Abstracts Category : Other

Sediment transport and bed material adjustments in the vicinity of Wilsey Dam : salmon spawning habitat implications

by Giles Andrew Shearing

Substrate requirements are an important component of the multifaceted spawning needs of salmon, and this research effort was directed at developing a greater understanding of sediment transport dynamics and bed material response in the Middle Shuswap River in consequence of the emplacement and subsequent management of Wilsey Dam. Downstream of Wilsey Dam the river provides spawning habitat for coho (Oncorhynchus kisutch), chinook (O. tshawytscha), pink (O. gorbuscha) and sockeye (O. nerka) salmon. This thesis suggests that sand dredged from deposits filling the upstream reservoir basin of the dam could be redeposited downstream when coupled with specific flow releases (100 cubic metres per second). This is seen as a viable option for sediment management on the Middle Shuswap River aimed at restoring sediment transport processes and preserving spawning habitat. Maintaining sediment transport processes after dam emplacement is an important consideration for ecological processes in rivers, consistent with the notion of holistic dam management (Ligon et al. 1995, Tharme 2003)An experimental underwater Automated Grain Sizing method was developed for determining the median grain size (D50) of glide facies throughout the 28.4 km study area. On this basis, estimates of viable salmon spawning habitat were updated from 2002 and mapped below (190,906 m2) and above (387,265 m2) Wilsey Dam. Grain size distributions showed a fining trend in the downstream direction for the Middle Shuswap River, with significant coarsening of bed substrate in the 0.2 km section immediately below the canyon downstream of Wilsey Dam. A one-dimensional (1D) sediment transport model, based on the Wilcock and Crowe (2003) transport equation, showed that sand reintroduced during spring freshet to a 1200 m reach below the dam flushed quickly through in the model. Gravel was also mobilized upon sand reintroduction. The model is an oversimplification of site conditions and would need to be field tested during sand reintroduction trials to establish model integrity. Research undertaken in this thesis contributes to the growing amount of literature on the biophysical impacts of hydroelectric dams and presents ways dam operators can approach and mitigate disruptions to sediment transport process and their resulting ecological impacts.