California Code, Water Code - WAT § 8609

(a) The board may designate floodways throughout the Sacramento and San Joaquin Rivers drainage to control encroachments in, and to preserve the flow regimens of, floodways for the purpose of protecting public improvements, lives, land use values, and improvements created in reliance upon historical flooding patterns.

(b) As used in this part, “Sacramento and San Joaquin Rivers drainage,” or equivalent language, means all lands currently and historically drained by the Sacramento River and the San Joaquin River and their tributaries and distributaries.

(c) This section is declaratory of existing law.