What This Solves
Designs stilling basins and impact basins to dissipate kinetic energy at culvert or pipe outlets, preventing downstream erosion.
Best Used When
- Outlet velocities exceed permissible limits for the downstream channel material
- You need to design a USBR-type stilling basin or FHWA impact basin
- You want to calculate the required basin dimensions and tailwater depth for a hydraulic jump
Do NOT Use When
- A simple riprap apron is sufficient for energy dissipation — Use Outlet Protection Calculator
- You only need to calculate the outlet velocity, not design a dissipation structure — Use Outlet Velocity Calculator
Key Assumptions
- Hydraulic jump forms within the basin at the calculated sequent depth
- Tailwater depth is sufficient to confine the jump within the basin
- Basin dimensions follow USBR or FHWA HEC-14 standard proportions
- Approach flow is fully developed and approximately uniform
- No significant debris or sediment loading that would reduce basin effectiveness
Input Quality Notes
Tailwater depth is critical for proper jump formation. Use downstream channel analysis or field data to estimate tailwater. If tailwater is too low, the jump will sweep out of the basin.
USBR Stilling Basin Selection
| Type | Froude | L/y2 |
|---|---|---|
| Type I | < 2.5 | 4 |
| Type II | > 4.5 (high V) | 4.3 |
| Type III | 4.5 - 17 | 2.8 |
| Type IV | 2.5 - 4.5 | 6 |
Type VI Impact Basin Limits
Maximum Discharge 400 cfs
Maximum Velocity 50 ft/s
Length/Width Ratio 1.33
Depth/Width Ratio 0.5
Impact basins are effective for small discharges and high velocities where space is limited.
Ready to Design
Select a dissipator type and enter flow parameters to design the basin.
For educational purposes only. Not a substitute for professional engineering judgment.
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Last verified: February 2026