Cal. Wat. Code § 12639
The works of improvement for the control, conservation and utilization of destructive flood waters and the reclamation and protection of lands that are susceptible to overflow by flood waters, which are described in this chapter, are adopted and authorized in the interest of the public welfare of the people of this State to be prosecuted substantially in accordance with the plans in the respective reports designated in this chapter.
If, however, there are any major project changes in the plan of improvement originally approved by the Congress and adopted and authorized by the State, which changes result in a substantial increase in the estimated cost of lands, easements and rights-of-way for the project, no money shall be reallocated by the State in aid of that portion of the project until the revised plan has been reviewed and approved by the department. Such approval shall be given if the department finds in its judgment that the benefits of the proposed works of improvement for the revised project will exceed the cost thereof and that the revised project appears to be the most economical project plan, considering construction costs, lands, easements and rights-of-way costs, and costs of operation and maintenance.
Ca. Water Code § 12639