What This Solves
Evaluates channel lining adequacy by comparing applied shear stress against permissible shear for grass, riprap, concrete, and other lining materials.
Best Used When
- You need to select an appropriate channel lining to prevent erosion at the design flow velocity
- You are checking whether an existing grass-lined or riprap-lined channel is stable under design conditions
- You want to compare permissible velocity or tractive force for different lining materials
Do NOT Use When
- You need to size riprap stone specifically using Isbash, USACE, or Maynord methods — Use Riprap Sizing Calculator
- You need to calculate flow capacity rather than lining stability — Use Manning's Channel Calculator
Key Assumptions
- Applied shear stress is calculated from channel geometry and flow depth (τ = γRS)
- Permissible shear values are from FHWA HEC-15 or equivalent design guides
- Channel geometry is uniform at the cross-section being analyzed
- Vegetation is fully established (for grass-lined channels)
- No significant wave action or turbulence beyond uniform flow conditions
Input Quality Notes
Permissible shear for grass varies significantly with grass species, density, and establishment. Use lower values for new plantings. Riprap permissible shear depends on stone quality and gradation.
Lining Properties
| Lining Type | n | Vmax (fps) | taumax (psf) |
|---|---|---|---|
| Bare Soil | 0.025 | 2 | 0.02 |
| Grass | 0.05 | 4 | 1 |
| Riprap | 0.04 | 14 | 4 |
| Gabion | 0.028 | 15 | 5 |
| Concrete | 0.015 | 20 | 10 |
Grass Retardance Classes (HEC-15)
| Class | Height | Condition |
|---|---|---|
| A | > 30 inches | Excellent stand, tall vegetation |
| B | 11-24 inches | Good stand, tall vegetation |
| C | 6-10 inches | Good stand, moderate length |
| D | 2-6 inches | Good stand, short |
| E | < 2 inches | Good stand, burned or very short |
Ready to Calculate
Select lining type and enter channel parameters to check adequacy.
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Last verified: February 2026