River temperature dynamics downstream of a shallow reservoir: process-based modelling to evaluate thermal mitigation strategies

This study focused on Alouette River, located in south coastal British Columbia. During summer, water is released from shallow reservoir at a near-constant rate from an outlet about 6-10 m below the water  surface. Outlet temperatures in summer 2013 were initially cool hypolimnetic water, followed by alternating cool and warm water associated with an internal seiche, and finally dominated by warm epilimnetic water during the period of highest water temperature. An energy-balance model was used to evaluate potential strategies to ameliorate thermal habitat conditions for Pacific salmon downstream of the dam. Restoration of deforested banks that represented 4% of the reach length reduced daily maximum temperatures by only about 0.5 °C , while releasing more flow exacerbated temperatures during the warmest week of the year. The only effective strategy for thermal amelioration would be to release water from deeper in the reservoir.