Water Supply Resilience
Drinking Water Resilience on the Hauraki Plains
Summary of Information
- The Hauraki Plains has 2 water treatment plants, providing 19 million litres per day to 6,500 people and approx. 110, 000 cows and other livestock.
- The pipe network used to deliver the treated water is 364km long with 224km of that being classed as brittle (iron, asbestos and concrete) pipes.
- We have started a pipe renewal programme to upgrade the brittle pipes.
- Water is supplied on-demand for urban properties and 24 hour supply for rural properties.
- Droughts and earthquakes are a big risk to our supply for both rural and urban properties.
- Rural properties should have 24 hours of water supply storage to help prepare their water supply for emergencies
We all rely on having safe water to drink. In the Hauraki Plains it is not only the 6,500 people who we provide safe water to, we also provide water to 110,000 cattle. Safe potable water is not only critical for life, but also supports the economy of the Hauraki Plains – and by extension the whole District.
Originally the Plains Water Supply System was not designed as an on-demand. As the two plants have been upgraded, we are able to supply an on-demand service to urban homes, however for rural properties and other high users we provide the demand over 24 hours i.e. farmers will receive what is needed, but over a 24 hour period. This means they will need extra storage to provide for use during the times when the demand is higher, such as during milking.
Water Treatment Plants:
The water for the Hauraki Plains communities is supplied from two interconnected water treatment plants (WTP). The larger plant at Kerepehi can produce 12.5 million litres per day. The smaller Waitakaruru plant can produce 6.5 million litres per day.
The Kerepehi WTP takes water from the Waihou River at the Pekapeka intake located on Hauraki Road. The Waitakaruru WTP takes water from the Mangatarata Stream. We also hold a consent to take water from the Waitakaruru River and store it in a former Quarry on Steen Road. We can store raw water during winter time to use in the warm summer months as both the Waitakaruru River and Mangatarata Streams often drop below the consented take-level. The raw water supply for Waitakaruru WTP is then used only from the Quarry Raw Water Reservoir
The plants treat the water to a high standard (both WTP’s produce water that exceeds the required drinking water standards). This is stored in potable water reservoirs (10ML at Kerepehi and 1.1ML at Waitakaruru) and then pumped out into the reticulation network by a series of booster pumps.
Our reticulation network (pipes and pumps) is made up of 364 kms of pipes – the oldest installed in the 1930’s. The reticulation network is made up of a combination of brittle (iron, asbestos and concrete) and ductile (uPVC, MDPE and alkathene) pipes. Unfortunately 224 km of the Plains reticulation network is classified as brittle.
There are 3 main risks to our water supply
- Pandemics such as Covid19
Covid19 brought into sharp focus the need to protect our teams to ensure that we have staff to both run our WTP’s and fix our network. The lessons learnt over this time stand us in good stead for any future events.
Drought effect on water availability:
We have resource consent conditions that limit the amount of water we can take from a water source. These limits are reduced further when river levels reach low levels during a drought. This means we can’t take enough water from the rivers to meet demand.
Drought effects on brittle pipes:
When the clay soil dries and cracks around a pipe, it can also cause the pipe to crack. Most pipes are around 1 metre deep, so it is usually only during a dry season that cracking occurs at this depth. These breaks can be difficult to locate even if it is a big break, they could be located in the middle of a paddock and spraying downwards so there is no visible sign. Breaks like this on larger pipes have caused temporary water shortages in the past.
The Kerepehi fault line runs generally north – south through Plains and out into the Firth of Thames.
In the event of even a small earthquake, we will likely see damage to our brittle pipes.
A large earthquake could see significant damage to our intake structures, raw water storage tanks, water treatment plants, treated water storage, booster pump-stations and our brittle networks. This means a significant, if not complete, loss of treated water supply for all of our communities.
We are preparing a new resource consent application to enable us to take additional water from the Waitakaruru Stream to fill the Quarry, increasing the resilience of our supply. This should help maintain our supply during periods of drought.
We have a works programme in place to replace the brittle pipes. This includes a current $6M replacement project for the raw water main for Kerepehi.
We are steadily replacing the network based on how critical the pipe is for the network. The more critical a pipe is for the overall network, the higher it is on the replacement list.
The brittle pipes are replaced with MDPE (Medium Density Polyethylene) pipes which are significantly more resilient.
We are also investigating the option to connect the Paeroa network to the Plains network. This will mean we can supply the Plains with water from the Paeroa Water Treatment Plant, if the treatment plants in the Plains are compromised.
Our communities will be provided with drinking water with tankers and water containers should the worse happen and we have a complete loss of supply from the treatment plants.
If you see a leak in the network, please contact our Service Request team either via phone on 07 862 8609 or 0800 734 834 (within the district) or online at www.hauraki-dc.govt.nz Remember a leak that looks small above ground may be a massive leak underground.
For those who live in towns, make sure you have your emergency kit ready for earthquake situations. Visit the https://getready.govt.nz/ website for more information.
Farms and Rural Properties
For farmers and rural properties, to make sure your supply is continuous, you will need to have 24 hours of storage onsite. If you don’t boost your supply, you may find you lose water pressure or water completely during times of peak demand.
If there is a large earthquake, farms may be without water, besides any 24 hour supply storage. Fonterra and Dairy NZ have shown that they can and will mobilise rural support during response to earthquakes. This was demonstrated during the Christchurch and Kaikoura earthquake events.
The length of time for the loss of potable water production, depends on the level of damage caused to infrastructure and which infrastructure is actually damaged.