mean surface water nitrogen concentrations with a loading of
17 kgN/ha/yr and irrigation. This loading is in addition to existing land use.
Surfacewater sub-zones
11 12 13 14 15 16 17 18 19 21 22
Load kgN/ha/yr
0.5 0.5 0.5 1 1 6.4 31.3 11.9 142.2 13.5 27.4
Surfacewater sub-zones
23 24 25 31 32 33 34 35 36 37 38 39
Load kgN/ha/yr
11.4 12.2 15 14.4 5.9 31.1 54.3 13.4 24.9 16.6 7.3 17
Monitoring
points: Surface
water site
River/stream name Calculated N
at site
(mg/L)
Observed
N
(mg/L)
Difference
calc-obs
273 Mangamate@SH50 bridge 1.59 1.08 0.51
284 Mangaonuku @ Tikokino Rd 2.77 1.66 1.11
286 Mangaonuku @ Argyll Rd 1.92 1.64 0.28
287 Mangaonuku@SH50 0.5 0.53 -0.03
26 Waipawa@RDS 0.9 0.63 0.27
356 Tukituki @SH50 0.21 0.18 0.03
20 Tukituki at Ongaonga Br 0.69 0.26 0.43
659 Kahahakuri@Plant. Rd Bridge 3.2 2.59 0.61
410 Kahahakuri@Ongaonga Rd 5.55 2.91 2.64
144 Tukipo@SH50 1.11 0.85 0.26
279 Tukipo@Burnside 2.54 2.08 0.46
21 Tukipo@Ashcott 2.51 1.1 1.41
398 Porangahau@Fraser 4.13 3.53 0.6
397 Porangahau@Oruawharo 2.74 1.91 0.83
405 Maharakeke@SH2 3.28 1.96 1.32
23 Tukituki@Coughlin 2.7 0.99 1.71
Y:\Science\Groundwater\Staff Files\Husam\old_work\Paul\Ruataniwha Plains - 09 Oct.doc 32
Concentrations of nitrogen in groundwater is predicted to increase because of irrigation
(Table 22). This calculation assumes full mixing of nitrogen with the full water column and
is a conservative estimate. Some of the estimates of mixing fractions (Section 7.8.2) produce
quite large predictions of nitrate concentrations (Table 23). This is generally at sites where
the estimate of the mixing ratio is low. For example, site 223 has an estimated mixing ratio of
0.03 from the calibration estimates i.e. the nitrogen load is mixed in 3% of the groundwater
flow. It is estimated (Table 23) that the nitrogen concentration after 50 years of irrigation will
be approximately 61 mg/L. Some 50-year estimates of nitrogen concentrations in Table 23
are greater than the estimated steady-state concentrations in Table 20. For example, Well
1377 has a predicted nitrogen concentration of 42.4 mg/L after 50 years. The predicted
steady-state concentration (Table 20) is 41.4 mg/L. Differences in concentration are because
the increases in concentration due to irrigation (Table 23) are added to the observed mean
nitrogen value, unlike the values in Table 23 which consider total zone loads.
Table 20. Steady-state mean groundwater nitrogen concentrations with a loading of
17 kgN/ha/yr and irrigation. This loading is in addition to existing land use.
Surface water zone subzones 11 12 13 14 15 16 17 18 19 21 22
Load kgN/ha/yr 0.5 0.5 0.5 1 1 6.4 31.3 11.9 142.2 13.5 27.4
Surface water zone subzones 23 24 25 31 32 33 34 35 36 37 38 39
Load kgN/ha/yr 11.4 12.2 15 14.4 5.9 31.1 54.3 13.4 24.9 16.6 7.3 17
Monitoring points:
groundwater
site
Calculated N
at site
(mg/L)
Observed
N
(mg/L)
Difference
calc-obs
Mixing
thickness
% of full
thickness
220 4.5 0.3 4.2 1
236 1.3 1 0.3 1
146 2.2 1 1.2 1
222 1.2 0.48 0.72 1
224 1.75 0.27 1.48 0.4
223 50 6.26 43.74 0.03
239 3.5 0.55 2.95 0.4
2227 4.5 3.52 0.98 0.4
233 1.6 0.42 1.18 0.25
2229 0.3 0.05 0.25 1
231 1.1 4.41 -3.31 1
229 3.6 0.55 3.05 1
1497 2.63 1.22 1.41 0.38
1377 41.43 22.6 18.83 0.07
Y:\Science\Groundwater\Staff Files\Husam\old_work\Paul\Ruataniwha Plains - 09 Oct.doc 33
Table 21. Nitrogen concentrations in surface water over 50 years, 17 kgN/ha/yr loading and irrigation. This loading is in addition to existing
land use.
Surface
site
Site name Observed
N
(mg/L)
Predicted concentrations (mg/L) with 17 kg/h/yr irrigation application
Year
1 2 5 10 20 30 50
273 Mangamate@SH50 bridge 1.08 1.08 1.08 1.08 1.08 1.18 1.18 1.18
284 Mangaonuku @ Tikokino Rd 1.66 1.66 1.76 1.86 1.96 2.06 2.16 2.16
26 Waipawa@RDS 0.63 0.63 0.63 0.73 0.83 0.93 0.93 0.93
410 Kahahakuri@Ongaonga Rd 2.91 2.91 3.01 3.51 3.91 4.91 5.31 5.41
659 Kahahakuri@Plant. Rd Bridge 2.59 2.59 2.69 2.89 3.09 3.19 3.19 3.29
20 Tukituki at Ongaonga Br 0.26 0.26 0.26 0.26 0.36 0.36 0.36 0.36
356 Tukituki @SH50 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8
23 Tukituki@Coughlin 0.99 1.09 1.19 1.29 1.49 1.69 1.69 1.79
21 Tukipo@Ashcott 1.1 1.3 1.4 1.6 1.8 1.9 1.9 1.9
144 Tukipo@SH50 0.85 0.85 0.85 0.95 1.05 1.15 1.15 1.15
279 Tukipo@Burnside 2.08 2.08 2.28 2.48 2.78 3.08 3.18 3.18
398 Porangahau@Fraser 3.53 3.93 4.03 4.13 4.13 4.13 4.13 4.13
397 Porangahau@Oruawharo 1.91 1.91 1.91 2.01 2.01 2.11 2.21 2.21
405 Porangahau@Oruawharo 1.96 2.26 2.36 2.56 2.56 2.66 2.76 2.76
Y:\Science\Groundwater\Staff Files\Husam\old_work\Paul\Ruataniwha Plains - 09 Oct.doc 34
Table 22. Nitrogen concentrations in groundwater over 50 years, loading of 17 kgN/ha/yr, and irrigation, assuming full mixing. This
loading is in addition to existing land use.
Nitrogen application: 17 kgN/ha/yr irrigation application
Well Observed N
(mg/L) Year
1 2 5 10 20 30 50
220 0.3 0.4 0.5 0.6 0.8 0.9 0.9 0.9
236 1 1 1.1 1.1 1.4 1.7 1.7 1.7
146 1 1.1 1.2 1.4 1.8 2.4 2.5 2.7
222 0.48 0.58 0.68 0.78 0.88 1.08 1.08 1.08
224 0.27 0.27 0.37 0.57 0.87 0.97 0.97 0.97
223 6.26 6.36 6.46 6.56 7.06 7.66 7.96 7.96
239 0.55 0.65 0.65 0.75 1.05 1.75 2.15 2.15
2227 3.52 3.62 3.72 4.02 4.02 4.02 4.02 4.22
233 0.42 0.52 0.62 0.82 0.82 0.82 0.82 0.82
2229 0.05 0.05 0.05 0.45 0.45 0.45 0.45 0.45
231 4.41 4.51 4.61 4.91 5.31 5.81 5.81 5.81
229 0.55 0.65 0.65 0.75 0.85 0.85 0.85 0.85
1497 1.22 1.22 1.32 1.52 1.72 2.02 2.12 2.12
1377 22.6 22.7 22.8 23.1 24 24.2 24.3 24.3
Y:\Science\Groundwater\Staff Files\Husam\old_work\Paul\Ruataniwha Plains - 09 Oct.doc 35
Table 23. Nitrogen concentrations in groundwater over 50 years, loading of 17 kgN/ha/yr and irrigation, assuming partial mixing. This
loading is in addition to existing land use.
Well Observed N
(mg/L)
Nitrogen application: 17 kgN/ha/yr irrigation application
Year
1 2 5 10 20 30 50
220 0.3 0.4 0.4 0.5 0.8 0.8 0.8 0.8
236 1 1.1 1.1 1.1 1.4 1.5 1.5 1.5
146 1 1.1 1.1 1.3 1.7 2 2.1 2.3
222 0.48 0.58 0.58 0.78 0.78 0.88 0.88 0.88
224 0.27 0.27 0.47 0.97 1.57 1.67 1.67 1.67
223 6.26 7.76 9.36 13.96 30.96 46.46 49.56 49.56
239 0.55 0.65 0.95 1.15 2.45 3.65 3.75 3.75
2227 3.52 3.62 3.92 4.32 4.52 4.52 4.62 4.72
233 0.42 0.42 0.82 1.52 1.52 1.52 1.52 1.52
2229 0.05 0.05 0.05 0.35 0.35 0.35 0.35 0.35
231 4.41 4.51 4.61 4.81 5.31 5.51 5.51 5.51
229 0.55 0.55 0.65 0.65 0.75 0.75 0.75 0.75
1497 1.22 1.22 1.42 1.92 2.52 3.12 3.12 3.12
1377 22.6 22.6 23.6 32.5 39.4 41.4 42.4 42.4
Y:\Science\Groundwater\Staff Files\Husam\old_work\Paul\Ruataniwha Plains - 09 Oct.doc 36
Table 24. Surface water nitrogen concentrations with a 92 kgN/ha/yr loading and
irrigation. This loading is in addition to existing land use.
Surface water subzones 11 12 13 14 15 16 17 18 19 21 22
Load kgN/ha/yr 0.5 0.5 0.5 1 1 16.9 45.8 42.5 196.1 64.3 51.4
Surface water subzones 23 24 25 31 32 33 34 35 36 37 38 39
Load kgN/ha/yr 48.6 48.2 81.4 78 9.9 58.2 91 33.1 77.4 90 39.4 92
Monitoring
points:
Surface water
site
River/stream name Calculated N
at site
mg/L
Observed
N
Difference
calc-obs
273 Mangamate@SH50 bridge 3.87 1.08 2.79
284 Mangaonuku @ Tikokino Rd 7.62 1.66 5.96
286 Mangaonuku @ Argyll Rd 3.14 1.64 1.5
287 Mangaonuku@SH50 0.5 0.53 -0.03
26 Waipawa@RDS 2.07 0.63 1.44
356 Tukituki @SH50 0.57 0.18 0.39
20 Tukituki at Ongaonga Br 2.59 0.26 2.33
659 Kahahakuri@Plant. Rd Bridge 5.99 2.59 3.4
410 Kahahakuri@Ongaonga Rd 17.21 2.91 14.3
144 Tukipo@SH50 1.86 0.85 1.01
279 Tukipo@Burnside 4.65 2.08 2.57
21 Tukipo@Ashcott 6.49 1.1 5.39
398 Porangahau@Fraser 6.93 3.53 3.4
397 Porangahau@Oruawharo 6.73 1.91 4.82
405 Maharakeke@SH2 9.36 1.96 7.4
23 Tukituki@Coughlin 6.3 0.99 5.31
Y:\Science\Groundwater\Staff Files\Husam\old_work\Paul\Ruataniwha Plains - 09 Oct.doc 37
Table 25. Groundwater nitrogen concentrations with a 92 kgN/ha/yr loading and
irrigation and partial mixing. This loading is in addition to existing land use.
Surface water zone subzones
11 12 13 14 15 16 17 18 19 21 22
Load kgN/ha/yr 0.5 0.5 0.5 1 1 16.9 45.8 42.5 196.1 64.3 51.4
Surface water zone subzones
23 24 25 31 32 33 34 35 36 37 38 39
Load kgN/ha/yr 48.6 48.2 81.4 78 9.9 58.2 91 33.1 77.4 90 39.4 92
Monitoring points:
groundwater
site
Calculated N
at site
mg/L
Observed
N
Difference
calc-obs
Mixing
thickness
% of full
thickness
220 6.7 0.3 6.4 1
236 3.7 1 2.7 1
146 8.1 1 7.1 1
222 3.2 0.48 2.72 1
224 8.25 0.27 7.98 0.4
223 246.67 6.26 240.41 0.03
239 17.75 0.55 17.2 0.4
2227 10.5 3.52 6.98 0.4
233 7.6 0.42 7.18 0.25
2229 1.7 0.05 1.65 1
231 6.1 4.41 1.69 1
229 4.7 0.55 4.15 1
1497 10.26 1.22 9.04 0.38
1377 132.86 22.6 110.26 0.07
Y:\Science\Groundwater\Staff Files\Husam\old_work\Paul\Ruataniwha Plains - 09 Oct.doc 38
Table 26. Nitrogen concentrations in surface water over 50 years, 92 kgN/ha/yr loading and irrigation. This loading is in addition to existing
land use.
Surface
site
Site name Observed
N
(mg/L)
Calculated N (mg/L) with 92 kg/ha/yr irrigation application
Year
1 2 5 10 20 30 50
273 Mangamate@SH50 bridge 1.08 1.08 1.08 1.08 1.38 1.48 1.58 1.58
284 Mangaonuku @ Tikokino Rd 1.66 1.86 2.06 2.56 3.46 3.96 4.16 4.26
26 Waipawa@RDS 0.63 0.73 0.83 1.23 1.83 2.13 2.23 2.33
410 Kahahakuri@Ongaonga Rd 2.91 3.11 3.61 6.01 8.31 13.81 15.71 16.21
659 Kahahakuri@Plant. Rd Bridge 2.59 2.79 2.99 4.09 5.29 6.09 6.09 6.19
20 Tukituki at Ongaonga Br 0.26 0.26 0.26 0.36 0.56 0.86 0.96 1.06
356 Tukituki @SH50 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8
23 Tukituki@Coughlin 0.99 1.59 2.09 2.89 3.79 4.69 4.89 5.09
21 Tukipo@Ashcott 1.1 2.2 3 3.9 5 5.4 5.5 5.6
144 Tukipo@SH50 0.85 0.85 0.85 1.15 1.85 2.25 2.45 2.45
279 Tukipo@Burnside 2.08 2.28 2.98 4.28 5.88 7.48 7.88 7.98
398 Porangahau@Fraser 3.53 5.53 6.13 6.63 6.73 6.73 6.73 6.73
397 Porangahau@Oruawharo 1.91 2.01 2.11 2.31 2.71 3.21 3.31 3.51
405 Porangahau@Oruawharo 1.96 3.46 4.26 4.96 5.46 5.96 6.06 6.26
Y:\Science\Groundwater\Staff Files\Husam\old_work\Paul\Ruataniwha Plains - 09 Oct.doc 39
Table 27. Nitrogen concentrations in groundwater over 50 years, 92 kgN/ha/yr loading and irrigation and partial mixing. This loading is in
addition to existing land use.
