(1) The board of supervisors of a drainage district lying west of the Cascade Mountains, whether or not organized under the Drainage District Act:
(a) Shall supervise and control flood control projects within the boundaries of their districts.
(b) May prescribe the width, grade and other specifications of flood control projects, drainage works or irrigation works described in this subsection.
(2) The board may construct and maintain flood control projects within the boundaries of their districts.