4.3 Water Quality – Lower Catchment and Coastal Catchments · Approximately 2 km below LSWA05b...
51
139 4.3 Water Quality – Lower Catchment and Coastal Catchments This section covers the remainder of the Little Swanport River from below the gauging station at LSWA05b to the lower gauging station (LSWA01), and includes the Green Tier/Rocka Rivulet catchment and Pepper Creek. The section also covers Ravensdale Rivulet, which flows into the Little Swanport estuary, and the coastal catchments of Buxton River and Lisdillon Rivulet. In all, 10 sites were monitored within this area. Following a brief description of the sites, monthly water quality monitoring data from the monitoring sites within the Little Swanport catchment is presented in sections 4.3.2 and 4.3.3. This is followed by presentation of the data from the coastal catchment monitoring sites in section 4.3.4. Continuous water quality data (temperature, turbidity, conductivity, pH and dissolved oxygen) from installations at Green Tier Creek at Wiggins Road (LSWA19) and Little Swanport River 3km upstream Tasman Highway (LSWA01), is presented in section 4.3.5. A number of flood events at LSWA01 were sampled by an autosampler, and analysis of selected variables and continuous data from the gauging station for these flood events is presented in section 4.2.6, and these are then used to estimate transport loads for the middle catchment in section 4.2.7. Section 4.3 of the water quality chapter is then summarised in at the end of this document. 4.3.1 Site descriptions Approximately 2 km below LSWA05b the Little Swanport River enters a section characterised by steep valley sides, steep bedslope and thick riparian zone of native species. This section is defined as geomorphic Zone 4 (Chapter 2) and extends to the lower gauging station (LSWA01) where there is some flood plain development (Figure 71). The river is controlled by dolerite bedrock and consists of boulder/bedrock cascades and deep pools. While there is some minor grazing in this part of the catchment, land use is dominated by forestry. The majority of the lower catchment is State Forest with a significant proportion of the southern part of the lower catchment contained within the Buckland Military Area (see Chapter 2). The steep valley slopes have largely restricted forestry operations in this section to the higher plateaux, leaving the tributary catchments that enter the Little Swanport River in this section largely undisturbed. The lower reaches of Rocka Rivulet and Green Tier are also characterised as geomorphic Zone 4 as is Pepper Creek. Ravensdale Rivulet is
Transcript of 4.3 Water Quality – Lower Catchment and Coastal Catchments · Approximately 2 km below LSWA05b...
139
4.3 Water Quality – Lower Catchment and Coastal Catchments
This section covers the remainder of the Little Swanport River from below the gauging station at
LSWA05b to the lower gauging station (LSWA01), and includes the Green Tier/Rocka Rivulet
catchment and Pepper Creek. The section also covers Ravensdale Rivulet, which flows into the
Little Swanport estuary, and the coastal catchments of Buxton River and Lisdillon Rivulet. In all,
10 sites were monitored within this area.
Following a brief description of the sites, monthly water quality monitoring data from the
monitoring sites within the Little Swanport catchment is presented in sections 4.3.2 and 4.3.3. This
is followed by presentation of the data from the coastal catchment monitoring sites in section 4.3.4.
Continuous water quality data (temperature, turbidity, conductivity, pH and dissolved oxygen) from
installations at Green Tier Creek at Wiggins Road (LSWA19) and Little Swanport River 3km
upstream Tasman Highway (LSWA01), is presented in section 4.3.5. A number of flood events at
LSWA01 were sampled by an autosampler, and analysis of selected variables and continuous data
from the gauging station for these flood events is presented in section 4.2.6, and these are then used
to estimate transport loads for the middle catchment in section 4.2.7. Section 4.3 of the water
quality chapter is then summarised in at the end of this document.
4.3.1 Site descriptions
Approximately 2 km below LSWA05b the Little Swanport River enters a section characterised by
steep valley sides, steep bedslope and thick riparian zone of native species. This section is defined
as geomorphic Zone 4 (Chapter 2) and extends to the lower gauging station (LSWA01) where there
is some flood plain development (Figure 71). The river is controlled by dolerite bedrock and
consists of boulder/bedrock cascades and deep pools. While there is some minor grazing in this part
of the catchment, land use is dominated by forestry. The majority of the lower catchment is State
Forest with a significant proportion of the southern part of the lower catchment contained within
the Buckland Military Area (see Chapter 2). The steep valley slopes have largely restricted forestry
operations in this section to the higher plateaux, leaving the tributary catchments that enter the
Little Swanport River in this section largely undisturbed. The lower reaches of Rocka Rivulet and
Green Tier are also characterised as geomorphic Zone 4 as is Pepper Creek. Ravensdale Rivulet is
140
considered part of the Little Swanport catchment as it enters the estuary. Ravensdale Rivulet,
Lisdillon Rivulet and Buxton River are described in more detail below.
Figure 71: Location of water quality monitoring sites in the lower catchment of the Little Swanport River.
Legend
LSWA01: Little Swanport River 3km u/s Tasman Hwy
LSWA02: Little Swanport River at Deep Hole
LSWA03: Little Swanport River d/s Green Tier Creek
LSWA17: Pepper Creek at Deep Hole
LSWA19: Green Tier Creek at Wiggins Rd
LSWA20: Green Tier Creek at Snug Rd
LSWA21 Rocka Rivulet
LSWA33: Ravensdale Rivulet
LSWA34: Lisdillon Rivulet
LSWA35: Buxton River
Green Tier Creek/Rocka Rivulet
Two sites in this catchment; Rocka Rivulet (LSWA21) and Green Tier Creek at Snug Road
(LSWA20), are within geomorphic Zone 1 (the upland chain of lagoons zone). Unlike the area of
the Eastern Marshes Rivulet catchment within this zone (LSWA23 and LSWA24), land clearance
in this part of the catchment has been less extensive, with pockets of remnant woodland and native
141
grassland remaining. The uppermost reaches of Green Tier Rivulet lie within State Forest and
although there is some disturbance from forestry operations, drainage areas contain good riparian
cover of native vegetation. The reaches immediately above LSWA20 have been cleared for grazing
and can be accessed by stock (Plate 21). Rocka Rivulet above LSWA21 flows through a shallow
elevated valley, which is thickly vegetated (Plate 23). The catchment above this site is within State
Forest, some minor logging occurred during the study period both above the site and in private land
downstream of the site. Green Tier Creek below LSWA20 to Green Tier Creek at Wiggins Road
Ford (LSWA19) is characterised as geomorphic Zone 4 and flows through a steep, narrow gorge
where it is joined by Rocka Rivulet, emerging from a similar gorge (Plate 22). The steep valley
sides are thickly vegetated and there is good riparian cover.
Plate 21: Green Tier Creek at Snug Road ford (LSWA20) at low and high flow. The small eroded dam (left) is inundated (right) at high
flow and is the point at which Stonehouse Creek enters Green Tier Creek (to the left of the photo).
Plate 22: Green Tier Creek at Wiggins Road (LSWA19), at low and high flow.
142
Plate 23: Rocka Rivulet (LSWA21), constrained within a shallow streambank at low flow (left) and at high flow spilling through the
shallow, heavily vegetated valley as seen along a bulldozed track which bisects it.
Pepper Creek
The catchment of Pepper Creek (LSWA17) is contained largely within the Buckland Military Area
and is largely undisturbed although there has been some erosion from roading (see Chapter 2). The
catchment has extensive cover of native woodland Plate 24). Pepper Creek is characterised as
geomorphic Zone 4 and consists of a series of pools and drops constrained by dolerite bedrock and
boulders. Pepper Creek enters the Little Swanport River immediately below the monitoring site at
Deep Hole (LSWA02).
Plate 24: Pepper Creek at Deep Hole (LSWA17) in low and moderate flow.
143
Little Swanport River
Three sites were monitored on the Little Swanport River in the lower catchment; Little Swanport
River downstream Green Tier Creek (LSWA03), Little Swanport River at Deep Hole (LSWA02)
and Little Swanport River 3km upstream Tasman Highway (LSWA01) where the lower gauging
station is situated. Below the gauging station at LSWA05b, the river continues to flow through
geomorphic Zone 3 (partly confined zone), where the river flats have been cleared for grazing.
Riverbank erosion is evident along this reach. Above the confluence with Green Tier Creek the
river enters the extended section defined as geomorphic zone 4 which continues to the lower
gauging station. This section has steep valley sides, excellent riparian vegetation and consists of
large pools separated by steep boulder/cobble riffles. The lower catchment is thickly covered with
native woodland and scrub.
Plate 25: Little Swanport River downstream Green Tier Creek (LSWA03) in low and high flow.
Plate 26: Little Swanport River at Deep Hole (LSWA02), in low flow looking upstream and in high flow, downstream.
144
Plate 27: Little Swanport River 3km upstream Tasman Highway (LSWA01), looking upstream from the gauging station in low flow (left)
and looking downstream in high flow (right) immediately above this section.
Coastal Catchments
Three coastal catchments were included in the study: Ravensdale Rivulet (LSWA33), Lisdillon
Rivulet (LSWA34) and Buxton River (LSWA35). Monitoring sites in all these catchments were
located near to their outlets, where they are crossed by the Tasman Highway. Ravensdale Rivulet
rises in the Buckland Military Area and drains steep forested country similar that of the lower Little
Swanport catchment. The lower half of the catchment has been cleared for grazing and a significant
proportion of the riparian vegetation has been removed (Plate 28). Ravensdale Rivulet flows into
the Little Swanport estuary. Both Lisdillon Rivulet and Buxton River catchments are contained
largely within State Forest and drain steep forested country before emerging onto the coastal plain
where there has been some land clearance for grazing. Both have relatively intact riparian
vegetation at the location where water quality sampling was undertaken (Plates 29 & 30). Lisdillon
Rivulet and Buxton River drain directly into Great Oyster Bay through small, coastal lagoons.
145
Plate 28: Ravensdale Rivulet at Tasman Highway (LSWA33) in low and high flow (taken from bridge at left).
Plate 29: Lisdillon Rivulet at Tasman Highway (LSWA34) in low flow and in high flow (right), view from the highway bridge looking down
at the same location.
Plate 30: Buxton River at Tasman Highway (LSWA35), at low flow (looking upstream) and (right) in high flow looking downstream from
the bridge at left.
146
4.3.2 Monthly Sampling
Turbidity
Monthly turbidity data is presented in Figure 72. Turbidity is low throughout the lower catchment
of the Little Swanport River during periods of baseflow as is the case throughout the middle and
upper catchments. There is little increase in turbidity from the middle to the lower catchment sites
of the Little Swanport River during periods of higher flow, and this can be attributed directly to the
low level of land use in the middle and lower catchment. The upper catchment of Green Tier Creek
has elevated turbidity, and this is likely to be related to geology as Rocka Rivulet also has relatively
elevated turbidity, despite the low level of catchment disturbance. Pepper Creek, by comparison,
has very low levels of turbidity.
Within the Little Swanport River, all lower catchment sites have medians below 2 NTU. It should
be noted that Little Swanport River below Green Tier (LSWA03) was not sampled during high
flow events in August 2003 and January 2004. Maximum turbidity recorded at Little Swanport
River 3km upstream Tasman Highway (LSWA01) and Little Swanport River at Deep Hole
(LSWA02) was 25.4 NTU and 18.9 NTU respectively and were recorded during the January 2004
high flow event. The ANZECC guideline for turbidity in Tasmanian rivers is 2-25 NTU. All
turbidity values recorded in the lower catchment were within or very close to this range.
