The Legislature intends that from time to time by law allocations from the General Fund for flood control projects will be made to pay for the cost of all lands, easements, and rights-of-way necessary for the construction of flood control projects adopted and authorized by the Legislature prior to March 12, 1946, and also those adopted and authorized on or after that date by the Congress of the United States, recommended by the department, and approved by the Legislature, in the order in which the Congress makes available funds for their construction.