USGS Washington Water Science Center
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Floodpath Project Summary
The Urban Natural Hazards Initiative, 1996-2001, brought together scientists from USGS hazards research into volcano, seismic, landslide, and hydrologic hazards, to investigate the utility of assessing hazards in a holistic manner, rather than discipline-by-discipline. The Puget Sound region was selected for the project area primarily because of the geographic intersection of these hazards in the region.
The Washington Water Science Center led the investigation into flood hazards, and after polling state and local governments, citizens, and the private sector (the insurance industry, notably), it was clear that flood hazards were poorly understood (namely, confusion with regard to what a “100-year” flood was, and whether it represented a “big” or “biggest” flood). (An analysis of the “100-year” flood from a regional perspective showed that for streams draining to Puget Sound, a “100-year” flood occurs on average every 4 ˝ years.) Additionally, forecasts that are made for a specific spot on a specific river, and referencing an often arbitrary measure of height, were not conveying much information to people that did not have firsthand knowledge of flood height/depth from experience. For example, a longtime resident may have learned the hard way that a “33 foot peak” means his access road will be flooded.
To address this, a pilot study in the Nisqually River basin was conducted that accomplished two things.
First, it developed the methodology to use existing Flood Insurance Studies to efficiently update the 100- and 500-year flow statistics used for Flood Insurance Rate Maps and the associated inundation maps. In addition, and building on this rapid map revision approach, flood inundation maps were prepared for every half-foot increment of flood depth. These maps could be used for any flood magnitude forecast by the National Weather Service’s River Forecast Center (RFC), by selecting the map that corresponded most closely to the forecast flood level. They could also be used in a “what-if?” fashion for situations where high value items could not be risked and someone may choose to select a flood map for a higher level than was forecast.
Taking the idea of mapping a specific forecast flood one step further, Floodpath was developed to input the actual RFC flood forecast (in the form of a forecast hydrograph), into a calibrated hydrodynamic model which would in turn provide the input to mapping programs which made forecast-specific maps. Because the input includes the time aspect of a flood arriving, peaking, and receding, these maps include the time-of-arrival, the peak depth, and the time-of-crest. These maps could then be distributed on the internet. In addition to the maps, users can select any location and generate a hydrograph (a plot of depth or flow over time) for that specific site, along with the typical suite of mapping utilities such as address locating.
The USGS Washington Water Science Center is looking for additional sites and partners to expand the use and utility of Floodpath. This includes locations with high vulnerability to flooding (as an opportunity to investigate using forecast flood maps to generate potential loss forecasts), and areas where tidal influence may significantly contribute to flood hazards.
For more information, contact:
Joseph L Jones, firstname.lastname@example.org, (253) 552-1684