Well Observed
N
(mg/L)
Calculated N (mg/L) with a 92 kgN/ha/yr irrigation application
Year
1 2 5 10 20 30 50
220 0.3 0.6 0.9 1.2 2.7 2.7 2.7 2.7
236 1 1.3 1.6 1.6 2.9 3.9 3.9 3.9
146 1 1.5 1.8 2.9 4.7 6.6 7.1 7.9
222 0.48 0.88 1.08 1.88 2.08 2.78 2.78 2.78
224 0.27 0.27 1.37 4.07 7.27 7.87 7.87 7.87
223 6.26 14.66 22.96 48.06 140.06 223.66 240.46 240.46
239 0.55 1.15 2.45 3.75 10.95 17.35 18.05 18.05
2227 3.52 4.22 5.72 7.92 8.62 8.62 9.42 10.12
233 0.42 0.42 2.72 6.32 6.32 6.32 6.32 6.32
2229 0.05 0.05 0.05 1.75 1.75 1.75 1.75 1.75
231 4.41 4.81 5.51 6.81 9.41 10.31 10.31 10.31
229 0.55 0.55 0.95 1.25 1.65 1.65 1.65 1.65
1497 1.22 1.22 2.42 4.92 8.02 11.72 11.72 11.72
1377 22.6 22.6 28 76.1 113.6 124.3 129.7 129.7
Y:\Science\Groundwater\Staff Files\Husam\old_work\Paul\Ruataniwha Plains - 09 Oct.doc 40
10.2 Irrigated crops and irrigated dairy
The mean nitrogen output with this land use is estimated as 92 kgN/ha/yr (Section 9.3).
Mean surface water quality estimates of nitrogen concentrations with a 92 kgN/ha/yr
application (Table 24) are higher than nitrogen concentrations with a 17 kgN/ha/yr
application. For example the Kahahakuri @ Ongaonga has a predicted mean nitrogen
concentration of 17.21 mg/L with a 92 kgN/ha/yr application and 5.5 mg/L concentration with
a 17 kgN/ha/yr application.
Mean groundwater nitrogen concentrations are predicted as a maximum of approximately
247 mg/L in well 223 with a 92 kgN/ha/yr application (Table 25). The two wells with a low
mixing ratio (well 223, 0.03 and well 1377, 0.07) both have an estimated nitrogen
concentration that is very high. This value is possible if the mixing zone at these wells is thin
as indicated by the mixing ratio.
Transient surface water mean concentrations (Table 26) at some sites show a levelling-off of
predicted concentrations in the medium term, e.g. concentrations at Porangahau @ Fraser (site
398) reach 6.73 mg/L by 10 years and do not increase further. Nitrogen concentrations at
other sites, e.g. Kahahakuri @ Ongaonga (site 410), continue to increase through the 50 year
period.
Transient groundwater concentrations (Table 27) are predicted to increase significantly in
some wells. For example, in well 223 it is predicted that the current mean concentration of
6.26 mg/L in well 223 is predicted to increase to around 240 mg/L after 30 years of irrigation
at 92 kgN/ha/yr. Well 223, and well 1377, are predicted to have the lowest mixing ratio of the
wells (Table 20) and so the effects of nitrogen injection on groundwater quality are amplified
in these wells.
11.0 NITROGEN CONCENTRATIONS IN RIVERS OVER 20 YEARS
River and stream nitrogen concentrations are estimated for 20 years after the commencement
of loading nitrogen to land. This model considers the travel-time of nitrogen in the
groundwater system. River and stream flow is considered as variable over time in this model.
Stream and river flow was assumed as constant over time in Section 10.
Y:\Science\Groundwater\Staff Files\Husam\old_work\Paul\Ruataniwha Plains - 09 Oct.doc 41
11.1 River and stream flow means
Transient nitrogen concentration predictions are made for the Waipawa @ RDS, Tukituki @
Tapairu Rd, and Kahahakuri @ Ongaonga sites (Appendix 2). Mean annual, seasonal, and
weekly flows are calculated from rated stage data. Gaps in the records occur. This results in
gaps in the calculation of mean flows. For example, only ten annual mean flows can be
calculated for Waipawa @ RDS in the period 22/4/88 to 22/1/2002. No annual mean flow
could be calculated for Kahahakuri @ Ongaonga.
11.2 Flows used in mixing calculations
11.2.1 Waipawa @ RD5, site 23235
The 10 available annual mean flows are used and this data is repeated for years 11 to 21. A
total of 48 seasonal flow averages (mean flow over three months starting in July 1988) are
calculated from the record and a total of 690 mean weekly flows are calculated.
11.2.2 Tukituki @ Tapairu Rd, site 23207
A total of 13 annual mean flows in the period July 1987 to 31/10/01 are calculated. A total of
56 mean seasonal flows are calculated and a total of 728 mean weekly flows are calculated.
11.2.3 Kahahakuri @ Ongaonga, site 23248
No mean annual flows can be calculated from observed data, with a starting month of July.
Five seasonal mean flows are calculated and 108 weekly flows are calculated.
11.3 Calculated nitrogen fluxes
Nitrogen loadings are calculated using the spreadsheet Ruasurfqualtransirri.xls (Appendix 4)
in the period 1 to 20 years after the commencement of irrigation in the three catchments of
each river/stream (Table 28). Background, i.e. current land use, and nitrogen inputs from the
western boundary of the Ruataniwha Plains are not considered. Therefore, estimations of
water quality are expressed as an increase due to irrigation loading. Seasonal and weekly
nitrogen fluxes are calculated from these annual figures by dividing the annual figure equally.
Y:\Science\Groundwater\Staff Files\Husam\old_work\Paul\Ruataniwha Plains - 09 Oct.doc 42
11.4 Calculated surface water flows
The surface water flows used in the mixing calculations are the mean of observed flows, with
the following modifications to generate 20-year flow mean annual records:
Waipawa @ RDS The pattern of mean annual flow in years 1 to 10 is
repeated in years 11 to 20.
Tukituki @ Tapairu Rd Annual mean flows are used for years 1 to 13. The
pattern of mean annual flow in years 1 to 7 is repeated in
years 14 to 20.
Kahahakuri @ Ongaonga The mean annual flow of over 20 years is generated from
a repeating pattern of 11%, 102%, 105%, 110%, 115%,
120%, 98%, 95%, 90%, 85% and 80% of the mean
seasonal flow.
Mean seasonal flow record are generated for a 12 year period as follows:
Waipawa @ RD5 48 seasonal mean flows, equivalent to 12 years of record
Tukituki @ Tapairu Rd 48 seasonal mean flows equivalent to 12 years of record
Kahahakuri @ Ongaonga Rd The five seasonal mean flows are repeated through 48
seasons.
Mean weekly flow records are generated for up to a 14 year period as follows:
Waipawa @ RD5 690 mean weekly flows
Tukituki @ Tapairu Rd 728 mean weekly flows
Kahahakuri @ Ongaonga The 108 mean weekly flow values from observations are
repeated to generate a 728 week synthetic record.
Y:\Science\Groundwater\Staff Files\Husam\old_work\Paul\Ruataniwha Plains - 09 Oct.doc 43
11.5 Calculated river and stream nitrogen concentrations
11.5.1 92 kgN/ha/yr irrigation
Mean annual nitrogen concentrations in the three rivers and streams generally increase with
time when considering annual average measurements (Table 28). This reflects increasing
nitrogen loads with time. The maximum nitrogen concentrations increases of 2.91 mg/L
(Waipawa, year 17), 6.37 mg/L (Tukituki, year 19) and 31.35 mg/L (Kahahakuri, year 20)
show the influence of flow volumes on the calculation of concentration. Higher
concentrations are predicted at times of lower flows because dilution of nitrogen is reduced.
Calculated weekly nitrogen concentrations in the Waipawa River reaches approximately 10
mg/L in week 505 (the week of the 9/4/88), Fig. 16. The maximum weekly nitrogen
concentration in the Tukituki River reaches around 25 mg/L in week 558 (week of the
24/3/98), Fig. 17. Minimum mean weekly nitrogen concentrations in the Kahahakuri Stream
reach over 25 mg/L towards the end of the period of weekly flow simulation (Fig. 18). These
predictions use observed flow measurements to generate mean flow values. Irrigation will
likely increase the mean flows so the estimated nitrogen concentrations represent a „worst
case‟ scenario.
Table 28. Nitrogen concentration in three rivers and streams over 20 years due to
irrigation of 92 kgN/ha/yr.
Year Waipawa@RDS
kgN/yr from land use
from irrigation
Average annual flow
(L/s)
Increase in
N concentration
(mg/L)
1 71300 14990 0.15
2 117300 14677 0.25
3 172500 22118 0.25
4 223100 17969 0.39
5 294400 12359 0.76
6 351900 26229 0.43
7 418600 8074 1.64
8 478400 15683 0.97
9 533600 14049 1.2
10 586500 13405 1.39
11 618700 14990 1.31
12 646300 14677 1.4
13 664700 22118 0.95
14 696900 17969 1.23
15 713000 12359 1.83
16 733700 26229 0.89
17 740600 8074 2.91
Y:\Science\Groundwater\Staff Files\Husam\old_work\Paul\Ruataniwha Plains - 09 Oct.doc 44
18 742900 15683 1.5
19 756700 14049 1.71
20 759000 13405 1.8
Year Tukituki @Tapairu Rd
kgN/yr from land use
from irrigation
Average annual flow
(L/s)
Increase in
N concentration
(mg/L)
1 299000 26726 0.35
2 506000 15933 1.01
3 646300 16111 1.27
4 770500 13147 1.86
5 897000 24053 1.18
6 1014300 8575 3.75
7 1127000 16895 2.12
8 1193700 14883 2.54
9 1274200 14592 2.77
10 1334000 11726 3.61
11 1354700 15220 2.82
12 1403000 10462 4.25
13 1442100 15074 3.03
14 1490400 26726 1.77
15 1541000 15933 3.07
16 1619200 16111 3.19
17 1676700 13147 4.04
18 1697400 24053 2.24
19 1722700 8575 6.37
20 1748000 16895 3.28
Year Kahahakuri@Ongaonga Rd
kgN/yr from land use
from irrigation
Average annual flow
(L/s)
Increase in
N concentration
(mg/L)
1 6900 388 0.56
2 23000 396 1.84
3 41400 407 3.23
4 66700 427 4.95
5 96600 446 6.87
6 121900 466 8.29
7 133400 380 11.13
8 149500 369 12.85
9 158700 349 14.42
10 170200 330 16.35
11 174800 310 17.88
12 181700 388 14.85
13 181700 396 14.55
14 197800 407 15.41
15 225400 427 16.74
16 273700 446 19.46
17 312800 466 21.29
18 324300 380 27.06
19 333500 369 28.66
20 345000 349 31.35
Y:\Science\Groundwater\Staff Files\Husam\old_work\Paul\Ruataniwha Plains - 09 Oct.doc 45
11.5.2 17 kgN/ha/yr irrigation
Annual (Table 29), seasonal, and weekly (Figs 19 to 21) nitrogen concentrations with a
17 kgN/ha/yr irrigation are predicted to be lower than with a 92 kgN/ha/yr irrigation. Annual
average concentrations with a 17 kgN/ha/yr irrigation are predicted to increase by at most
0.33 mg/L in the Waipawa River, 1.18 mg/L in the Tukituki River and around 5.8 mg/L in the
Kahahakuri Stream.
Maximum concentrations in the Waipawa River with a 17 kgN/ha/yr irrigation is predicted as
approximately 1.9 mg/L (Fig. 19), approximately 4.7 mg/L in the Tukituki River (Fig. 20) and
approximately 5 mg/L in the Kahahakuri Stream (Fig. 21).
Table 29. Nitrogen concentration in three rivers and streams over 20 years due to
irrigation of 17 kgN/ha/yr.
Year Waipawa@RDS
kgN/yr from land use
from irrigation
Average annual flow
(L/s)
Increase in
N concentration
(mg/L)
1 13175 14990 0.03
2 21675 14677 0.05
3 31875 22118 0.05
4 41225 17969 0.07
5 54400 12359 0.14
6 65025 26229 0.08
7 77350 8074 0.3
8 88400 15683 0.18
9 98600 14049 0.22
10 108375 13405 0.26
11 114325 14990 0.24
12 119425 14677 0.26
13 122825 22118 0.18
14 128775 17969 0.23
15 131750 12359 0.34
16 135575 26229 0.16
17 136850 8074 0.54
18 137275 15683 0.28
19 139825 14049 0.32
20 140250 13405 0.33
Year Tukituki @TapairuRd
kgN/yr from land use
from irrigation
Average annual flow
(L/s)
Increase in
N concentration
(mg/L)
1 55250 26726 0.07
2 93500 15933 0.19
3 119425 16111 0.24
4 142375 13147 0.34
5 165750 24053 0.22
6 187425 8575 0.69
Y:\Science\Groundwater\Staff Files\Husam\old_work\Paul\Ruataniwha Plains - 09 Oct.doc 46
7 208250 16895 0.39
8 220575 14883 0.47
9 235450 14592 0.51
10 246500 11726 0.67
11 250325 15220 0.52
12 259250 10462 0.79
13 266475 15074 0.56
14 275400 26726 0.33
15 284750 15933 0.57
16 299200 16111 0.59
17 309825 13147 0.75
18 313650 24053 0.41
19 318325 8575 1.18
20 323000 16895 0.61
Year Kahahakuri@Ongaonga Rd
kgN/yr from land use
from irrigation
Average annual flow
(L/s)
Increase in
N concentration
(mg/L)
1 1275 388 0.1
2 4250 396 0.34
3 7650 407 0.6
4 12325 427 0.92
5 17850 446 1.27
6 22525 466 1.53
7 24650 380 2.06
8 27625 369 2.37
9 29325 349 2.66
10 31450 330 3.02
11 32300 310 3.3
12 33575 388 2.74
13 33575 396 2.69
14 36550 407 2.85
15 41650 427 3.09
16 50575 446 3.6
17 57800 466 3.93
18 59925 380 5
19 61625 369 5.3
20 63750 349 5.79
12.0 RUATANIWHA PLAINS MONITORING NETWORK
Mass balance models, such as the nitrogen mass-balance model described in the report, rely
on estimates of chemical mass moving through the system. Estimates of nitrogen mass
moving through the Ruataniwha Plains system are provided from the following sources:
Nitrogen leaching from soil - HortResearch (pers. comm.) estimates in Table 6
Nitrogen concentration in rivers - HBRC monitoring network
Water flow in rivers - HBRC monitoring network
Nitrogen in groundwater - HBRC monitoring network
Y:\Science\Groundwater\Staff Files\Husam\old_work\Paul\Ruataniwha Plains - 09 Oct.doc 47
Water flow in groundwater - Ruataniwha Plains groundwater flow model
Ideally, the inputs and outputs of nitrogen mass would be known for each sub region.
