Analysis of Flood Hazards for a Residential Development

An investigation was carried out to investigate the flood potential at a proposed residential development located in Indio, California. The existing floodplain area adjacent to the project area is designated to receive flood flows originating from Thousand Palms Wash, The Indio Hills and the riverine drainage area along Interstate 10. These flood flows pass through the existing residential development via three flood control channels. A two-dimensional flood routing model (FLO-2D) was applied to study the progression of a flood flow in the interim floodplain area. Model results were analyzed to depict contour plots of the maximum flow depths in the interim floodplain for two discharge conditions that were simulated. The peak discharges entering the project area were estimated from the model results. Two flood control channels are proposed to accept these floodwaters and carry them out of the project area. The U.S. Army Corps of Engineers' River Analysis System (HEC-RAS) computer program was used to compute water surface profiles in the two flood control channels for the peak discharges. A sediment transport analysis was also conducted for one of the channels using the U.S. Army Corps of Engineers HEC-6 model. Model results showed that sediment passes through the system well and is not expected to interfere with the function of the flood control channel. Maintenance measures will be in place in order to clean the sediment out of the channel after a large flood event. The design water surface elevations in the flood control channel are based on the greater of either the HEC-RAS calculations using bulked flow, or the HEC-6 computed maximum water surface elevation using the unbulked flow. All sections have adequate freeboard between the design water surface elevation and the top of pad for the design flood event.