A portion of these outlets are very flat on their approach to the harbour which generally means they are influenced by high tide. 

The issue with the outlets is that if a rain fall event coincides with a high tide the ability of the stormwater network is severely restricted in discharging, thus building up within the network and restricting flow into the system from private properties meaning localised flooding or ponding, restricting flow from sumps or discharging at a point of least resistance within the network - , generally a manhole which are often situated on or across private property.
 
When considering an upgrade for these lowing lying areas that have tidal influence, you would generally have to build a large redundancy into the pipes within the network to cater for required storage during these events until tide reseeds. This can become very expensive with large amounts of capital invested for very minimal use. 

The WaStop was the perfect solution. It stops the tidal influence encroaching up the pipe and occupying vital network capacity - Saving capital expenditure in pipes and construction also ensuring a certain level of service. During a storm event, the flow begins to builds up behind the WaStop at the outlet - it takes very little head to open the Wa allowing normal discharge into the harbour, as the flow reseeds within the network and the pressure and head reduce the WaStop then adjusts and closes once again stopping infiltration. We are trialling them out in 5 different locations varying in size from 225mm up to a 1050mm.