(a) The board or the department may modify the boundaries of any established maintenance area or zones within the maintenance area, the description of works to be maintained within the maintenance area, and the determination of relative benefits within any zone, upon its own initiative or upon petition by the governing body of the local agency formerly responsible for the operation and maintenance of the unit or by the board of supervisors of the county in which all or a portion of the unit is located.
(b) The board or the department may consolidate maintenance areas that share a common boundary.