Wahleach Project Water Use Plan Wahleach Reservoir ... - BC Hydro

The Wahleach Water Use Plan Consultative Committee (WAH WUP CC)
recommended that the Wahleach Fertilization/Biomanipulation Program continue to
compensate for losses in productivity in the reservoir associated with the operational
related impacts of reservoir fluctuations and nutrient flushing. The WUP started in
2004 and this report summarizes the first three years of the fertilization program as a
WUP program.
2. Study Area
Wahleach Reservoir (49º10’W, 121º40’N) is located in the Skagit Range of the
Cascade Mountains in British Columbia, southwest of Hope BC (Fig. 1). The
reservoir was formed by the construction of the Wahleach dam in 1952. The dam
increased the original lake volume from approximately 17 x 10 6 m 3 to a storage volume
of approximately 60 x 10 6 m 3 at full pool. The surface area increased from
approximately 282 ha to 410 ha after impoundment and the water surface elevation
increased from 628.5 m to 641.6 m. Wahleach Lake Reservoir is 6.1 km long and
0.65 km wide at full pool (Fig. 1). Maximum depth at full pool is 26.6 m. The annual
drawdown occurs from fall to early spring when power generation is required and is
recharged in the spring and early summer by melting snow pack. The reservoir is
dimictic and typically has ice cover from December through March. It is thermally
stratified in June to October and maximum surface water temperatures are typically
approximately 24ºC.
The reservoir was typical of old aging reservoirs having low total phosphorus
concentrations (