Overall median turbidity throughout the length of the Little Swanport River (Figure 73) does not
vary greatly, with only a slight decrease downstream. It should be noted that the maximum
turbidity values for the upper catchment sites were recorded close to the peak of the August 2003
flood, the remainder of the sites were sampled on subsequent days. Conversely, upper catchment
sites were sampled prior to the peak of the January 2004 flood, which occurred during the sampling
of the lower and some middle catchment sites. Monthly turbidity at LSWA01 is shown in
Figure 74.
147
LSWA01 LSWA02 LSWA03 LSWA19 LSWA20 LSWA21 LSWA17
Turbidity NTU
0
5
10
15
20
25
30
35
40
Figure 72: Statistics for monthly turbidity data for sites in the lower catchment of the Little Swanport River.
LSWA01 LSWA02 LSWA05b LSWA06 LSWA10 LSWA12 LSWA14
Turbidity NTU
0
5
10
15
20
25
30
35
40
45
Figure 73: Statistics for monthly turbidity data for selected sites in the Little Swanport River.
148
0.00
5.00
10.00
15.00
20.00
25.00
30.00
27-Aug-03
10-Sep-03
24-Sep-03
8-O
ct-0
3
22-O
ct-0
3
5-Nov-03
19-Nov-03
3-Dec-03
17-Dec-03
31-Dec-03
14-Jan-04
28-Jan-04
11-Feb-04
25-Feb-04
10-M
ar-0
4
24-M
ar-0
4
7-Apr-0
4
21-Apr-0
4
5-M
ay-04
19-M
ay-04
2-Jun-04
16-Jun-04
30-Jun-04
14-Jul-04
28-Jul-04
11-Aug-04
25-Aug-04
8-Sep-04
22-Sep-04
6-O
ct-0
4
20-O
ct-0
4
3-Nov-04
Turbidity NTU
0.0000
2000 .0000
4000 .0000
6000 .0000
8000 .0000
10000.0000
12000.0000
Flow ML/day
turbidity
flow
Figure 74: Time series of monthly turbidity and modelled flow, Little Swanport River 3 km upstream Tasman Hwy (LSWA01).
A downstream decrease in turbidity occurs within Green Tier Creek (Figure 72) with a median
turbidity at Green Tier Creek at Wiggins Road (LSWA19) of 3.27 NTU, while Green Tier Creek at
Snug Road (LSWA20) had a median turbidity of 11.5 NTU. The processes driving this change is
likely to be the same as that described for Eastern Marshes Rivulet as the geomorphology of Green
Tier Creek is similar to that of Eastern Marshes Rivulet, with a change below LSWA20 from the
upland chain-of-lagoons zone to the confined zone. As with the Eastern Marshes catchment, there
is an associated change in land use from low relief grazing country with associated clearing of the
riparian and catchment vegetation, to a steep sided valley dominated by native woodland and scrub.
Waters in the upper catchment of Green Tier Creek are more turbid that that of Eastern Marshes
Rivulet, despite less intensive land use. This difference in turbidity is most likely related to
differences in geology and soils.
Rocka Rivulet (LSWA21), which flows into Green Tier Creek below LSWA20, has relatively
elevated turbidity (median 6.13 NTU), despite the catchment having a very low level of
disturbance. While it is possible that some unknown disturbance above this site such as roading,
may be responsible, it is more likely that the elevated turbidity is a natural condition related to the
presence of dolerite clays. Monthly turbidity results for the Green Tier Creek/Rocka Rivulet
catchment are shown in Figure 75.
149
During winter 2004, a series of high turbidity readings (Figure 75) were recorded throughout the
Green Tier/Rocka Rivulet catchment. These readings correspond to a general period of higher flow,
however they were not recorded during minor floods or freshes (see Plate 31). It is not known if
this higher turbidity is related to any particular land use activity (such as road works) or a natural
condition related to soil or geology, but it does illustrate that both Green Tier Rivulet and Rocka
Rivulet are prone to periods of elevated turbidity.
Plate 31: Green Tier Creek at Wiggins Road (LSWA19) with elevated turbidity (left) in June 2004 and (right) with low turbidity March
2004.
0.00
5.00
10.00
15.00
20.00
25.00
30.00
35.00
40.00
26-Aug-03
9-Sep-03
23-Sep-03
7-Oct-0
3
21-Oct-0
3
4-Nov-03
18-Nov-03
2-Dec-03
16-Dec-03
30-Dec-03
13-Jan-04
27-Jan-04
10-Feb-04
24-Feb-04
9-M
ar-0
4
23-M
ar-0
4
6-Apr-0
4
20-Apr-0
4
4-M
ay-04
18-M
ay-04
1-Jun-04
15-Jun-04
29-Jun-04
13-Jul-04
27-Jul-04
10-Aug-04
24-Aug-04
7-Sep-04
21-Sep-04
5-Oct-0
4
19-Oct-0
4
2-Nov-04
16-Nov-04
Turbidity NTU
0
200
400
600
800
1000
1200
1400
1600
1800
Flow ML/day
LSWA19
LSWA20
LSWA21
flow
Figure 75: Results from monthly turbidity sampling and modelled flow, Green Tier Creek and Rocka Rivulet.
150
Pepper Creek at Deep Hole (LSWA17) had a very low median turbidity of 0.78 NTU. Although
some disturbance in this catchment has been documented (see Chapter 2), the catchment is largely
undisturbed and consists of native woodland. It should be noted that this site was not sampled
during either high flow event, however a turbidity reading of 8.3 NTU was taken during the August
2003 event at Swanston Road ford (568 500E 5311 750N), approximately 2 km upstream from
LSWA17. This indicates that even in high flow, turbidity remains relatively low within Pepper
Creek.
Electrical Conductivity
Monthly conductivity for sites in the lower catchment is given in Figure 76. Conductivity at the
Little Swanport River sites is more moderate than the middle and upper catchment, however the
levels recorded are still high when considered from a State-wide perspective. Conductivity in the
lower catchment tributaries is generally less than that recorded for the tributaries in the middle and
upper catchment, and inflow of water from these tributaries to the lower reaches of the Little
Swanport River is likely to be the main reason for the lower conductivity in this part of the river
(Figure 77). As with the upper and middle catchment, conductivity remains highly variable, with
conductivity at Little Swanport 3km above Tasman Hwy (LSWA01) varying between 124.4 µS/cm
at high flow to 1264 µS/cm during very low flow in January 2004. The marked influence of flow
on conductivity is displayed in the monthly data for LSWA01 shown in Figure 78.
LSWA01 LSWA02 LSWA03 LSWA19 LSWA20 LSWA21 LSWA17
Conductivity uS/cm
0
100
200
300
400
500
600
700
800
900
1000
1100
1200
1300
1400
Figure 76: Statistics of monthly conductivity data for the lower catchment of the Little Swanport River.
151
LSWA01 LSWA02 LSWA05b LSWA06 LSWA10 LSWA12 LSWA14
Conductivity uS/cm
0
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
Figure 77: Statistics of monthly conductivity data for selected sites in the Little Swanport River.
0
200
400
600
800
1000
1200
1400
27-Aug-03
10-Sep-03
24-Sep-03
8-O
ct-0
3
22-O
ct-0
3
5-Nov-03
19-Nov-03
3-Dec-03
17-Dec-03
31-Dec-03
14-Jan-04
28-Jan-04
11-Feb-04
25-Feb-04
10-M
ar-0
4
24-M
ar-0
4
7-Apr-0
4
21-Apr-0
4
5-M
ay-04
19-M
ay-04
2-Jun-04
16-Jun-04
30-Jun-04
14-Jul-0
4
28-Jul-0
4
11-Aug-04
25-Aug-04
8-Sep-04
22-Sep-04
6-O
ct-0
4
20-O
ct-0
4
3-Nov-04
Conductivity uS/cm
0 .0000
2 000.000 0
4 000.000 0
6 000.000 0
8 000.000 0
1 0000.00 00
1 2000.00 00
Flow ML/day
c onductiv ity
f low
Figure 78: Results from monthly conductivity sampling and modelled flow, Little Swanport River 3 km upstream Tasman Hwy
(LSWA01).
As was found for turbidity, conductivity in Green Tier Creek decreases markedly between Green
Tier Creek at Snug Road (LSWA20) (median of 547 µS/cm) and Green Tier Creek at Wiggins
Road (LSWA19) (median of 268 µS/cm). There is also considerably less variability in conductivity
at LSWA19 than at LSWA20. The mechanism for this change is most likely to be the land use
changes within the Green Tier catchment described above. The very low median recorded for
152
Rocka Rivulet (LSWA21) (94.2 µS/cm) and the very low variability for this site is a possible
indicator of the natural conductivity regime in the upland streams of the catchment. As the
geomorphology at sites LSWA20 and LSWA21 are similar, the significant difference in
conductivity levels between the two sites may be a reflection of the differences in land use between
the two sites. Although the catchment geology for both streams is dominated by dolerite, it is also
so possible that conductivity differences may also be attributed in part to small-scale differences in
geology between the sites, as there are some marine sedimentary units mapped in the Green Tier
catchment.
Despite the catchment having very low disturbance, median conductivity at Pepper Creek at Deep
Hole (LSWA17) was relatively high (393 µS/cm). This may be related to the presence of
sedimentary rocks in the catchment, which are likely to produce more saline groundwaters (see
Chapter 2). These data further illustrate the high degree of spatial variation in salinity in
freshwaters of the catchment, reflecting the relative influence of local geology or marine aerosols
on water quality.
0
200
400
600
800
1000
1200
26-Aug-03
9-Sep-03
23-Sep-03
7-Oct-0
3
21-Oct-0
3
4-Nov-03
18-Nov-03
2-Dec-03
16-Dec-03
30-Dec-03
13-Jan-04
27-Jan-04
10-Feb-04
24-Feb-04
9-M
ar-0
4
23-M
ar-0
4
6-Apr-0
4
20-Apr-0
4
4-M
ay-04
18-M
ay-04
1-Jun-04
15-Jun-04
29-Jun-04
13-Jul-04
27-Jul-04
10-Aug-04
24-Aug-04
7-Sep-04
21-Sep-04
5-Oct-0
4
19-Oct-0
4
2-Nov-04
16-Nov-04
Conductivity uS/cm
0
200
400
600
800
1000
1200
1400
1600
1800
Flow ML/day
LSWA19
LSWA20
LSWA21
flow
Figure 79: Results from monthly conductivity sampling and modelled flow, Green Tier Creek and Rocka Rivulet.
153
Dissolved Oxygen
Median values for dissolved oxygen for the Little Swanport River and Green Tier Creek sites all
fall within the ANZECC guideline of 90-110% (Figure 80). The extreme high and low values
recorded from sites in the middle, and particularly in the upper catchment, were not observed for
sites in the lower catchment.
Despite the low level of disturbance in the catchment, both Rocka Rivulet (LSWA21) and Pepper
Creek at Deep Hole (LSWA17) recorded lowest median dissolved oxygen saturation (86% and
90% respectively). Low values recorded at Pepper Creek were recorded in low to very low flow,
while for Rocka Rivulet low values were recorded across a range of conditions. Pepper Creek flows
through a boulder/cobble substrate and in low flow consists of shallow pools connected by
subterranean flow, while Rocka Rivulet is uniformly shallow and flows through thick, overhanging
vegetation and has a substrate of fine sediment and aquatic plants. The relatively lower dissolved
oxygen at these sites is likely to be a function of natural conditions. Monthly statistics for dissolved
oxygen are presented in Figure 80, while Figure 81 shows the results for selected sites within the
Little Swanport River. In Figure 81, the variable nature of dissolved oxygen at locations in the
upper catchment is clearly illustrated and is related to the ephemeral nature of the hydrology of the
upper catchment as well as the level of disturbance and habitat modification (e.g. stock access and
clearance of riparian vegetation).
