Llyn Teifi Reservoir Spillway Rehabilitation

Llyn Teifi Reservoir Spillway Rehabilitation

Our requirement was to carry out rehabilitation works to the existing Llyn Teifi impounding reservoir dam wall structure.

Llyn Teifi reservoir is situated approximately 4 miles East of Pontrhydfendigaid, about 1500ft up the western slopes of the Cambrian Mountain, which can be reached by footpath from the south, or by a small road from Ffair Rhos, close to Pontrhydfendigaid. The lake was famed even in medieval times for the quality of trout and eel fishing to be had, the lake is still fished and now provides a drinking water supply for the surrounding area and the coastal belt of Ceredigion to the West.

The Teifi dam spillway is under the Reservoirs Act 1975, this Act requires reservoirs to be under supervision at all times and periodically inspected by specialist qualified civil engineers.  As a result of one of these inspections concerns were highlighted about the stability and deterioration of the concrete due to freeze/thaw action over many years. Therefore the need for refurbishment work was identified.

Kaymac Marine & Civil Engineering Ltd were commissioned to refurbish the structure. Ahead of mobilisation, the client carried out upgrades to the existing access roads to facilitate the delivery of the required welfare, plant and materials.

The rehabilitation works themselves consisted of diving activities below the water line and traditional civil engineering works on the spillway face.  Isolation measures were put in place including the installation of a temporary blanking plate to an outlet situated within the proximity of the diving working area.

The rehabilitation works to the front spillway face included breaking out sections of the existing concrete, drilling and fixing steel reinforcement ahead of installing a bespoke formwork system to allow the new concrete to be placed to the required design profile.  The concrete was placed in 3 vertical lifts to the required design level through utilizing a concrete pump positioned approximately 40m away.  Access for these works was achieved through the use of scaffold and mobile elevated platforms.  A new manhole chamber was constructed downstream of the structure to access the gravity drain feeder pipes installed through the structure to drain away any over-spill water between the membrane and the original dam.