Application of the New Approach to Analysis and Mapping Procedures for Non-Accredited Levees on a Pilot Program Reach
Presenter: Brady McDaniel and/or Swetcha Reddy1
Contributors: Andrey Shvidchenko and Ken Rood (Northwest Hydraulic Consultants)2;
Dan Charlton, Tesfaye Demissie, David Wilson, and Mark Johnson (Coachella Valley Water District)3; and
Robert Bezek (Federal Emergency Management Association)4
The Coachella Valley Water District (CVWD) and Northwest Hydraulic Consultants (NHC) are working with the Federal Emergency Management Association (FEMA) as part of a pilot program to implement the procedures outlined in the July 2013 document “Analysis and Mapping Procedures for Non-Accredited Levees,” often referred to as LAMP. The LAMP procedures have been applied to a 20-mile long reach of the Coachella Valley Stormwater Channel (CVSC) – from Monroe Street to the Salton Sea – where the levees are provisionally accredited and CVWD is not planning to certify them to FEMA in the near future.
The study began with development of steady and unsteady HEC-RAS models to analyze existing hydraulic conditions and evaluate “levee” and “no levee” conditions of the CVSC. The results from the HEC-RAS models plus channel and floodplain surveys were used to divide the system into reaches and select an appropriate LAMP analytic procedure for each reach. For the CVSC study area, the Structural-Based Inundation and Natural Valley procedures were applied to develop preliminary floodplain maps.
Application of the Structural-Based Inundation procedure required defining breach locationand their characteristics, implementing unsteady HEC-RAS modeling to determine flows through the breaches, and applying Flo-2D models to simulate inundation over the floodplain. Flo-2D was chosen to simulate floodplain inundation because of the flat overbank topography and interaction of flow with roadway features. The LAMP approach also requires that the Natural Valley Procedure be applied in reaches where Structural Based Inundation procedures are used to establish the outer limits of the floodplain and the HEC-RAS models were modified to determine inundation limits with this procedure. The preliminary floodplain map was then developed by combining results from all the breach locations and the Natural Valley Procedure.
1 Brady McDaniel (), Swetcha Reddy (): Northwest Hydraulic Consultants (NHC)
3950 Industrial Blvd, Suite #100c, West Sacramento CA 95691, (916) 371-7400
2Andrey Shvidchenko(), Ken Rood (): Northwest Hydraulic Consultants (NHC)
3950 Industrial Blvd, Suite #100c, West Sacramento CA 95691, (916) 371-7400
3Dan Charlton (), Tesfaye Demissie (), David Wilson (), and Mark Johnson (): Coachella Valley Water District (CVWD), PO Box 1058, Coachella, CA 92236,(760) 398-2651
4 Robert Bezek (): FEMA Region IX, 1111 Broadway, Suite 1200, Oakland, CA 94607, (510) 627-7274