1. What is the Rational Method Rainfall Intensity Formula?

The Rational Method rainfall intensity formula calculates the rainfall intensity (I) based on storm duration and empirical constants. It's commonly used in hydrology and civil engineering for drainage design and flood estimation.

2. How Does the Calculator Work?

The calculator uses the Rational Method formula:

Where:

• \( I \) — Rainfall intensity
• \( a \) — Empirical constant
• \( t \) — Storm duration in minutes
• \( b \) — Empirical constant
• \( c \) — Empirical constant

Explanation: The formula models how rainfall intensity decreases with increasing storm duration, with the constants a, b, and c being region-specific parameters.

3. Importance of Rainfall Intensity Calculation

Details: Accurate rainfall intensity estimation is crucial for designing drainage systems, culverts, and other hydraulic structures to handle expected stormwater flows.

4. Using the Calculator

Tips: Enter the empirical constants (a, b, c) and storm duration (t) in minutes. All values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: Where do I get the constants a, b, and c?
A: These are typically determined from local rainfall data and can be found in regional hydrology manuals or from meteorological agencies.

Q2: What are typical values for these constants?
A: Values vary by region, but common ranges are: a (20-100), b (5-30), c (0.5-1.5).

Q3: What units does this formula use?
A: The units depend on the constants used. Typically intensity is in mm/hr or in/hr, with duration in minutes.

Q4: What's the time range this formula is valid for?
A: Typically valid for storm durations between 5 minutes to 24 hours, but this depends on the data used to derive the constants.

Q5: Are there limitations to this formula?
A: It's empirical so only accurate for the region it was developed for. It doesn't account for rainfall variability within a storm.