Chehalis River Basin Early Flood Warning System (WA)

Following a devastating flood in December 2007, Chehalis River Basin stakeholders intensified efforts to mitigate flood risk in one of the most flood-impacted watersheds in the state of Washington by forming the Chehalis River Basin Flood Authority. The Authority quickly determined that improvements to the current early flood forecast and warning program for the Chehalis River Basin were needed.

On behalf of the Flood Authority, WEST Consultants worked with community groups, Indian tribes, and local governments within the basin to assess their current flood preparedness practices and needs. In addition, flood forecasting and related programs of the NWS, the USGS, NRCS, and the Washington State Department of Ecology were reviewed.  The findings led to a conceptual plan for improving the identification of flood threats, agency coordination, and communication with the public.

The plan as implemented includes a publicly accessible, Internet-based flood data collection, display, and information distribution system. Rain, stream, reservoir, wind, and temperature information are collected, displayed, and used in near real-time. Internet users access current data along with the latest NWS river forecasts for the basin, local traffic conditions, and other flood preparedness information. Flood inundation maps show the public and government officials where flooding is expected at each forecasted river stage.

In addition, ten automated rain gages, ten temperature sensors, and two additional stream gages were added to the existing flood threat detection system to facilitate monitoring.

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