However, environmental measurements provide only an approximation of mass transfers for
reasons including:
monitoring may not be in ideal locations to measure water quality and flow;
monitoring sites may only measure water quality or only measure water flow;
measurement of water quality or water flow may be sporadic leading to poor statistical
estimates;
surface water quality measurements may be biased by biological and chemical processes
taking place in the river/stream; and
the distribution of chemical species within groundwater is generally poorly known so
estimates of mean concentrations in groundwater probably have large errors.
The present monitoring network is assessed against an „ideal‟ monitoring network for using
mass-balance models in the Ruataniwha Plains. Locations of surface-water, and groundwater,
monitoring sites are discussed with the aim of designing a network that will be of use to
HBRC to assess the effects of future land use change.
12.1 Surface water monitoring
The present monitoring network is not ideal for monitoring the effects of land use in the sub
regions because most sub regions do not have „unique‟ monitoring sites. For example (Table
30), only six of the sub regions are associated with monitoring sites that may „uniquely‟
identify the effects of land use on water quality. In this case „unique‟ means that one surface
water quality at one site relates only to one sub zone.
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Table 30. Surface water sub-zones and „unique‟ identification of land use effects.
Surface water sub
zone
Present monitoring site ‘unique’
identification of land use effects
11 -
12 -
13 -
14 -
15 -
16 273
17 -
18 -
19 -
21 -
22 659
23 -
24 356
25 -
31 -
32 144
33 -
34 398
35 397
36 -
37 -
38 -
39 -
A „unique‟ monitoring location for each sub zone is unrealistic because of: the flow direction
of drainage, pattern of stream flow (or loss) to groundwater, flow direction of groundwater,
the definition of sub zone boundaries and the cumulative effects of land use means. However,
a monitoring network design that represents the cumulative effects of land use across the
Ruataniwha Plains is practical.
A set of surface water monitoring locations (Table 31) is proposed that will allow an estimate
of the effects of land use on surface water quality in each sub zone. A combination of 13
existing sites and 11 new sites should allow monitoring of the effects of land use through the
„chain‟ of cumulative effects (e.g. Table A4.5, panel titled „calc.stream N concentration‟).
HBRC could aim to collect water quantity and water quality information on a regular basis at
these sites.
Y:\Science\Groundwater\Staff Files\Husam\old_work\Paul\Ruataniwha Plains - 09 Oct.doc 49
Table 31. Surface water quality network that could allow the monitoring of land use in
each subzone.
Surface
water sub
zone
River/stream Location of potential monitoring site Location of site,
co-ordinate,
approx
11 Mangatahi Stream d/s of Argyll East bridge 120 426
12 Te Heka Stream d/s of conf. with Karawa Stream 108 474
13 Unnamed Stream end of Wharetoka Rd 102 502
14 Mangaonuku Stream #287, existing existing
15 Mangaonuku Stream d/s of conf. with Mangamate (east of
Creek Rd)
087 513
16 Mangamate Stream #273, existing existing
17 Mangaonuku Stream d/s of Wharetoka Rd bridge by approx.
1 km
099 495
18 Mangaonuku Stream #284, existing existing
19 Unnamed stream/drain As stream/drain crosses Kade Rd, near
Waipawa River
109 366
All zone 1 Waipawa River #26, at RDS existing
21 Kahahakuri Stream # 410, existing existing
22 Kahahakuri Stream #659, existing existing
23 Tukituki River #20, existing existing
24 Tukituki River #356, existing existing
25 Kahahakuri Stream u/s of conf. with Tukituki River (near
Lindsay Rd)
094 310
31 Tukipo River d/s of conf. with unnamed stream 048 316
32 Tukipo River d/s of conf. with Mangatewai River 960 305
33 Tukipo River #279, existing existing
34 Makaretu River off gravel road 987 284
35 Porangahau Stream #397, existing existing
36 Maharakeke Stream #405, existing existing
37 Tukipo River d/s of conf. of unnamed stream 062 311
38 Tukipo River #21, existing existing
39 All Zone 2
and Zone 3
Tukituki River #22, existing existing
A better understanding of the effects of land use will be obtained through a better
understanding of the „baseline‟ nitrogen concentrations in rivers and streams. Table 32
summarises the locations of monitoring sites required to estimate nitrogen concentrations of
rivers and streams entering Ruataniwha Plains. Twenty-eight sites are required to do this, and
five of these sites exist at present. The highest priority for new sites identified in Table 32 is
for measurements on the larger rivers. This is because the larger rivers carry the greatest mass
of nitrogen. Therefore the priority for new sites follow the relative flows and is, from highest
priority to lowest priority:
Tukituki
Tukipo
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Mangaonuku
Porangahau
other small streams
Table 32. Monitoring network that allows measurement of nitrogen entering the
Ruataniwha Plains through rivers and streams.
Name Proposed monitoring site Location of site,
co-ordinate approx.
Mangatahi Stream d/s of Argyll East bridge 120 426
Te Heka Stream d/s of conf. with Karawa Stream 108 474
Unnamed stream end of Wharetoka Rd 102 502
Mangaonuku Stream #287, existing existing
Mangamate Stream #273, existing existing
Mangamauku Stream d/s of conf. with Upokororo (near Hukawai) 029 514
Mangaoho Stream crossing of Holden Rd 023 492
Makaroro River #402, existing existing
Waipawa River #283, existing existing
Unnamed stream crossing of McLeod Rd, west of Springhill 988 443
Ongaonga Stream d/s of Ngaruru Rd crossing 993 414
Unnamed stream crossing Pettit Valley Rd 004 381
Tukituki River at Hylton Burn conf. (or „Folgers‟) 896 422
Tukipo River East of Deans Bush 926 364
Tukipo River #144, existing existing
Mangatewai River at SH50 942 300
Makaretu River at Ellison Rd bridge 815 283
Porangahau Stream at Ormondville Rd bridge 923 229
Awanui Stream at Aorangi Rd bridge 991 241
Unnamed stream at Hinerangi Rd bridge 997 207
Unnamed stream at Hinerangi Rd bridge 013 210
Seven westward draining
streams
crossing Maharakeke Rd and SH2 between
Maharakeke and San Hill
12.2 Groundwater monitoring
Groundwater monitoring wells allow the measurement of long-term effects of land use on
water. Groundwater in the Ruataniwha Plains travels north west to south easterly direction.
Therefore groundwater quality measurements in the north western plains will anticipate the
changes in groundwater quality in the east.
Groundwater monitoring sites in the area where rivers and streams are losing flow (Fig. 3) are
likely to record, broadly, the effects of downwards percolating groundwater. Monitoring sites
underlying thin soils in this area should give the earliest indication of the effects of land use
on water in the Ruataniwha Plains.
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The present network would be improved with the addition of monitoring wells in the area of
losing stream flow (Fig. 3) between Ongaonga and the Tukipo River. Preferred localities
would be below areas where the soil water holding capacity is low. The area of gaining
streams (Fig. 3) is relatively poorly monitored for groundwater quality. Some wells close to
the Mangaonuku Stream and the area of gaining streams between the Waipawa River and
Tukipo River would be useful to future assessments of groundwater discharge to surface
water.
Existing wells give a profile of nitrate concentration versus depth (Fig. 9). This information
could be improved in future to understand sub-regional nitrate profiles in groundwater by
measuring nitrate with other chemical species as wells are completed. Groundwater quality
information could be brought up to date by measurement of groundwater chemistry in wells
133, 135, 136, 138, 223, 1377, 1385 and 1487 as outlined in Section 7.8.1.
13.0 CONCLUSIONS
A model developed to predict the effects of land use in the Ruataniwha Plains on surface
water quality and groundwater quality. The model is Excel-based and is designed for
operation by non-expert modellers and is designed for ease of updating data used in the
model. The model includes input data of observed surface water quantity, surface water
quality, and groundwater quality at monitoring locations in the Ruataniwha Plains.
The model also includes data from the Ruataniwha Plains groundwater flow model such as
aquifer geometry and predictions of groundwater flow directions and predictions of
groundwater flow velocities under natural and irrigated conditions.
Surface water and groundwater capture zones are used to predict water quality and in these
zones the estimated groundwater travel time is considered in nitrogen transport calculations.
Nitrogen outputs from existing land uses may be compared with observed surface water
quality and observed groundwater quality with the model. The effects of sub-regional land
uses on water quality may be estimated with the model. The model may also estimate the
effects of point sources on water quality. Steady-state (i.e. constant flow) surface water and
groundwater quality, as result of land-use change, may be predicted. Groundwater quality and
surface water changes, as a response to land-use change, may be estimated over a time period
of years and decades.
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Model calibration required the matching of nitrogen generation from existing land use to
observed surface water and groundwater quality. A calibration of existing land use to
observed mean surface water quality indicates the most land uses in the Ruataniwha Plains are
generating 5 kgN/ha/yr or less. The area of largest nitrogen leaching is predicted to generate
130 kgN/ha/yr in an 800 ha sub-zone near the eastern Waipawa Gorge.
Nitrogen input from land use predicted by mean surface water quality measurements tends to
predict nitrogen concentrations in groundwater that are lower than observations, assuming
that groundwater is fully mixed. Groundwater quality measurements in the Ruataniwha
Plains indicates that groundwater is not fully mixed. Mixing ratios are calculated to and from
assumed land uses and capture zones. It is concluded that nitrogen is fully mixing in the top
10 m, or less, of aquifer in a number of examples.
The model is used to predict the effects of a nitrogen generation from a number of irrigated
land uses on surface water quality at 16 sites and groundwater quality at 14 sites. For
example, a land use of irrigated beef, generating an extra leaching of 17 kgN/ha/yr over the
Plains is predicted to cause mean surface water nitrogen concentration at the Kahahakuri @
Ongaonga Bridge to rise from 2.91 mg/L to 5.55 mg/L. A 92 kgN/ha/yr application over the
Plains, equivalent to a mixed cropping and dairy land use is predicted to raise mean nitrogen
concentrations at this site to 17.2 mg/L.
The time scale of the change in surface water quality is decadal - for example the mean
nitrogen concentration at Kahahakura @ Ongaonga Bridge is predicted to reach within 0.5
mg/L of the steady-state concentration for a 17 kgN/ha/yr application in 20-30 years after
commencement of irrigation.
Predictions of surface water quality based on annual, seasonal, and weekly mean flows are
made at three surface water sites. Nitrogen concentrations tend to increase with time because
of nitrogen input to streams increases with time. For example, a 17 kgN/ha/yr application is
predicted to increase mean Kahahakuri @ Ongaonga Bridge nitrogen concentrations by about
2.5 mg/L after 14 years of irrigation. Maximum nitrogen concentrations, when flow is
relatively low, also increase with time. For example, it is predicted that at 17 kgN/ha/yr will
result in nitrogen concentrations of about 5 mg/L greater than present at times of low flow
after 14 years of irrigation.
Y:\Science\Groundwater\Staff Files\Husam\old_work\Paul\Ruataniwha Plains - 09 Oct.doc 53
Nitrogen concentrations in groundwater are predicted to rise by less than 10 mg/L in 50 years
of 17 kgN/ha/yr irrigation assuming that nitrogen is fully mixed in the aquifer. Increases of
up to around 50 mg/L are predicted in 50 years with a 17 kg/ha/yr application and estimates of
partial mixing. The time-scale of changes in groundwater quality is also decadal, with some
groundwater quality showing predicted increases through the 50 years period of simulation.
14.0 REFERENCES
Chapelle, F. H., 1993. Ground-water Microbiology and Geochemistry. John Wiley & Sons,
N. Y. 424p.
Hawkes Bay Regional Council, 2001. State of the Environment Update 2001. Hawkes Bay
Regional Council. 106p.
Hawkes Bay Regional Council, 2001. Subsurface geology of the Ruataniwha Plains and
relation to hydrology. Environmental Management Group Internal Report EMI 0111.
17p + 10 figs.
Hawkes Bay Regional Council, 2000. Sate of the Environment Update 2000. Hawkes Bay
Regional Council. 102p.
Hawkes Bay Regional Council, 1999. Ruataniwha Plains conceptual hydrogeological model.
Environment Management Group Technical Report EMT 99/3. 56p.
Hawkes Bay Regional Council, 1998. Sustainable low flow project. Ruataniwha rivers
Waipawa-Tukipo-Tukituki. Environmental Management Group Technical Report
EMT 98/2. 106p.
Lincoln Environmental, 2002. Ruataniwha Plains Water Management Stage 1: potential
irrigation demand. Report No. 4477/2 (Parts 1 and 2).
Luba, L.D., 2001. Hawkes Bay. In Groundwaters of New Zealand. M.R. Rosen and P.A.
White (eds). New Zealand Hydrological Society Inc., Wellington. p367-380.
Y:\Science\Groundwater\Staff Files\Husam\old_work\Paul\Ruataniwha Plains - 09 Oct.doc 54
Murray, D.L., 2002. Modelling Ruataniwha Plains Groundwater. Report prepared for
Hawkes Bay Regional Council. 44p.
Sarrazin, U., 2002. Aquatic Habitat Survey of the Ruataniwha Plains. Draft report Hawkes
Bay Regional Council.
