Official plans shall become effective for a flood control district, and the district shall be deemed established when the board shall have completed suitable plans and adopted them as official plans and given the notice of such adoption provided for in section four of this act.
The board may proceed with the exercise of the powers granted by this act whenever an official plan has become effective, but no contract shall be let, agreement executed, or condemnation proceeding be begun requiring expenditures exceeding the amount of moneys appropriated for flood control projects and not already encumbered.
32 P.S. § 658