An acre foot is about 326,000 gallons. There are also many small reservoirs that trivially influence the flood control management, but are still able to hold water. Other parts of the water control system include Northern California's six thousand miles of levees owned by the Bureau of Reclamation. Problems arise in Northern California despite careful management of reservoirs. For instance, due to miscalculations of rainfall amount and storage capacity levels, the reservoirs may become too full and some water needs a place to go.
Dams can release a greater or lesser amount of water through different gates located on the dam.
In extreme situations there are usually emergency gates that can be opened to release a larger amounts of water. In the recent floods an emergency gate at Folsom Dam was opened because of a gate that had broken in the summer of 1996. Operators were surprised that they had to use the gate, because in the models of flood control the gate in theory should never have to be used. As the water travels from the dam, it enters a system of rivers and canals. Levees help to keep the river in its path.