Report – Virginia Weir, Conceptual overview of fish passage options

Virginia Weir presents a significant total, partial and temporal barrier to upstream fish migration on the upper reaches of the River Blackwater, with complete exclusion of juvenile salmonids, lamprey, and other species during most flow conditions. Following assessment of structural, ecological, hydromorphological, and heritage constraints, two fish passage measures were evaluated: full built-weir removal with a bedrock-linked rock ramp, and a confined rock ramp within the existing sluice channel.

The full removal option provides the greatest improvement in longitudinal connectivity, reinstates a degree of natural sediment transport, and restores over the largest reach of impounded river to natural riffle–pool–glide morphology, significantly enhancing salmonid spawning and nursery habitat. While sensitive receptors such as upstream wetlands and veteran treeline may experience water-level adjustment, the retention of the natural bedrock sill ensures moderated drawdown and protects against ecological shock.
Given the critical decline of salmonid populations in the Boyne–Blackwater system and the cumulative effect of 25 downstream weirs, the full removal option represents the most ecologically beneficial, climate-resilient, and future-proof solution. It maximises compliance with the Water Framework Directive and supports restoration objectives for the River Blackwater.