Y:\Science\Groundwater\Staff Files\Husam\old_work\Paul\Ruataniwha Plains - 09 Oct.doc 55
Extents of the Ruataniwha Plains
RiversRoads
N
0 4 8 Kilometers
Man
ga o nuku stream
Waipaw
a
Tukituki
Tukipo River
Makaretu Stream
Lake Hatuna
River
River
Figure 1. Ruataniwha Plains and location of rivers, streams and roads.
0 4 8 Kilometers
Extents of the Ruataniwha Plains
20m contours
N
Figure 2. Ruataniwha Plains - 20 m contours.
Y:\Science\Groundwater\Staff Files\Husam\old_work\Paul\Ruataniwha Plains - 09 Oct.doc 56
Extents of the Ruataniwha PlainsRivers40m contours
G Rivers and streams gain flow
L Rivers and streams lose flow
N No large loses or gains in flow
N
0 3 6 Kilometers
L
L
N
G
Figure 3. Regions of the Ruataniwha Plains where rivers and streams gain and lose flow.
Extents of the Ruataniwha Plains
Rivers, streams and overall ranking
1
2
3
4
0
40m contours
No assessment
Poor
Good
N
0 4 8 Kilometers
Figure 4. Rivers, streams and overall ranking (after Sarrazin, 2002).
Y:\Science\Groundwater\Staff Files\Husam\old_work\Paul\Ruataniwha Plains - 09 Oct.doc 57
Figure 5. Groundwater flow model grid of the Ruataniwha Plains with contours of
predicted groundwater level.
Y:\Science\Groundwater\Staff Files\Husam\old_work\Paul\Ruataniwha Plains - 09 Oct.doc 58
Figure 6. Scatter plot of ammonium vs. nitrate concentrations in Ruataniwha
groundwater samples. Very few samples contain measurable concentrations of
both ammonium and nitrate.
Figure 7. Scatter plot of nitrate vs. total nitrogen concentration for Ruataniwha
groundwater samples with more than 0.1 mg/l nitrate.
Y:\Science\Groundwater\Staff Files\Husam\old_work\Paul\Ruataniwha Plains - 09 Oct.doc 59
Figure 8. Scatter plot of ammonium vs. total nitrogen concentrations for Ruataniwha
groundwater samples with less than 0.1 mg/l nitrate.
Figure 9. Scatter plot of nitrate concentration vs. well depth for Ruataniwha groundwater
samples.
Y:\Science\Groundwater\Staff Files\Husam\old_work\Paul\Ruataniwha Plains - 09 Oct.doc 60
N
0 3 6 Kilometers
Extents of the Ruataniwha Plains
Zones
11
12
13
1415
16
17
18
21
19
22
25
2324
31
37
3635
34
33
32
39
38
Figure 10. Location of surface-water zones.
%
%
%
%
%%% %
%
%
%%
%
%%
%%
%
%
%
%
%
%
%
%
%
%
%
%
%
%
%
%
%%
%
%
%
%
%
%
%%
%
%%%% %
%%
%
17
18
19
20
2122 23
24
25
26
27
28
29
139
140
141
142
144
273
277
279
280
281
283
284
285
286
287
288
289
290
291
292
293, 294
356
397
398
402
405
410
413
414
659
2221
2292
2293
2294
2316
2403
22392315
% Surface water sites
Extents of the Ruataniwha Plains
40m contours
139
N
0 3 6 Kilometers
Figure 11. Location of surface-water monitoring sites.
Y:\Science\Groundwater\Staff Files\Husam\old_work\Paul\Ruataniwha Plains - 09 Oct.doc 61
Groundwater zones
Extents of the Ruataniwha Plains
Rivers
N
0 4 8 Kilometers
11
12
13
14
21,22,23
24
25
33
34
35
31, 32
Figure 12. Location of groundwater capture zones.
$$$$
$ $
$$$
$
$
$$
$$
$
$
$
$$
$
$
$
$
$
$
$
$
$
$$
$$
$
$
$$$
133
137
145
146
147
220221
222
223
224225
226
227
229
230
231
233
234
235
236
237
239
2431377
13851497
2224 2227
2229
2387
2597
2598, 2599
134135 136
138
1365
$ Groundwater sites
Extents of the Ruataniwha Plains
40m contours
236
N
0 3 6 Kilometers
Figure 13. Location of groundwater monitoring sites.
Y:\Science\Groundwater\Staff Files\Husam\old_work\Paul\Ruataniwha Plains - 09 Oct.doc 62
Figure 14. Estimated seepage velocity across the Ruataniwha Plains (m/day), non-
irrigated.
Figure 15. Estimated seepage velocity across the Ruataniwha Plains (m/day), irrigated
model.
Y:\Science\Groundwater\Staff Files\Husam\old_work\Paul\Ruataniwha Plains - 09 Oct.doc 63
0
2
4
6
8
10
12
0 200 400 600 800
Week number
N m
g/L
Figure 16. Predicted weekly nitrogen concentration in the Waipawa River @ RDS with a 92 kgN/ha/yr irrigation.
Y:\Science\Groundwater\Staff Files\Husam\old_work\Paul\Ruataniwha Plains - 09 Oct.doc 64
0
5
10
15
20
25
30
0 200 400 600 800
Week number
N m
g/L
Figure 17. Predicted weekly nitrogen concentration in the Tukituki River @ Tapairu Rd with a 92 kgN/ha/yr irrigation.
Y:\Science\Groundwater\Staff Files\Husam\old_work\Paul\Ruataniwha Plains - 09 Oct.doc 65
0
5
10
15
20
25
30
0 200 400 600 800
Week number
N m
g/L
Figure 18. Predicted weekly nitrogen concentration in the Kahahakuri @ Ongaonga with a 92 kgN/ha/yr irrigation.
Y:\Science\Groundwater\Staff Files\Husam\old_work\Paul\Ruataniwha Plains - 09 Oct.doc 66
0
0.5
1
1.5
2
0 200 400 600 800
Week number
N m
g/L
Figure 19. Predicted weekly nitrogen concentration in the Waipawa River @ RDS with a 17 kgN/ha/yr irrigation.
Y:\Science\Groundwater\Staff Files\Husam\old_work\Paul\Ruataniwha Plains - 09 Oct.doc 67
0
1
2
3
4
5
0 200 400 600 800
Week number
N m
g/L
Figure 20. Predicted weekly nitrogen concentration in the Tukituki River @ Tapairu Rd with a 17 kgN/ha/yr irrigation.
Y:\Science\Groundwater\Staff Files\Husam\old_work\Paul\Ruataniwha Plains - 09 Oct.doc 68
0
1
2
3
4
5
6
0 200 400 600 800
Week number
N m
g/L
Figure 21. Predicted weekly nitrogen concentration in the Kahahakuri @ Ongaonga with a 17 kgN/ha/yr irrigation.
Y:\Science\Groundwater\Staff Files\Husam\old_work\Paul\Ruataniwha Plains - 09 Oct.doc 69
Appendix 1. Copy of contract.
Ruataniwha Plains Nitrate Model
1. Study purpose
The principal aim of the study is to provide sufficient information to enable HBRC to
characterise the likely effects of the existing and two future land use scenarios on:
the nitrate concentrations in groundwater under both steady state and transient (non-steady
state) conditions;
the annual, seasonal and weekly river N concentrations at the points of discharge to
surface water, under both steady state and transient (non-steady state) conditions; and
the timeframes under which these effects to both groundwater and surface water are likely
to occur.
2. Project Scope
The scope of the study will be defined by the following;
The project area will be that area covered by the existing Ruataniwha Plains groundwater
model constructed by Dave Murray.
The land use scenarios to be modelled will be two potential future land use scenarios
identified for the future irrigation demand modelling conducted by Lincoln Ventures, and
the existing land use. Models of the scenarios to be completed by Lincoln Ventures by
the end of May 2002. To be paid for by HBRC separate to this contract.
Steady state conditions, in terms of groundwater quality and the effects on streams, will be
assumed to have occurred for the existing land use scenario (note: this assumption will
need to be confirmed during the study by a comparison of the groundwater travel time
estimations derived and a more detailed review of the existing SoE monitoring
information available).
Review of chemical conditions in the aquifer with a view to assessing whether nitrogen is
a conservative tracer
The nitrogen losses under various land uses in terms of kg/ha/yr will be derived from the
latest version of Overseer by Agresearch by the end of May 2002. To be paid by HBRC
separate to this contract.
Dave Murray will provide all groundwater flow model outputs required by the end of May
2002, to be paid for by HBRC, separate to this contract.
Realisation of the full extent of each of the future land use scenarios will be assumed to
occur over a 20 year period.
HBRC will provide information on, map locations of land uses, average and transient flow
in the receiving streams and rivers, groundwater and surface water quality data by the end
of May 2002.
Y:\Science\Groundwater\Staff Files\Husam\old_work\Paul\Ruataniwha Plains - 09 Oct.doc 70
This project will be expected to define groundwater capture zones if required.
3. Specific outputs required
The study outputs should include:
An estimate of the mass input of N, under both steady-state and transient conditions for
each scenario.
An estimate of groundwater flow direction and travel time across the Plains. This will be
linked to a separate HBRC project on water dating.
Estimates of groundwater outflow zones and contributing groundwater capture
zones/areas.
Estimates of in-groundwater mass N transport and concentrations by zone, and
aggregated, for each scenario.
Estimates of steady-state groundwater N concentrations.
Estimates of the steady-state nutrient mass discharge to each discharge area on an annual,
seasonal and weekly basis and aggregated, for each scenario
Estimates of transient mass discharge to each discharge area on an annual, seasonal and
weekly basis and aggregated, for each scenario
Estimates of the effects of the steady-state nutrient mass discharge from each discharge
area, on river N concentrations on an annual, seasonal and weekly basis, for each scenario.
Estimate of transient nutrient mass discharge from each discharge area, on river N
concentrations on an annual, seasonal and weekly basis, for each scenario.
4. Model calibration
The is groundwater quality information available for at least 12 long term groundwater
monitoring sites and up to 10 surface water sites. The model should aim to approximate the
actual results found at these sites under the existing land use.
5. Output presentation
The final report will include the information collated, model description, and present, and
discuss, the predictions. Graphical presentation of the information by way of contour maps
and the like will be used wherever possible.
Completion date: 31 August 2002, dependent on Lincoln Ventures, Agresearch, and
David Murray completing their work by the dates specified in this
contract.
Y:\Science\Groundwater\Staff Files\Husam\old_work\Paul\Ruataniwha Plains - 09 Oct.doc 71
Appendix 2. Hydrological data used in this study.
Physical hydrology - surface water (all sites include gauging measurements).
Table A2.1 TIDEDA file: Rpflow.mtd
Site Name On Off Comments
23205 Waipawa at Stewarts 990831 1011204
23207 Tukituki at Tapairu Rd 870529 1011031
23218 Makaroro at Burnt Bridge 750702 1011120
23220 Tukipo at SH50 (Punawai) 761229 1020123
23235 Waipawa at RDS 880422 1020122
23248 Kahahakuri at Ongaonga Rd Bridge 990826 1011227
23252 Tukituki at Folgers Lake 790511 1010903
1023211 Mangaonuku at Argyll Rd 991209 1011204
1223220 Waipawa at Pendle Hill 940624 1010815
Physical hydrology - groundwater.
Table A2.2 TIDEDA file: RPGWMan.mtd
Site Name On Off Comments
402001 Ruataniwha Plains at Springfield 920123 1020417
403001 Ruataniwha Plains at Greene 920123 950219
403003 Ruataniwha Plains at H.B.F.M. 920123 1020417
404001 Ruataniwha Plains at Hatuma 920422 1020417
884001 Ruataniwha Plains at Te Papa 920121 1020417
884005 Ruataniwha Plains at Feedlot 920204 1020417
884007 Ruataniwha Plains at Springhill 920204 1020417
884009 Ruataniwha Plains at Riddel 920204 1020417
884011 Ruataniwha Plains at Atherstone 920123 1011227
884013 Ruataniwha Plains at Thompsen 920123 1020417
884015 Ruataniwha Plains at Ingrams 970123 1020320
884017 Ruataniwha Plains at Kowhai Main (Worsnops) 981105 1020320
885001 Ruataniwha Plains at Glen Athol 920226 1020417
886001 Poukawa (Brownrigg) at Barkers (Cato) 1000628 1001115
887001 Poukawa (Brownrigg) at Homestead (Primer) 1000628 1001115
893001 Ruataniwha Plains at Lutz 920123 1020320
893003 Ruataniwha Plains at Kindar 920226 1020417
893005 Ruataniwha Plains at Totaranui 920226 1020417
893007 Ruataniwha Plains at Forest Gate 920226 1020417
893011 Ruataniwha Plains at Eldarado House 970210 1020417
894001 Ruataniwha Plains at Golf Club 920123 1020417
894003 Ruataniwha Plains at Livingstone 920123 1020417
894005 Ruataniwha Plains at Grocorp 920226 1020417
894007 Ruataniwha Plains at Donald 920123 1020417
894009 Ruataniwha Plains at Hudson 970123 1020327
894011 Ruataniwha Plains at Pacific Orchard 970123 1020417
895001 Ruataniwha Plains at Punanui (deep) 920204 1020417
895003 Ruataniwha Plains at Punanui (shallow) 920204 1020417
Y:\Science\Groundwater\Staff Files\Husam\old_work\Paul\Ruataniwha Plains - 09 Oct.doc 72
Table A2.3 TIDEDA file: RPGWAuto.mtd
Site Name On Off Comments
884001 Ruataniwha Plains at Te Papa 880816 1011127
884003 Ruataniwha Plains at Davenport Well 881123 920616
884005 Ruataniwha Plains at Feedlot 920302 1011003
884007 Ruataniwha Plains at Springhill 920310 1011127
884015 Ruataniwha Plains at Ingrams 961023 1000828
884017 Ruataniwha Plains at Kowhai Main (Worsnops) 971029 1011114
893011 Ruataniwha Plains at Eldorado House 961010 1000630
894007 Ruataniwha Plains at Eldorado Donalds 961023 1011128
894009 Ruataniwha Plains at Hudson 961002 1011128
894011 Ruataniwha Plains at Pacific Orchard 961211 1011003
895001 Ruataniwha Plains at Punanui No. 1 921001 1011128
895003 Ruataniwha Plains at Punanui No. 2 920703 940330
Table A2.4 Water chemistry - groundwater sites
SiteID SiteDesc
133 Takapau investigation bore 1
134 Takapau investigation bore 5
135 Takapau investigation bore 6
136 Smiths bore @ Oruawharo road
137 Fords bore @ Station road
138 Carmans house bore @ Station road
145 P Kings bore
146 Feedlot bore, Eastern Equities (Deer), Tikokino
147 EEC domestic bore
220 AR Eddy, Butler Rd, Tikokino
221 N Riddell, 300 Butler Rd, Tikokino
222 Glen Athol Farm, Tikokino Rd
223 Grocorp E, Thornton Orchard, Wakarara Rd, Ongaonga Pacific orchard, Plantation Rd
224 J Duncan McLean (Springhill), Wakarara Road, Ongaonga
225 OD Thompson, Wakarara Rd
226 Waipukurau Golf Club, Waipukarau
227 J Ormsby, Station Rd, Maharakeke
229 R Harrison, Paget Rd, Takapau
230 Lutz Kneesch, Fairfield Rd, Takapau
231 Livingstone, Ashcott Rd
233 Kinder, SH50 Ongaonga
234 HJ Talbot, Blackburn Rd, Ongaonga
235 Richmonds, HBFM Co, 116 Fraser Rd, Takapau
236 B Ingram, 1689 Tikokino Rd, Waipawa
237 Te Papa, Grocorp, SH50, Ongaonga
239 Grocorp, Goldwater Orchard, Swamp Rd, Ongaonga
243 Don & Allison Lynch, Oruawharo road, Takapau
1365 Grocorp Aitken (Pacific), Plantation Rd, Waipawa
1377 Carman's farm bore @ tap on pumpshed, Station road
1385 De Stackpoles house bore, Fraser road
1497 HBRC investigation bore, 1 st bore at oxidation pond, Fairfield road
2224 Jensen, Tukituki, Makaretu
2227 Meredith, Onga Onga
2229 Murdochs Well
2387 Warsnops, Corner SH50 and Makaroro Road
2597 Plantation Road Dairies, Bore 1 Plantation Road
2598 Plantation Road Dairies, Bore 2 Paddock 10 Sth side fence line
2599 Plantation Road Dairies, Bore 3 paddock 11 Nth side fence line
Y:\Science\Groundwater\Staff Files\Husam\old_work\Paul\Ruataniwha Plains - 09 Oct.doc 73
Table A2.5 Water chemistry - surface water sites.
