Wednesday, 25 January 2012: 8:45 AM
On the Use of Radar-Based Design Storms for Floodplain Delineation and Dam Safety
Room 245 (New Orleans Convention Center )
Over the past eighteen years the National Weather Service has installed a national network of WSR-88D Doppler radars. In Arizona this network includes radars near Flagstaff, Phoenix, Tucson and Yuma. The nearly continuous sampling of precipitation systems year-round provides a significant opportunity to update and upgrade the design storms used for floodplain delineation studies and the rehabilitation of dams and flood retarding structures or levees. Typically the design storms used for these studies are based on a set of rainfall frequency and areal reduction factors developed from data sets of rain gages and stream gages which may or may not be representative of the basin being modeled.
Radar presents the opportunity to sample the observed precipitation coverage and temporal distribution of the entire spectrum of storms from isolated thunderstorms to monsoon storm systems to sub-tropical disturbances to large general winter storms. Radar samples roughly half mile by half miles areas with temporal resolution of roughly every 5-minutes. Examples of 2-y to 500-yr design storms will be presented from the FEMA-approved South Boulder Creek Floodplain delineation study in Colorado and from PMP studies in Colorado, New Mexico and Arizona. The time has come for this NWS resource to become a standard for design storm development.