WET News

14 WET NEWS AUGUST 2015 I t is widely known that a significant proportion of East Anglia relies for its existence on the effective operation of widespread land drainage networks. Without these networks much of the region would not be able to function in the way that it does, and the population would be hard pressed to continue their lifestyles in the way they do in the modern world due to the high ground water levels. Much of the drainage to keep groundwater levels in check is achieved using local pumping stations that take water from the land drainage network and pump it into local rivers and drainage channels move the water out to sea so keeping the local area from flooding. These pumping stations are under the control of the Internal Drainage Boards (IDBs). However, contractors carrying out rehabilitation of a pumping station at a site near Kings Lynn discovered that a reverse syphon carrying water from the pump station to the main drainage channels that fed the local estuary had failed. There were fears that water normally carried by the syphon away from its local pumping station would cause problems. The failure of the syphon meant that water from the pumping station was not all removed from the network. Instead, it was being returned back into and potentially undermining the pumping station due to leakage in the syphon. This was also causing the river bank near the pumping station to erode. Minimal disruption It was causing problems in the pump station as water was recycling, meaning the pump station was working significantly harder than it should, incurring extra cost and potentially leading to significant flooding • Pumping stations are vital in keeping groundwater drainage levels in check. But when a reverse syphon failure was discovered at one station, there was a significant flood risk. Syphoning out pumping station leakage The pump station being served by the deteriorated syphon ONSITE DrAinAGe problems for the area. A…er careful consideration of the situation and the options available to affect a repair or replacement of the syphon by the project's main contractor, ADC East Anglia, working in close association with specialist consultant and supplier Dyno- Rod Norwich, it was decided that a lining option would offer the best solution with minimal disruption to the pumping network, the local residents and the importantly the environment. The project required remedial repairs to be made on the 22m long x 450mm diameter cast iron reverse syphon. To ensure the long-term effectiveness of the repair, CIPP Technical Services and product supplier CJ Kelly Associates were called in. A detailed look at the liners available, the resin options and the longevity required of the final installation as well the pressure fluctuations that would be encountered during the operational life of any liner led to the selection of a 450mm diameter, 7.5mm thick twin wall flexible liner. The 22m long twin wall liner used on the operation comprised two thinner walled polyester needle felt liners, which when laid and stitched together, formed a final 7.5mm thick liner with a single PU outer coating. The reason behind using the twin-wall liner option was that given the geometry of the reverse syphon the liner used not only needed to provide a strong, long-life final product but also needed to offer significant flexibility during the inversion process and to ensure an effective curing process. The twin wall liner also offers a better resin impregnation process for the MC thermos- reactive resin used. Once Project sPecs • repair or replace a reverse syphon at an iDB pumping station • Prevent river bank erosion • Provide and install a twin-wall liner to repair the reverse syphon techknow • A 450mm diameter, 7.5mm thick twin wall flexible liner was used • The twin wall liner used on the operation comprised two thinner walled polyester needle felt liners • The twin wall liner offers a better resin impregnation process for the MC thermos-reactive resin used • The blue pigmented resin enables control of the impregnation process "The project from the beginning had many issues. A remote location and access for plant to maintaining the flows during the works were all potential problems. However, combining the expertise of all parties involved, the job was accurately accessed, planned and completed on time" Steve Paige, ADC East Anglia need to know 1 iDBs are local public authorities established in areas of special drainage need in england and Wales 2 iDBs cover 1.2 million hectares of england and 28,500 hectares of Wales 3 The iDBs have permissive powers to manage water levels within their respective drainage districts 4 They operate and maintain more than 500 pumping stations Laying out the impregnated liner ready for inversion Curing the liner post inversion

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