Three Mills Lock
- Original design
- VolkerStevin, 2009
The 2017 programme is now past. We will be launching the 2018 programme in July.
Three Mills Lock is located in Prescott Channel that was built as part of the 1930s Flood Relief Works that aimed at minimising the risk of flooding. The new channel, named after the Chairman of the Lee Conservancy Board at the time, Major Sir William Prescott, was completed around 1935. As part of those works, a sluice was built by Ransomes & Rapier and erected within the Channel to control the level of water, but it was derelict by the 1960s and removed.
This impressive piece of waterway infrastructure is the product of a £20 million project started in March 2007. The lock, which was completed in 2009, allows both boats to access the Bow Back rivers and to control the tidal water levels above it.
Three Mills Lock was completed by British Waterways in partnership with The Olympic Delivery Authority, Transport for London, London Thames Gateway Development Corporation, the Department for Transport, the London Development Agency and Defra.
Like all locks this structure is designed to transport a boat from one water level to another by creating a sealed chamber which can be filled or emptied with the boat inside depending on the direction of travel. It has two key elements:
- The watertight chamber between the upper and lower body of water. In this case the chamber holds around 650,000 litres and can accommodate 2x350 ton barges
- The gates at either end of the chamber. These gates are sector gates and are operated electronically by the lock keeper. The lock can be filled or emptied in about 10 minutes.
The fish belly gates are so called because of their curved shape. They weigh around 20 ton each and are operated by a hydraulic mechanism that engages the piston. Sensors measure the levels of water and adjust the gates accordingly to either hold the water within the impounded area or release it and by doing so, controlling the water level within the Queen Elizabeth Olympic Park.
The fish pass is a purpose-designed structure that was required by, and developed in partnership, with the Environment Agency. It was required so that migratory fish can still travel upstream to breed. By building the lock we would have stopped their route. Migratory fish can find the pass because they can sense fresh water and will travel towards it.
The pass is made of a series of chambers set on a gradient that create a staircase the fish can swim through, a chamber at a time, using the slots in between them. When the water level below the lock is higher than that above, the pass is closed, but apparently the fish will stay in the area and wait for the next opportunity to travel north.
Without the weir, the lock would not retain a constant water level upstream as water could still flow through Three Mills Wall River and under the Mill. A second structure was required on Three Mills Wall River, which took the form of a weir made of three gates. This also enables the boat moored on this stretch of water to remain afloat at all times.