Curve Number Calculator

Curve Number Formula:

\[ CN = \frac{25400}{S_{CN} + 254} \]

Curve Number (CN):

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1. What is the Curve Number Formula?

The Curve Number (CN) is a hydrologic parameter used to predict direct runoff or infiltration from rainfall excess. It is based on the area's hydrologic soil group, land use, treatment and hydrologic condition.

2. How Does the Calculator Work?

The calculator uses the Curve Number formula:

\[ CN = \frac{25400}{S_{CN} + 254} \]

Where:

\( CN \) — Curve Number
\( S_{CN} \) — Potential Maximum Retention (Curve Number) in Millimeter

Explanation: The formula calculates the Curve Number based on the potential maximum retention parameter, which depends upon the soil vegetation land use complex of the catchment and also upon the antecedent soil moisture condition.

3. Importance of Curve Number Calculation

Details: Accurate Curve Number estimation is crucial for hydrologic modeling, predicting runoff volumes, designing drainage systems, and managing water resources in watersheds.

4. Using the Calculator

Tips: Enter the Potential Maximum Retention value in millimeters. The value must be valid (greater than 0).

5. Frequently Asked Questions (FAQ)

Q1: What factors influence the Curve Number?
A: Curve Number is based on the area's hydrologic soil group, land use, treatment and hydrologic condition of the catchment.

Q2: What are typical Curve Number values?
A: Curve Number values typically range from 30 to 100, with lower values indicating more permeable surfaces and higher values indicating more impervious surfaces.

Q3: How does antecedent moisture condition affect Curve Number?
A: Antecedent moisture condition significantly affects the Curve Number, with wetter conditions resulting in higher Curve Numbers and greater runoff potential.

Q4: What are the limitations of the Curve Number method?
A: The method assumes uniform rainfall distribution and may not accurately represent complex watersheds with heterogeneous land use patterns.

Q5: How is Curve Number used in practice?
A: Curve Number is widely used in the Soil Conservation Service (SCS) method for estimating runoff from rainfall in agricultural, urban, and forested watersheds.