Scour Design Parameters: CONTRACTION_LIVE_BED
HEC-18/HEC-20 scour estimation parameters for bridge hydraulics — pier scour CSU equation K1-K4 correction factors, Laursen contraction scour exponents, and Froehlich abutment scour shape/skew factors
| scour type | factor name | condition | factor description | factor value | factor value numeric (dimensionless) | notes |
|---|---|---|---|---|---|---|
| CONTRACTION_LIVE_BED | K1_mode1 | Mostly bedload transport: V*/w < 0.5 (sand) | Live-bed velocity exponent k1 for Mode 1 transport | 0.59 | 0.59 | V*=shear velocity; w=fall velocity of D50; Mode 1 is predominantly bedload |
| CONTRACTION_LIVE_BED | K1_mode2 | Intermittent suspension: 0.5 <= V*/w <= 2.0 (sand-gravel) | Live-bed velocity exponent k1 for Mode 2 transport | 0.69 | 0.69 | Mode 2 transport is mixed bedload and suspension |
| CONTRACTION_LIVE_BED | K1_mode3 | Mostly suspended transport: V*/w > 2.0 | Live-bed velocity exponent k1 for Mode 3 transport | 0.78 | 0.78 | Mode 3 is predominantly suspended load |
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