Flood Hazards

Flooding is the natural hazard of most concern in Washington and affect lives in the State every winter and spring. Flood monitoring, forecasting, and warning methods allow for planning of responses to potential floods, but flood-inundation maps needed by local planning agencies to assess flooding and floodplain issues are seriously outdated. Flood frequency and magnitude are the basis for many planning decisions, but limited databases and changing conditions make determination of 100-year floods and other frequency discharges an uncertain science. The effects of land alterations on the frequency and magnitude of floods is unclear. Urbanization creates large and small streamflow and ground-water flooding issues that seldom occurred in pre-development times, such as snow- and ice-clogged storm drains or flooding in low-lying areas because of rising ground-water levels. Effects of forest practices on runoff and flooding are contradictory and unclear. Dams alter the hydrology of a watershed, reduce channel capacities through sediment aggradation, and present unknown flood-related issues if removed. Increased technical information is needed on these flood-related issues.

Flood monitoring, forecasting, and warning methods
Accurate estimates of flood frequency and magnitude
Better understanding of the effects of urbanizaton, forestry, and other land-use practices on flooding
Understanding of the effects of dams on flooding and channel geomorphology

USGS gages on streams in Washington have provided information on flood monitoring since about 1900, and the present network of stations, computer links, and real-time data operated by the USGS remains one of the foremost networks in the country. The network provides real-time streamflow data from 160 gaging stations via radio, satellite, computer, and dedicated phone lines to local public utilities districts and power companies. Availability of real-time streamflow data on the Web now allows not only public agencies but the public themselves to make use of the information at critical times.

As part of the USGS Natural Hazards Project in the Seattle area, the Water Science Center developed a method for using real-time streamflow data, Geographic Information System mapping capabilities, and a computer delivery system to provide real-time maps of projected flood inundation and depth during storms. This Project also produced regional flood-frequency analyses, estimates of hazards caused by channel migration, and maps of areas prone to ground-water flooding. The USGS also conducts numerous flood-frequency and flood-simulation studies and updates flood-frequency analyses for the State. USGS scientists developed a flood-simulation model and a flood forecast system for the Puyallup River Basin and assessed flooding potential in the South Prairie Creek Basin. Some USGS projects include studies of key processes in major floods, such as rain on snow. Discharge measurements at more than 200 gaging stations throughout the State provide information on channel changes over the years.

Links to projects related to: Flood Hazards
Geomorphic Mapping, Dosewallips River High Resolution Geomorphic Mapping of the Dosewallips River Using Remotely Sensed Data: Method Development - Completed FY2004
Green River Geomorphic Responses Geomorphic Responses of the Middle Green River to Floods
Howard A. Hanson Reservoir Estimating Runoff-Season Inflows to the Howard A. Hanson Reservoir, Green River - Completed FY2002
Honduras Flood Mapping Flood-Hazard Mapping in Honduras - Completed FY2002
Evapotranspiration at Klamath Marsh and Lower Klamath National Wildlife Refuge Estimating Evapotranspiration at Klamath Marsh, Oregon, and Lower Klamath National Wildlife Refuge, California - Completed FY1999
Puget Hazards Urban Hydrologic and Geologic Hazards in the Puget Sound Area - Completed FY2003
Multispectral imaging, Puyallup River The integration of multispectral imaging and LIDAR to evaluate the geomorphic changes associated with a levee setback along the Puyallup River, WA - Completed FY2005
Puyallup Flood Alert Floodwater Monitoring and Simulation on the Puyallup River and Real-Time Flood Alert and Flood Simulation of River Discharges in the Puyallup River Basin - Completed 2001
South Prairie Creek Flood Potential of South Prairie Creek - Completed FY1999
Flood Frequencies Flood Frequencies in Washington - Completed FY1999
Ground-Water Records Collection of Basic Ground-Water Records, Washington
Hydrologic Urban Indicator Hydrologic Indicators of Urban Development in Western Washington Streams - Completed FY2002
Precipitation Records Collection of Basic Precipitation Records, Washington
Rain-on-Snow Events Magnitude and Frequency of Water Available for Runoff During Rain-on-Snow Events at Selected Sites in Washington State - Completed FY1996
Surface-Water Records Collection of Basic Surface-Water Records, Washington
Yakima Watershed and River Systems Management Program Yakima Watershed and River System Management Program (WARSMP) - Completed FY2002