S.D. Codified Laws § 1-16B-30
The maximum annual debt service shall be the capital reserve requirement. For purposes of computing the capital reserve requirement, the annual debt service for any fiscal year shall be equal to the sum of all interest payable during the fiscal year on all bonds outstanding on the date of computation, plus the principal amount of all bonds and notes outstanding on that date which mature during the fiscal year, all calculated on the assumption that bonds and notes will after that date cease to be outstanding. The moneys in the capital reserve fund may not be less than the capital reserve requirement, except when withdrawals are made for payments of principal, interest and redemption premiums may be made from the capital reserve fund if other moneys of the authority are not available.
SDCL 1-16B-30