<p>Magnitude, Frequency, and Trends of Floods in Washington State</p><p>A recent investigation into the magnitude and frequency of floods in Washington State computed the annual exceedance probability (AEP) statistics for 649 USGS operated, unregulated streamgages in and near the borders of the state using the recorded annual peak flows through the 2014 water year. This talk will be based on this investigation and describe flood hydrology in Washington State and the methods used to compute magnitude and frequency of floods. This type of data is important in floodplain management such as FEMA flood insurance studies, design of infrastructure near streams and location of buildings in a floodplain. The analysis is based on the assumption of stationarity—a concept that the flood hydrology we see today will be the same in the future. Within the context of a changing climate, we know that this is not a completely true assumption. We will look at the observed trends in peak discharges and how one might begin to account for the trends in a flood analysis.</p><p>Snoqualmie River near Carnation, WA, 1/5/2015. Photo 509 from King County, WA Historical flood photos available on the KingCounty iMap Interactive Mapping Tool accessed 4/18/2016 at http://gismaps.kingcounty.gov/iMap/</p>