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Portsmouth Flood Alleviations Scheme
The majority of the flow in wet weather is surface water, so the Portsmouth Flood Alleviations Scheme was created to divert surface water to the sea instead of entering the combined sewer. This would free up capacity in the existing infrastructure, allowing it to be used to provide protection against larger storms. In total, surface flow from 34 Hectares of paved area was diverted by the project.
The flow reduction initiatives have reduced the flow arriving at Eastney to the extent that the required flood risk protection level has been achieved. In order to reduce tidal infiltration and tidal restriction of CSO operation, new surface water pipes, culverts and swales were created, and several sections of the public sewer were remediated.
Pump management
The large diesel pumps at Eastney have an enormous capacity, with a combined ability to remove 6,500 litres per second. However, they take 15 to 30 minutes to build up to full speed so advance notice is necessary. The pump station is manned 24 hours/day and a network of 4 sewer water level sensors and 10 rainfall monitors delivers data via OTT Adcon radio telemetry to a catchment software model developed by Innovyze.
Employing the latest technology, OTT Pluvio2 raingauges are able to measure both rainfall amount and rainfall intensity. This is important because traditional raingauges simply supply historical data on the amount of precipitation, whereas near real-time access to precipitation intensity dramatically increases the speed with which the monitoring system is able to deliver storm warnings. Another key feature of these smart raingauges is their ability to operate reliably without the level of maintenance that is required by traditional raingauges. For example, they are able to issue alerts when maintenance is necessary.
Summarising, Rob McTaggart, technical lead at MWH says: “Collaboration with the community, and other stakeholders in Portsmouth, made it
possible for the project consortium to design and implement a solution that separated surface water to provide resilience, significantly boost flood protection and benefit the environment with the minimum of new infrastructure.
“Clearly, the flood alleviation scheme has been a success and as a result, the pumps at Eastney are called into action less often.
“The early warning system appears to be working very well. Some of the rainfall prediction data, provided by external sources, can sometimes provide erroneous projections because of the localised nature of precipitation events, so it is important to have a sufficient number of raingauges to ‘calibrate’ projections and deliver the level of precision required.”
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| December 2016 | drain TRADER 23
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