ESRL/PSD Seminar Series

Abstract

The Howard A. Hanson Dam (HHD) has brought flood protection to Washington's Green River Valley (GRV) for more than 40 years and opened the way for increased valley development near Seattle. The GRV is currently the home to the nation's 5th largest industrial park (2nd largest along the U.S. West Coast) and approximately 400,000 residents. Following a record high level of water behind the HHD in January 2009 and the discovery of increased seepage through the dam's abutment, the U.S. Army Corps of Engineers (USACE) declared the dam "unsafe." Before the HHD was constructed, floodwaters of the Green River periodically spread generally unimpeded across the GRV. Prior to the commissioning of the dam, the valley had flooded more than 30 times in 70 years. Based on this history and the fact the dam could not be relied upon for flood control for the upcoming 2009/10 winter season, the USACE originally estimated the threat of a significant flood in the GRV to be 1:3. Later in 2009 the USACE revised the flood threat based partly on temporary fixes to the dam's abutment. Nevertheless, the elevated risk of flooding naturally caused great concern among the public, and elected officials from Washington State requested NOAA to help mitigate this important crisis. NOAA's National Weather Service (NWS) and Office of Oceanic and Atmospheric Research worked together to respond rapidly to this crisis for the 2009/10 winter season, drawing from innovations developed in NWS offices and in NOAA's Hydrometeorology Testbed. In this talk, I will briefly describe the HHD and what happened to it, summarize key elements of NOAA's rapid response and their impacts, and recommend next steps to address the ongoing risk.