River Dever Project

Location: 1km of the River Dever, Hampshire, near Bullington.

Issue: Overwide, impounded, shaded, straight and silty channel providing uniform habitat leaving trout and grayling vulnerable to predation and limiting recruitment due to lack of spawning and juvenile habitat. 

Objective: Create more diverse habitat with variations in depth, flow velocity, light and shade. 

Method: Pools and riffles created with heavy machinery, including gravel introduction to create spawning riffles. Impoundment removed. Bankside tree work to increase light in the channel. Brushwood berms, flow deflectors, hinged trees, cover logs. Bank lowering and re-profiling.

Budget: £20,000.

WTT role: Lead partner — project design and delivery.

Partners: Landowner, Environment Agency, Fishing Breaks (fishing lessee), Springwise / 1% for the Planet. 

Project date and duration: Autumn 2016, 10 days. 

As part of the Environment Agency’s Test and Itchen Restoration Strategy, a section of the River Dever in Hampshire was identified as being in particular need of habitat improvement. The Wild Trout Trust assessed the site and proposed a project to introduce a greater diversity of channel widths and depths and a greater abundance of key habitat features. An impoundment at the downstream extent of the reach would need to be removed, light levels re-balanced and the river banks lowered in several places. Perhaps most importantly, improvements would need to be made to the riverbed to improve habitat for water crowfoot (Ranunculus sp.) and to introduce good quality spawning habitat for wild trout, grayling and other fish species.

The riverbed was without a natural pool-riffle sequence and was heavily infiltrated with fine sediment and compacted in places. The introduction of flow-deflecting woody habitat features alone would not provide sufficient improvement. In light of this limitation, a series of ​‘dig and dump’ pools were proposed. These would need to be very carefully planned and delicately delivered so as to help reinstate natural processes, providing long-term improvements to channel (geo) morphology (as well as being habitat features in their own right).

The project was funded by the Environment Agency, the landowner and with a donation from innovations networking company Springwise, via the 1% for the Planet environmental corporate responsibility scheme. In-kind contribution was also made by the Wild Trout Trust and fishery manager, Fishing Breaks (in the form of excellent river keeper, Jonny Walker).

WTT acted as both Principal Designer and Principal Contractor and the delivery of the project was separated into two phases. Phase 1 involved the removal of the impoundment (an old eel trap), substantial tree works and the creation of several in-stream woody features. Trees were felled in the most heavily-shaded section of the fishery to improve light levels and the arising woody material used to create a range of flow deflectors and marginal brushwood berms. A number of trees were hinged and laid directly into the river to provide different habitat features. At a particularly wide and uniform section, a new bank edge was created using alder and willow brushwood. Sparsholt students John Harrison and Charlie Walker volunteered their time and worked alongside WTT’s Mike Blackmore, keeper Jonny Walker and specialist contractor, Nick Lawrence. 

Heavy plant machinery arrived on site for Phase 2. Under the initial guidance of WTT’s Andy Thomas, plant operator and river project veteran, Rob Hillary, made the first dig and dump pools, as well as undertaking a significant bank lowering and re-profiling at the bottom of the beat, in the previously impounded section. Rob was also joined by plant operator and river restoration specialist contractor, Max Hardman, who worked on channel-narrowing and managing the near-constant deliveries of flint gravel. Rob continued the dig and dump operation under the guidance of Mike Blackmore.

Large (40mm+) flint gravel rejects were used to create new bank edges and to form the base of riffle features. Finer (20 – 40mm) gravel was used to form the bulk of the new riffle features and also to blind over excavated pools. Gravel was transported around the site using a 6 tonne, 360 degree swivelling tracked dumper driven by Mike Blackmore. This ensured that both ground disturbance and compaction were kept to an absolute minimum. After the excavation of several new pools, three long sections of riverbank were lowered to improve marginal habitat and provide better cover for juvenile trout. 

In total, 10 new pools were created, each with gravel glides at the tail end to provide spawning opportunities. 6 new riffles were created, 6 sections of bank were lowered and the channel was pinched in 14 places. 8 brushwood berms were created and 4 large woody debris cover habitat features installed. 7 log flow deflectors were also introduced, most positioned to provide scour through newly created pools. 200 tonnes of flint gravel was introduced. Approximately 1km of chalkstream was restored over 10 days. The budget for the entire project was £20,000.