Runoff For Phi Index For Practical Use Calculator

Formula Used:

\[ \text{Runoff in Cm from 24h Rainfall} = \text{Intensity of Rainfall} - (\Phi\text{-Index} \times 24) \] \[ R_{24h} = I - (\phi \times 24) \]

Runoff in Cm from 24h Rainfall (R_24h):

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1. What is the Runoff for Phi Index Formula?

The Runoff for Phi Index formula calculates the runoff in centimeters from a 24-hour rainfall event. It is based on the intensity of rainfall and the Φ-Index, which represents the constant infiltration capacity of the catchment area.

2. How Does the Calculator Work?

The calculator uses the formula:

\[ R_{24h} = I - (\phi \times 24) \]

Where:

\( R_{24h} \) — Runoff in Cm from 24h Rainfall (cm)
\( I \) — Intensity of Rainfall (cm/hr)
\( \phi \) — Φ-Index (cm/hr)

Explanation: The formula subtracts the total infiltration over 24 hours (Φ-Index multiplied by 24) from the total rainfall intensity to determine the runoff.

3. Importance of Runoff Calculation

Details: Accurate runoff calculation is crucial for water resource management, flood prediction, irrigation planning, and environmental impact assessments.

4. Using the Calculator

Tips: Enter the intensity of rainfall in cm/hr and the Φ-Index in cm/hr. Both values must be non-negative. The calculator will compute the runoff in centimeters for a 24-hour period.

5. Frequently Asked Questions (FAQ)

Q1: What is Φ-Index?
A: Φ-Index is the constant infiltration capacity of a catchment area that would yield the actual total runoff for a given rainfall amount.

Q2: How is intensity of rainfall measured?
A: Intensity of rainfall is typically measured using rain gauges and is expressed in centimeters per hour (cm/hr).

Q3: What factors affect runoff?
A: Runoff is affected by rainfall intensity, duration, soil type, land use, slope, and antecedent moisture conditions.

Q4: Can this formula be used for any duration?
A: This specific formula is designed for 24-hour rainfall events. For other durations, the formula would need to be adjusted accordingly.

Q5: What are typical values for Φ-Index?
A: Φ-Index values vary widely depending on soil type and land cover, ranging from 0.1 cm/hr for impervious surfaces to 2.5 cm/hr or more for highly permeable soils.