Cal. WAT § 128

(a) In times of extraordinary stress and of disaster, resulting from storms and floods, or where damage to watershed lands by forest fires has created an imminent threat of floods and damage by water, mud, or debris upon the occurrence of storms, the department may perform any work required or take any remedial measures necessary to avert, alleviate, repair, or restore damage or destruction to property having a general public and state interest and to protect the health, safety, convenience, and welfare of the general public of the state. In carrying out that work, the department may perform the work itself or through or in cooperation with any other state department or agency, the federal government, or any political subdivision, city, or district.

(b) This section is intended to supplement the emergency services of the state, and nothing in this section overrides or supersedes the authority of the Director of Emergency Services to coordinate and supervise state action, upon a declaration of a state of emergency, under the California Emergency Services Act (Chapter 7 (commencing with Section 8550) of Division 1 of Title 2 of the Government Code) or the Disaster Assistance Act (Chapter 7.5 (commencing with Section 8680) of that division).