Rehabilitation Work

1 - Installing deflectors: Deflectors or double deflectors (vortex weirs) were constructed of rock or log, or a combination. Installing these at suitable places increases stream flow or causes turbulence in the flow, which winnows silt out of the sediment leaving the gravel cleaner. These also help deflect flow away from soft, undercutting banks.

2 - Narrowing the stream: If the stream is made artificially wider than its carrying capacity, the flow slows down and fine sediment is deposited which fills the gravels with silt and causes excessive shallowing. The solution is to narrow the channel so that a reasonable flow is maintained even in low water, and allow silt to accumulate in the margin, forming a new bank.

3 - Inserting random boulders: Random boulders and rocks have the effect of causing turbulence in the flow of water, which causes scour of sediment, leading to the fine silt being winnowed out. Rocks in streams also give a permanent surface for moss to grow upon, which increases insect life and adds diversity. Rocks provide cover for small fish to hide, and provide boundaries for territorial fish, so having upstanding rocks in a stream will increase the number of fish it can hold.

4 - Pruning bushes: In a completely tunnelled section, cutting gaps of about 10m every 30m gives sufficient light for a healthy insect-based food chain to thrive in a river. Sunlight gaps were cut preferentially where riffles occur in the stream as this is where most invertebrates will live. Shade is left preferentially over pools as this is where fish come for summer shade. In densely wooded areas or in areas of mature trees, the lower branches were pruned to allow some light in. When cutting saplings; oak, alder, ash, hazel, whitethorn and holly were preferentially spared, and sycamores especially targeted along with other non-native, or particularly shade-forming trees. Allowing sunlight to the riverbank also allows grass, undergrowth and wildflowers, and even mosses and liverworths to grow, which decreases the amount of bare unbound soil that would be washed into a stream during floods and heavy rain.

5 - Stabilising banks: Where the normal flow of the river has been undercutting the bank, logs were pinned under the overhang using metre-long rebar pins. The pinned log stops access of the stream to the soft sediment. Rocks are piled on top of the logs so that they will fall behind it if erosion continues. These pinned logs both prevent erosion, and provide shelter and a hide for small fish from predators. Where possible, space was left under the log for at least some of its length, so that fish can take cover underneath.

6 - Fish hides: In places where no significant cover occurs for fish, any available stout branches were submerged lengthwise in the current, attached to the bank, so that fish can hide underneath.

7- River Ford: Where animals were crossing the river, it was neccesary to create a ford suitable for animals to cross without further erosion and silt movement. Initially large flat stones were positioned in the stream to form a stable base and a path down and up from the river was created using stones and gravel. Animals were guided to the ford by way of fencing.