HSPF Study for Clark County, Washington Flood Insurance Study

A FEMA Flood Insurance Study was conducted along 116 stream miles of 20 streams in Clark County, in the vicinity of Vancouver, WA.  A hydrologic analysis was performed as part of the analysis which included the review of an existing HSPF Model of the Salmon Creek basin.  Ground surveys were conducted using a combination of the latest GPS and Optical Total Station equipment for all of the channel cross-sections and hydraulic structures.  This allowed for all of the survey data to be quickly and easily geo-referenced to existing National Geodetic Survey (NGS) monuments, resulting in easy integration with recently acquired digital 2-foot contour mapping and aerial orthophotography. 

HEC-RAS 3.1 is being used to perform the hydraulic analysis which includes levees, inline weirs, bridges and culverts as well as multiple separate overbank (split-flow) reaches.  Water surface profiles for the 10, 50, 100, and 500-year flow events as well as the 100-year floodway are being determined. All geometry data within the hydraulic model will maintain its geo-referencing so that the output data can be post-processed using automated mapping and display techniques in ArcView GIS.  After thorough in-house and FEMA review, the submitted digital floodplain and floodway maps will be used as a basis for new Digital Flood Insurance Rate Map (DFIRM) for Clark County, WA.