How is the spillway design flood determined for dam safety?

Spillway Design Flood (SDF) determination: (1) Dam hazard classification based on downstream consequences (high, significant, low), (2) Select design standard - high hazard typically uses PMF (Probable Maximum Flood = runoff from PMP), lower hazard may use percentage of PMF or frequency-based flood (1:10,000), (3) Develop design hydrograph using PMP temporal distribution and unit hydrograph or distributed model, (4) Route through reservoir to get peak outflow and maximum water level, (5) Add freeboard for wind/wave setup. Incremental damage analysis may justify reduced standards where no incremental damage from dam failure.