EW and MRP balance river flows

Published: Fri 10 Sep 2010 03:40 PM
EW and MRP balance river flows to manage flood risk
Environment Waikato is working closely with Mighty River Power to carefully control the release of water from Lake Taupo through the Waikato Hydro System ahead of forecast rain this weekend.
As a precaution, Mighty River Power is releasing water from Lake Taupo and Lake Karapiro to create more storage for expected high inflows in the Taupo area.
The move comes as up to 60 mm of rain is forecast to fall on already sodden catchments over an 18-hour period from tomorrow evening.
“Lake Taupo is still 13cm below its maximum control level, but we need to create some storage because catchments are saturated and the lake’s tributaries will respond quickly to any rain,” EW emergency management officer Adam Munro said.
While the Taupo Gates, just north of Taupo under the SH 1 bridge, provide some ability to control the amount of water flowing down the Waikato River, there is little effective storage in the hydro dams on the river so the water has to keep flowing.
“We’re keeping a very close eye on rainfall and river levels and working with Mighty River Power to carefully balance flows through the upper, middle and lower Waikato.”
Mr Munro said people could expect to see high river levels over the next few days and needed to be alert to the possibility of rapidly rising streams and rivers.
Environment Waikato staff are out in the field, checking pumps, floodgates and stopbanks. Staff are also monitoring river levels and rainfall, and are alerting landowners, councils and other stakeholders when early warning river levels are triggered.
Information on rainfall and river levels, and up to date situation reports on the weather are available at, or on the following info lines:
Ohinemuri, Kauaeranga and Waihou – 0832 25 334
Piako, Waitoa, Thames tide – 0832 25 335
Waipa, lower Waikato – 0832 25 336
Taupo basin, Awakino – 0832 25 337
Calls cost 12c a minute from a standard telephone. Calls from cell phones and pay phones are charged at cell phone and pay phone rates.
Environment Waikato’s flood protection schemes
• On average, enough water to fill an Olympic-sized swimming pool every 3.5 seconds is pumping down the Waikato River past Ngaruawahia – the river is currently flowing at 3 times its average rate.
• During flood events Environment Waikato and Mighty River Power work closely to manage water flows through the Waikato River hydro system, which can help to alleviate flooding further downstream.
• On behalf of ratepayers, Environment Waikato manages approximately $400 million worth of assets such as stop banks, flood gates, pump stations and drains designed to protect huge stretches of land in our region from flooding
• A lot of people don’t even realise these flood protection schemes exist because they are so carefully integrated into the surrounding landscape But if they weren’t there, large areas of the region, including the north Waikato and Hauraki Plains, would be under water for months at a time.
• There are three big flood protection schemes: the Lower Waikato Waipa scheme, the Waihou Valley scheme and the Piako River scheme. There are other, smaller schemes such as the Tauranga Taupo scheme, Tongariro and schemes in the Coromandel.
• The lower Waikato Waipa scheme is the largest. It includes 255km of stop banks, which protect about 26,000 hectares of land from flooding. The stop banks stretch from Huntly to Port Waikato, where the Waikato River empties into the sea. They also protect the Otorohanga town and areas along the Mangawara River near Taupiri.
• The lower Waikato Waipa flood protection scheme involves 240 flood gates, which allow drainage when river levels are low and pump water off farmland when river levels are high. The scheme also includes 65 flood pumps.
• Rainfall and river level information is fed in through a network of rainfall and river level monitoring stations around the region. Environment Waikato has 47 river flow recorder stations and has access to 19 other flow recorders owned by other agencies, such as NIWA. We also have 24 rainfall monitoring stations, and 29 stations that monitor water levels in Whangamarino wetland, the tidal reaches of the Waikato, Waihou and Piako/Waitoa rivers and the lakes of the lower Waikato catchment.
• As flood alarms are triggered, some stakeholders are alerted via telephone, while others are updated through text messages and emails.

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