California's damming of the Sierras and construction of the aquifers were primarily about flood control. Supporting the growing population came secondary (that's the easy part). An enormous effort was put into diverting melting snowpack into mountain valleys. This essentially created the northern and middle parts of the Central Valley, on top of creating sustainable year-round sources of fresh water for the developing coastal cities.
Downstream destruction is of concern because that entire region depends on flood control. The habitability and agricultural production of the corridor between Oroville and Sacramento relies upon, and was created by, the flood control of Plumas, Yolo, Butte, etc counties. There are a number of canals, diversions, and reservoirs both above and below the Oroville to further control flow the dam as it reaches our rivers. However, most of the re-routing is also man-made and thus untested for such an event.
Downstream destruction is of concern because that entire region depends on flood control. The habitability and agricultural production of the corridor between Oroville and Sacramento relies upon, and was created by, the flood control of Plumas, Yolo, Butte, etc counties. There are a number of canals, diversions, and reservoirs both above and below the Oroville to further control flow the dam as it reaches our rivers. However, most of the re-routing is also man-made and thus untested for such an event.