Desmond Scrimonger, PE. Senior Principal Engineer Operations
Wellington Water, New Zealand

The build-up of sand can be a problem for many outfalls. When sand builds up against a valve it inhibits its ability to open, or close, depending upon where the sand builds up. If sand builds up against the valve preventing it from opening there is a risk of upstream flooding.

This was the situation in Porirua where sand built up regularly against a flap valve. Maintenance teams where sent to the location twice a week to dig the sand out allowing flow through the flap valve when required.

WaStop, with its pulsating flow action, flushes sand out from the front of the WaStop allowing flow through the valve when required. In extreme situations, such as in one site in Porirua, an overflow can be used to help liquidize the sand to assist the valve open. In this particular situation the valve could be filled 2/3 with wet sand. Once the overflow is activated the valves have enough pressure behind them to open and allow flow.

Approximately two months after installation the pulsating flow exhibited by the WaStop ensures that sand no longer builds up in front of the valve,

“I truly do believe WaStop are exceptional devices that have a valid place on the global stage in helping combat rising sea levels or flood levels, while providing a real level of comfort around performance over investment.”

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