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: marcus.koll@gdc.govt.nz

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