In the case of a grant under subdivision (b) of Section 12884.2 for the part of the construction cost of a dam and reservoir properly allocated to recreational functions of statewide interest and a grant under subdivision (a) of Section 12884.2 for the part of the construction cost of the proposed project properly allocated to the enhancement of fish and wildlife, the department may provide in the grant contract that the public agency shall deposit a portion of the grant into a special account or fund and shall use the money deposited, and its increments, solely for the construction of specified onshore recreation facilities until the construction cost of the facilities is paid. In acting under this section, the department may reserve for the construction of onshore recreation facilities only the portions of such grants which, in the department’s judgment, will not be needed for the payment of the construction cost of the dam and reservoir, in the case of a grant under subdivision (b) of Section 12884.2, or the construction cost of any project facilities other than the onshore recreation facilities, in the case of a grant under subdivision (a) of Section 12884.2.