Ecological Flows for a Large Hydroelectric Reservoir Regulated River System: Will Projected Climate Change Bring About Beneficial Opportunities?

English Abstract:

The Peace River in Western Canada has been regulated since 1968 with a large dam and storage reservoir for the production of hydroelectricity. The reservoir releases feed a run-of-the-river facility, and there are plans to add two more run-of-the-river dams downstream. Previous studies have found that flows emanating from the mountain headwaters have increased by ca. 250% during the winter low flow period and peak summer flows have decreased by ca. 35% - both associated with the introduction of hydroelectric operations. Although reduced by tributary inflow, this alteration in the flow regime was transferred more than a thousand kilometers downstream to the internationally important Peace-Athabasca Delta (PAD). The PAD ecosystem is influenced by occasional ice-jam and open-water flood events that recharge lake and wetland basins with varying degrees of connectivity to the main flow system. Reservoir spillage is a rare occurrence on this reservoir system. For instance, additional reservoir flow was released in the spring of 1996 to enhance natural hydro-climatological conditions in the lower watershed, conducive to the formation of ice-jams, and associated overland flooding in the Peace Delta. The Williston Reservoir was lowered by ~3m during the summer of 1996 in response to a sink-hole in the earth dam, generating near natural summer flows on the lower Peace River that helped raise the connected lake system into contiguous wetlands. Most recently, additional flow was released from the reservoir over the summer of 2012 in response to above average snowpack/rainfall and runoff in mountain headwaters. The objective of this presentation is twofold: i) examine the hydroclimatic drivers of these atypical historical flow releases; and (ii) examine the projected impacts of climate change on the timing and quantity of water available for hydropower generation. Based on our understanding of historical flow release events and projected climate change effects on streamflow into the Williston Reservoir, the goal of this study is to develop ecologically-relevant flow release recommendations that will contribute to the maintenance/sustainability of downstream deltaic ecosystem.