California Code, Water Code - WAT § 8410

(a) Construction of structures in the designated floodway which may endanger life or significantly restrict the carrying capacity of the designated floodway shall be prohibited.  For the purpose of this subdivision, the word “structures” does not include public utility electric, gas, or communication lines which may be located within the designated floodway;  provided, that any permit or permits as may be required by law, other than this chapter, to so locate such lines have been granted.

(b) Developments shall be permitted within the restrictive zone in accordance with local agency policy, giving full consideration to the protection of human life and the carrying capacity of the flood plain.