Slowing the Flow in Bicknoller Combe

The Bicknoller Combe catchment area is described as “flashy” by the experts, meaning that “its streamflow can increase considerably and has little restraint down a moderate gradient”.  In times of prolonged heavy rain, run off has resulted in localised drainage problems in the village at Dashwoods Lane. 

To help prevent this and do more for its “landscaping” remit, QE suggested that trees be planted in a couple of small specific areas in the combe to help reduce run-off, and that woody dams be installed to slow the flow of the stream. 

The project blossomed and a partnership was formed with the National Trust (the owners of the Combe), Somerset Rivers Authority (who funded it), the AONB, FWAG, WWT, and Friends of Quantock, who after receiving the agreement of other key stakeholders (Natural England, the Commoners, the County Council and Bicknoller Parish Council) set about seeing it through.  

The possibility of growing trees by natural regeneration was discarded on the advice of the Commoners, and the scheme was concentrated on four leaky woody dams along the upper, non-wooded course of the Combe stream. 

Leaky woody dams are a natural green flood management option.  The structures are made from logs and branches which mimic naturally fallen trees across a stream, and are built in such a way that fish (if there are any!) and gravel can move along the stream uninhibited. 

Leaky Woody Dams – Structure Configuration & Securing

Their benefit comes after heavy rainfall events when the streamflow rises. 

They restrict, and slow the flow of water which lowers and lengthens the peak flow further downstream, allowing the water time to flow away without rising too quickly and causing streams to break their banks and result in flooding.

The logs used to build the four dams in Bicknoller Combe were sourced from trees at the lower end of the combe that had been blown over, or were in need of safety pollarding. 

They were hauled up the Combe by traditional low impact Ardennes heavy horsepower.  In fact the whole operation has been a no-emission exercise.

Hauling the Logs – Kate and Ardennes Working Horse “Sol”

It is clear that a few seasons will have to pass before the intended effects of the dams can be seen.  Please do not expect an overnight slowing of the flow!

Maintenance will of course be required when dams cease to be leaky or are in danger of collapse.  The responsibility for this maintenance has been assumed by the National Trust and the AONB. 

QE invites walkers from our local communities to engage with them and help by alerting us on email if they think that a dam looks as if it has ceased to be leaky and needs maintenance. 

There is little doubt that the main thrust in making the project a reality has come from a joint WWT/FWAG SW/AONB team using funding from the Somerset Rivers Authority. 

Milly, Ross & Bill Building Woody Dam 1
Dam 2 built

QE is especially grateful to Milly Bowden (FWAG) and Iain Porter (Quantock Hills AONB Manager as from 1st April) who have played significant roles in the project’s realisation.

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