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Published: 2017-04-06 15:00:00

Issued at 3pm

Tight management of flows out of Lake Karapiro last night helped prevent more significant flooding through Hamilton city and the lower Waikato River catchment.

Analysis by Waikato Regional Council staff today shows work by the council and hydro dams operator Mercury helped keep the Waikato River level through the city below the trigger point where Ann St residents in Hamilton would need to be evacuated.

The river level in the city peaked at 15.8 metres above sea level last night, 20 centimetres below the 16 metres trigger point. At 2pm today it was sitting at 15.6 metres.

“We had great co-operation from Mercury last night and that helped us keep residents safe,” said the council’s regional hazards team leader Rick Liefting. He noted Hamilton civil defence had sandbags ready for deployment and was on standby to evacuate residents.

Mr Liefting warned earlier today that some river levels around the region are likely to stay elevated for some time, preventing the draining of surface flooding, meaning people need to stay alert around waterways. (See full details at: https://www.waikatoregion.govt.nz/community/whats-happening/news/media-releases/watch-out-for-waikato-waterways-even-though-worst-of-heavy-rain-over/).

He said ongoing work with Mercury would be required to monitor, manage and respond to river level issues downstream of Lake Karapiro and in the wider Waikato and Waipa rivers catchment.

“In consultation with the council, Mercury has been proactively managing flows out of Karapiro by utilising river storage to mitigate the flows. As seen in the Ann St example, this has been effective in preventing considerably higher flows through Hamilton and the lower Waikato,” Mr Liefting said.

The situation now, however, is that there is very little extra (if any) storage left within the Waikato hydro scheme waterways, downstream of Taupo. That means the discharge out of Karapiro needs to remain high at a constant 600 cubic metres a second (cumecs).

“This will ensure that storage capacity progressively becomes available upstream of Karapiro as soon as reasonably possible. That will help us in the management of the inevitable rainfall events we tend to get over autumn and winter. We already have some predicted rain for the region next week,” said Mr Liefting.

The effect of this high 600 cumecs discharge – coupled with the recent rainfall in the lower Waikato River catchment – will be a sustained period of higher river levels downstream of Karapiro and slower drainage of surface flooding in that catchment.

“Current water levels in the lower Waikato River downstream from Lake Karapiro are predicted to remain elevated for some time, at least into next week and possibly longer.

“The council’s flood control assets in the lower Waikato are working well and to their design standards. However, elevated river levels outside of those controlled by our schemes mean that surface waters that would normally drain into the Waikato system are likely to recede very slowly.”

Mr Liefting acknowledged this may cause some frustrations but added it was extremely important to help ensure sufficient in-river storage further upstream to cope with the impacts of winter weather.

“Any property owners experiencing difficulties as a result of ongoing high river levels and surface flooding can contact us for advice and assistance.”

More information on river levels is available at

https://www.waikatoregion.govt.nz/environment/real-time-monitoring-information/