Usk Bridge Merthyr Road Llanfoist Monmouthshire

Description

The proposal is for the construction of a new fish pass at Abergavenny bridge, Llanfoist. Abergavenny Bridge is orientated perpendicular to flow across the River Usk, with a total length of 62m . The bridge apron, which terminates in a vertical drop which is exposed in low flows, presents a barrier to fish migration . The apron is considered a significant barrier to shad, although they are occasionally observed upstream, as well as other fish species such as lamprey. The shallow apron also delays salmonid passage during low flows, particularly the sloping glacis towards the disused railway bridge abutments. A fish pass has been determined as the best solution to this barrier. The pass will comprise a notch in the concrete apron below Arch 2 (second arch from the true right bank), in which perturbation boulders will be evenly spaced. This will provide an area of deeper, slower flowing water for fish to move through. This is hoped to be particularly beneficial to shad populations, which migrate upstream to spawn during summer (primarily June/July) when river flows are often at their lowest. The bridge, which is owned by Monmouthshire County Council, is a Scheduled Monument and Grade II* listed structure. The proposed works are therefore to be carried out under Scheduled Monument Consent with appropriate archaeological supervision. The proposed design of the new fish pass comprises a ?notch? within the concrete apron. This notch will require the cutting of a channel into the concrete, approximately 3.6m wide and 700-800mm below the existing level. These dimensions have been chosen to ensure that the final level is effective as a fish pass. It was decided that the most appropriate arch to locate the fish pass was Arch 2, so as to optimise hydraulics of the fish-pass and the lower depth of the apron as compared to the other arches, which minimises the depth of excavation. To provide a 5% gradient (and therefore appropriate velocities), the channel will need to