Implementation of a comprehensive flood warning system in west central Washington

Two catastrophic floods in the Chehalis River Basin in west central Washington in the past decade prompted several initiatives to manage flood risk in the basin. One initiative was the development of a comprehensive flood warning system to improve emergency response to developing flood threats and to improve the operating environment for future dams and or levees in the basin. After a needs analysis canvassing stakeholders with interests in the basin, a flood warning system was implemented that included an expanded rain, temperature, and stream gage network, an internet based data collection, management and distribution system, as well as inundation mapping for approximately 100 miles of stream channel. The system leveraged existing automated gage networks in the region, an internet based data management service, and National Weather Service river forecasts to form the core of the system. The web site features total public access to observed hydrometeorological data, weather forecasts, quantitative precipitation and temperature forecasts, local road conditions as well as links to other critical flood preparedness resources. A sophisticated alarm manager is included that enables automatic message transmission via email or text messaging to mobile devices when user specified alarm criteria are met. Neighborhood level inundation mapping keyed to the full range of National Weather Service river forecasts covering initial monitoring stages through minor, moderate and major flooding is included. Residents can clearly see where and when flooding will occur relative to homes, critical facilities, and avenues of ingress and egress in advance of anticipated flooding. The Chehalis River Basin flood warning system will be described and summarized. In addition, it will be shown how the system is easily scalable to statewide application.