Creating improved instream habitat and enhancing salmon angling potential using a sub-surface stone





The Project

Changes within the River Blackwater catchment over an extended period of time have resulted in many and sometimes drastic changes within the river itself. Due to a combination of environmental factors, an island formerly located in the centre of the River Blackwater downstream of Clondulane Weir was scoured out. During low flow conditions, this area was exceptionally good for salmon angling. As the island was no longer present, flows detrimental to successful fly fishing prevailed and Careysville Fishery wanted to recreate what was once one of their most productive stretches.




The Rivus Solution

After an initial site visit to discuss the problem and plan, Rivus set about undertaking detailed instream surveys to ensure a solution which would fit in with the surrounding environment could be formulated. As this site is within the Blackwater River (Cork/ Waterford) SAC, this necessitated an assessment of possible impacts to the qualifying interests and integrity of the designated site.


To ensure works could be conducted within a sensitive environment, it was imperative that construction works were designed to be clean and the finished structure was durable in a range of high flow velocities. The final design incorporated the use of suitably sized rip-rap to create a sub-surface rubble mattress which created suitable flows conducive to salmon fly fishing. Dimensions and angles for the mattress were carefully considered to ensure flows generated from the structure suited angling downstream in the most suitable conditions. This type of work requires a sensitive touch and attention to detail so that the finished structure blends in with its surrounding environment.




The Result


Constructed near the end of the instream works season in 2019, angling has taken place along this new stretch of water for one complete angling season and it has proven to be the most productive stretch within the Careysville Fishery. Many high flow flood events have occurred since its completion and these have only served to increase its durability by seeding it further with river gravels. In achieving this outcome, instream riverbed heterogeneity has been promoted to the benefit of all aquatic flora and fauna species.