1. What is the Rational Method Rainfall Intensity Equation?

The Rational Method Rainfall Intensity Equation calculates the average rainfall intensity (I) by dividing the total rainfall depth (P) by the duration of the rainfall (t). This is a fundamental equation in hydrology for determining rainfall rates.

2. How Does the Calculator Work?

The calculator uses the Rational Method equation:

Where:

• \( I \) — Rainfall intensity (in/hr)
• \( P \) — Total rainfall depth (in)
• \( t \) — Duration of rainfall (hr)

Explanation: The equation provides the average intensity of rainfall over a given duration, which is crucial for hydrologic calculations and design of drainage systems.

3. Importance of Rainfall Intensity Calculation

Details: Rainfall intensity is a key parameter in hydrologic analysis, used for designing stormwater management systems, calculating peak runoff rates, and assessing flood risks.

4. Using the Calculator

Tips: Enter rainfall depth in inches and duration in hours. Both values must be positive numbers. The calculator will compute the average rainfall intensity in inches per hour.

5. Frequently Asked Questions (FAQ)

Q1: What units should I use for this calculation?
A: The calculator uses inches for rainfall depth and hours for duration, resulting in intensity in inches per hour (in/hr).

Q2: How accurate is this simple equation?
A: While simple, it provides the average intensity. For more complex analysis, time-varying intensity methods may be needed.

Q3: What's a typical rainfall intensity value?
A: Varies by location and storm duration. Short-duration storms may have intensities of 1-10 in/hr, while longer storms are typically less intense.

Q4: Can I use metric units?
A: The calculator uses imperial units. For metric, convert mm to inches (1 inch = 25.4 mm) before calculation.

Q5: How does this relate to the Rational Method for runoff?
A: This intensity calculation is often used as input to the Rational Method formula Q = CIA for peak runoff rate estimation.