Mapping of Potential Flooding Within Renton's Green River Flood Plain
The maps linked below represent the areas within the City of Renton that could be flooded due to the reduced flood storage capacity at the US Army Corps of Engineer’s Howard Hanson Dam. (Highway 167 west to the Green River and Renton’s southern boundary north to the Burlington Northern railway corridor). However it is important to understand that there are three key variables that will determine the likelihood of flooding: characteristics of the storm, the level of the flood pool behind the dam, and the volume of flow in the river. These variables will determine the operation of the dam, which in turn will determine flow volumes in the river.
The following maps show areas that could be flooded based upon hydraulic modeling of Green River flood flows above the normal maximum flow of 12,000 cfs (cubic feet per second)*. The hydraulic modeling is based upon assumptions about levels of flood storage at the Howard Hanson Dam, levee conditions along the Green River, weather conditions, and other assumptions. The depth and extent of actual flooding will vary based upon the actual magnitude of the flood event, flood storage provided at the dam, and levee conditions.
* The US Army Corps of Engineers predicts there is a 33% likelihood of flows exceeding 12,000 cfs this flood season.
The following maps are an interpretation of potential flood areas within the City of Renton, relative to river flows in cubic feet per second at the Green River Auburn gage:
Flood Scenario for river flows up to 13,900 cfs.
The City of Renton estimates a 4% chance the Green River flow will reach 13,900 cfs this flood season.
Flood Scenario for river flows up to 17,600 cfs.
The City of Renton estimates a 2-3% chance the Green River flow will reach 17,600 cfs this flood season.
Flood Scenario for river flows up to 25,000 cfs.
The City of Renton estimates a 1-2% chance the Green River flow will reach 25,000 cfs this flood season.
Evacuation Routes for Green River Flood Plain
In the event of flooding in the Green River flood plain, this Evacuation Map provides recommended emergency evacuation routes within the city limits of the City of Renton.
- The hydraulic modeling used to generate these maps assumes no breaching of the Green River levee system.
- The maps provided are an interpretation of statistical based hydraulic modeling and may not accurately portray actual future flood events.
- The above estimates do not include potential breach of a river levee, which could increase flooding in Renton above the levels depicted in the maps.