In August 2016 we were contracted by Kent Wildlife Trust to install a backwater on the River Eden near Penshurst in Kent.
The river Eden is in the upper reaches of the Medway catchment and joins with the Upper Medway approximately 1 km downstream from Penshurst.
What is a backwater and why is it needed?
A backwater is an aquatic habitat connected to the main channel, sometimes only during higher water levels. Backwaters can be formed naturally as a river migrates across its floodplain, cutting off meanders.
Backwater habitats can be used on rivers that have been straightened or resectioned to increase the diversity of flow, habitat and ecology.
In this case we were asked to install a backwater that would provide two important functions for the river depending on the flow. In high flows, the backwater would become a refuge of slack water for adult fish to rest in until the normal flows return. In normal flows, the shallower water left in the backwater will warm up quicker than the main channel and act as a nursery area promoting the growth of young fish fry.
Photo provided by Kent Wildlife Trust of project area last Winter 2015
What we did
The project got off to a quick start with local tree surgeon Ivan Carson, from Penshurst Tree Surgery, making short work of the 3 cricket bat willows.
These willows were coppiced to near ground level to allow more sunlight to reach the backwater – helping to raise water temperature during normal flows. A bonus benefit of this tree removal is a reduction in the amount of leaf litter entering the backwater, reducing future maintenance.
With a tight schedule, work on the backwater commenced. First the old fence was removed and the topsoil was stripped back.
Our expert excavator, Jimmy, started shaping the backwater entrance. All the spoil we removed was tracked to the far end of the landowner’s orchard to improve their existing track.
Everything seemed to be going smoothly until Jimmy’s bucket hit something solid! This turned out to be a huge tree trunk of approx 1 m diameter running parallel to the river, across the backwater entrance.
With no idea how long the trunk might be, we decided to remove the central section. Most of it was actually below water level, which meant our saw wasn’t quite up to the job. Fortunately, Ivan kindly lent us one of his and the obstacle was overcome by our very own Toby.
The silver lining of this small delay was that we didn’t need to install any large woody as cover for fish. We even spotted a Perch of approx. 1.5 lbs sunning itself in the shallows until it was spooked, and darted underneath one of the remaining stumps – woody cover in action!
Whilst Jimmy was finishing off the backwater, Toby and Alex started to install the new fencing around the backwater. This fencing will exclude cattle from the backwater, preventing over-grazing and reducing bank erosion.
With the backwater construction complete, it was time to add the plants. Marginal plant plugs were added around the backwater, and wild flower seed was scattered on the ground to provide some ground cover before winter.
The landowner seemed really happy with the final result – especially once he saw all the marginal plants.
The project took 6 days to complete and we look forward to seeing how the backwater matures overtime. Lots of fish fry were spotted on our most recent site visit which suggests we did a good job!