Green River & Howard Hanson Dam Information
The U.S. Army Corps of Engineers (USACE) manages the Howard Hanson Dam near the headwaters of the Green River. The dam provides flood water storage, controls the flow into the river below the dam and reduces the risk of flooding in the Green River Valley/floodplain. After the January 2009 flood season USACE discovered accelerated seepage through the right abutment of the dam. As a result of this finding, USACE determined the dam would not be able to hold as much water during heavy rains. This situation created a higher possibility of flooding in areas of Renton located in the floodplain.
The Army Corps of Engineers completed an interim fix to address the problem in November of 2009 and in the spring of 2010 began testing the dam. Tests showed that those repairs improved the control of seepage through the area of concern. The Corps was able to hold a pool of 1,167 feet above sea level (48 percent of full) for more than two months without seeing any problems. This provided additional confidence in the storage capacity of the dam for the flood season. At the same time, the Corps initiated the study to determine how best to permanently repair the dam
New investigations, testing, and engineering analyses have been performed and work has been done on the necessary repairs. For details on the improvements, see the fact sheet provided by the Corps.