The Oroville Dam 2017 - Spillway Incident. Possible Causes and Solutions

The subject of this thesis is the 2017 Oroville Dam spillway incident. This event is yet another example of the severe problems the United States has with maintaining its large infrastructure. However, in order to better understand how events unfolded, it is first necessary to conduct a detailed analysis of Oroville Dam and the basic elements of its location, the Feather River Basin. An assessment of the hydroclimatic characteristics of the area reveals it to have a Mediterranean climate, indicated by heavy precipitation during the winter months, producing floods during the spring, followed by almost completely dry summers. From a geological standpoint, the area near Oroville Dam contains metavolcanic rock, which is of adequate hardness, but it is also significantly weathered, especially near the ground surface. This thesis also contains a summary of various Oroville Dam design elements, as well as a full history of its construction. This analysis reveals hidden clues that help identify the causes of the 2017 incident. Most significantly, design criteria for the main and emergency spillways appear much more relaxed than those of the main structure. Next, a study of the previous significant floods that occurred at Oroville Dam is conducted. This reveals that reservoir levels were much higher during the 2017 incident compared to other events, which indicates a need to lower the minimum flood control elevation. Futhermore, this thesis includes an extensive timeline of the 2017 incident events, including the damages to Oroville Dam’s main spillway chute and area downstream of the emergency spillway. After further research, initial cause of the main spillway failure is defined as concrete chute floor slab uplift, caused due to faults in the drain system below it. In addition, perusal of previous official inspection reports reveals that under current practice standards, if a comparable incident occurs again, its indications are unlikely to be detected in time. Finally, recommendations are made in order to avoid similar events from happening in the future. For Oroville Dam, this means lowering the minimum flood control elevation level and creating a fully armored concrete emergency spillway. In the short term, informal inspections by the authorities that operate large structures in the United States can discover faults before they turn into accidents. However, a more long-term plan to effectively repair and maintain the country’s existing infrastructure needs to be put into action immediately.