Calculator
Example data table
| Scenario | Area (m²) | Slope (%) | Length (m) | Soil | Cover | Practice | Est. Soil Loss (t/ha/yr) | Risk |
|---|---|---|---|---|---|---|---|---|
| Small grading pad | 1,200 | 5 | 20 | Loam | Mulch | Contour Grading | ~4–8 | Low–Moderate |
| Long exposed slope | 6,000 | 12 | 45 | Silt Loam | Rough-Graded Site | None | ~15–35 | High |
| Stabilized embankment | 8,500 | 18 | 35 | Clay Loam | Erosion Control Blanket | Diversion Swales | ~6–14 | Moderate |
Formula used
Soil loss is estimated with the Universal Soil Loss Equation: A = R × K × LS × C × P
- A = average annual soil loss (tons/acre/year).
- R = rainfall erosivity factor (estimated or entered).
- K = soil erodibility factor (from soil selection).
- LS = slope length and steepness factor (from slope inputs).
- C = cover management factor (from cover selection).
- P = support practice factor (from practice selection).
Peak runoff uses the rational method: Q = Crunoff × i × A where intensity i is converted to m/s and area A is m².
How to use this calculator
- Enter the disturbed site area and choose the correct unit.
- Measure slope percent and the flow-path length before a break.
- Select soil, cover, and practice options closest to field conditions.
- Choose an R method: estimate from annual rainfall or enter R directly.
- Set storm intensity and runoff surface to estimate peak runoff.
- Click Calculate and review risk, runoff, and suggested controls.
- Download CSV/PDF for planning notes, permits, or site reports.
Professional guide to erosion control planning
1) Why erosion control protects schedule and cost
Freshly graded soil can lose sediment in the first storm. Even 1,000–3,000 m² of exposed ground can clog inlets, stain pavements, and trigger rework. A quick estimate helps crews prioritize stabilization while equipment is already on site and access is easiest. This supports permits, budgets, and cleaner downstream drains.
2) Interpreting the USLE factors
The soil-loss model uses A = R×K×LS×C×P. K reflects erodibility (many silt-rich soils behave higher than sands). C represents cover protection; mulch and blankets can cut erosion dramatically. P reflects practices like contouring or terracing that interrupt flow paths.
3) Slope percent and length drive LS
LS increases with steepness and uninterrupted slope length. Moving from 5% to 15% grade can multiply predicted loss, especially when flow paths exceed 30–50 m. Breaking slopes with benches, diversion swales, or grade changes is often the fastest way to reduce LS.
4) Cover options and expected reductions
Cover is usually the biggest lever. Rough grading alone may reduce losses versus bare soil, but mulch typically performs near the 10% range when applied uniformly. Erosion control blankets and matting can approach 5% when edges are trenched, overlapped, and pinned correctly.
5) Practices that reduce P efficiently
Contour grading commonly lowers P in planning screens, while terracing or benching can reduce it further on long slopes. Diversion swales route runoff to stable outlets. Check dams can slow temporary channels and trap coarse material, but they still need maintenance and outlet protection.
6) Peak runoff for inlet and channel checks
Peak runoff uses Q = Crunoff·i·A. Intensities of 25–75 mm/hr are often used for sizing checks, and disturbed subgrade typically has higher runoff response than vegetated ground. A safety factor around 1.1–1.3 helps account for changing drainage during earthworks.
7) Converting risk into sediment storage planning
USLE is annualized, so short-term containment still matters. A simple storage screen can scale with risk: start near 0.5% of disturbed area for low risk, 1% for moderate, 2% for high, and 3% for very high conditions. Confirm local standards before finalizing.
8) Field verification and maintenance cadence
Use outputs to plan inspections, not replace them. Walk flow paths after rainfall, verify fences are on contour, and stabilize outlets. Many crews clean traps when they are about half full to preserve capacity. Document dates, photos, and corrective actions for compliance.
FAQs
1) Is this calculator intended for final design?
No. It is a planning and screening tool for comparing options quickly. Final designs should follow local regulations, project drawings, and qualified engineering judgment for drainage, basin sizing, and stabilized outlets.
2) What rainfall input should I use for intensity?
Use a storm intensity that matches your local design check, such as a short-duration event used for inlet protection. If you are unsure, test several values (for example 25, 50, and 75 mm/hr) to see sensitivity.
3) Why does slope length matter so much?
Longer flow paths allow runoff to concentrate and gain energy, which increases rilling and sediment transport. Adding grade breaks, benches, or diversions shortens the effective length and can reduce predicted soil loss significantly.
4) How do I choose soil type if I have mixed soils?
Select the most erosion-prone soil present on the disturbed area, or run separate scenarios for each soil zone. Using the higher K option is conservative for planning controls and inspection frequency.
5) What does the risk level mean in practice?
Risk bands summarize the soil-loss rate in t/ha/yr. Higher risk suggests faster stabilization, stronger perimeter controls, and larger sediment storage. Use the band to prioritize phasing, not to replace permit criteria.
6) When should I use a custom runoff coefficient?
Use custom C when you have site data, local guidance, or measured behavior that differs from the preset surfaces. Keep values within realistic ranges (roughly 0.05–0.99) and document why you selected them.
7) Can I use this for sediment basin volume directly?
The storage volume is a planning estimate that scales with risk and area. Basin sizing should also consider drainage area, drawdown time, outlet control, and local requirements. Treat the value as a starting point for layout discussions.