Media Release

13 June 2012

Continued flood protection of Makara Valley & Elsthorpe community investigated

Work is underway by the Hawke’s Bay Regional Council to ensure the continued protection of the Makara Valley and Elsthorpe community from the risk of flooding.

During one of Hawke’s Bay Regional Council’s regular dam inspections on 31 May, a sinkhole was found in the face of the largest dam (No.1 Dam, Kokatewai Road, off Kairakau Road).

The local community has been informed and Engineering specialists, Damwatch Services Ltd, have now visited the site and will soon report back to HBRC.

HBRC Group Manager, Asset Management Mike Adye says the situation is that the bottom of the corrugated steel pipeline at the base of the dam has rusted in places.

He says when the pipe was flowing full, as it did in April 2011 and again in January 2012, turbulence caused fill material from around the pipe to be sucked out, which made a void around the outside of the pipe. The top face of the dam has subsequently given way and dropped down into the cavity, creating a sinkhole in the dam face.

“Our first priority is the safety of people downstream of the dam. However, there is no risk to them while the weather remains fine with no significant rainfall events forecast. There is no current risk as there is no water in the dam,” says Mr Adye.

He says HBRC engineers have three diggers on standby should severe weather be forecast. The diggers would be used to reduce the height of the dam to ensure there is no risk to public safety.

“If the dam is reduced in height there will however be a potential risk to farmland and property

downstream of the dam. Forecast rainfall at a level above 35mm in one hour, 45mm in 1 ½ hours,

50mm in 2 hours, or over 100mm in 3 hours would be of significant concern and prompt HBRC to

mobilise these diggers.”

Mike Adye says HBRC is keeping the local community updated on the situation and during the next two months HBRC engineers will work with Damwatch Services Ltd to identify the best option for the continued protection of the Makara Valley and Elsthorpe community. HBRC is also liaising with Central Hawke’s Bay District Council.

Background

Five Makara and Atua Valley flood detention dams were constructed in the early 1980s, following a series of severe flood events in the early 1970s. After those floods, local landowners asked the then Hawke’s Bay Catchment Board (now HBRC) to investigate the control of flooding and erosion in the catchment.

A flood detention dam is constructed across a valley to temporarily hold excess flood water in a specific ponding area. In normal weather conditions the dam is empty, with in-flowing water exiting through a pipe in the face of the dam. During storm events the capacity of the pipe is exceeded and water builds up or ‘ponds’ behind the dam.
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