Howard Hanson Dam’s reservoir has reached 1,147 feet above sea level, the point at which the U.S. Army Corps of Engineers and scientists on the ground begin intensive, around-the-clock monitoring.

Last month, the Seattle District of Corps began allowing water levels to rise slowly within the reservoir for the annual spring fill of the reservoir, a normal dam operation to provide summer and fall water supply for various purposes.

During this pool rise, the Corps will conduct testing and in-depth investigations of the dam’s current effectiveness. The plan targets a maximum pool elevation of 1,167 feet, unless engineers, geologists, and other scientific experts on the ground see anything troubling, in which case the reservoir level can be reduced as appropriate. Additionally, throughout the reservoir fill, the Corps will constantly monitor the performance of the dam including special electromagnetic and dye tests to measure the effects of the pool on the right abutment. Because of the damage sustained to the abutment in 2009, a higher frequency of monitoring is prudent once the pool exceeds elevation 1,147 feet.

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, four-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.

The Corps operates the Howard Hanson Dam project, which provides flood damage reduction 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.

More details can be found at http://www.nws.usace.army.mil.