River levels exceed flood design capability
Thursday, 6 April 2017 11:35 a.m.
Eastern Bay rivers reached warning levels overnight and Bay of Plenty Regional Council’s flood management is making every effort to protect communities.
The Matahina Dam was lowered to 71.5m (5.3m below the design flood level) in anticipation of this event. The dam is spilling a total of 780 cubic metres per second to reduce an expected peak inflow of 950 cubic metres into the dam. This peak inflow is expected to be about midday today (April 6).
Flood manager Peter Blackwood says this is a significant event that is beyond the Matahina scheme’s design capacity for a 100-year flood event.
The Whakatāne and Rangitāiki River levels are still very high.The Whakatāne River peaked at 8.33m at 6am today and had dropped to 8.03m by 10.25am.
High tide at 2.52pm this afternoon but is not expected to have an impact on either river, Peter says.
While the rain has stopped, the risk of stop bank breaches is still moderate and Bay of Plenty Regional Council’s flood management team is working to divert water away from Edgecumbe to reduce this risk. The Reids Central floodway spillway is in operation and rivers and drainage staff are closely monitoring the situation.
Evacuations of Edgecumbe are continuing.
Trustpower operates the Matahina Hydro-Electric Power Scheme on the Rangitaiki River. The regional council works with Trustpower to better mitigate flood risk and reduce the impact of erosion of the river banks. This includes pre-lowering the Matahina Dam when a significant flood event is forecast, to maximise storage of floodwaters in the dam and reduce the flood peak downstream of the dam. The above action was taken in accordance with this operation.