Quantifying the Impact of Rain-On-Snow Induced Flooding in the Western United States

Serious flooding can happen when rain falls on snow, which we call a rain-on-snow (ROS) event. Increasing our understanding of the behavior of floods resulting from ROS events can help us design better systems to manage flood water and prevent it from causing damage. This thesis explores how ROS events affect streamflow in the Western United States by examining the weather conditions that precede a streamflow surge. We classify stream surges as ROS or non-ROS induced based on these weather conditions, which helps us separate floods caused by ROS events from those caused by other factors. By comparing these different types of floods, we find that ROS induced floods are generally 3-20% larger than other floods. Engineers can use these findings and data to conservatively adjust drainage system designs, like culverts, to better handle the increased water flow during ROS events. This will reduce potential damage and make our road and building structures better able to handle extreme flooding.