Going all the way on the Cray
Posted on November 23, 2010
A little London Chalkstream near Sidcup which has been diligently looked after in recent years by Thames21’s Ashe Hurst got another shot in the arm on Thursday and Friday last week. Two of the WTT’s conservation officers (Andy Thomas and Paul Gaskell) did two days of specific habitat improvement works in order to train the Thames21 staff and volunteers (including local youngsters who have been excluded from schools). A variety of uses of woody debris, brash bundles, wire, stakes and metal pin fixings were used to promote localised scouring of the stream bed, sorting and cleaning of spawning gravels and submerged “brashy” cover for juvenile fish.
The videos below show the increase in flow and change from “concreted” immobile gravels (with dark algal growth) to mobile and silt free (light coloured)particles at the pinch point created by an upstream “V” flow deflector
The flows prior to the installation of the upstream V were much more sluggish and favoured the deposition of silt. Now there is much more variety in current pace and depth.
The upstream V featured in the video clips (above)showing the focussed flow and pale gravel displaced following loosening with a metal spike. Potential spawning habitat and holding pot for adult fish
Single log flow deflector to encourage localised scour and promote more meandering flow
Brashy cover to provide habitat for fry and parr (here in a spot too shady to allow marginal plant growth)
Mini transverse log — note pronounced undershot scouring flows bubbling up on the downstream side of the log (to the right)producing patch of self-cleaning gravel and holding pot for fish
The pictures cover just a small selection of what was installed over the two day training visit and this will also be extensively added to by Ashe and his teams of volunteers in the coming months. Ultimately, it is hoped that self-sustaining populations of wild trout can be re-established in this once degraded chalkstream. What is for certain is that local volunteers like Gaynor and Alan who worked like trojans for both days are absolutely passionate about caring for their local urban river.
Well done guys.