(a) Determination of rate. Under the Act the California Debris Commission will determine and prescribe with respect to each debris dam or other works the rate of tax payable in the area served by the particular debris dam or works. The Secretary of the Army will notify the Secretary of the Treasury of the rate of tax fixed with respect to each debris dam or works as such rate becomes known.

(b) Measure of tax. The tax is payable annually on the basis of the number of cubic yards mined from the natural bank by the hydraulic process during the taxable year.