Abstract
In February 2017, damage was discovered on Oroville Dam’s main spillway. This prompted officials to reduce the spillway flow to assess the damage. Eventually, this allowed the lake levels to rise and flow over the emergency spillway, where they discovered severe erosion on the dry side of the concrete weir. This erosion threatened to collapse the concrete weir, which would have sent a 9.1-meter (30-feet) tall wall of water into the Feather River, threatening downstream communities. Unfortunately, officials lacked an inundation model of the emergency spillway at the time of the event. Since officials only possessed an inundation model of a total collapse of the main dam, they ended up evacuating more people than necessary. This study aims to create a 2D HEC-RAS model of a breach of Oroville Dam’s Emergency Spillway using the conditions at the time of the February 2017 event. To create this model, a large variety of data was needed. Terrain/elevation data was obtained from the California Department of Water Resources(DWR) and the U.S. Geological Survey’s National Elevation Dataset. Land cover data was obtained from the Multi-Resolution Land Characteristics Consortium. Oroville Dam data was obtained from a DWR Technical Report. Flow data was obtained from the California Data Exchange Center website. All this data was used as inputs for the Hydrologic Engineering Center’s River Analysis System (HEC-RAS) version 5.0.5 to generate floodplain maps. These maps were then analyzed to create mortality and property damage maps. Upon reviewing the mortality and property damage maps, it was discovered that only a relatively small part of the study area would be significantly impacted by a breach of the emergency spillway. The affected area is Downtown Oroville. This area is less than 13.7 square kilometers (5.3 miles) in size. For any given location in the most severely affected area, a safe location could be reached in less than 2 miles. The breach flows take between 15 and 25 minutes to start flooding Oroville. This makes it difficult to evacuate without adequate preparation. Fortunately, Oroville Dam is heavily monitored. During the crisis, evacuation orders were given shortly after it was discovered that erosion on the emergency spillway was proceeding much faster than anticipated.