South East Rivers Trust

Obstruction at the A3 (Part 2)


We head back to where the Hogsmill flows under the A3. Work started here in September when we used 230t to create a close to nature pool pass. For those that missed the blog and want to catch up on the story, here is the link

http://www.southeastriverstrust.org/obstruction-at-the-a3-but-in-the-river-not-on-the-road/

Before I move onto the recent work I would like to update you how the pool pass is settling in. After being repeatedly battered by high flows the structure has stayed put and is bedding in nicely. The clean Purbeck stones have dulled with algae and vegetation which had been previously overshaded is beginning to establish on the banks. Plenty of roach, dace and chub have taken up residence in the top two pools, as spotted by the keen angler’s eyes of the TAC guys this week.

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The close-to-nature pool pass created in September is bedding in nicely

The final stage in making this unsightly structure passable was to address the fast and shallow flows down the spillway and through the culvert. Darryl-Clifton Dey at the EA very kindly donated 11 purpose built recycled plastic baffles to the cause. Under the skilled hands of Norm Fairey, the baffles were cut, drilled and had stainless steel angle attached. This meant that they could be taken out of the van, put into their predetermined positions and secured. Sounds simple and in truth it was. Needless to say some head scratching and minor on-site modifications were required but generally speaking it worked incredibly well.

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Shallow and fast flows over the spillway and through the culvert
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The flat-pack style baffles ready to go in

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Great help and good company came from the Thames Anglers’ Conservancy guys, Dave Harvey, Keith Collett and Patrick Barker who kindly gave up two days to help with the project. The weather behaved, river levels were kindly low and with teamwork to be proud of, the job was a pleasure to be part of.

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The TAC guys hard at work
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Drilling another hole before fixing the baffles with resin and stud
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Keith, Patrick and Dave. A great team!

The result, a completely passable structure. Flows down the previously impassable spillway are now slower and deeper. The water snakes and winds its way through the staggered 300mm gaps in each baffle line. The shallow point through the culvert now has more than enough depth for fish to pass.

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Before the work…
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and after.

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The pool pass in the foreground and newly installed baffles behind

With this site now passable, the work over the previous two and a half years through the Defra funded Catchment Restoration Fund has opened up the upper 6.5km of the Hogsmill. This has involved the removal of four weirs, two large scale close-to-nature pool passes, one rock ramp and two baffle installations. The work is not yet complete though, soon we will be addressing the last few structures that remain impassable downstream, meaning that the recently caught wild brown trout caught at Kingston can, in theory, swim up to the chalk stream waters in Ewell.

Once again, as always, we had the kind help of many to address this issue at the A3. Darryl at the EA for his advice and for providing the baffles, Norm for manufacturing them and of course, the much appreciated and brilliant input from the TAC guys. Thanks to you all.

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