BEFORE THE GISBORNE DISTRICT COUNCIL
IN THE MATTER of the Resource Management Act 1991
AND
IN THE MATTER the Gisborne District Council Proposed
Regional Freshwater Plan
Statement of Evidence of Marcus Koll
On Behalf of the Water Utilities Section, Gisborne District Council
4 October 2016
Gisborne District Council
P.O. Box 747
Gisborne 4010
Marcus Koll
Water Team Leader
Water Utilities Section
Email: [email protected]
Mob: 0274862332
Introduction
1. My name is Marcus Koll. I am an employee of the Gisborne District Council where I hold
the position of Water Supply Team Leader since 2007.
2. I am responsible for the collection, treatment and distribution of potable water on a 24/7
basis for the City of Gisborne, and also the townships of Manutuke, Te Karaka and
Whatatutu.
3. My evidence outlines the operational complexity of the water supply network with specific
emphasis on the interaction of the Waipaoa Water Augmentation Treatment Plant that
extracts water from the Waipaoa River and the Waingake Water Treatment Plant, which
extracts water from the Te Arai Bush and three Dams known as the Mangapoike Dams.
Scope of evidence
My evidence covers the following:
4. Waipaoa River Source
4.1. Brief description of Gisborne Water Supply
The Council operates and maintains the Gisborne City water supply from its source
supply, being the Mangapoike Dams, Te Arai Bush Intake and the Waipaoa River, via
water treatment infrastructure at Waingake and Waipaoa to the water reticulation
network, including Reservoirs, Pump Stations and the connections from the street
mains to all serviced property boundaries. All commercial / industrial water
connections are metered and Council charges for actual water used. The water
pricing model also accounts for high water users who pay more due to availability
charges.
4.2. Purpose of the Waipaoa Water Treatment Plant
The Waipaoa Water Treatment Plant (or Waipaoa Augmentation Plant) was
constructed during the recovery process after Cyclone Bola, which occurred in March
1988. During this event, Gisborne City became aware of its isolation and dependency
on the Waingake water supply facility. As part of the rebuilding process it was
identified that an alternative water source and treatment facility was required to
provide security of supply and the Waipaoa Water Treatment Plant (WTP) was
constructed and commissioned by 1991 to augment the existing Waingake supply.
The Waipaoa WTP has the ability to produce water volumes up to 200litres per second
or 720m³/hr or 17,000m³ per day for an emergency take only. The plant runs on several
pre-set modes, refer to Table 1 below.
Source Capacity for Various Operational Scenarios
Capacity
Source Operation [l/s] [m3/hr] [m3/day]
Average Annual Water
Demand Gravity 179 646 15,500
Waingake WTP Winter Low
Flows Gravity 139 500 12,000
Waingake WTP Peak Summer
flows Booster pumping 296 1,066 25,600
Waipaoa WTP - Emergency Max. Emergency Take 200 720 17,280
Waipaoa WTP – Max Max. Normal operation 150 540 12,960
Waipaoa WTP – Med Pres-set modes 100 360 8,640
Waipaoa WTP– Min Pres-set modes 50 180 4,320
Table 1: Source Capacity for Various Operational Scenarios
The Waipaoa supply has shown on a number of occasions the critical role it plays in
the overall provision of water services to Gisborne City. Supply from Waingake has
been lost 2 times and the Waipaoa plant has meet the emergency needs of the city.
During several drought events, the Waipaoa supply was able to augment the
Waingake supply ensuring residential and commercial customers noticed only
minimal or no reduction to their level of service.
4.3. Waipaoa Source Resource Consents
a) WS-2011-104932-00: Gives consent for Council to take 12,960 m3/day at a
maximum rate of 150 L/s (540 m3/hr) from the Waipaoa River for the Gisborne
Municipal Water Supply.
b) WS-2011-104931: Specifies that under emergency conditions (as defined by the
consent) and when the Waipaoa River discharge at the Kanakanaia Bridge
falls below 1.3m3/s (1,300 l/s) the take ‘shall only occur as specifically
authorised by the Environmental Services Manager of Gisborne District
Council’.
