page_title: Cut-off Channel
section_title: Flora and fauna
hierarchical_section_title: Cut-off Channel / Flora and fauna
caption_attribution_description: English: Cross section of a syphon fish weir used to connect the Cut-off Channel to the River Wissey without compromising the flood defences
context_page_description: The Cut-off Channel is a man-made waterway which runs along the eastern edge of the Fens in Norfolk and Suffolk, England. It was constructed in the 1950s and 1960s as part of flood defence measures, and carries the headwaters of the River Wissey, River Lark and River Little Ouse in times of flood, delivering them to Denver Sluice on the River Great Ouse. In the summer months, it is also used as part of a water supply scheme for drinking water in Essex.
  The scheme was first suggested by the drainage engineer Cornelius Vermuyden in 1639, but was not pursued at the time, probably because of the cost. It was again suggested by John Rennie in 1810, but again the cost was prohibitive. Flooding events in 1937 and 1939 caused the newly formed Great Ouse Catchment Board to resurrect the plan, and disastrous floods in 1947 resulted in construction starting in 1954, as part of a bigger scheme to address the issues faced by communities living near to the Great Ouse. in 1968, water companies in Essex developed a plan to transfer drinking water from the Great Ouse to reservoirs at Abberton and Hanningfield.
context_section_description: The channel provides a variety of habitats, because is passes through different soil types along its length. Near Fordham and West Dereham, the river bed is composed of Sandringham Sands with coarse pebbles and a high quartz content. In these conditions, the channel becomes choked with dense mats of the green algae Cladophora glomerata and Canadian pond weed. Near Methwold and Feltwell, the underlying rocks are chalk, resulting in the bed being covered in fine silts, on which little aquatic flora grows. Near Hockwold cum Wilton, flora is dominated by shining pondweed and Canadian pond weed. Surveys in 1997 and 1998 found that the channel has been colonised by a small population of depressed river mussel, which were first found at Brookville, near Methwold, where the bed consists of fine chalky silts. The intake for the Ely-Ouse to Essex Transfer Scheme is at Blackdyke, and in order to prevent the intakes getting clogged with vegetation, a stretch of about 0.6 miles (1 km) either side of the intake is dredged with a dragline each year. The channel, which is about 16 feet (4.9 m) deep at this point, supports blanket weed at the sides, and the bed consists of chalk silt. Examination of the dredgings revealed irregular distributions of the depressed river mussel in this location as well.
  Under the Water Framework Directive, there is an obligation to achieve good chemical and ecological status on all bodies of water within the EU. The Cut-off Channel failed to meet these requirements, because fish could enter the channel at Denver sluice, and become trapped, with no access to suitable habitat or links to other waterways. The solution adopted was to provide a fish pass between the channel and the River Wissey. There is a difference in level of about 8.2 feet (2.5 m) where they cross, and any solution needed to maintain the integrity of the flood defence structures, while being suitable for a variety of fish types, including gudgeon, perch, pike and roach. The solution adopted was a syphon fish pass, designed in Holland, but adapted to suit the UK conditions. This included an integrated eel pass, cut off valves to allow the syphon to be isolated, and telemetry monitoring. The construction project lasted for nine months in 2013, and cost £407,000, although installation of the syphon was achieved in just four days. The Environment Agency worked with Hull International Fisheries Institute to assess its initial effectiveness, and developed a five-year plan with Cranfield University for ongoing monitoring, to include study of trout spawning runs and silver eel migration.
caption: Cross section of the syphon fish weir used to connect the Cut-off Channel to the River Wissey without compromising the flood defences
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