Every two seconds, enough water to fill an Olympic-sized swimming pool is pumping past Ngaruawahia through the Waikato River today, as recent heavy rain continues to drain through the catchment.
It is about three times the river’s average flow – but Environment Waikato’s lower Waikato and Waipa flood control scheme is handling it well so far.
The scheme 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 mighty Waikato River empties into the sea. They also protect Otorohanga town and areas along the Mangawara River near Taupiri.
The flood protection scheme also involves 240 flood gates, which allow drainage when river levels are low and pump water off farmland when river levels are high.
There are 65 flood pumps in the scheme, all of which have been running continuously for the past 10 days, as heavy rain has drenched the region.
Collectively, the pumps are draining 60 cubic metres of water off the land every second and emptying it into the Waikato River and its tributaries. That’s enough water to fill an Olympic-sized swimming pool in 40 seconds.
Environment Waikato staff have been working around the clock checking stop banks, flood gates and pumps are operating as designed over the past week.
“The scheme is designed to protect people and property from a one-in-100-year flood event and it’s working well at this stage,” Environment Waikato emergency management officer Adam Munro said.
“Although the river levels are high, based on current weather predictions we are still not expecting water to spill over any Environment Waikato stop banks or the Rangiriri spillway next to SH1.”
In some areas, water is traveling through sandy soils underneath stop banks and cause seepage on the other side, but this is natural and expected.
“Our staff are keeping a close eye on the situation and sandbagging to stabilise areas where this is occurring around Environment Waikato stop banks,” Mr Munro said.
The Waikato River is still rising today, but the rate of rise has slowed to about 4cm a day, compared with about 10cm a day yesterday.
“Based on current weather predictions, finer weather between now and Friday should see water levels in the Waikato River start to level off over the next couple of days,” Mr Munro said.
“However more rain is predicted on Friday and we are continuing to watch the rivers and closely manage the flood protection scheme.”