The Effects of Future Extreme Precipitation Events on Stream Hydrology and Hydraulics of Stream Crossing Structures

Low water crossings (LWCs) are susceptible to changes in intensity and incidence of extreme precipitation events with regards to infrastructure usability, resilience, and safety and if an increase in extreme events is realized, infrastructures near river systems are likely to have increased flood risk and associated mitigation costs. Precipitation frequency estimates were calculated for a range of annual return intervals (ARIs) and durations for three different time periods 1970-1989, 1980-1999, and 1990-2009. The results suggest the assumption that precipitation is stationary over time is not valid for the three Midwest regions. In addition, an analysis of projected precipitation data from four dynamically downscaled CMIP5 global climate models was completed for a range of design storms. The average projected (2080-2099) design storm across all locations, durations, and return periods is larger than the corresponding observed design storm. The projected climate model precipitation was applied to hydrologic models to determine projected stream flow characteristics and compared to current stream flow characteristics. The projected design flow and continuous stream flow hydrographs were routed through hydraulic models to determine usability and sustainability of current LWC structures and feasibility of alternative designs for projected flow regimes. The riverine crossing structures considered for this study are projected to see an increase in the magnitude and frequency of high flow events by the end of this century. The projected (2080-2099) 10-yr event is on the order of the present 50-yr event for many of the studied streams, suggesting possible future conditions should be considered when designing new infrastructure.