Oroville Dam, just east of the town of Oroville in California’s Central Valley, is one of the largest reservoirs in the world. It allocates the Feather River for use in California’s massive statewide water system. Like most dams, it had seen its share of minor structural issues after being completed in 1968—but the spillway failure of February 2017 was completely different. On February 7, 2017, heavy rainfall from a series of storms necessitated the release of 50,000 cubic feet of water per second from Oroville Dam. This flow rate caused substantial damage to the main spillway. Then, on February 11, water started to flow down the emergency spillway—sparking concern and prompting the evacuation of adjacent communities in risk-prone areas the following day. The imagery below shows Oroville Dam before and after the emergency spillway was used. Oroville Dam before and after Using AnswerFactory powered by GBDX, water (and thus water change) can be automatically extracted from DigitalGlobe imagery with Protogen. The extracted data is then outputted as vectors that can be further analyzed or implemented into other GIS operations, providing additional resources for informed decision making on the ground. Image on left captured February 25, 2013; image on right captured August 23, 2016 While the overflow of Oroville Dam may not have been predictable, the general monitoring of Oroville Lake (and, for that matter, every lake and reservoir globally) can provide situational awareness and indications of change. After all, change is the outcome of time. Imagery from USGS/Landsat-8 With Landsat 8 imagery over Oroville Lake taken from 2013 through 2016, ENVI-based water extractions can be easily executed using AnswerFactory to produce vectors that represent water—allowing area measurements to be derived. The area of a vector representing extracted water cannot accurately translate into surface area, and certainly not into lake-wide water volume. It can however, help distinguish water change and present an overall trend in water levels. Water Vector AreaReservoir Capacity California’s Department of Water Resources has made historic and real-time water data on reservoirs—including water levels at Oroville Lake—publicly available. This is the source of the reservoir capacity data in the graph on the right. Although absolute water levels cannot be derived from this current vector extraction method, the similar trends in both vector area and reservoir capacity suggest information can be gathered and monitoring can be achieved—helping state and local governments anticipate and react to events like those at Oroville Dam in February 2017. Want to learn more about AnswerFactory? Click here.
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