Water & Wastewater Treatment

WWT January 2017

Water & Wastewater Treatment Magazine

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www.wwtonline.co.uk | WWT | JANUARY 2017 | 15 Project focus Wastewater and drainage Smart' flood alleviation system protects Portsmouth Project focus I n late 2014, Southern Water completed a major project to reduce the risk of sewer flooding in parts of Portsmouth and Southsea. Substantial works were undertaken to divert runoff and tidal ingress, and a 'smart' hydrometeorological ● Smart hydrometereological system monitors flood risk in south coast city ● Real-time sewer level monitoring informs computer catchment model ● Flow reduction initiatives ease pressure on key pumping station catchment-wide water model. This decision support system provides advance notice for staff at the Eastney pumping station that diverts large quantities of water to storage tanks during periods of heavy rain. Through the development of a smart sewer network, Southern Water has dramatically reduced the risk of flooding in Portsmouth whilst also delivering substantial environmental benefits. Background Portsmouth was one of the first cities in the UK to benefit from a dedicated sewerage system in 1865. At that time, the system combined foul and surface water systems, and was adequate because with fewer paved areas the flows were lower, and because flows were discharged into the sea untreated. Since that time, the City of Portsmouth's drainage network has continued to develop but has remained dependent on the use of combined sewers and the Eastney Pumping Station. The city is now served by two interceptor sewers that run north to south on the western and eastern sides of the island. These interceptor sewers carry the combined sewage flows to Eastney. In dry weather, flows arriving at Eastney are screened and pumped to Budds Farm WwTW for treatment. These flows, together with treated flows from the Havant catchment, then gravitate back to Eastney and are pumped down the long sea outfall. Historically, during periods of high rainfall, the incoming flows exceeded the capacity of the system and excess flow was pumped from the Eastney pump station to storm tanks at Fort Cumberland. These tanks have a capacity of 40,000m 3 and are filled before any flows are discharged to the sea via the short sea outfall, and then emptied back to Eastney a"er the storm has passed. However, due to the quantity of storm water arriving at Eastney prior to the flood alleviation project, and allowing for filling and emptying the tanks, in a typical year 650,000m 3 of screened wastewater was discharged via the outfall at Fort Cumberland, in the South East of Portsmouth at the mouth of the Langstone Harbour. Approximately 60% of the catchment consists of built up areas, 80% of which drain to the Eastney pump station. This means that nearly half of the entire surface area of Portsmouth drains to Eastney, which causes extremely large flows during monitoring system was installed to enable prompt diversion of excess water during periods of high rainfall. Sewer level monitoring is undertaken in real-time and intelligent raingauges (smart sensors) combine with radio telemetry to inform a computer based A map showing the Portsmouth sewerage system, with the two main interceptor sewers in blue

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