Restoring Pearl Mussel Habitat on the River Shin

 

 

The flow regime downstream of the SSE dam diversion on the River Shin is unnatural both in terms of volume and flow variability. Compensation flows are low and estimated to be half of the natural Q99 in the spawning season. High flow events are restricted to times when the dam is over-topped with a sudden and unnatural steep rise in flows. In addition to impacting the flow regime, the dam also significantly restricts sediment transport processes that limits the supply of alluvial material resulting in bed coarsening /armouring, and a deterioration of spawning habitat downstream of the dam.

In 2009, SSE commissioned the Northern Rivers Institute to examine the habitat below the Shin Diversion Dam. This report recommended re-examining the flow regime as well as considering gravel augmentation.

In 2012, SEPA Hydrology also conducted an assessment of the morphological impacts caused by the Shin hydro scheme. Among the recommended actions of this report, examining the flow regime and considering gravel augmentation were included.

The aim of the design is to restore habitat along a ~1.7km section of the upper Shin by introducing gravels and implementing secured large wood structures (LWS) to the channel. The LWS will provide direct habitat diversity, induce the development of physical diversity and act to maintain the introduced gravels in-situ.