Cal. Sts. & Hy. Code § 2808.7
This division does not apply to proceedings commenced before or after January 1, 1985, for the construction or acquisition, or both, of flood control and drainage works, including the acquisition of rights-of-way and easements necessary in connection with those improvements, if the chief engineer of a city, county, or flood control district exercising flood control powers over the majority of the area to be protected by the proposed flood control or drainage works finds the works to be necessary to protect life and property from injury and damage from flooding as a result of a 100-year design storm and that finding is made in writing and spread upon the minutes of the legislative body conducting the proceedings, and if that necessity is also found to exist by resolution adopted by the affirmative vote of four-fifths of the members thereof. The finding made by the legislative body pursuant to this section shall be final and conclusive upon all persons in the absence of actual fraud.
Ca. Sts. and High. Code § 2808.7