Stonebyres and Bonnington Hydro Stations These are both run-of-river hydro schemes; the river passes through a weir and then into a slightly sloped tunnel ending with an open- air tank. At Bonnington the tunnel is 150m and at Stonebyres it is shorter, only 50m. The tank is known as the surge-tank as it absorbs sudden changes, so if the plant is shutdown suddenly the water pressure in the tunnel doesn’t increase as dramatically and cause any damage to the pipeline. Some water doesn’t pass through the weir but only a fairly small amount, as when it was built the Clyde was much dirtier so they didn’t need to worry about migratory fish. Nowadays, when planning a new hydro scheme, you’d have to have compensation water and possibly fish ladders. The Clyde is cleaner now so they do get migratory fish, but they are naturally prevented from coming as far as the stations by steep waterfalls. From the tank it splits into two routes, one for each turbine. The entrance to these can be automatically closed if there is a malfunction, or for controlled shutdown. To make the water enter the turbine uniformly it is forced in a snail-shell shape. We went inside the section beneath the generator and saw the guiding vanes which are adjusted to control the volume of water. It starts with the vanes at 20% to get the turbine up to the correct speed to connect to the grid. Once it reaches that speed it locks so that any further increase will produce load. The amount that the guide vanes are opened is also controlled by a water level detector in the weir, so that if the level increases above the optimal 50mm below the top of the weir, the vanes are opened more to keep the water level where they want it. If the water level continues to rise Guide vanes Pipeline