Low Flow Augmentation

The UTRCA stores water in Wildwood and Pittock Reservoirs in order to:

• reduce downstream flooding from snow melt and/or rain, and
• supplement stream flows during dry periods.

Each year before the spring snow melt (February to April), these two reservoirs reach their lowest levels. Because their potential storage capacity is at its maximum, the reservoirs can usually contain all the runoff that reaches them from snow melt and spring rains. Hydrology staff coordinate reservoir operations with observations and forecasts of downstream water levels on various watercourses to minimize some of the impact of flooding. The dams’ safety is ensured by allowing for the possibility of more severe situations.

Following spring runoff the reservoir levels are jockeyed toward a summer starting level for May and June. The weather can have a major effect on if and when the reservoirs reach the desired level.

During the summer and early fall, there is much less runoff from precipitation than in the spring or late fall, and streams drop to very low levels. The water stored in the reservoirs during the snow melt and spring rainfalls is released to supplement downstream flows. The reservoir water levels drop throughout the summer as more water is released than comes into the reservoirs from upstream. Summer storm runoff can cause some fluctuations in the reservoirs but these are usually substantially less than in the spring and fall.

Wildwood and Pittock Reservoirs continue dropping in the fall until the winter levels are reached in early December. This brings the operating season full cycle, ready for whatever the next year brings.