15 CAR § 23-505 – Spillway design flood (SDF) for dams

(a) The size and hazard classifications are combined to determine the hydrologic criteria for dams.
(b) The minimum acceptable spillway design floods (SDFs) for dams are shown in Table 3.

(c) The minimum hydrologic criteria may be reduced if properly prepared dam breach analyses show that dam failure during the SDF would cause an increase in flood level of one foot (1’) or less at, and downstream of, the first:

(1) Habitable structure; or

(2) Financially significant development.

Table 3Spillway Design Flood for Dams
Hazard Classification	Size	Spillway Design Flood
Low	Small	.25 PMF
Intermediate	.25 to .50 PMF
*Large	.50 to .75 PMF
Significant	Small	.25 to .50 PMF
Intermediate	.50 to PMF
Large	PMF
High	Small	.50 PMF to PMF
Intermediate	PMF
Large	PMF
Note: Where ranges are given in this table, the spillway design flood shall be determined by straight line interpolation, based upon the effective height of dam or maximum storage, whichever computed SDF is greater.*SDF shall be extrapolated at the same rate of change as an intermediate size dam to a maximum of .75 PMF.