All increased flowage resulting from operation of a plan shall be available for nonconsumptive use to all riparians. A person shall not utilize for waste assimilation, or divert from the stream, any surplus water created by release from dams operated under this part, except in accordance with the plan. The amount of surplus water released from any impoundment shall be determined by the department by the use of well-recognized engineering computations. The boards may charge users of the surplus water for waste assimilation or consumptive use, except those making an incidental, noncommercial, or recreational use, a reasonable fee or rate for the quantity of water or for the benefits they receive. Those users who contribute to the construction, maintenance, or operation of the dams may be charged a reduced fee or no fee, but the fees and rates charged by the boards shall be sufficient at all times to defray all costs, expenses, and other financial burdens assumed by the boards in the construction, maintenance, and operation of the dams.