The Oroville Dam is located on the Feather River in Northern California, east of the city of Oroville. The dam is an earth-filled embankment design and was built between 1961 and 1968. The dam is built on the geological terrain called Smartville Ophiolite Complex. It is described as steeply dipping and strongly foliated meta-basalt, meta-diabase, and meta-sediments; it has some sheeted dices, and the entire area is strongly foliated. The construction is 770 feet high, 44 feet taller than the Hoover Dam, making it the highest dam in the U.S. The main spillway is concrete-covered; the emergency spillway is a 30- foot concrete weir. When it is overtopped by water, water flows over unconsolidated sediment and soil. The emergency spillway was designed to have a water capacity of 450,000 cubic feet per second.
The failure occurred on February 7, 2017, when a large sinkhole developed in the main spillway. Water released from the lake through the spillway was halted to assess the damage, which caused the quick rise of Lake Oroville water levels. On February 11, an emergency spillway was used for the first time in the dam’s history. The next day, headwater erosion threatened to undercut the concrete weir, which could result in complete dam failure, causing the entire lake to drain into the valley downstream. Ultimately, the main spillway increased water release to 100,000 cubic feet per second to limit the damage to the emergency spillway; many residents were evacuated. As a result, the valley was flooded, but on February 14, the Lake Oroville water level dropped.
Failure predictors date back to 2002 when the Yuba County Water Agency concluded if the emergency spillway were used, extensive erosion would take place. Additionally, during 2005 relicensing, environmental groups concluded it was necessary to armor or otherwise reconstruct the ungated spillway. Contrary to the design of the emergency spillway, significant erosion occurred with only 12,600 cubic feet per second of water flow, which identifies significant design flaws. Thus, the main reasons for the failure were structural weaknesses, geological features of the location, as well, as operational and management conditions (Koskinas et al. 15). To prevent failure, it was necessary to conduct more frequent inspections of the state of the dam, as well as carry out repairs and structural changes in accordance with the comments. In particular, the development of the spillway had to take into account geological conditions, which could be taken into account during early inspections.
Work Cited
Koskinas, Aristotelis, et al. “Insights into the Oroville Dam 2017 Spillway Incident.” Geosciences, vol. 9, no. 1, 2019, pp. 1-24.