Dredging of On-Line Lake

This project was to dredge the accumulated sediment from an on-line lake. On-line meaning a watercourse normally flows through it and on this occasion several ground water springs rose into it. This meant alot of pumping was required to divert and remove as much water as possible to facilitate removal of the silt!

The upstream inlet of the watercourse into the lake was temporarily dammed and a pump set up to over pump this water down the length of the lake and into the lake below.

Silt control measures were put in place downstream and the sluice was then opened on the dam and the lake slowly drained to reveal the extent of the silt present.

A temporary access ramp formed with brick rubble was formed at the downstream end of the lake which was the only possible access in off the dam.

The dredging works commenced with the silt loaded into wheeled dumpers to be spread on adjacent farmland for soil improvement.

Additional pumps were set up on the dam to deal with the multiple springs rising into the lake which were diverted to the pumps as the dredging progressed.

At the peak of the works there were 6 diesel pumps running 24 hours to control the water entering this lake. Even with this pumping the water and the silt were sufficiently in contact to mean that we were moving watery silt like ʻsoupʼ which is a much slower process than moving ʻdrierʼ in situ silt which has no contact with water during the works. However we got there in the end!

Once the dredging works were complete we carried out some repair works to the banks and the island using hazel faggot bundles and pre-established coir rolls to provide a new sustainable revetment.