Hydraulics & drainage · Flooding & scour
Pier scour (CSU / HEC-18) calculator
Local scour depth ys = 2.0 K1 K2 K3 a (y1/a)^0.35 Fr^0.43.
Standard: FHWA HEC-18 CSU equation
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Inputs in the worked example
The live calculator starts with these values; change any of them and every result, check and diagram updates instantly.
| Input | Value | Unit |
|---|---|---|
| Pier width | 1.2 | m |
| Approach flow depth | 3.5 | m |
| Approach velocity | 2.2 | m/s |
| Nose shape K1 | 1.0 round / circular | |
| Angle of attack K2 | 1 | |
| Bed condition K3 | 1.1 | |
| Foundation depth below bed | 5 | m |
Worked example — results
| Result | Value | Unit |
|---|---|---|
| Froude V/√(g y1) | 0.375 | |
| Scour depth | 2.52 | m |
| Cap 2.4a (Fr ≤ 0.8) | 2.88 | m |
| Design scour | 2.52 | m |
- ✓ Foundation below scour
Method, formulas and assumptions
- Froude V/√(g y1) = 2.2/SQRT(9.81*3.5) = 0.37545
- Scour depth = 2*1*1*1.1*1.2*(3.5/1.2)^0.35*0.37545^0.43 = 2.5198 m
- Cap 2.4a (Fr ≤ 0.8) = IF(0.37545<=0.8,2.4,3)*1.2 = 2.88 m
- Design scour = MIN(2.5198,2.88) = 2.5198 m
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For preliminary design and education. Check every result against the current standard and your own engineering judgement before use.