LSWA01 LSWA02 LSWA03 LSWA19 LSWA20 LSWA21 LSWA17
Dissolved Oxygen %saturation
60
65
70
75
80
85
90
95
100
105
110
115
120
Figure 80: Statistics of monthly dissolved oxygen data for the lower catchment of the Little Swanport River.
154
LSWA01 LSWA02 LSWA05b LSWA06 LSWA10 LSWA12 LSWA14
Dissolved Oxygen %saturation
0
25
50
75
100
125
150
175
200
225
250
Figure 81: Statistics of monthly dissolved oxygen data for selected sites in the Little Swanport River.
Temperature
Summary statistics for monthly temperature data are presented in Table 20. Rocka Rivulet had a
significantly lower median temperature than other sites within the lower catchment (7.15 °C), a
consequence of its high elevation and thick, shading riparian vegetation. Summary statistics for
temperature at selected sites in the Little Swanport River are given in Table 21.
Table 20: Summary statistics for monthly temperature data for the lower catchment of the Little Swanport River.
Little
Swanport
River 3km u/s
Tasman Hwy
Little
Swanport
River at Deep
Hole
Little
Swanport
River d/s
Green Tier
Creek
Green Tier
Creek at
Wiggins
Road
Green Tier
Creek at
Manning
Road
Rocka Rivulet Pepper Creek
at Deep hole
Median 12.45 13.05 13.0 12.4 14.0 7.15 11.8
Maximum 22.2 24.4 21.8 21.8 23.2 16.1 20.4
Minimum 3.2 3.8 4.7 5.5 4.3 2.8 4.3
Samples 16 16 13 15 15 16 14
155
Table 21: Summary statistics for monthly temperature data for selected sites in the Little Swanport River.
Little
Swanport
River 3km u/s
Tasman Hwy
Little
Swanport
River at Deep
Hole
Little
Swanport
River d/s
Eastern
Marshes Rvt.
Little
Swanport
River u/s
Eastern
Marshes Rvt.
Little
Swanport
River at
Swanston
Road
Little
Swanport
River lower
Inglewood
Road
Little
Swanport
River upper
Inglewood
Road
Median 12.45 13.05 12.4 11.3 10.6 10.7 12.75
Maximum 22.2 24.4 20.8 25.3 26 25.6 24.9
Minimum 3.2 3.8 4.8 4.9 4.4 3.7 4.2
Samples 16 16 16 16 16 16 16
In-stream pH
In-stream pH at sites located lower in the Little Swanport River is slightly more alkaline (summary
statistics for selected sites within the Little Swanport River are given in Table 22.) when compared
with sites in the middle catchment. Median values for Pepper Creek and Rocka Rivulet are more
neutral (7.45 and 7.4), possibly through the influence of vegetation. The results are similar to those
recorded for Pages Creek in the middle catchment. Summary statistics for monthly in-stream pH
data for the lower catchment are presented in Table 23.
Table 22: Summary statistics for monthly in-stream pH data for selected sites in the Little Swanport River.
Little
Swanport
River 3km u/s
Tasman Hwy
Little
Swanport
River at Deep
Hole
Little
Swanport
River d/s
Eastern
Marshes Rvt.
Little
Swanport
River u/s
Eastern
Marshes Rvt.
Little
Swanport
River at
Swanston
Road
Little
Swanport
River lower
Inglewood
Road
Little
Swanport
River upper
Inglewood
Road
Median 8.03 7.95 7.76 7.73 7.84 7.86 7.62
Maximum 8.61 8.27 8.14 8.09 8.38 8.32 10.16
Minimum 7.22 6.45 6.75 6.72 7.12 7.27 6.55
Samples 16 16 16 16 16 16 16
156
Table 23: Summary statistics for monthly in-stream pH data for the lower catchment of the Little Swanport River.
Little
Swanport
River 3km u/s
Tasman Hwy
Little
Swanport
River at Deep
Hole
Little
Swanport
River d/s
Green Tier
Creek
Green Tier
Creek at
Wiggins
Road
Green Tier
Creek at
Manning
Road
Rocka Rivulet Pepper Creek
at Deep hole
Median 8.03 7.95 7.97 7.93 8.02 7.4 7.45
Maximum 8.61 8.27 8.55 8.45 8.64 7.83 7.81
Minimum 7.22 6.45 7.36 6.75 7.56 6.2 7.12
Samples 16 16 13 15 15 16 14
4.3.3 Nutrients
Four sites in the lower catchment were sampled monthly for nutrients: Little Swanport River 3km
upstream Tasman Hwy (LSWA01), Little Swanport River at Deep Hole (LSWA02), Green Tier
Creek at Wiggins Road (LSWA19) and Rocka Rivulet (LSWA21).
Total Nitrogen
Median total nitrogen concentration at LSWA01 and LSWA02 (0.5 mg/l) is slightly less than at
LSWA05b, the next upstream site on the Little Swanport River where median total nitrogen
concentration was 0.84 mg/L (Figure 82). The lower medians at LSWA01 and LSWA02 are a
result of dilution from inputs of tributaries with low total nitrogen, combined with a significant
decline in land use activity in the lower catchment. The higher median at LSWA05b is most likely
a result of inputs of total nitrogen from Nutting Garden Rivulet. Monthly results for LSWA01 are
shown in Figure 84.
The effect of land use on total nitrogen concentration was also apparent in Green Tier Creek.
Where total nitrogen was sampled at the upper site on Green Tier Creek (LSWA20), it was
significantly higher (3 samples at baseflow: median 0.9 mg/L) than concentrations at Wiggins Road
(LSWA19). As with turbidity, this change can be attributed to the change in land use below
LSWA20. Total nitrogen levels in Rocka Rivulet (median 0.2 mg/L) show the naturally low levels
in undisturbed catchments, although the maximum at this site (0.775 mg/L), recorded during high
flow in January 2004, indicates that total nitrogen can reach high peaks during flow events.
Monthly changes in total nitrogen concentration at Green Tier Creek and Rocka Rivulet are
presented in Figure 85.
157
LSWA01 LSWA02 LSWA05b LSWA10 LSWA14
Total Nitrogen mg/L
0.00
0.25
0.50
0.75
1.00
1.25
1.50
1.75
2.00
2.25
2.50
2.75
3.00
3.25
3.50
3.75
Figure 82: Statistics of total nitrogen data for selected sites in the Little Swanport River.
LSWA01 LSWA02 LSWA19 LSWA21
Total Nitrogen mg/L
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.1
1.2
1.3
1.4
Figure XXXX: Statistics of monthly total nitrogen data for the lower
Figure 83: Statistics of monthly total nitrogen data for the lower catchment of the Little Swanport River.
158
0
0.2
0.4
0.6
0.8
1
1.2
1.4
27-Aug-03
10-Sep-03
24-Sep-03
8-Oct-0
3
22-Oct-0
3
5-Nov-03
19-Nov-03
3-Dec-03
17-Dec-03
31-Dec-03
14-Jan-04
28-Jan-04
11-Feb-04
25-Feb-04
10-M
ar-0
4
24-M
ar-0
4
7-Apr-0
4
21-Apr-0
4
5-M
ay-04
19-M
ay-04
2-Jun-04
16-Jun-04
30-Jun-04
14-Jul-04
28-Jul-04
11-Aug-04
25-Aug-04
8-Sep-04
22-Sep-04
6-Oct-0
4
20-Oct-0
4
3-Nov-04
Total Nitrogen mg/L
0.0000
2000.0000
4000.0000
6000.0000
8000.0000
10000.0000
12000.0000
Flow ML/day
LSWA01
LSWA19
LSWA21
flow
Figure 84: Results from monthly total nitrogen sampling, Little Swanport River 3 km upstream Tasman Hwy. (LSWA01), Green Tier
Creek at Wiggins Rd. (LSWA19) and Rocka Rivulet (LSWA21).
Nitrate
Median nitrate concentration at all sites in the lower catchment was well below the ANZECC
guideline of 0.19 mg/l. The results for Rocka Rivulet show very little variability, while all the
remaining sites had very high maximum values in comparison with median values. All these values
were recorded during the high flow event of August 2003. This result again illustrates the role of
rainfall and flow in the transport of nitrate from the soil profile, discussed in section 4.1 of this
report, and is also illustrated by the results for flood events where nitrate was analysed (section
4.2.5). Statistics for monthly nitrate data is presented in Figure 85.
159
LSWA01 LSWA02 LSWA19 LSWA21
Nitrate mg/L
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
0.50
Figure 85: Statistics of monthly nitrate data for the lower catchment of the Little Swanport River.
Total Phosphorous
Monthly statistics for total phosphorous at sites in the lower catchment are presented as boxplots in
Figure 86. Median total phosphorous at all sites was below the ANZECC guideline value of
0.013 mg/L. Maximum values were all recorded during high flow events. When total phosphorous
concentration at sites along the length of the Little Swanport River (Figure 87) is examined, median
total phosphorous is higher and significantly more variable at sites in the upper reaches of the river
system, particularly at LSWA14.
The results for Rocka Rivulet show a relatively small variation over a range of flows, despite
having maximum values exceeding the ANZECC guideline. This demonstrates that even in
catchments with minimal disturbance natural concentrations of total phosphorus may exceed
standard guidelines and that it is preferable for catchment specific triggers to be formulated. There
is greater variation within Green Tier Creek, with the upper site (LSWA20) having significantly
higher levels of total phosphorous than LSWA19 (3 samples at baseflow: median 0.037 mg/L).
This result again reflects the influence of land use on this catchment, with total phosphorous levels
within Green Tier Creek originating from the grazing land above the upper site, LSWA20. The
monthly variation in total phosphorus at Green Tier Creek and Rocka Rivulet is shown in
Figure 88.
160
LSWA01 LSWA02 LSWA19 LSWA21
Total Phosphorous mg/L
0.000
0.005
0.010
0.015
0.020
0.025
0.030
0.035
0.040
Figure 86: Statistics of monthly total phosphorous data for the lower catchment of the Little Swanport River.
LSWA01 LSWA02 LSWA05b LSWA10 LSWA14
Total Phosphorous mg/L
0.00
0.05
0.10
0.15
0.60
0.70
0.80
Figure 87: Statistics of total phosphorous data for selected sites in the Little Swanport River.
161
0
0.005
0.01
0.015
0.02
0.025
0.03
0.035
0.04
0.045
27-Aug-03
10-Sep-03
24-Sep-03
8-Oct-0
3
22-Oct-0
3
5-Nov-03
19-Nov-03
3-Dec-03
17-Dec-03
31-Dec-03
14-Jan-04
28-Jan-04
11-Feb-04
25-Feb-04
10-M
ar-0
4
24-M
ar-0
4
7-Apr-0
4
21-Apr-0
4
5-M
ay-04
19-M
ay-04
2-Jun-04
16-Jun-04
30-Jun-04
14-Jul-04
28-Jul-04
11-Aug-04
25-Aug-04
8-Sep-04
22-Sep-04
6-Oct-0
4
20-Oct-0
4
3-Nov-04
Total Phosphorous mg/L
0.0000
2000.0000
4000.0000
6000.0000
8000.0000
10000.0000
12000.0000
Flow ML/day
LSWA01
LSWA19
LSWA21
f low
Figure 88: Results from monthly total phosphorous sampling, Little Swanport River 3 km upstream Tasman Hwy. (LSWA01), Green
Tier Creek at Wiggins Rd. (LSWA19) and Rocka Rivulet (LSWA21) with modelled flow at LSWA01.