4.4. Waipaoa Water Treatment Plant Operation
Currently there are three scenarios, which determine the operation of the Waipaoa
Water treatment Plant (WTP):
a) The Mangapoike dam water storage is heading towards (or is at) critical low
levels and below Councils intervention line (Potential Drought).
Extraordinary operational circumstances
b) the Waingake water source is unavailable due to an unforeseen supply issue:
i. Technical defect (i.e. trunk main break)
ii. Source water quality issue / treatment compliance issue
c) The health and well-being of the Gisborne Customers is likely to be adversely
affected
iii. Insufficient water in city reservoirs caused by excess peak summer
demand which requires a short augmentation (3 to 5 days) to allow
water restrictions to be implemented and refill reservoirs. (Emergency).
iv. Water quality issue with the Waingake supply, duration unknown
(Emergency)
[4.4a] assumes a potential drought and Water Utilities will be imposing staged water
restrictions.
[4.b] is an emergency and there may be some water able to be sourced from the
Te Arai depending on the location of the break major restrictions including
industry are likely to be affected.
[4.4c(iii)] typically results from a series of unforeseen extremely hot days driven by
high domestic usage mainly irrigation and topping up swimming pools
when reservoir levels have not yet recovered. This pushes storage in the city
below acceptable levels and could result in running out of water in the city in
elevated areas and loss of firefighting capacity.
[4.4c(iv)] this is a likely source contamination, it would be an emergency and
would need to provide water solely from Waipaoa and would result in
major water restrictions.
4.5. Historic Operation of Waipaoa WTP 2005 -2015
Between November 2005 and November 2015 the Waipaoa Water Treatment plant
supplied water to Gisborne on ten different occasions totalling 91 days of operation.
The supply duration ranged from one day (20 January 2006) to 53 days of continuous
operation during the 2012/13 drought event (12 February – 5 April 2013). The Waipaoa
River had not reached the 1,300 litres per second low flow threshold during the dates
stipulated in Table 1 below.
Total production over that period was 746,954m3. Average daily production was
8,208m3/d. This equates to an average take of 95l/s.
Table 2: Waipaoa WTP Operation 2005 - 2015
5. Te Arai River Source
5.1. Brief Description of the Waingake Water Supply
The Waingake Water supply consists of two distinct water catchments, the
Mangapoike Dam Catchment and the Te Arai Bush catchment. Table 2 explains the
distribution of the two sources.
Waipaoa WTP Operation 2005 - 2015
Year Dates # days
<1,300l/s
River low
flow
Re
stri
ctio
ns Main Reason for
Waipaoa Operation
Dam
Storage
Peak
Demand
2005/06
2/11/2005 3/11/2005 2 No No No No
20/01/2006 20/01/2006 1 No No Yes Yes
9/03/2006 9/03/2006 1 No No Yes Yes
15/03/2006 16/03/2006 2 No No Yes Yes
2006/07 26/01/2007 27/01/2007 2 No No Yes Yes
2007/08 - - - - - Yes -
2008/09 12/12/2008 22/12/2008 11 No Yes Yes No
2009/10 - - - - - Yes -
2010/11 - - - - - - -
2011/12 - - - - - - -
2012/13 12/02/2013 5/04/2013 53 No Yes Yes Yes
2013/14 8/01/2014 17/01/2014 10 No Yes No Yes
2014/15 11/02/2015 13/02/2015 3 No Yes Yes Yes
17/03/2015 20/03/2015 4 No Yes Yes Yes
2015/16 26/11/2015 27/11/2015 2 No No Yes No
Total 91
Waingake Annual Water Production [2015/16]
Source Quantity [m3/annum] Split [%]
Mangapoike Dams (3) 3,803,235 65.6%
Te Arai Bush Catchment 1,969,560 34.4%
Total Waingake Production 5,772,800 100%
Table 3: Waingake Annual Water Production Figures 2015/16
5.2. Purpose of the Te Arai Bush Catchment
The Te Arai Bush Catchment consists of 1,100 ha of land of high intrinsic value as a
gene pool for flora and fauna. It remains the finest example of undisturbed dense
native bush on East Coast soft hill country. The area boasts diverse vegetation and
soil character. The Te Arai Bush Catchment protected by a QEII covenant on the land.
