Sec. 31516.

(1) Spillway capacity shall meet the following minimum criteria:

(a) Low hazard potential dams shall be capable of passing the 100-year flood, or the flood of record, whichever is greater.

(b) Significant hazard potential dams shall be capable of passing the 200-year flood, or the flood of record, whichever is greater.

(c) High hazard potential dams, less than 40 feet in height, as measured from the 200-year design flood elevation to the lowest downstream toe elevation, shall be capable of passing the 200-year flood, or the flood of record, whichever is greater.

(d) High hazard potential dams, 40 feet or greater in height, as measured from the 200-year design flood elevation to the lowest downstream toe elevation, shall be capable of passing the half probable maximum flood. The half probable maximum flood criterion may be reduced to not less than the 200-year flood, with proper documentation evidencing a failure of a dam under half probable maximum flood conditions will not cause additional flood damage or loss of life.

(e) Spillway design capacity shall not be less than the flood of record.

(2) Freeboard shall be considered when determining spillway capacity.

(3) If a dam cannot pass the design flood, an auxiliary spillway must be provided. The owner must document, to the satisfaction of the department, that the dam has sufficient spillway capacity, and that proper means are available to operate the spillway or spillways during the design flood.

History: Add. 1995, Act 59, Imd. Eff. May 24, 1995 Popular Name: Act 451Popular Name: NREPA