4.3.4 Water quality of the coastal catchments
Turbidity
Median turbidity at all the coastal catchment sites was below 5 NTU (Figure 89). Highest values at
were recorded all sites during high flows in January 2004, with Ravensdale Rivulet having a
significantly higher maximum (36.5 NTU) than Lisdillon Rivulet (25.3 NTU) or Buxton River
(27 NTU). Both Lisdillon Rivulet and Buxton River have catchments that are largely contained
within State Forest and are characterised by steep sided valleys dominated by native woodland.
These are similar to areas of the Little Swanport catchment defined as geomorphic Zone 4 (the
confined zone). The middle and lower catchment of Ravensdale Rivulet has been cleared for
grazing and agriculture and has an impoverished riparian zone compared to both Lisdillon Rivulet
and Buxton River. This difference in land use is reflected in a number of water quality parameters.
During high flow, overland runoff in the Ravensdale Rivulet catchment will pick up higher
quantities of sediment and organic material due to increased disturbance. In addition, the loss of
riparian vegetation and the impact on the streambed and banks from stock will increase erosion
during high flow, leading to higher turbidity. While the level of disturbance in the Buxton River
and Lisdillon Rivulet catchments is low, both watercourses are crossed by forestry roads in the
upper catchments, and both sampling sites may be impacted by this. Forestry roads have been
recognised as a primary source of runoff and sediments in forested catchments (Takken et. al.,
162
2005). It is not known what, if any, forestry activities took place in these catchments before, or
during, the study.
LSWA33 LSWA34 LSWA35
Turbidity NTU
0
5
10
15
20
25
30
35
40
Figure 89: Statistics of monthly turbidity data for the coastal catchments.
Electrical Conductivity
Boxplots illustrating the monthly conductivity results are presented in Figure 90. Median
conductivity is relatively low in both Lisdillon Rivulet (261 µS/cm) and Buxton River (249
µS/cm). Both sites also recorded a low degree of seasonal variation in conductivity, a feature of the
data for Rocka Rivulet, which also has a low degree of catchment disturbance. In contrast to these,
Ravensdale Rivulet had a very high median conductivity (1002 µS/cm) and a higher degree of
variability with values ranging from 153 µS/cm to 1460 µS/cm. There are a number of factors that
are likely to explain this difference. The geology of both Buxton River and Lisdillon catchments is
predominantly one of dolerite with some minor areas of sediment. Although the geology of the
upper reaches of Ravensdale Rivulet is also dolerite, the lower half of the catchment consists of
Triassic sandstone. This difference in geology is also reflected in the lower relief of the lower
Ravensdale catchment, which may have an important influence on groundwater dynamics. An
investigation of saline groundwaters in the White Hut Rivulet catchment, immediately to the north
of Ravensdale Rivulet (Dell, 2000) found an average groundwater salinity of 4756 µS/cm, with a
range of 656 µS/cm to 26800 µS/cm. The report from that investigation indicated that the main
source of salt is the accumulation of dissolved salts from wind, rain and salt spray. Since Buxton
163
River and Lisdillon Rivulet are also subject to these processes, the difference between the
conductivity results from these catchments and those from Ravensdale Rivulet are likely to be a
result of differences in land use and groundwater dynamics and characteristics, as well as
geological differences. Land clearing in the Ravensdale Rivulet may have resulted in increased salt
levels in groundwater and shallower groundwater levels. Vegetation was identified by Dell (2000)
as an important management tool in controlling salinity issues.
The investigation of the White Hut Creek area also found that groundwater conductivity was
significantly reduced following rainfall, and this would also seem be the case for Ravensdale
Rivulet where the lowest conductivity reading (153 µS/cm) was recorded after a period of heavy
rainfall in September 2004.
LSWA33 LSWA34 LSWA35
Conductivity uS/cm
0
100
200
300
400
500
600
700
800
900
1000
1100
1200
1300
1400
1500
1600
Figure 90: Statistics of monthly conductivity data for the coastal catchments.
Dissolved Oxygen, Temperature and In-stream pH
Results for dissolved oxygen, temperature and in-stream pH are shown in Table 24. Median
dissolved oxygen at all sites was relatively low, within the range 75-85%. In comparison to the
majority of sites in the Little Swanport catchment, median in-stream pH recorded for the coastal
catchments is more neutral.
164
Table 24: Summary statistics for monthly in-dissolved oxygen (DO), water temperature and pH data for coastal rivers.
Ravensdale Rivulet Lisdillon Rivulet Buxton River
DO Temperature pH DO Temperature pH DO Temperature pH
Median 83.1 13.2 7.45 83.9 11.1 7.44 74.45 12.1 7.35
Maximum 118.2 20.7 7.95 93.2 18.9 7.81 103.4 20.2 7.84
Minimum 62.8 6.7 6.97 65.3 4.8 6.65 53.2 3.2 6.87
Samples 16 15 16 16 16 16 16 16 16
Nutrients
Only Ravensdale Rivulet (LSWA33) was sampled on a monthly basis for nutrients. Results of
monthly monitoring for total nitrogen, nitrate and total phosphorous are shown in Figures 91 and
92.
Median total nitrogen at this site is marginally below the ANZECC guideline of 0.48 mg/L. Highest
concentrations of total nitrogen were recorded the floods of January 2004 and August 2003. During
baseflow conditions, concentrations of total nitrogen were higher in summer/autumn and lower in
winter/spring.
Nitrate levels also declined through winter and spring. During summer, soil microbes increase
nitrate storage in soils. Fertiliser application can also increase soil nitrate. Subsequent rainfall
events during winter and spring create a pulse of nitrate concentration in the river, as infiltration of
rainwater flushes nitrate from the soil profile. During the January 2004 flood, nitrate concentration
(0.497 mg/L) at LSWA33 was not significantly different to that recorded during baseflow
conditions during summer and autumn. However, as the sampling was conducted at the height of
the flood, it is likely that peak nitrate concentrations had already occurred. The primary source of
total nitrogen in the river at the time of sampling was likely to be organic nitrogen carried as
suspended particulate material. During winter and spring more frequent rain events also tend to
flush this material from the catchment.
Median total phosphorous at LSWA33 (0.008 mg/L) is below the ANZECC guideline. In general,
total phosphorous levels follow the same seasonal and flow related trend as total nitrogen. During
165
the flood event of January 2004 total phosphorous was recorded at 0.058 mg/L. In general, levels of
total phosporous in Ravensdale Rivulet are low.
Total Nitrogen Nitrate Total Phosphorous
Total Nitrogen and Nitrate mg/L
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.1
1.2
1.3
1.4
1.5
1.6
1.7
1.8
1.9
2.0
Total Phosphorous mg/L
0.005
0.010
0.015
0.020
0.025
0.030
0.035
0.040
0.045
0.050
0.055
0.060
Figure 91: Statistics of monthly nutrient data for the Ravensdale Rivulet
0
0.2
0 .4
0 .6
0 .8
1
1 .2
1 .4
1 .6
1 .8
2
20-Aug-03
3-Sep-03
17-Sep-03
1-O
ct-0
3
15-O
ct-0
3
29-O
ct-0
3
12-Nov-03
26-Nov-03
10-Dec-03
24-Dec-03
7-Jan-04
21-Jan-04
4-Feb-04
18-Feb-04
3-M
ar-0
4
17-M
ar-0
4
31-M
ar-0
4
14-Apr-0
4
28-Apr-0
4
12-M
ay-04
26-M
ay-04
9-Jun-04
23-Jun-04
7-Jul-0
4
21-Jul-0
4
4-Aug-04
18-Aug-04
1-Sep-04
15-Sep-04
29-Sep-04
13-O
ct-0
4
27-O
ct-0
4
10-Nov-04
Total Nitrogen, Nitrate mg/L
0
200
400
600
800
1000
1200
1400
Flow ML/day
to tal n itrogen
n itra te
flow
Figure 92: Monthly results for total nitrogen and nitrate at Ravensdale Rivulet (LSWA33) plotted along with modelled flow at LSWA01.
166
4.3.5 Continuous Water Quality
Multi-probes measuring temperature, conductivity, dissolved oxygen, turbidity and in-stream pH
were deployed at Green Tier Creek at Wiggins Road (LSWA19) and Little Swanport River 3km
upstream Tasman Highway (LSWA01). A stream gauging station was established at LSWA01 on
22 March 2004. In addition to recording water level, this station measured temperature,
conductivity, and turbidity at 15-minute intervals. At the time of writing no rating had been
developed for this station, therefore modelled flow data have been used (see discussion below). All
continuous water quality data has been edited using monthly spot samples and data of poor quality
(>20% difference with spot readings) has been removed.
The continuous water quality data collected from multi-probes presented in this report are short
term in nature, and cannot be used to determine seasonal trends. In this report these data are used
only to provide some indication of general water quality characteristics at each site.
Modelled flow for each site is presented in this section. It is included as an aid to the interpretation
and presentation of the continuous water quality data and to provide some context as to the
magnitude of a given flow associated with changes in water quality. The flow data has been derived
from a rainfall/runoff model for the catchment developed as part of the water management planning
process (SKM, 2004). This model is based on long term rainfall data and is more accurate in
modelling a long-term flow record rather than the short-term records presented here, however there
is good agreement, between the modelled flow hydrographs and the level hydrograph at the lower
gauging station.
Green Tier Creek at Wiggins Road (LSWA19)
A multi-probe was installed at this site from 22 July to 18 November 2004. During this period three
flow events occurred, the highest reaching 319 ML/day in mid-August. At this site a flow of
936 ML/day or greater can be expected approximately every year while a flow of 567 ML/day or
greater can be expected approximately every six months.
The continuous data shows that turbidity at this site is generally low with a median of 3.13 NTU
(Figure 93). Turbidity remained below 5 NTU for 46% of the period of record and above 25 NTU
for about 4%. Maximum turbidity was 36.21 NTU, recorded during a small flow peak of
167
248 ML/day in November 2004. In comparison, a peak turbidity of 18.7 NTU was recorded from
continuous monitoring during this event at Eastern Marshes Rivulet at Swanston (LSWA22). This
site had a median turbidity over the same period of 0.87 NTU. This suggests that the Green Tier
Creek/Rocka Rivulet catchment contributes greater sediment loads than Eastern Marshes Rivulet
despite the less intensive land use, possibly due to differences in geology and soils.
0
5
10
15
20
25
30
35
40
22-Jul-04
25-Jul-04
27-Jul-04
29-Jul-04
1-Aug-04
3-Aug-04
5-Aug-04
8-Aug-04
10-Aug-04
13-Aug-04
15-Aug-04
17-Aug-04
20-Aug-04
22-Aug-04
25-Aug-04
28-Aug-04
30-Aug-04
2-Sep-04
4-Sep-04
6-Sep-04
9-Sep-04
11-Sep-04
14-Sep-04
16-Sep-04
18-Sep-04
21-Sep-04
23-Sep-04
25-Sep-04
28-Sep-04
30-Sep-04
3-Oct-0
4
5-Oct-0
4
8-Oct-0
4
10-Oct-0
4
13-Oct-0
4
15-Oct-0
4
18-Oct-0
4
20-Oct-0
4
22-Oct-0
4
25-Oct-0
4
27-Oct-0
4
30-Oct-0
4
1-Nov-04
3-Nov-04
6-Nov-04
8-Nov-04
10-Nov-04
13-Nov-04
15-Nov-04
18-Nov-04
Turbidity NTU
0
50
100
150
200
250
300
350
Flow ML/day
turbidity
flow
Figure 93: Continuous turbidity data and modelled flow at Green Tier at Wiggins Road (LSWA19).
