Last Sunday afternoon an evacuation, the authorities issued orders to the people in Oroville California. In the aftermath of finding erosion in the secondary spillway of the Oroville Dam, about 188,000 people evacuated. The officials that watch and measure the depth of the Oroville Lake stated that the water levels had decreased that night when they allowed the lake to flow through the heavily damaged main spillway.

However, even with the spillway, cleared officials had no way to fix the erosion thanks to a low budget. Their first idea was to block the crevasse with rocks dropped by helicopters but no work was started after they saw how the lake flowed and realized that their resources were rather limited. Given that erosion is the constant grinding of water against stone, or in this case concrete, over time erosion will cause considerable damage. Depending on how advanced the stage of erosion is there might not be a way to fix the dam.

The dam is very important to the government’s run water delivery system; dam send water all over the central valley and Southern California. The emergency spillway was built to hold around 250,000 cubic feet of water entering per sec; yet by midday Sunday it was under 8,000 cubic feet. The main spillway’s erosion – thanks to the heavy rain the week before – caused large chucks of concrete to be thrown free from the dam, and created a hole that continued to grow from its 200-foot long and 30-foot deep start. Luckily, after some time the crumbling of the main spillway stopped and even though water was running through it the crumbling did not start again.