SiteID SiteDesc
17 Tukituki river u/s Waipukurau oxidation pond discharge @ SH 2 bridge
18 Waipawa river @ Waipawa @ SH 2
19 Makaretu river @ SH 50
20 Tukituki river @ Onga Onga road bridge
21 Tukipo river @ Ashcott road
22 Tukituki river @ Pukeora
23 Tukituki river @ Coughlin road
24 Tukituki river u/s Waipukurau oxidation pond discharge
25 Tukituki river d/s Waipukurau pond discharge @ gauge station, Tapairu Rd
26 Waipawa river u/s solid waste site @ gauge station "RDS"
27 Waipawa river d/s Waipawa oxidation pond discharge @ Walker Road
28 Tukituki river d/s Waipawa river confluence
29 Tukituki river d/s Tamumu solid waste site
139 Maharakeke stream @ Station road
140 Maharakeke stream @ Oruawharo road
141 Makaretu stream @ Fairfield (Burnside) road
142 Makaretu stream @ Stubbs road
144 Tukipo river @ State Highway 50 @ gauge station (Punawai)
273 Mangamate stream @ State Highway 50 bridge
277 Mangatarata stream u/s Tukituki river confluence @ Mangatarata road bridge
279 Tukipo river u/s Maharakeke stream confluence @ Burnside road bridge
280 Waipawa river at SH 50
281 Tukituki river @ Tamumu bridge
283 Waipawa river at Wakarara road crossing (u/s Makaroro stream confluence)
284 Mangaonuku stream u/s Waipawa river at Tikokino road
285 Papanui stream u/s Tukituki river confluence @ Middle road bridge
286 Mangaonuku stream @ Argyll East road
287 Mangaonuku stream @ SH 50 bridge 3 u/s Mangamate stream confluence
288 Papanui stream @ Elsthorpe Road Bridge (u/s Otane waste water discharge)
289 Papanui stream d/s Otane waste water works discharge (alternative for Middle road bridge site?)
290 Makaretu river @ Paget/Ellison road bridge
291 Waipawa river @ North Block road
292 Makaroro stream u/s Dutch creek @ Wakarara road
293 Papanui stream 20m d/s Te Aute College waste water discharge
294 Papanui stream d/s Te Aute College waste water discharge @ SH2 culvert
356 Tukituki river @ State Highway 50 @ gauge station
397 Porangahau stream at Oruawharo road
398 Porangahau stream at Fraser road
402 Makaroro river at Makaroro road
405 Maharakeke stream at SH 2
410 Kahahakuri stream at Ongaonga (Fairfield) road
413 Porangahau stream tributary u/s Takapau dump
414 Porangahau stream tributary d/s Takapau dump
659 Kahahakuri stream @ Plantation road bridge
2221 Tukituki River 50 upstream Waipukurau oxidation pond outlet drain
2239 Tukituki River 50 metres downstream of confluence of the Waipukurau oxidation pond outlet
2292 Tukituki River 1000m downstream of the Waipukurau Oxidation Pond outlet drain confluence
2293 Tukituki River 2000m downstream of the Waipukurau Oxidation Pond outlet drain confluence
2294 Tukituki River, 100m upstream Waipawa river confluence
2315 Tukituki River 200m downstream of the Waipukurau Oxidation Pond outlet drain confluence
2316 Tukituki River 400m downstream of the Waipukurau Oxidation Pond outlet drain confluence
2403 Tukituki River @ Shag Rock
Y:\Science\Groundwater\Staff Files\Husam\old_work\Paul\Ruataniwha Plains - 09 Oct.doc 74
Appendix 3. Mean flow and mean water chemistry values.
Table A3.1 Mean flow from TIDEDA records.
Site Location Period of record Monthly mean
flow m3/s
23205 Waipawa at Stewarts 31/08/99 - 04/12/01 9.4
23207 Tukituki at Tapairu Road 29/05/87 - 31/10/01 15.1
23218 Makaroro at Burnt Bridge 02/07/75 - May 1991 6.12
23220 Tukipo at SH50 29/12/76 - 23/01/02 1.5
23235 Waipawa at RDS 22/04/88 - 22/01/02 16.1
23248 Kahahakuri at Onga Onga Road Bridge 26/08/99 - 27/12/01 0.516
1023211 Mangaonuku @ Argyll Road 09/12/99 - 04/12/01 2.148
Table A3.2 Mean flows estimated by Geoff Wood from available gaugings or correlations.
Monitoring
points:
Surface
water
quality site
River/stream name Co-ordinates Estimated
mean
water flow
at site
m**3/s
273 Mangamate@SH50
bridge
2807300 6152300 0.47
284 Mangaonuku @
Tikokino Rd
2811300 6138400 3.6
287 Mangaonuku@SH50 2808573 6155198 0.28 reasonable estimate, R2 = 0.86
356 Tukituki @SH50 2796500 6135600 4.20
20 Tukituki at Ongaonga Br 2807326 6132667 4.22
659 Kahahakuri@Plant. Rd
Bridge
2805010 6137800 - insufficient data
279 Tukipo@Burnside 2794737 6132377 2.99
21 Tukipo@Ashcott 2808000 6131000 7.7
398 Porangahau@Fraser 2799853 6128722 - insufficient data. Only 1 concurrent
gauging with Tukipo site. Ratio of the
2 (58/361 * Tukipo mean of 1500)
gives mean at this site as 0.24 m3/s.
397 Porangahau@Oruawharo 2797710 6125906 0.67 rough r2 (0.79), probably reasonable
at mean flow - at least the mean is
interpolated and not extrapolated!.
405 Maharakeke@SH2 2806838 6129896 1.38 r2=0.87, n=5, valid 'x' flow range
=700l/s, "mean" x value =1500 l/s
Y:\Science\Groundwater\Staff Files\Husam\old_work\Paul\Ruataniwha Plains - 09 Oct.doc 75
Table A3.3 Mean nitrogen concentrations in groundwater.
Site Nitrate-nitrogen Period of record Ammonia-nitrogen* Period of record
133 21.6 14/04/83 - 18/09/92
134 5.4 25/05/84 - 18/04/95
135 13.8 03/05/82 - 22/09/92
136 14.03 14/04/88 - 18/04/95
137 1.66 30/07/81 - 18/09/92
138 31.5 30/07/81 - 18/04/95
145 0.75 28/04/93 - 12/06/95
146 1.00 28/04/93 - 27/11/01
147 0.38 28/04/93 - 20/09/94
220 0.35 06/09/94 - 28/11/01
221 0.15 06/09/94 - 28/11/01
222 0.48 05/10/94 - 17/05/95
223 6.26 18/11/88 - 26/11/97
224 0.09 22/11/94 - 27/11/01 0.27 21/04/95 - 27/11/01
225 0.90 06/09/94 - 12/06/95
226 0.04 06/09/94 - 03/10/01 0.38 05/10/94 - 03/10/01
227 0.07 06/09/94 - 11/02/97 0.37 05/10/94 - 11/02/97
229 0.08 06/09/94 - 28/11/01 0.55 05/10/94 - 28/11/01
230 0.04 06/09/94 - 02/10/00 0.46 05/10/94 - 02/10/00
231 4.41 06/09/94 - 28/11/01
233 0.42 06/09/94 - 13/06/00
234 0.15 06/09/94 - 23/03/95 2.03 05/10/94, 02/11/94
(two values)
235 0.01 06/09/94 - 20/03/02 0.54 05/10/94 - 28/11/01
236 0.58 18/11/83 - 28/11/01
237 0.14 09/03/94 - 27/11/01 0.02 14/02/97 - 27/11/01
239 0.07 09/03/94 - 28/11/01 0.82 11/02/97 - 28/11/01
243 0.09 06/09/94 - 21/03/01 1.77 05/10/94 - 21/03/01
1365 0.01 06/10/88 - 28/11/01 0.22 26/11/97 - 28/11/01
1377 22.6 30/07/81 - 15/08/89
1385 10.4 30/07/81 - 23/03/95
1497 1.22 08/12/82 - 06/08/87
2224 0.03 14/02/97 - 03/12/99 0.04 14/02/97 - 03/12/99
2227 3.52 14/02/97 - 03/10/01
2229 0.05 14/02/97 - 02/10/00
2387 1.5 02/10/00 (one value)
2597 6.29 22/01/01 - 07/03/02
2599 5.1 22/01/01 - 07/03/02
* Most wells have ammonia-nitrogen detections. The values here are means from wells
where NH4 is the indicator of nitrogen (Table 1).
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Table A3.4 Mean nitrogen concentrations in surface water.
Mean Concentrations mg/L
Site Nitrate-
nitrogen Period of record
Dissolved
inorganic nitrogen Period of record
20 0.26 13/09/90 - 10/05/00 0.38 28/04/98 - 10/05/00
21 1.10 09/08/77 - 09/01/97 - -
23 0.99 13/09/90 - 20/07/94 - -
26 0.63 13/09/90 - 10/05/00 0.77 24/06/98 - 10/05/00
144 0.85 09/08/77 - 19/02/02 0.99 28/04/98 - 19/02/02
273 1.08 09/08/77 - 04/03/98 - -
279 2.08 20/07/94 - 09/01/97 - -
280 0.17 09/08/77 - 19/02/02 0.17 03/12/98 - 19/02/02
283 0.10 09/08/77 - 10/05/00 0.11 28/04/98 - 10/05/00
284 1.66 13/11/78 - 09/01/97 - -
286 1.64 11/07/94 - 19/02/02 1.29 16/08/00 - 19/02/02
287 0.53 09/08/77 - 10/05/00 1.23 28/04/98 - 10/05/00
290 0.07 11/07/94 - 10/05/00 0.20 03/01/98 - 10/05/00
356 0.8 09/08/77 - 19/02/02 0.23 28/04/98 - 19/02/02
397 1.91 09/08/77 - 10/05/00 1.51 28/07/98 - 10/05/00
398 3.53 30/06/81 - 23/03/95 - -
402 0.14 09/08/77 - 22/01/97 - -
405 1.96 09/08/77 - 07/01/77 - -
410 2.91 16/07/82 - 10/05/00 3.23 25/02/99 - 10/05/00
659 2.59 07/12/94 - 03/12/98 4.29 28/07/98, 03/12/98 (2 values)
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Appendix 4. Contents of Excel spreadsheets and worksheets.
A4.1 Excel spreadsheet Ruasteadystate.xls
This contains worksheets for simulating water quality using non-irrigated seepage velocities
with broadly, the following purposes:
Model development: Ruatbase
MZ
SWZ
SWZ Mon
GW Inf Zones
GW Mon
Irricells
Irr SWZ
gwflow
streams
Running the model: N summary
surfqualpredicts
gwqualpredicts
N bkg
Nirri
Npoint
Intermediate workings: Z1A bkg, Z1B bkg, Z2 bkg, Z3A bkg, Z3B bkg, Bkg sum
Z1A irri, Z1B irri, Z2 irri, Z3A irri Z3B irri, Irr sum
N load all
Other: STDM+10, Wells Dm, Gwq.sites, Swg.sites, test
The worksheets used for running the model are updated should model properties change (e.g.
altering surface water zones is outlined in Appendix 5, Section 5.3).
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Ruatbase - a base map of the region
A worksheet that represents the extent of the groundwater flow model of the Ruataniwha
Plains:
80 rows by 100 columns
500 m by 500 m cell size
Inactive cells = grey, and a value of 0
Active cells = white, and a value of 1
MZ - the major zones
Definitions of zones in the Ruataniwha Plains model:
0 = outside the model area, or stream beds
1 = zone where the water quality effects of landuse are likely to reside in the Waipawa
River, which includes the catchments of the:
Mangaonuku Stream, and other northern streams, Waipawa River
some land on the south side of the Waipawa River is included where there is
evidence that the land drains to the Waipawa River through surface water or
groundwater
2 = zone between the Waipawa River and Tukituki River where the water quality effects
of landuse are likely to reside in the Tukituki River. This excludes the Tukipo River.
3 = zone south of the Tukituki River where the water quality effects of landuse are likely
to reside in the Tukipo River catchment. The zone includes the catchments of the
Tukipo River, Makaretu River, Porangahau Stream, and Maharakeke Stream.