Electrical conductivity at this site is relatively low (Figure 94), with a median of 329 µS/cm and a
maximum of 420 µS/cm. Conductivity at this site is considerably lower than other sub-catchments
within the Little Swanport River. Median conductivity from continuous water quality data over the
same time period from Eastern Marshes Rivulet was 740 µS/cm.
This site has good levels of dissolved oxygen with concentration exceeding 8 mg/l for the entire
period of record (Figure 95), although levels showed a clear decline with the onset of spring. This
site has good riparian cover and diurnal temperature variations are moderate and this is also
reflected in the magnitude of diurnal changes in dissolved oxygen.
Maximum and minimum temperatures were 20.71 oC and 2.59
oC respectively. As with Eastern
Marshes Rivulet, which also has good riparian shading, maximum temperatures at this site were
moderate and diurnal fluctuations were also more moderate compared to Nutting Garden Rivulet
and Little Swanport River at Swanston Road.
168
150
200
250
300
350
400
450
22-Jul-04
25-Jul-04
27-Jul-04
30-Jul-04
1-Aug-04
4-Aug-04
6-Aug-04
9-Aug-04
11-Aug-04
14-Aug-04
16-Aug-04
19-Aug-04
21-Aug-04
25-Aug-04
27-Aug-04
30-Aug-04
2-Sep-04
4-Sep-04
7-Sep-04
9-Sep-04
12-Sep-04
14-Sep-04
17-Sep-04
19-Sep-04
22-Sep-04
24-Sep-04
27-Sep-04
30-Sep-04
2-Oct-04
5-Oct-04
7-Oct-04
10-Oct-04
13-Oct-04
15-Oct-04
18-Oct-04
20-Oct-04
23-Oct-04
25-Oct-04
28-Oct-04
30-Oct-04
2-Nov-04
5-Nov-04
7-Nov-04
10-Nov-04
12-Nov-04
15-Nov-04
17-Nov-04
Conductivity us/cm
050
100
150
200
250
300
350
Flow ML/day
conductivity
flow
Figure 94: Continuous conductivity data and m
odelled flow at Green Tier at Wiggins Road (LSWA19).
89
10
11
12
13
14
15
16
22-Jul-04
25-Jul-04
27-Jul-04
29-Jul-04
1-Aug-04
3-Aug-04
6-Aug-04
8-Aug-04
11-Aug-04
13-Aug-04
15-Aug-04
18-Aug-04
20-Aug-04
24-Aug-04
26-Aug-04
28-Aug-04
31-Aug-04
2-Sep-04
5-Sep-04
7-Sep-04
10-Sep-04
12-Sep-04
14-Sep-04
17-Sep-04
19-Sep-04
22-Sep-04
24-Sep-04
27-Sep-04
29-Sep-04
2-Oct-04
4-Oct-04
7-Oct-04
9-Oct-04
12-Oct-04
14-Oct-04
17-Oct-04
19-Oct-04
22-Oct-04
24-Oct-04
26-Oct-04
29-Oct-04
31-Oct-04
3-Nov-04
5-Nov-04
7-Nov-04
10-Nov-04
12-Nov-04
15-Nov-04
17-Nov-04
Dissolved Oxygen mg/L
050
100
150
200
250
300
350
Flow ML/day
dissolved oxygen
flow
Figure 95: Continuous dissolved oxygen data and m
odelled flow at Green Tier at Wiggins Road (LSWA19).
In-stream pH displayed a large daily variation, changing by as much as a whole pH unit during low
flows in late winter. M
edian pH at this site was 8.13, with a m
axim
um and m
inim
um of 9.02 and
7.69 respectively. In comparison, diurnal variations at Eastern Marshes Rivulet at Swanston
remained fairly constant throughout the monitoring period and were of sm
aller m
agnitude.
169
2
4
6
8
10
12
14
16
18
20
22
22-Jul-04
25-Jul-04
27-Jul-04
30-Jul-04
1-Aug-04
4-Aug-04
6-Aug-04
9-Aug-04
12-Aug-04
14-Aug-04
17-Aug-04
19-Aug-04
22-Aug-04
25-Aug-04
28-Aug-04
30-Aug-04
2-Sep-04
4-Sep-04
7-Sep-04
10-Sep-04
12-Sep-04
15-Sep-04
17-Sep-04
20-Sep-04
22-Sep-04
25-Sep-04
27-Sep-04
30-Sep-04
3-Oct-0
4
5-Oct-0
4
8-Oct-0
4
11-Oct-0
4
13-Oct-0
4
16-Oct-0
4
19-Oct-0
4
21-Oct-0
4
24-Oct-0
4
26-Oct-0
4
29-Oct-0
4
31-Oct-0
4
3-Nov-04
5-Nov-04
8-Nov-04
10-Nov-04
13-Nov-04
16-Nov-04
Temperature Deg C
0
50
100
150
200
250
300
350
Flow ML/day
temperature
flow
Figure 96: Continuous temperature data and modelled flow at Green Tier at Wiggins Road (LSWA19).
7.5
7.7
7.9
8.1
8.3
8.5
8.7
8.9
9.1
22-Jul-04
25-Jul-04
27-Jul-04
30-Jul-04
1-Aug-04
4-Aug-04
6-Aug-04
9-Aug-04
11-Aug-04
14-Aug-04
16-Aug-04
19-Aug-04
21-Aug-04
25-Aug-04
27-Aug-04
30-Aug-04
1-Sep-04
4-Sep-04
6-Sep-04
9-Sep-04
11-Sep-04
14-Sep-04
16-Sep-04
19-Sep-04
21-Sep-04
24-Sep-04
26-Sep-04
29-Sep-04
1-Oct-0
4
4-Oct-0
4
7-Oct-0
4
9-Oct-0
4
12-Oct-0
4
15-Oct-0
4
17-Oct-0
4
20-Oct-0
4
22-Oct-0
4
25-Oct-0
4
27-Oct-0
4
30-Oct-0
4
1-Nov-04
4-Nov-04
6-Nov-04
9-Nov-04
11-Nov-04
14-Nov-04
16-Nov-04
pH
0
50
100
150
200
250
300
350
Flow ML/day
pH
flow
Figure 97: Continuous in-stream pH data and modelled flow at Green Tier at Wiggins Road (LSWA19).
Little Swanport River 3 km upstream Tasman Highway (LSWA01)
A stream gauging station was installed at this site on 23 March 2004. Water level, temperature,
turbidity and electrical conductivity were measured at 15-minute intervals. This data was quality
coded and calibrated using monthly spot samples. Data that exceeds spot readings by over 20% has
not been used in this report. Aggregated daily data is presented for 2004 and 2005. As indicated
earlier, no rating has been developed for this site, therefore modelled daily flow has been used. Due
170
to instrument problems there is little good turbidity data for 2004-05, so only data from 6 October
2005 to 16 May 2006 (the end of available modelled flow data), is presented. A multi-probe was
installed at this site from 20 October 2003 to 10 February 2004 and dissolved oxygen and pH data
from this probe is also presented.
During 2004-2005, maximum daily flow at LSWA01 was 13,529 ML/day which occurred during a
storm event in September 2005. River level during this event peaked at 4.606 m above the cease to
flow point. This event can be expected to occur approximately once every 5 years while a flow of
6200 ML/day or greater can be expected on an annual basis. Changes in water quality during this
particular flood are examined in more detail in section 4.3.6. Flow at LSWA01 was below
22 ML/day for 90% of the period of record.
Turbidity at this site over the period of monitoring generally varied in response to change in flow
conditions (Figure 98). A series of small events through spring 2005 produced spikes in turbidity
during this period. A maximum turbidity of 42.9 NTU was recorded in October 2005 during a flow
of 3,939 ML/day. Mean turbidity in October, November and December 2005 was 14.5, 9.6 and 7.9
NTU respectively. Low flows throughout summer and early autumn 2006 resulted in much lower
turbidity with a monthly mean turbidity below 3 NTU for January to May 2006 and a maximum
turbidity of only 4.6 NTU. Overall, turbidity remained below 5 NTU for 68% of the time period
and above 25 NTU for less than 1%.
In a pattern that is consistent across many sites in the catchment, conductivity rose steadily during
periods of baseflow, before dropping substantially with flow events, even when events were
relatively small (<2,000 ML/day). The variability in flow during 2004-05 is therefore also reflected
in conductivity levels (Figure 99). The wetter spring of 2005 resulted in lower conductivity
compared to that in spring 2004. Mean conductivity in September and October 2004 was 741
µS/cm and 836 µS/cm, while for the corresponding months in 2005 it was 383 µS/cm and 352
µS/cm respectively. Conductivity exceeded 800 µS/cm during 2004 for 24% of the record, while in
2005 that level was exceeded for only 4%.
171
0 5
10
15
20
25
30
6-Oct-05
11-Oct-05
16-Oct-05
21-Oct-05
26-Oct-05
31-Oct-05
5-Nov-05
10-Nov-05
15-Nov-05
20-Nov-05
25-Nov-05
30-Nov-05
5-Dec-05
10-Dec-05
15-Dec-05
20-Dec-05
25-Dec-05
30-Dec-05
4-Jan-06
9-Jan-06
14-Jan-06
19-Jan-06
24-Jan-06
29-Jan-06
3-Feb-06
8-Feb-06
13-Feb-06
18-Feb-06
23-Feb-06
28-Feb-06
5-Mar-06
10-Mar-06
15-Mar-06
20-Mar-06
25-Mar-06
30-Mar-06
4-Apr-06
9-Apr-06
14-Apr-06
19-Apr-06
24-Apr-06
29-Apr-06
4-May-06
9-May-06
14-May-06
Turbidity NTU
0 2000
4000
6000
8000
10000
12000
14000
16000
Flow ML/day
turbidity
flow
Figure 98: D
aily aggregated tu
rbidity at L
ittle Swanport R
iver 3
km upstre
am Tasman Hwy with m
odelled flo
w.
0
200
400
600
800
1000
1200
2-May-04
16-May-04
30-May-04
13-Jun-04
27-Jun-04
11-Jul-04
25-Jul-04
8-Aug-04
22-Aug-04
5-Sep-04
19-Sep-04
3-Oct-04
17-Oct-04
31-Oct-04
14-Nov-04
28-Nov-04
12-Dec-04
26-Dec-04
9-Jan-05
23-Jan-05
6-Feb-05
20-Feb-05
6-Mar-05
20-Mar-05
3-Apr-05
17-Apr-05
1-May-05
15-May-05
29-May-05
12-Jun-05
26-Jun-05
10-Jul-05
24-Jul-05
7-Aug-05
21-Aug-05
4-Sep-05
18-Sep-05
2-Oct-05
16-Oct-05
30-Oct-05
13-Nov-05
27-Nov-05
11-Dec-05
25-Dec-05
Conductivity uS/cm
0 2000
4000
6000
8000
10000
12000
14000
16000
Flow ML/day
conductivity
flow
Figure 99: D
aily aggregated conductivity at L
ittle Swanport R
iver 3
km upstre
am Tasman Hwy w
ith m
odelled flo
w.
