Case Studies

Type of work

Design and install of communal water storage system to service 7 properties located on the Kawarau Arm (Southbank) of Lake Dunstan.  The purpose of the scheme is to mitigate risk of damage to water supply and irrigation systems drawing water from the lake during periods of high flow in the Kawarau River.

Problem that needed solving

The construction of the Clyde dam near Cromwell and subsequent flooding of the Kawarau and Clutha rivers to create Lake Dunstan has changed the upstream flow and sediment behaviour. 

The Kawarau arm of the lake was formerly the Kawarau River, a tributary of the Clutha River and it had two distinct reaches - the reach from the Kawarau Gorge to the Bannockburn Bridge and the reach from the Bannockburn Bridge to Cornish Point.

Siltation in the lake, particularly in the Kawarau Arm, had been an issue for water users.

Seven properties located on the Southbank have consents to draw water from the river for irrigation purposes.  Irrigation is essential for the production of wine grapes and vines that have successfully been planted on land previously identified as marginal for pasture or orchards.

To ensure security of water supply during periods of high river flow, a robust water storage and irrigation solution was required.

Size/scale of project

7 private residential properties.  

Irrigation Services were the main contractor undertaking the design, product selection and installation of the irrigation components, working closely with local electrical, construction and civil works contractors to complete the scheme.

Complexities and challenges

With multiple stakeholders and system users, coordination and communication between all parties was critical to ensuring the successful completion of the project. Irrigation Services took a lead role in this and as the main contractor provided centralised and regular updates to all involved.

Most of the properties had established irrigation systems in place so there was a desire to minimise cost by reusing equipment where possible. 

This was an achievement the project is proud of with four of the users, existing pumps being repurposed.

Description of outcome/solution

The solution implemented consists of two parts; Irrigation and Potable water.  For irrigation purposes water is pumped via a concrete sump located in a water storage pond adjacent to the Kawarau River.  Water is transferred in a rising main to water storage tanks situated on top of the terrace approximately 20m above river level.

Potable water is pumped via a bore into a rising main and stored in a tank also situated on the terrace.  From the water storage tanks individual users pump water into their respective reticulation systems.

Components used include:

• Irrigation Sump Pumps:2 x Sakuragawa
• Individual reticulation pumps: 4 x new pumps (1 x Goulds and 3 x Lowara) 4 x reused Lowara pumps
• Tanks: 4 x RX Plastics 33,000 litre tanks
• Irrigation Rising Main: 225mm MDPE
• Potable Rising Main: 32mm LDPE
• Sump: 2.050 diameter
• Pipe from sump to pond: 400mm MDPE

Details

Location

Lake Dunstan, Central Otago

Client

Contact Energy and 7 Residential Properties

Year

2017