SWZ - surface-water zones
This worksheet defines sections of the Ruataniwha Plains where the effects of landuse may be
represented at surface water quality monitoring sites. Numbers are two-digit (Fig. 10, Table
A4.1), with the first digit being a major zone (1, 2 or 3). The pattern of stream flow gains and
losses (Fig. 3) are a consideration in defining these zones. Generally monitoring sites are
sited in gaining zones. This is because sites in losing zones are less likely to be affected by
land use.
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A4.1. Location of surface-water zones.
Zone Number Location
11 Mangatahi Stream catchment
12 Te Heka Stream, and others east of Mangaonuku Stream
13 Catchments east of Mangaonuku Stream
14 Catchment of the Mangaonuku Stream
15 Catchment of the Mangaonuku Stream
16 Catchment of the Mangamate Stream
17 Catchment of the Mangamauku Stream + unnamed stream that crosses
SH50 at Richardson‟s Bridge
18 Area between Mangamauku Stream, Waipawa River
19 Area around Waipawa River, eastern Ruataniwha Plains
21 Area between Waipawa River and Lindsay water race (approx)
22 Area between Kahahakuri Stream and Lindsay water race
23 Area between Kahahakuri Stream and Tukituki River (west)
24 Tukituki River terraces u/s of SH50
25 Kahahakuri Stream to Tukituki River (east)
31 Tukituki River to Tukipo River
32 Tukipo River to Mangatewai River (north)
33 Tukipo River to south of Mangatewai River
34 Tukipo River to Makaretu River (west)
35 Makaretu River to Porangahau Stream (west)
36 Makaretu River to Maharakeke Stream
37 Tukipo River to Makaretu River (east)
38 Makaretu River at eastern Ruataniwha Plains
39 Tukituki River to Tukipo River (west)
SWZ Mon - surface-water quality monitoring sites
The locations of the following surface water quality monitoring sites (Fig. 11, Table A4.2) of
some sites listed in Appendix 2 and Appendix 3.
Table A4.2. Hawkes Bay Regional Council surface-water quality monitoring sites.
Site River/Stream
287 Mangaonuku
273 Mangamate
286 Mangaonuku
402 Makaroro
283 Waipawa
280 Waipawa
284 Mangaonuku
659 Kahahakuri
410 Kahahakuri
356 Tukituki
26 Waipawa
20 Tukituki
144 Tukipo
21 Tukipo
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22 Tukituki
279 Tukipo
405 Maharakeke
23 Tukituki
398 Porangahau
397 Porangahau
290 Makaretu
GW Inf zones - groundwater capture zones
Cells that are within the capture zone of selected groundwater monitoring sites are tabulated.
Cells are identified through flowpaths identified by the Ruataniwha Plains MODFLOW
steady-state model. The capture zones (Fig. 12) are associated with groundwater monitoring
sites (Fig. 13) as in Table A4.3.
Table A4.3. Groundwater capture zones and monitoring wells.
Capture zone
number
Groundwater well
number (sheet
GWmon)
Depth of well
11 220 45.7
12 236 65.8
13 146 12.4
14 222 21.8
21 224 75
22 223 55.5
23 239 142
24 2227 ?
25 233 46.3
31 2229 ?
32 231 22.6
33 229 24.4
34 1497 ?
35 1377 7
The capture zone includes the cell of each monitoring well.
GW mon - location of groundwater quality monitoring sites
As with the sheet „GW inf zones‟ but with the locations and numbers, of all groundwater
quality monitoring sites indicated.
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Table A4.4. Summary of all nitrogen loadings to the Ruataniwha Plains.
Point Sources
Surface
zones
Loading Irrigation Loading Number of cells
Total loading
1/cells Total output
kgN/ha/year kgN/ha/year per ha kgN/yr
11 0 11 0 0 0 25 0
12 0 12 0
13 0 13 0
14 0 14 0
15 0 15 0
16 0 16 0
17 0 17 0
18 0 18 0
19 0 19 0
21 0 21 0
22 0 22 0
23 0 23 0
24 0 24 0
25 0 25 0
31 0 31 0
32 0 32 0
33 0 33 0
34 0 34 0
35 0 35 0
36 0 36 0
37 0 37 0
38 0 38 0
39 0 39 0
kgN/yr kgN/yr kgN/yr
Sums 0 0 0
N balance
N inputs kgN/yr Check sum of N applied through land use
(from the Nloadall sheet) Background land use 0
Irrigation 0 kgN/ha/yr 1/cells/ha kgN/yr
Point sources 0
Sum land use 0 0 25 0
Through u/s stream/river boundaries: 94217
Total N inputs 94217
N outputs kgN/yr
Waipawa River
Through u/s boundary 28067
From land use 0
Sum 28067
Tukituki River
Through u/s boundary 45727
From Zone 2 0
From Zone 3 0
Sum 45727
Other u/s river boundaries 20423
Sum of N outputs: 94217
Balance (Out –In) 0
Percent difference 0 %
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N Summary - a summary of nitrogen inputs and outputs
A summary of all nitrogen applications (Table A4.4) to Ruataniwha Plains land as specified
by the three worksheets: „N bkg‟, „N irri‟, and „N point‟.
The nitrogen loadings are summarised by surface water zones from the three „nitrogen-
loading‟ worksheets as kg N/ha/yr. Sums are calculated as kg N/yr.
This sheet has a nitrogen balance calculation which has the following components:
Inputs: Land sources - background, irrigation and point sources.
Influent nitrogen through boundary river/streams: Mangaonuku, Mangamate,
Waipawa, Tukituki.
Outputs: Nitrogen output through rivers: Waipawa River and Tukituki River.
A balance equation measures the difference between outputs and inputs and expresses this as
kg N/yr and percentage difference. The difference between output and input should be less
than 10%. Differences should only arise because of rounding of numbers in the worksheets.
Surfqualpredicts
Predictions of steady-state nitrogen concentrations at 16 surface sites.
gwqualpredicts
Predictions of groundwater nitrogen concentrations at 14 groundwater sites.
N bkg - current nitrogen loadings to land
This worksheet (for example Table A4.5 for Zone 1) estimates the current nitrogen loadings
on land as evidenced by surface and groundwater quality.
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Table A4.5. Nitrogen loadings to land in Zone 1.
Zone loads
Major zones Zone 1
Input data
Surface water subzones
Load kgN/ha/yr
Cells in sub zone
ha
Background Output
kgN/yr
Nloadall total output sum for zones
kgN/ha/yr
l/ cells per per ha
Total output kgN/yr
11 0 144 3600 0 0 25 0 12 0 119 2975 0 0 25 0
13 0 110 2750 0 0 25 0
14 0 47 1175 0 0 25 0 15 0 66 1650 0 0 25 0
16 0 128 3200 0 0 25 0
17 0 129 3225 0 0 25 0 18 0 616 15400 0 0 25 0
19 0 32 800 0 0 25 0
Monitoring points:
Surface water site
River/stream name N conc. in stream
at model boundary mg/L
water flow at model
boundary m**3/s
water flow at site
m**3/s
273 Mangamate@SH50 bridge 1.08 0.47 0.47
284 Mangaonuku @ Tikokino Rd 0.5 0.28 3.6 286 Mangaonuku @ Argyll Rd 0.5 0.28 2.1
287 Mangaonuku@SH50 0.5 0.28 0.28 26 Waipawa@RDS 0.1 8.9 16.1
Calc.stream N concentration
Monitoring points: Surface water
zone contributions
Cells in
sub zone
ha
bkgrd Mass
of N at RuaT
boundary
kgN/yr
Water flow
at RuaT boundary
m**3/yr
bkgrd
RuaT Output
kgN/yr
water flow
at site m**3/yr
bkgrd
Calc N at site
at site
mg/L
Obs
N
Nloadall
Total output
sum for
zones kgN/yr
Nloadall
Calc N at site
at site
mg/L
Surface water site
273 Mangamate@
SH50 bridge
16 128 3200 16007.6736 14821920 0 14821920 1.1 1.08 0 1.1
284 Mangaonuku @
Tikokino Rd
11+12+13+14+
15+16+17+18
1359 33975 4415.04 8830080 0 113529600 0 1.66 0 0
286 Mangaonuku @
Argyll Rd
13+14+15+16+
17
480 12000 4415.04 8830080 0 66225600 0.1 1.64 0 0.1
287 Mangaonuku@
SH50
14+15 113 2825 4415.04 8830080 0 8830080 0.5 0.53 0 0.5
26 Waipawa@RDS 11+12+13+14+
15+16+17+18+
19
1391 34775 28067.04 280670400 0 507729600 0.1 0.63 0 0.1
Groundwater site
Vert. capture ratio (1=fully penetrating) gw zone bkgrd Calc N
Obs N Nloadall Calc N
220 1 11 0 0.3 0
236 1 12 0 1 0 146 1 13 0 1 0
222 1 14 0 0.48 0
The format of this sheet is, for each zone:
1) a list of surface water subzones, loading rates (variable), zone size (ha) and calculated
nitrogen input (kg N/yr),
2) a list of surface water monitoring sites, influent nitrogen concentrations (if a stream
crosses the upstream model boundary), flow rates at the upstream model boundary,
and flow rates at the measuring sites,
3) calculated nitrogen concentration at observation sites, considering influent nitrogen
mass and mass-loading from landuse,
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4) observed nitrate-nitrogen, or ammonia-nitrogen, concentrations at the observation site,
5) groundwater monitoring site and capture zone number,
6) calculated nitrogen concentration at observation sites, and
7) observed nitrate-nitrogen, on ammonia-nitrogen, concentrations at groundwater
monitoring sites.
A nitrogen balance model is at the foot of the worksheet. Zone-by-zone nitrogen inputs are
compared with nitrogen outputs. Estimated nitrogen concentrations in the Tukituki River,
downstream of the confluence with the Tukipo River, are compared with observations.
Nirri - nitrogen loadings to land from irrigation
This sheet is used to apply nitrogen for four types of land use to the surface water zones that
are within the Ruataniwha Plains groundwater model irrigated zone.
Table A4.6. Nitrogen application from irrigation.
Irrigation sources
N outputs Land use type A B C Fallow
kgN/ha/yr 100 20 10 0
Zone
number
Irrigate
d cells
in SWZ
Irrigated
ha in
SWZ
Land use type
ha
N application
kgN/yr
Total N kgN/yr Equiv zone irrig N
kgN/ha/yr
zone zones A B C Fallow A B C Fallow
11 0 0 0 0 0 0 0 0 0 0 0 0 12 0 0 0 0 0 0 0 0 0 0 0 0
13 0 0 0 0 0 0 0 0 0 0 0 0
14 0 0 0 0 0 0 0 0 0 0 0 0 15 0 0 0 0 0 0 0 0 0 0 0 0
16 18 450 0 0 0 450 0 0 0 0 0 0
17 25 625 0 0 0 625 0 0 0 0 0 0 18 251 6275 0 0 0 6275 0 0 0 0 0 0
19 23 575 0 0 0 575 0 0 0 0 0 0
21 149 3725 0 0 0 3725 0 0 0 0 0 0
22 47 1175 0 0 0 1175 0 0 0 0 0 0 23 110 2750 0 0 0 2750 0 0 0 0 0 0
24 25 625 0 0 0 625 0 0 0 0 0 0
25 69 1725 0 0 0 1725 0 0 0 0 0 0
31 173 4325 0 0 0 4325 0 0 0 0 0 0
32 19 475 0 0 0 475 0 0 0 0 0 0
33 86 2150 0 0 0 2150 0 0 0 0 0 0
34 47 1175 0 0 0 1175 0 0 0 0 0 0
35 45 1125 0 0 0 1125 0 0 0 0 0 0 36 98 2450 0 0 0 2450 0 0 0 0 0 0
37 44 1100 0 0 0 1100 0 0 0 0 0 0
38 3 75 0 0 0 75 0 0 0 0 0 0 39 7 175 0 0 0 175 0 0 0 0 0 0
sum 30975 0 0 0 30975 sum 0 0 0 0 0
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The four landuses have associated nitrogen applications in the example in Table A4.6 have
associated nitrogen applications to groundwater as in Table A4.7.
Table A4.7. Nitrogen applications used to demonstrate Table A4.6.
The number of hectares used for each land use is listed by surface water zone (Table A4.6).
The N application (in kgN/yr) is calculated by multiplying the number of ha of a particular
land use by the N application rate (in kgN/ha/yr). The total N application is summed across
the different land uses for each surface water zone, and then back calculated to produce an
„average‟ N loading rate (in kgN/ha/yr) across the whole surface water zone.
Npoint - nitrogen application from point sources
This sheet contains a list of surface water and groundwater monitoring sites with observed
and calculated nitrogen concentrations (Table A4.8). The worksheet also contains a map of
the Ruataniwha Plains as cells. Each cell represents a point-source of nitrogen with an
application to land of kg N/ha/yr over the whole 500 m by 500 m (25 ha) cell. A table on this
worksheet (Table A4.8) compares predicted and observed nitrogen at surface and
groundwater monitoring sites.
Land use Nitrogen application
(kg N/ha/yr)
A 100
B 20
C 10
Fallow 0
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Table A4.8. Site-by-site nitrogen summary on the N point worksheet.
Zone 3 Calc N at site Obs
Calc N at site Obs Surface water at site (tot) N
Surface water at site (tot) N sites mg/L
sites mg/L 144 0 0.85
273 1.1 1.08 279 0 2.08
284 0 1.66 21 0 1.1
286 0.1 1.64 398 0 3.53
287 0.5 0.53 397 0 1.91
26 0.1 0.63 405 0 1.96
23 temp
Groundwater
sites
220 0 0.3
236 0 1 Groundwater sites
146 0 1 2229 0 0.05
222 0 0.48 231 0 4.41
*229 0 0.55
Zone 2 Calc N at site Obs 1497 0 1.22
Surface water at site (tot) N 1377 0 22.6
sites mg/L
356 0.1 0.8 Calc N. conc Obs
20 0.1 0.26 at site (tot)
659 0 2.59
410 0 2.91 Tukituki@Site 23 0.1 0.99
Groundwater
sites
*224 0 0.27
223 0 6.26
*239 0 0.55
2227 0 3.52
233 0 0.42
Irricells
Cells that are irrigated in the Ruataniwha Plains groundwater model are set to a value of 2.
Irr SWZ
This lists the surface water zone cells that are irrigated in the Ruataniwha Plains groundwater
model.
Z1A bkg, Z1B bkg
Nitrogen application for existing landuse, by cell, in Zone 1, from sheet N bkg.
Z2 bkg
Nitrogen application for existing landuse, by cell, in Zone 2, from sheet N bkg.