172
As mentioned above, continuous dissolved oxygen data was collected from the multi-probe logger
that was temporarily installed at this site. This time series is displayed below in Figure 100.
Dissolved oxygen exceeded 6 mg/L during the entire period of monitoring, though it dropped close
to this on two occasions during November 2003 when there was virtually no flow in the river. Daily
fluctuations in dissolved oxygen gradually increased in magnitude over December 2003 and were
changing by as much as 5 mg/L in late January 2004 before a significant flood event normalised
conditions. A major factor causing these large daily changes in oxygen was the growth of green
algae in the river during the stable, warm conditions that prevailed in December (see Figure 101).
6
7
8
9
10
11
12
13
14
15
20-Oct-0
3
22-Oct-0
3
25-Oct-0
3
27-Oct-0
3
29-Oct-0
3
31-Oct-0
3
3-Nov-03
5-Nov-03
7-Nov-03
10-Nov-03
12-Nov-03
14-Nov-03
16-Nov-03
19-Nov-03
21-Nov-03
23-Nov-03
25-Nov-03
28-Nov-03
30-Nov-03
2-Dec-03
5-Dec-03
7-Dec-03
9-Dec-03
11-Dec-03
14-Dec-03
16-Dec-03
18-Dec-03
20-Dec-03
23-Dec-03
25-Dec-03
27-Dec-03
30-Dec-03
1-Jan-04
3-Jan-04
5-Jan-04
8-Jan-04
10-Jan-04
12-Jan-04
14-Jan-04
17-Jan-04
19-Jan-04
21-Jan-04
24-Jan-04
26-Jan-04
28-Jan-04
30-Jan-04
2-Feb-04
4-Feb-04
6-Feb-04
8-Feb-04
Dissolved Oxygen mg/L
0
2000
4000
6000
8000
10000
12000
Flow ML/day
dissolved oxygen
flow
Figure 100: Continuous dissolved oxygen at Little Swanport River 3 km upstream Tasman Hwy with modelled flow.
Peak water temperature recorded at LSWA01 during 2004-05 was an extraordinary 27.9 oC, and
temperature in the river between December 2004 and February 2005 exceeded 21 oC 52% of the
time, clearly indicating that during prolonged dry periods water temperature has the potential to
cause physiological stress to aquatic biota. Although the riparian vegetation is largely intact, the
river is shallow and wide in this lower section.
173
05
10
15
20
25
24-Mar-04
7-Apr-04
21-Apr-04
5-May-04
19-May-04
2-Jun-04
16-Jun-04
30-Jun-04
14-Jul-04
28-Jul-04
11-Aug-04
25-Aug-04
8-Sep-04
22-Sep-04
6-Oct-04
20-Oct-04
3-Nov-04
17-Nov-04
1-Dec-04
15-Dec-04
29-Dec-04
12-Jan-05
26-Jan-05
9-Feb-05
23-Feb-05
9-Mar-05
23-Mar-05
6-Apr-05
20-Apr-05
4-May-05
18-May-05
1-Jun-05
15-Jun-05
29-Jun-05
13-Jul-05
27-Jul-05
10-Aug-05
24-Aug-05
7-Sep-05
21-Sep-05
5-Oct-05
19-Oct-05
2-Nov-05
16-Nov-05
30-Nov-05
14-Dec-05
28-Dec-05
Water Temperature Deg C
02000
4000
6000
8000
10000
12000
14000
16000
Flow ML/day
water temperature
flow
Figure 101: Daily aggregated water temperature at Little Swanport River 3 km upstream Tasman Hwy with m
odelled flow.
In-stream pH data was also sourced from the multi-probe installation. Median pH over the period of
record is 8.18, consistent with results from elsew
here in the catchment, w
hich show that the river
system is slightly alkaline (Figure 102). In-stream pH dropped below 7 only during the January
2004 flood, a result of dilute runoff entering the system. Diurnal variations were less pronounced
that for dissolved oxygen.
6.57
7.58
8.59
20-Oct-03
23-Oct-03
25-Oct-03
27-Oct-03
30-Oct-03
1-Nov-03
4-Nov-03
6-Nov-03
9-Nov-03
11-Nov-03
14-Nov-03
16-Nov-03
18-Nov-03
21-Nov-03
23-Nov-03
26-Nov-03
28-Nov-03
1-Dec-03
3-Dec-03
5-Dec-03
8-Dec-03
10-Dec-03
13-Dec-03
15-Dec-03
18-Dec-03
20-Dec-03
23-Dec-03
25-Dec-03
27-Dec-03
30-Dec-03
1-Jan-04
4-Jan-04
6-Jan-04
9-Jan-04
11-Jan-04
13-Jan-04
16-Jan-04
18-Jan-04
21-Jan-04
23-Jan-04
26-Jan-04
28-Jan-04
31-Jan-04
2-Feb-04
4-Feb-04
7-Feb-04
9-Feb-04
pH
02000
4000
6000
8000
10000
12000
Flow ML/day
pH
flow
Figure 102: Continuous pH at Little Swanport River 3 km upstream Tasman Hwy with m
odelled flow.
174
4.3.6 Flood sampling
Little Swanport River 3km upstream Tasman Hwy
A flood sampler was installed at LSWA01 on the Little Swanport River during the latter stages of
the study and this enabled several floods to be sampled after the completion of the study. The
results from two events are presented in this section: a minor event of August 2005 and a larger
event in September 2005. The August and September 2005 events were also sampled at the upper
gauging station (LSWA05b) in the middle catchment, and the results are also discussed for at in
section 4.2.5.
Not all parameters that were sampled are discussed here. Only those that illustrate fundamental or
characteristic water quality changes with flow are presented. It should be noted that the relationship
between any particular parameter and flow varies with the magnitude and timing of any individual
event, and is also influenced by the preceding flow and weather conditions. For example, a flow
event of a given magnitude in late summer is likely to have a different water quality signature than
an identical event in late winter when the catchment is wet.
In presenting the data graphically, modelled daily flow has not been used, as it does not provide an
appropriate indication of flow changes over the short periods of single flood events. River level
data recorded at the station is used in preference. The modelled flow data from the rainfall/runoff
model for the catchment is used to give an indication of the flood magnitude and to provide the
return interval.
Flood Event – August 2005
This flood event peaked at an aggregated daily flow of 3,148 ML/day with a maximum river level
of 1.27m above the cease to flow point recorded on 31 August 2005 at 16:45, eight hours after the
flood peak at the upper gauging station at LSWA05b. A flood of this magnitude or larger is
expected to occur at this location on the river at least once every six months, and therefore
represents a frequent event in the hydrology of the river.
Turbidity measurements taken from the water samples collected by the autosampler have been used
to examine changes in turbidity, as continuous turbidity from the sensor at the gauging station were
not recorded due to equipment failure. Maximum recorded turbidity was 26.5 NTU and the peak in
turbidity occurred 5 hours after the peak in river level (Figure 103). This differs from the results
175
from LSWA05b, where the turbidity peak occurred just prior to the flood peak. Since the maximum
turbidity at LSWA05b for this flood was almost the same (23.4 NTU), this tends to suggest that the
source of most of the sediment carried by the river during this event originated from the middle and
upper catchments.
0
5
10
15
20
25
30
29-Aug-05
29-Aug-05
29-Aug-05
29-Aug-05
29-Aug-05
29-Aug-05
30-Aug-05
30-Aug-05
30-Aug-05
30-Aug-05
30-Aug-05
30-Aug-05
31-Aug-05
31-Aug-05
31-Aug-05
31-Aug-05
31-Aug-05
1-Sep-05
1-Sep-05
1-Sep-05
1-Sep-05
1-Sep-05
1-Sep-05
2-Sep-05
2-Sep-05
2-Sep-05
2-Sep-05
2-Sep-05
2-Sep-05
3-Sep-05
3-Sep-05
3-Sep-05
3-Sep-05
3-Sep-05
4-Sep-05
4-Sep-05
4-Sep-05
4-Sep-05
4-Sep-05
4-Sep-05
5-Sep-05
5-Sep-05
5-Sep-05
5-Sep-05
5-Sep-05
5-Sep-05
6-Sep-05
6-Sep-05
6-Sep-05
Turbidity NTU
0
0.2
0.4
0.6
0.8
1
1.2
1.4
River level m
turbidity
level
Figure 103: Turbidity and river level during a flood event at Little Swanport River 3km upstream Tasman Hwy (LSWA01), August 2005.
Total suspended solids concentration mirrors changes in turbidity with the exception of a single
high reading just prior to the flood peak (23 mg/L), that may reflect very localised runoff to the
river during this event (Figure 104). The maximum total suspended solids concentration recorded
from LSWA05b for this event was 32 mg/L, again indicating that the middle and upper catchments
contributed a large proportion of the sediment transported during this event.
176
0
5
10
15
20
25
29-Aug-05
29-Aug-05
29-Aug-05
29-Aug-05
29-Aug-05
29-Aug-05
30-Aug-05
30-Aug-05
30-Aug-05
30-Aug-05
30-Aug-05
30-Aug-05
31-Aug-05
31-Aug-05
31-Aug-05
31-Aug-05
31-Aug-05
1-Sep-05
1-Sep-05
1-Sep-05
1-Sep-05
1-Sep-05
1-Sep-05
2-Sep-05
2-Sep-05
2-Sep-05
2-Sep-05
2-Sep-05
2-Sep-05
3-Sep-05
3-Sep-05
3-Sep-05
3-Sep-05
3-Sep-05
4-Sep-05
4-Sep-05
4-Sep-05
4-Sep-05
4-Sep-05
4-Sep-05
5-Sep-05
5-Sep-05
5-Sep-05
5-Sep-05
5-Sep-05
5-Sep-05
6-Sep-05
6-Sep-05
6-Sep-05
Total Supspended Solids mg/L
0
0.2
0.4
0.6
0.8
1
1.2
1.4
River level m
total suspended solids
level
Figure 104: Total suspended solids and river level during a flood event at Little Swanport River 3km upstream Tasman Hwy (LSWA01),
August 2005.
As expected, the pattern of change in conductivity is markedly different to that for turbidity (Figure
105). During this event, conductivity drops from above 700 µS/cm prior to the rise in river level to
a minimum of 380 µS/cm, 6 hours after the peak in river level. The minimum conductivity
recorded for this event at LSWA05b upstream (337 µS/cm) occurred much closer to the peak in
river level at that site, illustrating the greater responsiveness of sites at more elevated locations
where dilution is more immediate during and following rainfall.
Conductivity at LSWA01 subsequent to the flood peak rebounds to over 630 µS/cm, about 12
hours after the minimum, and then declines slowly in line with the flood recession.
