Wild Trout Trust Conservation awards 2008
CBE is awarded ‘runner up’ in the 2008 professional category for the combined 3km river restoration projects from Hunts Green downstream to Woodspeen Mill.
Project news report:
RESTORATION OF RIVER LAMBOURN SSSI from HUNTS GREEN downstream TO WOODSPEEN MILL
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| 'Before' showing crayfish damage at Hunts Green |
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'After 18 months' showing recovering habitat in restored channel |
Background:
The River Lambourn in England’s southern county of Berkshire, was afforded 'Site of Special Scientific Interest' (SSSI) status in recognitionof its unique chalk stream features. The river enjoys unusually cold, spring-fed flows that support a diverse in–stream flora and fauna including luxuriant beds of Water Buttercup (Ranunuculus spp) , an abundance of aquatic invertebrates such as the fresh water shrimp, Gammarus pulex and the fast-swimming Baetis nymphs beloved of the trout angler. Bull head, stone loach, wild brown trout and Grayling are predominant fish species whilst the latter provide world class fly fishing for those fortunate enough to have access to this small but pristine chalk stream.
Significant sections of the river, however, are classified by Natural England as being in ‘unfavourable condition’. This is primarily due to the presence of historic milling structures whose permanently closed hatches have backed up flows and reduced velocity for decades, causing life-supporting river gravels to vanish under deep deposits of sediment. The Lambourn is no stranger to the post-WW II practice of government-sponsored ‘land drainage improvements’ and 'flood defence' operations that have contributed wholesale to low quality habitat, loss of characteristic macrophytes and poor populations of wild fish. As a point of interest, during the project planning phase, correspondence came to light between a local fishing club secretary and a well-know river keeper during the 60’s which confirmed suspicions that the unnaturally large and deep cavities in the river bed were specifically excavated to provide holding pools for artificially stocked trout. Channel engineering (Dredging) was the prevailing activity of that era both for land drainage and fishery management and there is evidence to suggest that the two interests collaborated over the use of water authority machinery to achieve their separate aims.
Key project objectives - the 3 km project was undertaken in two separate stages.
Phase I - The first 850m section at Hunts Green was completed in late 2006/7 under a Natural England-funded initiative. The work involved re-instatement of the channel plan form to rectify serious bank erosion and channel over widening caused by the burrowing of American Signal crayfish. Dredged reaches of slow-flowing, canal-like water were reclaimed with gravel and new banks were also reconstructed with gravel to prevent crayfish undermining the new margins. Ranunculus was re-planted into the new gravel beds and logs and branches (lLWD/CWD) were introduced to create wetted, percolating backwaters.
Phase II - The second phase of work comprised two closely linked projects funded by EA Thames during 2007/8. The first, at Woodspeen mill, involved permanent dismantling of the milling structures, creation of a low-level spillway and restoration of the 300m heavily sedimented mill leat. The leat itself was dismantled by removal of the sheet pile retaining walls down to the new water level. New low-level banks were installed using ‘Coirnet’ geotextiles retained by hardwood posts and back-filled with material from bank re–profiling to define the new bank edge.
With the impoundment at Woodspeen removed, works began upstream to restore 1800m of heavily sedimented, over-widened channel, much of it with precipitous vertical banks following the sudden drop in levels. Over mature bank-side Willow and Alder trees were used where available to introduce meanders and create on-line marginal wetlands and slow-filtering backwaters. Significant quantities of gravel were excavated from the adjacent floodplain water meadows and used throughout the project to re-claim the dredged river bed thereby providing a natural substrate for the re-planting of Ranunculus and other macrophytes. Site-won gravel was also used extensively to provide a foundation for new signal crayfish-resistant river banks.
The judging pannel concluded with the following comment:
''Removal of the major impounding structure at Woodspeen had a beneficial impact evident for almost 1km upstream.
Changes in level, velocities and stream–habitat diversity have been remarkable. Ranunculus growth has been substantial in places where growth has never been recorded in recent history. Counts of spawning redds were encouraging and improved fish–numbers in the reach probably will result in a reduced stocking regime next season. The river has been re–connected to its floodplain with associated benefits for a variety of wetland species: the borrow pits that were left following the removal of gravel are being re–shaped as part of the wetland creation scheme. The judges admired the large size of the project: the planning and installation of specific features at particular points all were working well together to produce a superb mosaic of habitats for fish and other flora and fauna to resolve the sensitivities of blending with and incorporating modern garden–design in properties adjacent to the river. "
A detailed project construction report is currently being compiled.