Over the past few days a crisis has played out surrounding the Oroville Dam in California.
It started with a hole developing in the dam spillway (1). In response, the California Department of Water Resources closed the spillway on February 7. But due to high rainfall, the water levels in the dam kept rising until they eventually overflowed the emergency spillway (2). However, it soon became apparent that the water was eroding the soil at the base of the emergency spillway and there was concern that it might collapse. This resulted in an evacuation order on February 12th, affecting around 188,000 people who live in the danger zone downstream of the dam. At some point the main spillway was reopened and by February 14th the water levels were low enough that officials lifted the evacuation order.
There is an animation here showing the areas that would have been flooded if the emergency spillway had failed.
Google has recently released recent imagery of the area from DigitalGlobe’s ‘FirstLook’ program captured on February 13th.
Oroville Dam, February 13th, 2017. Image credit: DigitalGlobe.
The image quality is poor but we can see some erosion below the emergency spill way. The image was captured after the water levels has subsided somewhat and the water was no-longer flowing over the emergency spill way. We can also see where the hole in the main spillway causes the water to turn white and spill out of the spillway.
A close up of the dam as seen in Google Earth’s 3D imagery. Bottom left: Emergency spillway. Centre: Main spillway. Top right: Main dam wall.