Riprap Basin Design for a Small Catchment

The purpose of the study was to adapt an economical hydraulic structure design to an ungaged watershed. A dangerous drop in the streambed formed 35 ft. away from a residential bridge. The drop is inching closer to the culvert bridge causing serious concern. Streambed erosion is a damaging force that can cause damage to bridge and hydraulic structures. EPA Basin software was used to delineate the watershed containing the target bridge for the study. Simulation software such as HEC HMS to first model different design storms to get watershed data and HEC RAS to simulate the stage discharge at the target bridge location. Both simulation software's were also used to model known storm data from the 2008 Ike Storm as a comparison to gage the watershed. The ungaged watershed was also compared to three surrounding watersheds using daily flow observation data at the following stations: Hart Ditch, Deep River, and Little Calumet to calculate proportioned 25 yr. storm flow discharge using Weibul's plotting position formula. Through different data comparisons, the computer simulation flow data for a 25 yr. storm of 393.1 CFS. Computer simulation flow data was also compared with National Streamflow Statistic (NSS) software, which computed a discharge 212.24 CFS. x The ranges of values High, Medium, and Low were developed in order to establish an optimal design range that will be economical as well as fit the existing site conditions. Multiple types of field data was gathered over the course of the study such as cross sectional and topographic survey data for computer simulations, sieve test data or determining soil gradation of the streambed and embankments, and digital flow data for hydraulic structure design. Data gathered over the course of the study helped determine that a riprap energy dissipator should be adapted for the site because of environmental conditions and economics. Along with dissipator design, an alternative construction plan was also outlined.