California Code, Public Contract Code - PCC § 20996

The governing body of the district may, upon receiving request therefor, cause to be designed and inserted in the specifications and contract for any flood control channel or storm drain, as to any portion thereof planned to be constructed under this act as an open channel, provision for the construction in conjunction therewith of facilities for the covering or crossing over of any such portion, or a part of such portion if, in the judgment of the governing body, such crossing or covering will not impair the usefulness of the flood control channel or storm drain and will not be otherwise adverse to the best interests of the district;  provided, however, that as to any such requested covering or crossing facilities the costs of design and construction are to be fully borne by the requesting party or parties.

The governing body of the district may expend funds of the district for the construction of facilities for the covering or crossing over of any portion of existing flood control channels or storm drains of the district whenever it determines such expenditures to be in the best interests of the district.  The district may also expend for such purpose any funds provided it by any local agency within the district for the construction of facilities for the covering or crossing over of any portion of existing flood control channels or storm drains of the district.