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Drainage Flow Rate Formula:
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The Drainage Calculation Formula (Q = C × I × A) calculates the drainage flow rate from a catchment area. It's a fundamental equation in hydrology and civil engineering used for designing drainage systems, stormwater management, and flood control.
The calculator uses the drainage flow rate formula:
Where:
Explanation: The formula calculates the peak rate of runoff from a drainage area by multiplying the runoff coefficient (which represents the fraction of rainfall that becomes surface runoff), rainfall intensity, and the catchment area.
Details: Accurate drainage calculations are essential for designing effective stormwater management systems, preventing flooding, sizing drainage pipes and channels, and ensuring proper infrastructure design for urban and rural areas.
Tips: Enter the runoff coefficient (typically between 0-1), rainfall intensity in meters per second, and catchment area in square meters. All values must be positive numbers.
Q1: What is a typical range for runoff coefficient (C)?
A: Runoff coefficients typically range from 0.05-0.95, with higher values for impervious surfaces like concrete (0.8-0.95) and lower values for permeable surfaces like forested areas (0.05-0.20).
Q2: How is rainfall intensity typically measured?
A: Rainfall intensity is usually measured in mm/hour but must be converted to m/s for this calculation (1 mm/hr = 2.77778×10⁻⁷ m/s).
Q3: What factors affect the runoff coefficient?
A: Surface type, slope, soil type, vegetation cover, antecedent moisture conditions, and rainfall duration all influence the runoff coefficient value.
Q4: When is this formula most applicable?
A: This rational formula is most appropriate for small drainage areas (typically less than 80 hectares) with relatively uniform characteristics.
Q5: Are there limitations to this formula?
A: Yes, it assumes uniform rainfall distribution, steady rainfall intensity, and doesn't account for storage effects or infiltration rates changing during a storm event.