Design of Flood Protection for Transportation Alignments on Alluvial Fans

Abstract

The method of floodplain delineation on alluvial fans developed for the National Flood Insurance Program (NFIP) may be modified to provide estimates of peak flood flows of specified return periods at transportation alignments, such as aqueducts or railroads, crossing alluvial fans. The modified methodology divides the total length of the alignment into segments, and the peak flow expected in each segment during a flood event is estimated as a function of the return period of the event, the segment length, and the location of the alignment on the alluvial fan. This estimate of the peak flow can be used to properly size the facilities such as dikes, berms, and culverts to protect the alignment from flood damage. The proposed methodology has potential applications in any environment where transportation alignments must cross alluvial fans on which the hydraulic processes are similar to those for which the NFIP methodology was developed. An example of the use of this methodology is provided.