By Chris Gardner
In 2015 the South East Rivers Trust was awarded a £31k grant through the Department of Environment Food and Rural Affairs (DEFRA) Catchment Partnership Action Fund (CPAF) to deliver fish passage and habitat improvements on the River Dour in Dover. All these improvements would be designed to increase the health and resilience of the river environment for fish and other species, to meet the requirements of the EU Water Framework Directive.
The River Dour is a short (4 km) little chalkstream that rises in a rural setting but soon flows through the highly urban centre of Dover. This delightful little river boasts a healthy brown trout population, but the habitat is highly degraded due to urbanisation and impounded / fragmented due to a legacy of watermills.
We assessed the urban part of the catchment by walkover survey, looking for potential projects. These were then prioritised on a cost-benefit basis, resulting in four sites where fish and eel passage could be addressed. Two were simple fish and eel passage easements and two were sites for eel passes.
Work began in October 2015 with a volunteer event at Minnis Lane near the aptly named village of River. An old watermill ruin at the site presented a complete barrier to fish and eel passage. The main part of the weir was very high and a fish pass here would have been way beyond the budget available. However, a parallel channel had one small step weir and an over wide shallow section of channel upstream that made this route impassable. To make this passable to fish and eels, we fitted a wooden box to the downstream end of the small step weir had a wooden box, to raise the water level up the step so fish could navigate it. We also used faggot bundles as flow deflectors to define a deeper channel through the over wide shallow section. Many thanks to Anita for helping to organise the volunteers and to the volunteers for their hard work! You know who you are!
In May 2016, we also fitted two eel passes to Halfords Weir and Lorne Road weirs. These are large weir structures that will require technical fish passes in the future to make them passable to fish, but eel passes were achievable with the budget we had available. The Halfords weir site was quite straightforward – the setup of the weir allowed a simple gravity-fed pass to be fitted. Eel passes allow eels to move over weirs through a piece of conduit which contains brush bristles that provide a crawling medium. Water passes through the pass to provide attraction flow and passes are located at the edge of the weir as studies have shown that eels predominantly use river margins as migration corridors.
The Lorne Road site was more complicated, because this eel pass needed to go up and over the weir, so a gravity-fed option wasn’t appropriate. Instead, we designed this pass to be fed with a water pump to provide attraction flow. Many thanks to Malcolm and Mick at the Lorne Road Mill building who allowed us to tap into their power supply! Also many thanks to Paul and Simon for their work building the passes – your help was very much appreciated.
We delivered the final aspect of the project later in spring 2016. Morrison’s weir (near Morrison’s supermarket) presented a barrier to juvenile life stages of trout and eel. To improve its pass-ability, the weir was notched in the middle to provide a streaming flow that fish can swim up, instead of a small drop and a thin plunging flow that fish can’t easily negotiate. Bristles were also fitted into the notch so eel could climb up.