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Z3A bkg, Z3B bkg
Nitrogen application for existing landuse, by cell, in Zone 3, from sheet N bkg.
Bkg sum
Sum of nitrogen applications for existing landuse, by cell in all zones, from sheet N bkg.
Z1A irr, Z1B irr
Nitrogen application from irrigation, by cell, in Zone 1. Used by Nirr.
Z2 irr
Nitrogen application from irrigation, by cell, in Zone 2. Used by Nirr.
Z3A irr, Z3B irr
Nitrogen application from irrigation, by cell in Zone 3. Used by Nirr.
Irr sum
Sum of nitrogen applications from irrigation, by cell, from all zones, from sheet Nirr.
N load all
Sum of all cell-by-cell nitrogen loadings i.e. Bkg sum + Irr sum + N point.
gwflow
Predicted groundwater flow rates from Ruataniwha Plains MODFLOW model predictions of
e-w and n-s flow rates. Units are m3/s.
Streams
Stream locations.
STDM+10
Stream number - this is the Ruataniwha Plains groundwater model stream number plus 10
(Table A4.9).
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Table A4.9. Stream number and stream name.
Stream
Number Stream Name
11 Mangamate
12 Mangaonuku1
13 Mangaonuku2
14 Mangamauku
15 Mangaonuku3
16 Mangaoho
17 Mangaonuku4
18 Mangatahi
19 Mangaonuku5
20 Makaroro
21 Waipawa
22 Waipawa2
23 Waipawa3
24 Tukituki1
25 Maharakeke1
26 Porangahau
27 Maharakeke2
28 Makaretu1
29 Makaretu2
30 Tukipo1
31 Tangarewai
32 Tukipo2
33 Mangatewai
34 Tukipo3
35 Tukipo4
36 Tukituki2
37 Kahahakuri
38 Tukituki3
WellsDm
Location of monitoring wells (=2) used in the Ruataniwha Plains MODFLOW groundwater
flow model.
Gwq.sites
Location of HBRC groundwater quality monitoring sites (=2).
Swq.sites
Location of HBRC surface water quality monitoring sites (=2).
test
Test worksheet.
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A4.2. Excel spreadsheet Ruagwflux.xls
This spreadsheet is used to calculate groundwater seepage velocity of values from, and
derived values from the steady-state, non-irrigated model. The spreadsheet contains the
following worksheets with, broadly, the purpose of:
Input data: rhtflux
fntflux
heads
aquifer base
porosity
Worksheets: Totalflux (m3/day)
Totalflux (m3/s)
Gradient rht
Gradient fnt
Aq thick
Seepagevelrht
Seepagevelfnt
Combined seepage velocity
rhtflux right (west to east) groundwater flow from steady-state simulation
(m3/day), non-irrigated
fntflux front (north to south) groundwater flow from steady-state simulation
(m3/day), non-irrigated
Totalflux (m3/day) magnitude of vector of rhtflux and fntflux, non-irrigated
Totalflux (m3/s) magnitude of vector of rhtflux and fntflux, non-irrigated
Heads predicted groundwater level (m) from steady-state flow model
Gradient rht west to east head gradient across 1 km (three cells)
Gradient fnt north to south head gradient across 1 km (three cells)
Aquifer base base of aquifer used in steady-state flow model
Aq thick thickness of saturated zone in steady-state flow model
Porosity porosity, set to 0.2
Seepagevelrht calculated west to east seepage velocity = rhtflux/Aq thick/500/porosity
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Seepage vel fnt calculated north to south seepage velocity = fntflux/Aq thick/500/
porosity
Combined seepage magnitude of the vector of seepagevelrht and seepagevelfnt (m/day),
velocity Fig. 14
A4.3 Excel spreadsheet Ruagwqualtrans.xls
This spreadsheet is used to predict groundwater quality changes with time without irrigation
and contains the following worksheets with, broadly, the purpose of:
Input data: Gwzones
Welldist
Seepage velocity
Irrig sum
Calculation worksheet: Travel time (d)
Travel time (yr)
tt le 1yr
tt le 2yr
tt le 5yr
tt le 10yr
tt le 20yr
tt le 30yr
tt le 50yr
Output: Zone loads
Trans conc
Summary
Gwzones groundwater capture zones, as in Rautsteadystate.xls
Welldist distances of cells from monitoring wells (m), all groundwater zones,
cell-centre to cell-centre
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Seepage velocity seepage velocity (from Ruagwflux.xls) (m/day), non-irrigated
Travel time (d) predicted travel time (non-irrigated) to monitoring wells (days) =
Welldist/Seepage velocity. Note that the travel time for the whole travel
path is not considered, i.e. the seepage velocity in each cell is assumed
to represent the average seepage velocity over the travel path
Travel time (yr) predicted travel time to monitoring wells (years). Travel time set to 0.5
yr for the cells containing monitoring wells.
Irrig sum sum of irrigation from Ruatsteadystate.xls
tt le 1yr N applications of cells within 1 years travel time of monitoring wells
tt le 2 yr N applications of cells within 2 years travel time of monitoring wells
tt le 5 yr N applications of cells within 5 years travel time of monitoring wells
tt le 10 yr N applications of cells within 10 years travel time of monitoring wells
tt le 20 yr N applications of cells within 20 years travel time of monitoring wells
tt le 30 yr N applications of cells within 30 years travel time of monitoring wells
tt le 50 yr N applications of cells within 50 years travel time of monitoring wells
Zone loads Total N loadings on each zone, 1 to 50 years, non-irrigated
Trans conc Calculations of transient groundwater (1 to 50 years) quality with
irrigation applications
Summary Calculations of transient groundwater (1 to 50 years) quality with
irrigation applications
This spreadsheet is actively linked to Ruatsteadystate.xls.
A4.4 Excel spreadsheet Ruasurfflowdist.xls
This spreadsheet is used to calculate travel times of groundwater that discharges to surface
water, using non-irrigated groundwater seepage velocities. Input, calculation and output
worksheets are as follows:
Input data: surf zones
16 to 39
seep vel
Calculation worksheets: surf dist
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Output: travel time (d)
travel time (y)
surf zones surface water zones as in Ruasteadystate.xls
16 to 39 travel distances to surface water, as follows:
Worksheet „destination‟ travel route to monitoring site:
Surface zone Destination cell Pathway
16 cell BU18 groundwater
17 cell BX22 groundwater
18 cell CA34 groundwater
19 cell CB52 groundwater
21 cell BW50 groundwater
22 cell BN46 groundwater
23 cell BU56 groundwater
24 cell AZ51 groundwater/surface water
25 cell BY58 groundwater
31 nearest river cell groundwater/surface water
32 cell AT57 groundwater
33 cell AY62 groundwater
34 nearest river cell groundwater/surface water
35 cell BB71 groundwater
36 cell BT63 groundwater/surface water
37 nearest river cell groundwater/surface water
38 nearest river cell groundwater/surface water
39 nearest river cell groundwater/surface water
surf dist all the distances from sheets 16 to 39
seep vel groundwater seepage velocity, non-irrigated
travel time (d) groundwater travel time, days, non-irrigated
travel time (y) groundwater travel time, years, non-irrigated
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A4.5 Excel spreadsheet Ruasurfqualtrans.xls
This spreadsheet is used to predict groundwater quality changes with time for seepage
velocities with non-irrigated land and contains the following worksheets for the following
purposes:
Input data: surf zones
surf dist
seepage velocity
travel time (d)
travel time (yr)
Irrig sum
Calculation worksheets: tt le 1yr
tt le 2yr
tt le 5yr
tt le 10yr
tt le 20yr
tt le 50yr
Output: zone loads
trans conc
summary
surf zones surface water zones (from Ruasteadystate.xls)
surf dist distance of travel to surface water monitoring sites
seepage velocity groundwater seepage velocity, non-irrigated
travel time (d) groundwater travel times (days), non-irrigated
travel time (yr) groundwater travel times (years), non-irrigated
Irrigsum sum of cell-by-cell irrigation (kgN/ha/yr) (from Ruasteadystate.xls)
tt le 1 yr N applications of cells within a travel time of less than 1 year of surface
monitoring sites
tt le 2 yr N applications of cells within a travel time of less than 2 years of
surface monitoring sites
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tt le 5 yr N applications of cells within a travel time of less than 5 years of
surface monitoring sites
tt le 10 yr N applications of cells within a travel time of less than 10 years of
surface monitoring sites
tt le 20 yr N applications of cells within a travel time of less than 20 years of
surface monitoring sites
tt le 50 yr N applications of cells within a travel time of less than 50 years of
surface monitoring sites
zone loads predicted loading from zones 1 to 50 years
trans conc predicted transient N concentrations for 14 surface-water monitoring
sites for 1 to 50 years due to irrigation. Concentrations due to irrigation
are added to the currently-observed concentration.
summary predicted transient N concentrations for 14 surface-water monitoring
sites for 1 to 50 years due to irrigation. Concentrations due to irrigation
are added to the currently-observed concentration.
A4.6 Excel spreadsheet Ruagwfluxirri.xls
The worksheets in this spreadsheet are the same as Ruagwflux.xls and use the MODFLOW
model steady-state solution with irrigation to calculate groundwater cell-by-cell seepage
velocities.
A4.7 Excel spreadsheet Ruagwqualtransirri.xls
The worksheets in this spreadsheet are the same as Ruagwqualtrans.xls and use the
MODFLOW model steady-state solution with irrigation to estimate transient groundwater
quality in response to irrigation.
A4.8 Excel spreadsheet Ruasurfflowdistirri.xls
The worksheets in this spreadsheet are the same as Ruasurfflowdist.xls and use predicted
groundwater travel times with irrigation.
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A4.9 Excel spreadsheet Ruasurfqualtransirri.xls
The worksheets in this spreadsheet are the same as Ruasurfqualtrans.xls and use predicted
groundwater travel times with irrigation.
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Appendix 5. Operation of the Excel spreadsheets.
1.0 NITROGEN LOADING
The are three ways to „load‟ nitrogen to the Ruataniwha Plains model: „background‟,
„irrigation‟, and „point sources‟. Data is entered in the Ruasteadystate.xls spreadsheet or the
Ruasteadystateirri.xls spreadsheet (Appendix 4). These two spreadsheets differ with
Ruasteadystate.xls representing groundwater flow in the Ruataniwha Plains without irrigation
and Ruasteadystateirri.xls representing groundwater flow with irrigation.
1.1 Background nitrogen loading
„Background‟ loading of nitrogen is used to match current land use with current mean
nitrogen concentrations in surface water and groundwater (section 7.8).
Nitrogen is applied to surface-water zones (Table A4.1) at the same rate through the zone and
is entered through worksheet „Nbkg‟.
Nitrogen loadings are entered for each zone in the blue-coloured cells in the worksheet. For
example 100 kgN/ha/yr is entered for zone 19 in Table A5.1 and predictions of surface water
quality (e.g. 0.59 mg/L at site 26, Table A5.2) and groundwater quality (e.g. 0.6 mg/L at site
222 Table A5.3). A vertical capture ratio (section 7.8.2, Table A5.3) may be defined so that
estimates of groundwater quality are based on partial mixing of nitrogen with groundwater.
Table A5.1 Entering nitrogen loadings in surface water zones, Nbkg worksheet.
Zone 1 Nloadall 1/ Nloadall
Input data Background Total output cells Total output mean loading
Surface water Load Cells in subzone ha Output sum for zones per ha
subzones kgN/ha/yr kgN/yr kgN/ha/yr kgN/yr kgN/ha/yr
11 0.5 144 3600 1800 72 25 1800 0.5
12 0.5 119 2975 1487.5 59.5 25 1487.5 0.5
13 0.5 110 2750 1375 55 25 1375 0.5
14 1 47 1175 1175 47 25 1175 1
15 1 66 1650 1650 66 25 1650 1
16 4 128 3200 12800 818 25 20450 6.4
17 28 129 3225 90300 4037 25 100925 31.3
18 5 616 15400 77000 7347 25 183675 11.9
19 100 32 800 80000 3591 25 89775 112.2
sum 267587.5
1.2 ‘Irrigation’ nitrogen
Nitrogen from irrigation is loaded through the worksheet Nirri. It is somewhat of a misnomer
to call this nitrogen from irrigation as the nitrogen can be from any land use, irrigated or non-
irrigated. Four types of land uses, with four nitrogen leaching rates (Table A5.4) are used to
represent the mix of land uses on the plains. The nitrogen outputs from each land use may be
adjusted by the user (Table A5.4).
Nitrogen leaching rates, and land areas, may be entered in the cells coloured blue on the
worksheet. In an example zone 19 (Table A5.4), with a total of 575 irrigable hectares in the
zone, has a land use scenario of: 100 ha of land use „A‟, 200 ha of land use „B‟, 100 ha of land
use „C‟ and 175 ha of „fallow‟ land.
N loading
on zone 19
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The „fallow‟ land use is calculated from the total irrigable hectares in the zone minus the sum
of land uses „A‟, „B‟ and „C‟. An error will occur in this spreadsheet (Table A5.5) if the sum
of land uses A, B, and C is greater than the total irrigable area.
Table A5.2 Example of estimation of nitrogen concentration of surface water monitoring
site 26, „Nbkg‟ worksheet.
River/stream name N conc. in stream water flow water flow
at model boundary at model boundary at site
mg/L m**3/s m**3/s
Mangamate@SH50 bridge 0.5 0.2 0.47
Mangaonuku @ Tikokino Rd 0.5 0.1 3.6
Mangaonuku @ Argyll Rd 0.5 0.1 2.1
Mangaonuku@SH50 0.5 0.1 0.28
Waipawa@RDS 0.1 9.4 16.1
bkgrd bkgrd bkgrd
Mass of N at Water flow at RuaT water flow Calc N at site Obs
Surface water zone Cells in subzone ha RuaT boundary RuaT boundary Output at site at site N
contributions kgN/yr m**3/yr kgN/yr m**3/yr mg/L
16 128 3200 3153.6 6307200 12800 14821920 1.08 1.08
11+12+13+14+15+16+17+18 1359 33975 1576.8 3153600 187587.5 113529600 1.67 1.66
13+14+15+16+17 480 12000 1576.8 3153600 107300 66225600 1.64 1.64
14+15 113 2825 1576.8 3153600 2825 8830080 0.5 0.53
11+12+13+14+15+16+17+18+19 1391 34775 29643.84 296438400 267587.5 507729600 0.59 0.63
Table A5.3 Example of estimation of nitrogen concentration of groundwater at site 222,
„Nbkg‟ worksheet.
