Any municipal corporation intending to seek state participating funds shall, within thirty days after final adoption of its annual budget for flood control purposes, report the amount thereof, to the engineer of the county within whose boundaries the municipal corporation lies. The county engineer shall submit such reports, together with reports from the county itself, to the department of ecology. On the basis of all such budget reports received, the department may thereupon prepare a tentative and preliminary plan for the orderly and most beneficial allocation of funds from the flood control assistance account for the ensuing calendar year. Soil conservation districts shall be exempted from the provisions of this section.