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Rainwater Harvesting Formula:
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The rainwater harvesting calculation formula estimates the volume of water that can be collected from a catchment area during rainfall. It considers the collection area, rainfall amount, and runoff coefficient to provide an accurate estimation of harvestable water.
The calculator uses the rainwater harvesting formula:
Where:
Explanation: The formula calculates the theoretical volume of rainwater that can be harvested from a given surface area, adjusted by the runoff coefficient that accounts for losses due to evaporation, absorption, and other factors.
Details: Accurate rainwater harvesting calculation is crucial for designing efficient water collection systems, determining storage tank sizes, and planning sustainable water management strategies for residential, agricultural, and commercial applications.
Tips: Enter catchment area in square meters, rainfall in millimeters, and runoff coefficient (typically 0.6-0.9 for roof surfaces, 0.1-0.3 for permeable surfaces). All values must be positive numbers.
Q1: What is a typical runoff coefficient value?
A: For impervious surfaces like roofs, coefficients range from 0.8-0.95. For lawns and permeable surfaces, values range from 0.05-0.35 depending on soil type and slope.
Q2: Why convert rainfall from mm to meters?
A: Since 1 mm rainfall = 1 liter per square meter, we convert to meters (divide by 1000) to get volume in cubic meters for consistency with area units.
Q3: How accurate is this calculation?
A: The calculation provides a theoretical maximum. Actual harvest depends on collection efficiency, first-flush diversion, and system losses.
Q4: Can this be used for large-scale planning?
A: Yes, the formula scales for any size area from small rooftops to large watershed catchment areas.
Q5: What factors affect the runoff coefficient?
A: Surface material, slope, rainfall intensity, antecedent moisture conditions, and surface roughness all influence the runoff coefficient value.