Seattle – Water managers have begun slowly filling the reservoir at Howard Hanson Dam at the headwaters of the Green River. As is typical, the Army Corps of Engineers slowly begins annual spring fill of the reservoir in late February, allowing water levels to rise within Howard Hanson Dam’s reservoir.
The process takes roughly three months to refill the reservoir. The current plan targets a maximum pool elevation of 1,167 feet above sea level. A 1,167 foot elevation pool has been the spring refill target since 2007.
Water stored during the spring refill of the reservoir will be used to provide water supply to the City of Tacoma and its water supply partners. Additionally, at least three-fifths of the reservoir’s supply will be used to augment downstream flows to help endangered species of fish, including Chinook and steelhead. Project managers believe that the regulated downstream flows will aid spawning and other life-cycle events for the fish.
Snowpack in the Green River Basin is at a near record low level. The virtual absence of snowpack, coupled with recent dry conditions, has resulted in a low water supply outlook and a high likelihood that Green River flows could be well below average this spring. Low runoff could result in challenging spring refill conditions for Howard Hanson Dam unless normal or above normal rainfall patterns develop in the spring and early summer.
The Corps operates the Howard Hanson Dam project, which provides flood risk management to the Green River valley, low-flow augmentation to the Green River for environmental benefits, and water supply to the City of Tacoma and its water supply partners.
Release no. 15-003