177
300
350
400
450
500
550
600
650
700
750
800
29-Aug-05
29-Aug-05
29-Aug-05
29-Aug-05
29-Aug-05
29-Aug-05
30-Aug-05
30-Aug-05
30-Aug-05
30-Aug-05
30-Aug-05
31-Aug-05
31-Aug-05
31-Aug-05
31-Aug-05
31-Aug-05
1-Sep-05
1-Sep-05
1-Sep-05
1-Sep-05
1-Sep-05
2-Sep-05
2-Sep-05
2-Sep-05
2-Sep-05
2-Sep-05
3-Sep-05
3-Sep-05
3-Sep-05
3-Sep-05
3-Sep-05
4-Sep-05
4-Sep-05
4-Sep-05
4-Sep-05
4-Sep-05
5-Sep-05
5-Sep-05
5-Sep-05
5-Sep-05
5-Sep-05
6-Sep-05
6-Sep-05
Conductivity uS/cm
0
0.2
0.4
0.6
0.8
1
1.2
1.4
River level m
conductivity
level
Figure 105: Continuous electrical conductivity and river level during a flood event at Little Swanport River 3km upstream Tasman Hwy
(LSWA01), August 2005.
Changes in total nitrogen (Figure 106) and total phosphorous (Figure 107) concentrations follow
that of turbidity, with maximum values occurring about 7 hours after the peak in river level.
However concentration of both parameters remained elevated for a more sustained period following
the flood peak. Maximum total nitrogen and total phosphorous for this event (1.17 mg/L and 0.05
mg/L) were less than those recorded at LSWA05b for this event (1.64 mg/L and 0.071 mg/L
respectively). This could also be seen as evidence that the majority of the nutrients transported
during this event originated from the upper and middle catchment, and that inflows to the river
below LSWA05b have only a small dilution effect on nutrient concentration. The final sample,
taken over 5 days after the flood peak, had a total nitrogen and total phosphorous concentration of
0.649 mg/L and 0.021 mg/l. For comparison, median total nitrogen and total phosphorous
concentrations from monthly sampling at LSWA01 is 0.5 mg/L and 0.012 mg/L, and this indicates
that it takes some time for nutrient concentrations to diminish.
178
0
0.2
0.4
0.6
0.81
1.2
1.4
29-Aug-05
29-Aug-05
29-Aug-05
29-Aug-05
29-Aug-05
29-Aug-05
30-Aug-05
30-Aug-05
30-Aug-05
30-Aug-05
30-Aug-05
31-Aug-05
31-Aug-05
31-Aug-05
31-Aug-05
31-Aug-05
1-Sep-05
1-Sep-05
1-Sep-05
1-Sep-05
1-Sep-05
1-Sep-05
2-Sep-05
2-Sep-05
2-Sep-05
2-Sep-05
2-Sep-05
3-Sep-05
3-Sep-05
3-Sep-05
3-Sep-05
3-Sep-05
4-Sep-05
4-Sep-05
4-Sep-05
4-Sep-05
4-Sep-05
4-Sep-05
5-Sep-05
5-Sep-05
5-Sep-05
5-Sep-05
5-Sep-05
6-Sep-05
6-Sep-05
6-Sep-05
Total Nitrogen mg/L
00.2
0.4
0.6
0.8
11.2
1.4
River level m
total nitrogen
level
Figure 106: Total nitrogen and river level during a flood event at Little Swanport River 3km upstream Tasman Hwy (LSWA01), A
ugust
2005.
0
0.01
0.02
0.03
0.04
0.05
0.06
29-Aug-05
29-Aug-05
29-Aug-05
29-Aug-05
29-Aug-05
29-Aug-05
30-Aug-05
30-Aug-05
30-Aug-05
30-Aug-05
30-Aug-05
31-Aug-05
31-Aug-05
31-Aug-05
31-Aug-05
31-Aug-05
1-Sep-05
1-Sep-05
1-Sep-05
1-Sep-05
1-Sep-05
1-Sep-05
2-Sep-05
2-Sep-05
2-Sep-05
2-Sep-05
2-Sep-05
3-Sep-05
3-Sep-05
3-Sep-05
3-Sep-05
3-Sep-05
4-Sep-05
4-Sep-05
4-Sep-05
4-Sep-05
4-Sep-05
4-Sep-05
5-Sep-05
5-Sep-05
5-Sep-05
5-Sep-05
5-Sep-05
6-Sep-05
6-Sep-05
6-Sep-05
Total Phosphorous mg/L
00.2
0.4
0.6
0.8
11.2
1.4
River level m
total phosphorous
level
Figure 107: Total phosphorous and river level during a flood event at Little Swanport R
iver 3km upstream Tasman H
wy (LSWA01),
August 2005.
179
Flood Event – September 2005
This flood event was much larger than that which occurred in the previous month. This event
peaked at a river level of 4.606 m above the cease to flow point, and is estimated to have had an
aggregated daily flow of 13,529 ML/day. The peak occurred on 12 September 2005 at 6:15AM, 2
hours after the peak recorded at the upstream gauging station at LSWA05b, providing an indication
that the rainfall generating this flood was more widespread and intense. A flood of this magnitude
or greater can be expected to occur approximately once every 5 years.
Given the magnitude and intensity of this event, it should be expected that maximum turbidity
would be much higher than the August event, despite the previous event having transported most of
the loose material in the river. From the autosampler, a maximum turbidity of 92 NTU was
recorded during the flood peak (Figure 108). Since the data from August showed that turbidity in
this section of the river appears to peak some time after the flood peak, it is possible that turbidity
may have exceeded this value as there are no readings available immediately after the flood peak.
Again, since the maximum turbidity recorded at LSWA01 during this event is only marginally
greater that that recorded at LSWA05b for this event (section 4.2.5), it appears that most of the
sediment transported during this event was derived from the middle and upper catchments.
Unlike the event of August, conductivity (Figure 109) exhibited a small but sharp spike 6 hours
prior to the flood peak, before falling to 148 µS/cm during the peak of the event. Unlike the August
2004 flood there is no ‘rebound’ in conductivity following the flood peak, showing that events of
this magnitude cause significant dilution of salinity in the river system. Mean conductivity at this
site as determined from continuous data for 2004-2005 is 593 µS/cm. Conductivity following the
flood peak only exceeded the long-term mean for the site 3 weeks after the flood peak, giving an
indication of the persistence of dilution from events such as these.
180
0
10
20
30
40
50
60
70
80
90
100
10-Sep-05
10-Sep-05
10-Sep-05
10-Sep-05
10-Sep-05
10-Sep-05
10-Sep-05
11-Sep-05
11-Sep-05
11-Sep-05
11-Sep-05
11-Sep-05
11-Sep-05
12-Sep-05
12-Sep-05
12-Sep-05
12-Sep-05
12-Sep-05
12-Sep-05
12-Sep-05
13-Sep-05
13-Sep-05
13-Sep-05
13-Sep-05
13-Sep-05
13-Sep-05
14-Sep-05
14-Sep-05
14-Sep-05
14-Sep-05
14-Sep-05
14-Sep-05
15-Sep-05
15-Sep-05
15-Sep-05
15-Sep-05
15-Sep-05
15-Sep-05
15-Sep-05
16-Sep-05
16-Sep-05
16-Sep-05
16-Sep-05
16-Sep-05
16-Sep-05
Turbidity NTU
00.5
11.5
22.5
33.5
44.5
5
River level m
turbidity
level
Figure 108: Turbidity and river level during a flood event at Little Swanport River 3km upstream Tasman Hwy (LSWA01), August 2005.
0
100
200
300
400
500
600
700
10-Sep-05
10-Sep-05
10-Sep-05
10-Sep-05
10-Sep-05
10-Sep-05
10-Sep-05
11-Sep-05
11-Sep-05
11-Sep-05
11-Sep-05
11-Sep-05
11-Sep-05
12-Sep-05
12-Sep-05
12-Sep-05
12-Sep-05
12-Sep-05
12-Sep-05
12-Sep-05
13-Sep-05
13-Sep-05
13-Sep-05
13-Sep-05
13-Sep-05
13-Sep-05
14-Sep-05
14-Sep-05
14-Sep-05
14-Sep-05
14-Sep-05
14-Sep-05
15-Sep-05
15-Sep-05
15-Sep-05
15-Sep-05
15-Sep-05
15-Sep-05
15-Sep-05
16-Sep-05
16-Sep-05
16-Sep-05
16-Sep-05
16-Sep-05
16-Sep-05
Conductivity uS/cm
00.5
11.5
22.5
33.5
44.5
5
River level m
conductivity
level
Figure 109: Continuous electrical conductivity and river level during a flood event at Little Swanport River 3km upstream Tasman Hwy
(LSWA01), August 2005.
181
4.3.7 Lower Catchment Export Loads
Background
Estimates of catchment transport loads can only be undertaken where streamflow data and water
quality data is readily available. In the lower region of the Little Swanport catchment, monitoring
of river level was carried out at station LWSA01. River level data from this station was used along
with the SKM hydrologic model for the Little Swanport catchment (SKM, 2004) to generate daily
streamflow for the period 1st February 2004 to 28
th February 2006.
As mentioned in section 4.2.6, during this study transport load estimates have been made using
water quality data from monthly and flood sampling, as well as continuous monitoring of the
parameters of conductivity and turbidity. A total of 322 spot samples for turbidity and 241 samples
for conductivity were collected at this LSWA01 on the Little Swanport River. Fewer samples for
nutrients were analysed, with 121 samples assessed for total phosphorus and nitrogen, and 84 of
these were concurrently analysed for suspended and dissolved solids. The plots below (Figures 110
to 111) show the times when samples were taken, and gives some indication of the spread of
hydrologic conditions over which sampling occurred. Table 25 provides the descriptive statistics
for the combined data.
0.000
0.200
0.400
0.600
0.800
1.000
1.200
22/03/2004
29/03/2004
6/04/2004
13/04/2004
20/04/2004
28/04/2004
5/05/2004
12/05/2004
19/05/2004
27/05/2004
3/06/2004
10/06/2004
18/06/2004
25/06/2004
2/07/2004
9/07/2004
17/07/2004
24/07/2004
31/07/2004
8/08/2004
15/08/2004
22/08/2004
30/08/2004
6/09/2004
13/09/2004
20/09/2004
28/09/2004
5/10/2004
12/10/2004
20/10/2004
27/10/2004
3/11/2004
10/11/2004
18/11/2004
25/11/2004
2/12/2004
10/12/2004
17/12/2004
24/12/2004
31/12/2004
Level (Metres)
Level (m)
Monthly Samples
Figure 110: Time series plot showing the change in water level at LSWA01 between March and December 2004, and times when
water samples were collected at the station.
182
0.000
0.500
1.000
1.500
2.000
2.500
3.000
3.500
4.000
4.500
5.000
1/01/2005
13/01/2005
25/01/2005
6/02/2005
18/02/2005
2/03/2005
14/03/2005
26/03/2005
7/04/2005
19/04/2005
1/05/2005
13/05/2005
25/05/2005
6/06/2005
18/06/2005
30/06/2005
12/07/2005
24/07/2005
5/08/2005
17/08/2005
29/08/2005
3/09/2005
6/09/2005
9/09/2005
12/09/2005
15/09/2005
18/09/2005
21/09/2005
24/09/2005
27/09/2005
1/10/2005
9/10/2005
12/10/2005
22/10/2005
25/10/2005
28/10/2005
9/11/2005
21/11/2005
3/12/2005
Level (Metres)
Level (m)
Monthly Samples
Flood Samples
Figure111: Time series plot showing the change in water level at LSWA01 during 2005, and times when water samples were collected
at the station.
Table 25: Descriptive statistics of WQ data for Little Swanport River 3 km upstream of the Tasman Highway (LSWA01).
