Hydrology and Hydraulic Analysis for a Drainage Rehabilitation Project on Interstate Highway 80 in California

The drainage systems on Interstate Highway 80 (I-80) at Emigrant Gap in California were built in 1950s. After more than 50 years of service, most of these systems are in poor conditions and need major rehabilitation. A procedure has been developed to perform hydrology and hydraulic analysis for these systems, based on information available to design engineers, including as-built plans, Geological Survey (USGS) maps, aerial images, etc. The design flood volumes are calculated using the Rational Method and the National Resources Conservation Services TR-55 method, while the hydraulic capacities of drainage systems are calculated using the software program CulvertMaster. The results show that the capacities of many culverts are reduced as a result of the proposed rehabilitation work, which is not expected by engineers who used to believe that a smoother surface might offset the reduction in cross section area on flow capacity. This paper summarizes the procedures and methods used in this project to determine the final rehabilitation treatments.