SEATTLE DISTRICT

Home
Home > Missions > Civil Works > Locks and Dams > Howard Hanson Dam > Green River Flood Risk Maps

Green River Valley Flood Risk Maps

The maps on this Web page show four potential scenarios, based on flows in the Green River as measured at Auburn. These scenario maps are intended to provide the public with an idea of the range of flooding that could occur. However, the scenarios cannot consider every uncertainty associated with an actual flood event.

In short, these are not the only scenarios possible, but allow for planning degrees of response. The maps do not take into consideration work being done along the river in regards to levee fortification and again may not accurately reflect inundation. The maps are meant to inform the public of potential risks, but do not display all the hazards associated with flooding such as loss of electricity, closed transportation routes, etc. The public should communicate with their city and/or county to understand the potential impacts, responses, and methods of warning notification and communication.

One size map is a full size map that must be printed on a plotter printer (46" x 36"). The other map may be printed on 11 x 17 * These maps are only guidelines and do not consider the inherent uncertainties associated with all the unknown variables that may happen during an actual flood event. In short, these are not the only scenarios possible, but represent degrees of response needed.

The maps are provided by the Corps in an effort to provide as much knowledge for the public to plan and prepare for the increased risk due to the decreased operational capacity of the Howard Hanson Dam.

  • The Corps will do everything in its power to minimize the flooding downstream without jeopardizing a catastrophic failure of Howard Hanson Dam.
  • The maps are based on computer modeling and may vary from actual events. 
  • The flows shown in these scenarios are not flows that will be released. 
  • The flows represent a range of flow conditions that were evaluated for planning purposes to understand the consequences of types of operations at the dam, which could be necessary due to reduced operational capacity.
  • There is no probability associated with these flows. 
  • These maps are NOT evacuation maps, they are estimates of the level of inundation based on a range of scenarios.   
  • The maps do not take into consideration any recent work being done along the river in regards to levee fortification or private flood protection which will change the way in which flood waters spread across the land, and again may not accurately reflect inundation.  

Please note:  Even given that these documents are PDFs, they are still large files and depending upon your connection, may take a while to load. Additionally, you should have at least Adobe Reader version 7 in order to access the documents.