Howard Hanson Dam

Background
The U.S. Army Corps of Engineers (USACE) manages the Howard Hanson Dam near the headwaters of the Green River. The dam helps maintain water storage and reduces the risk of flooding in the Green River Valley/floodplain. After this winter’s storms, USACE discovered accelerated leakage through the right abutment of the dam.

As a result of this finding, USACE has determined the dam will be unable to hold as much water during heavy rains. This situation creates a higher possibility of flooding in areas of Renton located in the floodplain (Highway 167 west to the Green River and Renton’s southern boundary north to the Burlington Northern railway corridor).
Although it would take a catastrophic event for the floodwaters to reach downtown Renton and significant flooding may not occur, there is a heightened risk of flooding within the Green River floodplain and areas surrounding the floodplain due to the condition of the dam.

The Army Corps of Engineers has made an interim fix to address the problem but won’t be able to test it until next summer when the risk of flooding is lower. They continue to work to find a solution to structural issues affecting the dam, but a permanent repair may take 3 to 5 years to complete. In the meantime, the lower Green River Valley will be threatened by seasonal flooding not seen in fifty years.