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Stormwater Runoff Volume Calculator

Stormwater Runoff Volume Calculator

Stormwater Runoff Volume Calculator

Calculate the total runoff volume using the NRCS (SCS) method.
First, determine the runoff depth using:
\[ S = \frac{25400}{CN} – 254 \quad \text{and} \quad Q = \begin{cases} 0, & P \le 0.2S \\ \frac{(P-0.2S)^2}{P+0.8S}, & P > 0.2S \end{cases} \] Then, convert runoff depth (mm) to volume (m³) over the drainage area.

* Enter rainfall depth (mm), curve number (CN), and drainage area (ha).

Step 1: Enter Data

Example: 50 mm

Typical values: 30–100

Example: 1 ha (1 ha = 10,000 m²)

Equations:
\( S = \frac{25400}{CN} – 254 \) (mm),
\( Q = \begin{cases} 0, & P \le 0.2S \\ \frac{(P-0.2S)^2}{P+0.8S}, & P > 0.2S \end{cases} \) (mm),
Runoff Volume \( V = \frac{Q}{1000} \times \text{Area (m}^2\text{)} \), where \( \text{Area (m}^2\text{)} = \text{Area (ha)} \times 10000 \).

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