Groundwater site Vert. capture ratio (1=fully penetrating) gw zone Calc N Obs N
220 1 11 4 0.3
236 1 12 0.8 1
146 1 13 0.9 1
222 1 14 0.6 0.48
1.3 ‘Point source’ nitrogen
Nitrogen loadings from point sources may be entered through the „N point‟ worksheet. This
worksheet represents the Ruataniwha Plains as a set of 500 m by 500 m cells. The user can
enter nitrogen loading, as kgN/ha/yr, to cells representing the land on the plains coloured blue
on the worksheet. Point loadings may not be entered into cells representing rivers and
streams. These cells are coloured yellow on the worksheet.
2.0 NITROGEN BALANCE
Nitrogen loadings are summarised in the worksheet „Nsummary‟. loadings from background,
irrigation, and point sources are summed with nitrogen inputs from rivers across the western
boundary. These are compared with nitrogen outputs through the Waipawa and Tukituki
rivers (Table A5.6). In the example the total nitrogen loading to the plains is 817752 kgN/yr.
This includes 770763 coming from land use and 46989 kgN/yr coming into the Ruataniwha
Plains from boundary streams and rivers. A total of 297232 kgN/yr is predicted as leaving the
Ruataniwha Plains through Waipawa River and 515789 kgN/yr is predicted as leaving the
plains through the Tukituki River.
Note: The balance of nitrogen (e.g. Table A5.6) should always be close to zero. A balance
significantly different from zero probably means that a worksheet has been corrupted.
Estimated N
concentration at
site 26
Estimated N
concentration
at site 222
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Table A5.4 Example of land use loadings of zone 19, „Nirri‟ worksheet.
Irrigation sources
N outputs
Land use type A B C Fallow
kgN/ha/yr 5 10 20 0
Adjust these values
Irrigable Irrigable Land use type N application Total N
Zone number cells in SWZ ha in SWZ ha kgN/yr kgN/yr
zone zones A B C Fallow A B C Fallow
11 0 0 0 0 0 0 0 0 0 0 0
12 0 0 0 0 0 0 0 0 0 0 0
13 0 0 0 0 0 0 0 0 0 0 0
14 0 0 0 0 0 0 0 0 0 0 0
15 0 0 0 0 0 0 0 0 0 0 0
16 18 450 0 0 0 450 0 0 0 0 0
17 25 625 0 0 0 625 0 0 0 0 0
18 251 6275 0 0 0 6275 0 0 0 0 0
19 23 575 100 200 100 175 500 2000 2000 0 4500
Table A5.5 Example of an error in entering the land use areas for zone 19, „Nirri‟
worksheet.
Irrigation sources
N outputs
Land use type A B C Fallow
kgN/ha/yr 5 10 20 0
Adjust these values
Irrigable Irrigable Land use type N application Total N Equiv zone irrig N
Zone number cells in SWZ ha in SWZ ha kgN/yr kgN/yr kgN/ha/yr
zone zones A B C Fallow A B C Fallow
11 0 0 0 0 0 0 0 0 0 0 0 0
12 0 0 0 0 0 0 0 0 0 0 0 0
13 0 0 0 0 0 0 0 0 0 0 0 0
14 0 0 0 0 0 0 0 0 0 0 0 0
15 0 0 0 0 0 0 0 0 0 0 0 0
16 18 450 0 0 0 450 0 0 0 0 0 0
17 25 625 0 0 0 625 0 0 0 0 0 0
18 251 6275 0 0 0 6275 0 0 0 0 0 0
19 23 575 200 200 200 ERROR 1000 2000 4000 #VALUE! #VALUE! #VALUE!
Nitrogen outputs
may be adjusted by
the user
Land use in zone 19 is:
100 ha of „A‟, 200 ha of
„B‟, 100 ha of „C‟ and
175 ha of „Fallow‟.
Irrigable hectares in zone 19
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Table A5.6 Example of nitrogen balance calculations, „Nsummary‟ worksheet.
N balance
N inputs kgN/yr
Background land use 770763
Irrigation 0
Point sources 0
Sum land use 770763
Boundary streams/rivers: 46989
Total N inputs 817752
N outputs kgN/yr
Waipawa River
From river boundary 29644
From land use 267588
Sum 297232
Tukituki River
From river boundary 12614
From Zone 2 113700
From Zone 3 389475
Sum 515789
Other river boundaries 4730
Sum of N outputs: 817751
Balance (Out -In) -1
Percent difference 0 %
3.0 SURFACE WATER QUALITY PREDICTIONS
These are made on the „Nbkgrd‟ worksheet (Table A5.7) and echoed on the „Npoint‟
worksheet (Table A5.8).
4.0 GROUNDWATER QUALITY PREDICTIONS
These are made on the „Nbkgrd‟ worksheet (Table A5.9) and echoed on the „Npoint‟
worksheet.
5.0 MAINTENANCE OF SPREADSHEETS
5.1 Changing groundwater flow velocities
Groundwater flow velocities (Darcy) occur in the spreadsheets Ruagwflux.xls and
Ruagwfluxirri.xls. These spreadsheets are used to calculate the seepage velocities used in the
non-irrigated steady-state model, irrigated steady state model and transient models).
Sum of nitrogen inputs
Sum of nitrogen outputs
Balance
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Table A5.7 Example of stream nitrogen concentrations, „Nbkgrd‟ worksheet.
Calc.stream N concentration bkgrd bkgrd bkgrd Nloadall Nloadall
Monitoring points: Mass of N at Water flow at RuaT water flow Calc N at site Obs Total output Calc N at site
Surface water Surface water zone Cells in subzone ha RuaT boundary RuaT boundary Output at site at site N sum for zones at site
site contributions kgN/yr m**3/yr kgN/yr m**3/yr mg/L kgN/yr mg/L
273 16 128 3200 3153.6 6307200 12800 14821920 1.08 1.08 12800 1.08
284 11+12+13+14+15+16+17+18 1359 33975 1576.8 3153600 187587.5 113529600 1.67 1.66 187587.5 1.67
286 13+14+15+16+17 480 12000 1576.8 3153600 107300 66225600 1.64 1.64 107300 1.64
287 14+15 113 2825 1576.8 3153600 2825 8830080 0.5 0.53 2825 0.5
26 11+12+13+14+15+16+17+18+19 1391 34775 29643.84 296438400 267587.5 507729600 0.59 0.63 267587.5 0.59
Surface water
monitoring sites
N conc. due to
„background‟
land use
Observed mean
concentration
N conc. due to:
„background‟ +
„irrigation‟ +
„point‟ land
uses
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Table A5.8 Example of stream nitrogen concentrations, „Npoint‟ worksheet.
Zone 1
Surface water Calc N at site Obs
sites at site (tot) N
mg/L
273 1.08 1.08
284 1.67 1.66
286 1.64 1.64
287 0.5 0.53
26 0.59 0.63
Use the following procedure to calculate seepage velocity:
1) Paste-out Darcy west-to-east velocities from the steady-state Ruataniwha Plains model
output file into the „rhtflux‟ worksheet.
2) Paste-out Darcy north-to-south velocities from the steady-state Ruataniwha Plains
model output file into the „fntflux‟ worksheet.
3) Paste-out calculated groundwater heads from the steady-state Ruataniwha Plains
model output file into the „heads‟ worksheet.
4) Enter model of the aquifer base into to „Aquifer base‟ worksheet, if required.
5) Enter model porosities into „porosity‟ worksheet if required.
6) Copy the calculated non-irrigated seepage velocities in the „Total flux (m3/s)‟
worksheet into the Ruasteadystate.xls worksheet „gwflow‟.
7) Copy the calculated irrigated seepage velocities in the „Total flux (m3/s)‟ worksheet
into the Ruasteadystateirri.xls worksheet „gwflow‟.
5.2 Changing observed surface water and groundwater nitrogen concentrations
These are typed into the „Nbkd‟ worksheet (Table A5.7 and Table A5.9).
5.3 Adjusting the capture zones for surface water monitoring sites and groundwater
monitoring sites
Type the number of the zone into the „SWZ‟ worksheet to edit the surface water zone e.g.
change a boundary etc.
Type the number of the zone in the worksheet „GW inf zones‟ to edit the groundwater zone
e.g. change a boundary etc.
Surface water
monitoring site
N conc. due to
all land use
Observed mean
concentration
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5.4 Adding new surface water or groundwater zones
First, delete a zone from the „SWZ‟ worksheet (surface water zones) or „GW inf zones‟
(groundwater zones). Type the code for the new zone into the same worksheet. Note that the
code number must be the same code number as the zone that has been deleted. This is
because a limited number of zone codes are available. The location of the zones is defined by
the codes on the worksheets.
Table A5.9 Example of groundwater nitrogen concentrations „Nbkgrd‟ worksheet.
bkgrd Nloadall
Groundwater site Vert. capture ratio (1=fully penetrating) gw zone Calc N Obs N Calc N
220 1 11 4 0.3 4
236 1 12 0.8 1 0.8
146 1 13 0.9 1 0.9
222 1 14 0.6 0.48 0.6
5.5 Update seepage velocities in ‘transient’ calculations
5.5.1 Groundwater travel times to monitoring wells The excel files Ruagwflowdist.xls and Ruagwflowdistirri.xls are used to estimate the travel
times in days and years through the groundwater system to monitoring wells.
Seepage velocities may require updating: paste seepage velocities (as m/day) out of
Ruagwflux.xls „combined seepage velocity‟ worksheet (for non-irrigated seepage velocities),
or Ruagwfluxirri.xls „combined seepage velocity‟ worksheet (for irrigated seepage velocities).
5.5.2 Travel times to surface water monitoring sites
Travel times through the groundwater system to surface water monitoring sites are calculated
in the Excel files Ruasurfflowdist.xls and Ruasurfflowdistirri.xls. Worksheets list the travel
distance to the surface water monitoring site using estimated groundwater flow directions and
seepage velocities derived from Ruataniwha Plains groundwater flow models. Travel times
use groundwater seepage velocity calculations from the non-irrigated, or irrigated,
groundwater flow models.
Seepage velocities may require updating: paste seepage velocities (as m/day) out of
Ruagwflux.xls „combined seepage velocity‟ worksheet (for non-irrigated seepage velocities)
or Ruagwfluxirri.xls „combined seepage velocity‟ worksheet (for irrigated seepage velocities)
into the spreadsheets Ruasurfflowdist.xls and Ruasurfflowdistirri.xls.
5.5.3 Transient calculations The sheets Ruagwqualtrans.xls, Ruagwqualtransirri.xls, Ruasurfqualtrans.xls and
Ruasurfqualtransirri.xls are used to estimate future nitrogen concentrations in groundwater
and surface water. Changes in water quality are estimated over a 50 year period following a
Groundwater
monitoring
site
N conc. due to
„background‟
land use
Observed
mean
concentration
N conc. due to:
„background‟ +
„irrigation‟ +
„point‟ land uses
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change in land-use in the spreadsheets at the time of writing. Water quality is estimated at 1,
2, 5, 10, 20, 30 and 50 years in the current version of the spreadsheets.
The following input data sets will require updating if seepage velocities are updated.
Well dist (m) - from Ruagwflowdist.xls
Surf dist (m) - from Ruasurfflowdist.xls
Seepage velocity - either non-irrigated (from Ruagwflux.xls) or irrigated (from
Ruagwfluxirri.xls)
Travel time (d) - non-irrigated (from Ruasurfflowdist.xls) or irrigated (from
Ruasurfflowdistirri.xls)
Travel time (yr) - non-irrigated (from Ruasurfflowdist.xls) or irrigated (from
Ruasurfflowdistirri.xls).
The sheets Ruagwqualtrans.xls, Ruagwqualtransirri.xls, Ruasurfqualtrans.xls and
Ruasurfqualtransirri.xls can be used to estimate future nitrogen concentrations at any time as
follows:
Enter a new time, in years in cell b1 of the worksheets titled „tt le 1 yr‟ and
rename the worksheet with the correct year.
The „Trans conc.‟ worksheet contains the summary of surface and groundwater quality. This
calculates nitrogen concentrations above the background level. Adjust the figures in Column
G is the background levels require change.
6.0 ASSUMPTIONS
Assumptions used in the building of the spreadsheets are noted in this section.
6.1 Surface water zones
It is assumed that the nitrogen drainage in a surface water zone will be fully „captured‟ by the
monitoring site associated with the zone. Surface water monitoring sites are chosen in
reaches of rivers and streams where groundwater is thought to be flowing to the streams. It is
possible drainage-carrying groundwater discharges downstream of a monitoring point.
6.2 Groundwater capture
The groundwater capture zones are estimated by eye from contour lines predicted by the
Ruataniwha Plains groundwater model. It may be that local groundwater flow directions are
different from the modelled flow directions. It is also be possible that the capture zones are of
different extents than estimated in this work.
6.3 Mixing in surface water
It is assumed that the nitrogen in drainage is fully mixed with surface water. This may not be
the case. Stratification of nitrogen in surface water may give rise to higher local
concentrations of nitrogen.
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6.4 Groundwater mixing ratio
Groundwater mixing ratios are chosen so that the mean of observed groundwater chemistry
measurements matches the predictions of nitrogen in drainage given by „calibration‟ of the
land use to observed surface water nitrogen concentrations. The vertical profile of nitrogen
concentrations is unknown locally, so the mixing ratio is therefore unknown.
Some clue to the vertical mixing of nitrogen in the Ruataniwha Plains is given by nitrogen
concentrations and well depth data (Fig. 9). It is unknown any regional pattern (e.g. Fig. 9) is
valid at the local scale.
6.5 Water balance
It is assumed that all water entering the Ruataniwha Plains leaves via the Waipawa and
Tukituki rivers. Water enters the Ruataniwha Plains in rivers across the northern and western
boundaries of the plains, and in rainfall recharge to groundwater on the plains.
6.6 Chemistry balance
It is assumed that all nitrogen entering the Ruataniwha Plains leaves via the Waipawa and
Tukituki rivers. Nitrogen enters the Ruataniwha Plains in rivers across the northern and
western boundaries of the plains, and in rainfall recharge to groundwater on the plains.
7.0 SPREADSHEET SECURITY
A number of worksheets have „locked‟ cells. This is to prevent users from inadvertently
corrupting worksheets. The code to unlock worksheet cells is „ruataniwha‟.