Storm Drain Calculator
Calculate storm drain capacity and sizing requirements. Estimate drainage needs based on rainfall intensity, area coverage, and pipe specifications.
Step 1: Drainage Area Details
Understanding Runoff Coefficient
The runoff coefficient (C) represents the fraction of rainfall that becomes surface runoff. Values range from 0 (all water infiltrates) to 1 (all water runs off). Impervious surfaces have higher coefficients.
Step 2: Rainfall & Pipe Details
About Rainfall Intensity
Rainfall intensity is the rate at which rain falls, typically measured in inches or millimeters per hour. Higher intensities require larger drainage capacity. Check local rainfall data for design standards.
Drainage Calculation Results
Required Peak Flow Rate
Pipe Size Comparison
| Pipe Diameter | Flow Capacity | Required Slope | Status |
|---|
Flow Rate Breakdown
Rational Method Formula
Q = C × i × A
Where: Q = Peak discharge (flow rate), C = Runoff coefficient, i = Rainfall intensity, A = Drainage area. This is the standard Rational Method for estimating peak stormwater runoff.
Manning’s Equation for Pipe Flow
Q = (1.486/n) × A × R^(2/3) × S^(1/2)
Where: Q = Flow capacity, n = Manning’s roughness coefficient, A = Cross-sectional area, R = Hydraulic radius, S = Slope. Used to calculate pipe capacity.
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