Managing & Maintaining our water channels
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left: Reinstated meander loop at Great Ryburgh Common less than 1 year after construction.
above: Restored sections of channel provide improved habitat for species such as brown trout and bullhead.
Implementation of the strategy
To date the RWRS has worked with landowners to complete three major restoration schemes, at Bintree, Great Ryburgh Common and at Ryburgh End. As well as fitting into the local landscape, the key aim of the restoration schemes is to increase the ecological and physical habitat potential, and detailed monitoring has been undertaken to record the biological response to habitat improvements.
Taking the example of Great Ryburgh Common, where a 350m meander loop has been reinstated and a series of in-channel features installed, post-construction electric fishing surveys have produced excellent results, with nearly 400 fish being captured representing thirteen species. This compares to the previous year’s results from the old straightened channel, which yielded only 31 fish, and demonstrates how river restoration has acted to improve local habitat quality for a wide range of fish, including good numbers of native
“ three major
restoration schemes have been completed”
brown trout and target species such as bullhead and brook lamprey.
As well as monitoring fish, the responses of other important biological communities of the river ecosystem have been assessed in the new meander loop and original channel reaches. Again, results after one year are very promising, with a number of typical chalk stream plant species for which the river is designated having colonised the new channel. These include water starwort, lesser water- parsnip and whorl-grass. Colonisation by aquatic invertebrates of the habitats in the new meander loop was almost immediate. The communities which have developed on the gravels installed as part of the scheme are species rich and typical of “natural” free flowing gravel bed sections which are rare at a local scale. The invertebrate communities contain the aquatic life stages of over fifteen species of mayfly, caddisfly and stonefly, indicating a healthy system, good water quality and, importantly, good habitat variability as a result of the restoration works.
Current scheme progress
Works are currently nearing completion on the latest project, at Swanton Morley. As with other schemes this is being implemented by the Environment Agency’s in-house workforce. Traditional restoration schemes have tended
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to take place between late August through to March to avoid the main fish spawning and breeding bird seasons. This is the first time works have commenced earlier in the year and this has necessitated a carefully planned and stringent programme of mitigation measures.
The river channel at Swanton Morley is similar to much of the Wensum, being over wide and over deep with little flow variation. The restoration works have involved creating channel diversity through the installation of gravel glides, pools, lateral shelves (berms) and woody debris, together with selective tree planting to create riparian shade and removal of spoil banks to improve floodplain connectivity.
The changes to the river channel have been designed to ensure that under all flows the finest material is kept on the move, but under bank full conditions the coarser materials, which provide the best habitat, will not.
A small meander loop has been reinstated with a plug placed in the existing straight channel to divert flows along the loop. The meander loop, cut off by a straight channel excavated as part of a land drainage scheme in the 1950s, had become silted up and required de-silting to expose the natural hard bed consisting of pockets of gravel and chalk. The channel sinuosity has been further increased with the use of woody debris.
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