No 12 on the Hogsmill obstruction hit list was the River Club weir.
With very shallow flows plunging over its crest, and a drop of 0.7 m between the upstream and downstream water levels, this weir on the Hogsmill near Tolworth was a complete barrier to fish passage under the majority of flow conditions. On each flank, the concrete and stone abutment walls were also structurally failing.
After lengthy discussions, in the course of which no justification for keeping or maintaining this weir could be established, we worked with the Environment Agency and Thames Rivers Trust to undertake a full weir removal.
Once we had accessed and prepared the worksite, we began breaking up the main part of the weir using a long reach excavator with a hydraulic breaker attachment. It’s amazing how solid parts of these structures are, but our operator Roo’s patience eventually prevailed!
Over 30 tonnes of concrete was removed from the channel and collected by a grab lorry.
The stone walls were then broken up, and the new bank profiles were installed using a range of sustainable and biodegradable materials. Native marginal plants and seed were then added to the new banks, which over time will provide erosion control and great habitat.
It’s great to see the channel upstream already returning to a more natural state. Within a few days of removing the weir, a resident koi carp had moved from the upstream pool and was enjoying exploring some new habitat. This bodes well for all our native fish species we know are in other parts of the Hogsmill.
We had fantastic weather throughout the duration of the project, although we could really do with some rain, as most of the rivers across the South East of the UK are experiencing extreme drought conditions.
A big thanks goes to to our local Environment Agency staff, Thames Rivers Trust, The River Club, two very supportive landowners and Roo Newby for his excavator operating skills.
We’ll now be focusing on the six remaining obstructions to fish passage with our aim of restoring this lovely (previously neglected) river to a more natural and improved ecological state.
Why remove weirs? Some excellent diagrams on how weirs affect river habitat and geomorphology have been produced by the Wild Trout Trust and you can also read our article on how weirs affect fish communities.
Before and After photos
The Timelapse Video