Easement for migratory fish at the Tunnel and Weir at Ynysybwl on the River Clydach. Grid Ref: ST0606 9423
This was a barrier upstream of the Cwm farm project that was a hindrance to migratory fish and needed to be worked on to complement the one below to help the fish to continue to travel upriver to reach the spawning gravels and nursery areas of the River Clydach and its tributaries. This weir was built to allow the old colliery to be able to abstract water. Water was an important factor in the industrial revolution for many of the industries along the rivers of the valleys.
The barrier to migratory fish was identified by Environment Agency Wales (EAW) representatives during a walk over survey to discuss options with the South East Wales Rivers Trust during August/September 2010. Establishing land ownerships for permission to access the site to carry out this work proved very difficult. However, with the help of the EAW we managed to identify all the landowners concerned and eventually obtain the necessary written permissions.Construction of the pre-barrage type weir began on Monday 11th October 2010 and was completed the following day. This also included some bank stabilization and reinforcement work, requested by SEWRT to stop erosion on the right hand bank downstream of the weir.
The barrier comprised a concrete weir approx. 2 metres high across the full width of the weir with a shallow plunge pool (approx. 0.4 meters deep) downstream. This meant migrating fish to jump approx.0.6 meters to overcome the barrier. They could only do this during times of high river flows. There was also an added complication as the pool above the weir connected directly to a tunnel that was approximately 100 mtr long.The tunnel, we discovered, was the original river bed with a roadway constructed over it. Various options were discussed and it was finally decided to place a large timber baulk at the tunnel entrance to raise the level of the water in the tunnel.
Above and below are pictures of the work being carried out to install a baulk of timber across the tunnel exit. This will have the effect of raising the level of water in the tunnel creating deeper pockets of water to allow fish to rest and move upstream. The final picture shows the timber in place. This was fixed by using bolts and a chemical fixer.
Various options were considered regarding the weir and it was agreed that the best option would be, to build a pre-barrage type boulder weir downstream of the existing weir, to effectively raise the level of water in the existing plunge pool, thereby reducing the height of jump necessary to approx. 0.3 meters. This was considered acceptable.
Various contractors were approached to carry out this work and eventually Spencer Davies/ McCarthy were selected and engaged to carry out the work as they came in with the lowest quote.
Views of the weir before work began. The one on the left is looking downstream; the one on the right gives an impression of the height of the weir. Note the valve mid stream.
The above labove picture (left) shows the completed weir. Note the height of the water around the valve. The picture (right) shows the armoured bank. We insisted on the bank being protected as this covered all heights of water in the future.
Photographs were taken before any corrective action work had been carried out, which clearly showed the extent of the barrier problem, and also on completion of the easement,which, clearly showed that the barrier was no longer an issue.
The effectiveness of eliminating this barrier to fish migration will be monitored during 2011-12 from reports of migratory fish passing over this easement and by the analysis of future EAW electro-fishing surveys, which, hopefully, will indicate the presence of migratory fish, fry and parr, upstream of this location.
Money for this project was provided by EAW through the agreed mitigation funding paid by Cardiff when the barrage was built.
