A. The bonds of the district authorized to be issued at an election shall be designated as series bonds, and the series shall be numbered consecutively as authorized. All bonds of each series when issued shall be negotiable and of like force and effect. The bonds shall be payable in money of the United States and shall be due as follows:

1. 1. At the expiration of twenty-one years, not less than five per cent of the whole amount and number of bonds.
2. 2. At the expiration of twenty-two years, not less than six per cent of the whole amount and number of bonds.
3. 3. At the expiration of twenty-three years, not less than seven per cent of the whole amount and number of bonds.
4. 4. At the expiration of twenty-four years, not less than eight per cent of the whole amount and number of bonds.
5. 5. At the expiration of twenty-five years, not less than nine per cent of the whole amount and number of bonds.
6. 6. At the expiration of twenty-six years, not less than ten per cent of the whole amount and number of bonds.
7. 7. At the expiration of twenty-seven years, not less than eleven per cent of the whole amount and number of bonds.
8. 8. At the expiration of twenty-eight years, not less than thirteen per cent of the whole amount and number of bonds.
9. 9. At the expiration of twenty-nine years, not less than fifteen per cent of the whole amount and number of bonds.
10. 10. At the expiration of thirty years, not less than a percentage sufficient to pay the remainder of the bonds.