Electrical conductivity
(µµµµS/cm)
Turbidity
(NTU)
TSS
(mg/L)
TDS
(mg/L)
TN
(mg/L)
TP
(mg/L)
N= 241 322 85 84 121 121
Mean 276 18.1 12.95 234 0.904 0.031
Median 236 18.1 9 224 0.85 0.028
Minimum 81.6 0.48 < 1 115 0.239 < 0.005
Maximum 1264 92 166 428 4.35 0.216
Load estimation
The method for the derivation of transport load estimates was the same as that used for other rivers
in Tasmania assessed under the ‘State of Rivers’ program (eg. DPIWE 1999; DPIWE 2003a &
2003b). As stated above, conductivity and turbidity were continuously monitored at LWSA01 using
instream sensors and logging equipment. Where gaps in either of these water quality records
occurred as a result of probe or power failure, data for the period was modelled based on known
relationships between changes in flow and changes in each of the parameters. Where data from spot
samples was available, these were used to verify or correct the real and modelled data.
Estimates of transport loads have been made for nitrogen, phosphorus, suspended solids and total
salt. The method for estimating loads is based on the development of relationships of each of these
183
parameters to turbidity or conductivity at the time of sampling. This was done using regression
analysis. Figures 112 & 113 show the relationships between conductivity and dissolved solids and
that between turbidity and total nitrogen at LWSA01, and the degree of correlation that exists in
each case (expressed in the form of the R2 value). The equations that describe the regression for
each parameter, and their corresponding R2 values, are given in Table 26. The relationships
between turbidity and nitrogen and phosphorus were best described using linear regressions, while
for conductivity and dissolved solids the relationship was best approximated using a power curve.
For turbidity and suspended solids there is a preponderance of data near to the x-axis, with fewer
high concentration data. In this case, a polynomial curve appears to best reflect the relationship
between these two parameters.
y = 6.2725x0.6465
R2 = 0.8592
0
100
200
300
400
500
600
0 100 200 300 400 500 600 700 800 900 1000
Electrical conductivity (microSiemens per cm)
Total dissolved solids (mg/L)
Figure 112: Correlation between electrical conductivity and total dissolved solids (salt) at the Little Swanport River 3 km u/s Tasman
Hwy. (LWSA01).
184
y = 0.0244x + 0.4528
R2 = 0.664
0
0.5
1
1.5
2
2.5
3
0 10 20 30 40 50 60
Turbidity (NTU)
Total nitrogen (mg/L)
Figure 113: Correlation between turbidity and total nitrogen at the Little Swanport River 3 km u/s Tasman Hwy. (LWSA01).
Table 26: Mathematical expression of the relationships between the various water quality parameters (and their corresponding
correlation values) at LWSA01 on the Little Swanport River 3 km u/s Tasman Highway.
Relationship R-squared No. samples
[Total dissolved solids] = 6.2725*EC0.6465 0.8592 84
[TSS] = 0.0269*Turbidity2 – 0.0821*Turbidity 0.6846 85
[Total Nitrogen] = 0.0244*Turbidity + 0.4528 0.664 121
[Total Phosphorus] = 0.0014*Turbidity + 0.0051 0.8112 121
Having established these relationships, continuously recorded turbidity was then transformed into
continuous time series of phosphorus, nitrogen and suspended solids concentrations. In a similar
manner, the continuous record for conductivity was also transformed into a continuous record of
total salt concentration. To provide an estimate of the instantaneous load for each parameter, the
transformed time series data were then simply multiplied by the coincident discharge volume for
that time period. To simplify the calculations the data was aggregated into daily time periods, thus
providing a daily load estimate.
Transport Load Estimates
The monthly transport load estimates for LSWA01 are shown in Table 27 below. During some
periods, when flow and turbidity at this site was very low, load estimates for suspended solids were
deemed to be ‘negligible’. From this table it can been seen that variation in loads generally follow
changes in discharge, and this is displayed more graphically by the plot for discharge and monthly
185
nitrogen load in Figure 114. During this study, the largest flood event occurred on 12 September
2005, when the river reached an estimated discharge of about 13,000 Ml/day. The total estimated
nutrient and salt loads for this event were;
Total phosphorus = 787 kg
Total nitrogen = 18,638 kg
Total suspended solids = 480,718 kg
Total dissolved solids (salt) = 3,633 tonnes
This single event constituted about 50% of the total discharge for the month, and carried 70% of the
TP load for the month, 63% of the TN load for the month, and 50% of the salt load for the month.
This emphasises the influence that hydrology has on the transport of nutrients within the river
system.
The load data from Table 27 can be used to derive export coefficients (also known as ‘catchment
export coefficients’) for the Little Swanport catchment that can then allow a more valid comparison
with other catchments of varying sizes and hydrology. Raw load data can be converted to export
coefficients by simply dividing the annual transport load estimated to pass a point on the river, by
the volume of rainfall that has occurred per kilometre of catchment area. The unit for the export
coefficient is therefore kg/mm/km2 and is equivalent to total load per megalitre of discharge. This
is usually calculated using annual data.
For the Little Swanport River 3 km u/s Tasman Highway (LSWA01) the annual export coefficients
shown in Table 28 have been calculated based on 12 month periods from February 2004. These
can be compared to coefficients from other Tasmanian catchments that have been studied under the
‘State of Rivers’ program (Table 29), and it shows that the coefficients for the Little Swanport
River at LSWA01 are in the middle to lower end of the range. Factors that tend to affect these
figures most are rainfall experienced during the study period (if below average rainfall occurs then
figures will be lower), and the level of catchment disturbance from agriculture and forestry.
186
Table 27: Estimated monthly discharge (Ml/d) and nutrients load for the Little Swanport River 3 km u/s Tasman Highway (LSWA01)
between February 2004 and February 2006.
MONTH Discharge
(ML)
TP Load
(kg)
TN Load
(kg)
TSS Load
(kg)
TDS Load
(tonnes)
Feb-04 5,036 136 4,205 32,723 -
Mar-04 1,079 11 588 83 501
Apr-04 4,217 48 2,366 717 1,721
May-04 3,104 34 1,725 413 1,155
Jun-04 11,733 149 6,874 4,752 4,967
Jul-04 12,097 266 9,036 43,187 5,239
Aug-04 7,834 169 5,796 27,147 3,756
Sep-04 3,683 46 2,141 1,227 1,377
Oct-04 3,507 39 1,951 482 1,647
Nov-04 5,611 130 4,312 28,545 2,199
Dec-04 1,402 16 793 282 580
Jan-05 1,898 22 1,078 404 933
Feb-05 11,358 249 8,478 40,426 3,611
Mar-05 1,179 11 617 negligible 458
Apr-05 2,594 22 1,321 negligible 906
May-05 1,287 10 645 negligible 436
Jun-05 11,033 111 5,956 600 4,876
Jul-05 4,959 54 2,745 810 1,719
Aug-05 7,322 118 4,719 13,840 1,937
Sep-05 27,086 1,120 29,369 542,131 7,476
Oct-05 14,869 308 10,774 39,568 3,924
Nov-05 4,091 52 2,388 2,319 1,541
Dec-05 5,557 99 3,742 10,798 2,422
Jan-06 1,846 13 903 negligible 910
Feb-06 2,775 18 1,316 negligible 1,130
TOTAL 154,383 3,233 112,522 790,057 5,4291
187
4,205
588
2,366
1,725
6,874
9,036
5,796
2,1411,951
4,312
7931,078
8,478
617
1,321
645
5,956
2,745
4,719
29,369
10,774
2,388
3,742
9031,316
0
2,000
4,000
6,000
8,000
10,000
12,000
14,000
Feb-04 Jan-05 Jan-06
Daily discharge (ML/d) OR Load TN (kg)
Monthly load N (kg)
Daily discharge (ML/d)
Figure 114: Variation in daily discharge at LSWA01 plotted along with estimated monthly load of nitrogen transported by the river at
this site on the Little Swanport River.
Table 28: Export coefficients for the Little Swanport River 3 km u/s Tasman Highway (LSWA01) derived from data collected between
February 2004 and February 2006.
MONTH Catchment area (km2) Discharge
(ML)
Total P
(kg/mm/km2)
Total N
(kg/mm/km2)
Feb 2004 to Jan 2005 600 61,202 0.017 0.668
Feb 2005 to Jan 2006 600 93,182 0.023 0.769
188
Table 29 Export coefficients for a variety of Tasmanian rivers. Results for rivers where data has been collected over several years
have been averaged.
Catchment Years of
Data
Catchment
Area
(km2)
Mean Annual
Discharge
(ML)
Total P
(kg/mm/km-2)
Total N
(kg/mm/km-2)
Jordan River at Mauriceton 3 742 8,117 0.23 1.346
Coal River at Richmond 9mths 536 4,485 0.011 0.42
North Esk River at Ballroom 2 363 138,949 0.005 0.098
North Esk River at Corra Linn 2 870 417,204 0.002 0.046
Duck River at Scotchtown 3 339 141,172 0.532 1.67
Montagu River at Stuarts Road 3 323 98,778 0.800 2.66
Inglis River at railway bridge 3 175 116,030 0.081 1.16
Pipers River 1 298 96,700 0.083 1.17
Brid River 1 136 40,986 0.066 1.13
Meander River at Strathbridge 3 1,012 427,904 0.058 0.67
Liffey River 3 224 80,661 0.052 0.78
South Esk at Perth 3 3,280 624,508 0.034 0.66
Break O’Day River 3 240 53,177 0.065 0.94
Huon River above Judbury 1 2,097 2,562,475 0.010 0.33
Kermandie River** 1 130 36,760* 0.122 1.42
* Estimated flow data
** Export figures include nutrients discharged to the river from the Geeveston sewage treatment plant.
189
4.3.8 Summary
There is a dramatic change in land use in the lower catchment and this change has a corresponding
influence on water quality. Below the gauging station at LSWA05b, the Little Swanport River
enters a gorge that extends through to the lower gauging station at LSWA01. Steep valley sides
have made this landscape unsuitable for clearing and the riparian and surrounding vegetation is
largely intact. This is also true for the lower half of the Green Tier catchment and the many
tributaries that enter the river throughout the lower catchment.
This reduction in land use and disturbance has two main effects on water quality. Firstly, the
diffuse inputs of sediment, salts and nutrients from cleared agricultural land that impact on water
quality in the upper catchment does not occur to any significant degree in the lower catchment. The
exception to this is the upper catchment of Green Tier Creek where land use clearly impacts on
water quality. Secondly, inputs from forested tributaries result in a dilution effect in the Little
Swanport River, improving overall water quality. Flood sampling and the subsequent calculation of
transport loads also suggests that a disproportionate quantity of sediment, salt and nutrients is
derived from the upper catchment.
The reduction in land use and disturbance, combined with increased inflow to the Little Swanport
River from the middle and lower catchment, has resulted in a continual improvement in
conductivity, a significant reduction in extremes of dissolved oxygen and a reduction in median and
maximum concentrations of total nitrogen.
Sampling in Pepper Creek and Rocka Rivulet demonstrates the natural variability in water quality
that can occur between two relatively undisturbed catchments, with Rocka Rivulet having elevated
turbidity and low conductivity while Pepper Creek has very low turbidity and higher conductivity.
This is most likely to reflect differences in soils and geology between the two catchments, however
most water quality parameters measured at these sites showed lower variability in comparison to
the more disturbed sites.
The higher natural turbidity evident in Rocka Rivulet is most likely a result of clay soils derived
from the dolerite geology, which is also present in the upper catchment of Green Tier Rivulet.
However land use has increased the susceptibility of this part of the catchment to increased
suspended sediment resulting in higher median and maximum turbidity values.