The Te Arai Bush Catchment provides about 34% of the City’s total annual water
demand. Winter take averages from the Te Arai are 500-600 m³/hr (139-167 l/s), which
can be considered the single water source during the low demand season (winter).
During the high to peak demand season however, take averages are only 100-200
m³/hr (28-55 l/s), the fast majority of summer demand is taken from the Mangapoike
Dams.
During and immediately after heavy rainfall events, the water in the Te Arai River
becomes dirty from sediment, it is harder to treat and increases the risk of
contamination with the treatment process adopted at Waingake. During these
periods the bush intake is isolated and dam water only is utilised.
5.3. Management of the Mangapoike Dams
The Catchment size of the Mangapoike Dams 450 hectares and contains of three
Dams, HC Williams Dam (Earth), Clapcott Dam (Concrete) and Sang Dam (Earth).
The purpose of the dams is twofold; to supply clear water when the Te Arai river is dirty
and to provide the bulk of the summer water. The Dams are located on the Wairoa
side of the Wharerata divide to capture the orographic rainfall.
An analysis of the rainfall patterns and historic dam levels was used to establish an
intervention line for Dam volumes as shown in Appendix 2. The blue line represents
actual combined water storage levels of the three dams at a given time. The red line
represents where the minimum storage levels should be to avoid security of supply
issues. Once the red line is approached or crossed, it triggers intervention by
introducing city wide water restrictions and/or the running of the Waipaoa
Augmentation Plant.
As Dam levels drop so does the water quality, water quality is maintain by aeration but
as the levels fall even lower water quality cannot be guaranteed and would suggest
that not all of the water will be usable.
Between 2005 and 2012 (8yrs) the Dam levels went below the intervention line twice.
The water can gravitate from the Dams to Waingake but as demand increases
booster pumping is required. There are 2 booster pump stations between the Dams
and the Te Arai Intake.
5.4. City Reservoirs
Council has three main bulk storage Reservoirs within the city limits, Hospital Hill
(38,000m3), Knob Hill (8,800m3) and Taumata (3,800m3). There are five other high levels
reservoirs of small capacity serving small low pressure areas and used to help reduce
system pressures.
During summer, the water operators constantly review the weather forecast to predict
the weekly water demand and set a flow rate to maintain storage in the Reservoirs,
but also allow sufficient space for water to enter so that the city pipe network is not
over-pressurised causing pipe breaks.
The treatment plants are operated in a steady state to ensure compliant water and
to reduce the risk of mechanical breakdowns, both within the treatment plant and
the reticulation network.
Hospital Hill Reservoir was constructed as part of the recovery phase from Cyclone
Bola to provide greater resilience, Gisborne City has more operational water storage
than most cities in NZ of similar size and capacity. It recognises the fact that it takes
between 16 and 36 hrs to produce potable water from the Waipaoa Water Treatment
Plant depending at what level of readiness it is in. During peak summer demand, there
is an increased potential for the Waingake Supply to be augmented. It is then that the
Waipaoa WTP is prepared for operation to reduce the start-up time.
Reservoir storage can be easily lost during periods of high demand, there can be a
lag time to respond and can quite easily exceed the amount of water that can be
provided from Waingake. While the City reservoirs are there to act as a buffer for
demand, any booster pump failures or other operational issues can result in major loss
of storage in our reservoirs, which triggers the need run the Waipaoa WTP to
compensate. Equally there is a large lag time before imposed water restrictions have
an effect on suppressing water demand which would allow City water storage to be
recovered in our reservoirs.
Marcus Koll
4 October 2016
Appendix 1: Overview of the Gisborne City Water Supply
Appendix 2: Operational Dam Curves Mangapoike Dams
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