River Alyn habitat scheme completed

The Welsh Dee Trust undertook a survey of the River Alyn (Tributary of The Dee) from just below Mold to the confluence with the Dee at Almere Ferry. The total length surveyed was 26Km (16 miles)

The nature of the survey was to identify areas that would benefit from instream and riparian habitat improvement, diffuse rural pollution, point source pollution, bank erosion and invasive non-native species (Himalayan Balsam & Japanese Knotweed).  Several areas were identified that would benefit for instream improvements.

As funds are limited, we had to look for projects that would give the greatest cost benefit.  A further survey in the Pontblyddyn area highlighted what should be good spawning areas for Brown Trout and Sea Trout, but even though the gravels looked good they were in fact too compacted. It was decided to install upstream facing groynes to create a scour pool and naturally grade the gravels. 

A river running through a forest  Description automatically generated
Installed groynes divert flows creating pools and scoured gravels, both vital habitat for fish.

      

The River Alyn through Pontblyddyn is quite uniform and lacks diversity.  Areas were selected to improve biodiversity. Upstream offset timber groynes were installed to move the flow around creating a range of habitats.

A path with trees on the side of a river  Description automatically generated

Other areas identified that would benefit from instream work were deep pools on the outside of bends.  There was some degree of erosion that puts silt in the river and although rivers need silt loading, too much can have an adverse effect in clogging gravels, smothering fish eggs and invertebrates and irritating fish gills and eyes.  Brash revetment was installed on the outside of the bends to reduce/eliminate erosion and create habitat for adult fish.

Brash pinned onto the outside of bends provide cover for fish and reduce erosion of the bank.

We thought about undertaking the work in September 2018, but the areas would need time to consolidate before the winter floods, so the projects were shelved until the Spring of 2019.  The work taking place in May 2019 as instream work isn’t allowed until the end of April. This would allow time through the Summer and early Autumn for the vegetation to consolidate before the winter floods.  How wrong we were!  Two weeks after the work was completed, we had the worst floods since 2000/1.  The river rose in excess of 6 feet.  Would all our work wash away as it hadn’t had time to consolidate? There was a degree of optimism as the timber groynes had been secured very well during construction. When the water dropped the groynes were still in place and areas had started to scour out and grade the gravels.  The brash revetment on the outside of the bends had held and by chance nature had given us a helping hand by causing the top of the banks to collapse slightly putting vegetation on top of the revetment, so accelerating the consolidation.

This was a jointly funded project with the local angling club (Wrexham & District Anglers). The Welsh Dee Trust were the lead and Project Managers.

Once the river settled after the high water and the work started to consolidate it has been reported that shoals of minnows have started to be seen upstream of the groynes and fish are rising in the pools adjacent to the brash revetment.  There will be further visits to see if there are any redds on the newly graded gravels – that would be the icing on the cake!