Report on works at Cyfarthfa Park feeder weir Taff Fechan.
The project at the feeder weir was to raise the pool level immediately downstream of the weir, in particular to decrease the height of the step at the base of the rock slide which leads up to the notch in the weir lip which is used as the fish pass. The method chosen was a blockstone pre-barrage made from stone salvaged from the river banks and bed in the immediate vicinity of the works. The route of the new barrage was chosen to arc from a notch in the bedrock of the left bank through 2 existing large boulders and then onto the gently sloping bedrock of the right bank. Works were carried out on 25th April 2019 using a 5 tonne excavator to move the stones into position with some final fettling done by hand. The final arrangement has the primary fish slot through the new barrage slightly right of river centre with smaller gaps elsewhere. The step at the base of the rockslide was approximately 300mm high before work began and this has been reduced to around 75mm, it is highly likely with even a very modest increase in flow rate the step will disappear. Overall the structure seems solid and well anchored except for the right bank where as mentioned previously it is sitting directly on to sloping bedrock, it will be worth monitoring this over time