Harbors and Navigation Code § 5881

All bonds issued under this part shall be payable substantially in the following manner:

A part to be determined by the board of supervisors, which shall be not less than one-fortieth part of the whole indebtedness, shall be paid each year on a date, and at a place to be fixed by the board of supervisors, and designated in the bonds, together with interest on all sums unpaid at that date.