In conformance with the duty prescribed in Section 12642, it shall be the responsibility and duty of local public agencies, now existing or hereafter formed, including counties and public districts, affected by the plan for flood control adopted and authorized in Section 12710, to give assurances satisfactory to the Secretary of the Army and the department that such local public agencies will maintain and operate said flood control works after their completion and hold and save the State and the United States free from damage due to the construction and operation of said works.