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Rain Water Harvesting Design Process
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Rain Water Harvesting Design Process
| S.No | Design Objective | Formula / Norm used |
| 1 | Formula for calculating Yearly Rainwater Runoff generated by a catchment (its RWH Potential) | Catchment Area X Runoff Coefficient X Average Yearly Rainfall |
| 2 | Formula for calculating average Hourly Rainwater Runoff generated by a catchment | Catchment Area (A) X Runoff Coefficient (R) X Average Hourly Rainfall |
| 3 | Runoff Coefficients for typical urban surfaces found in catchment areas | Green Areas – 0.2 |
| Paved Areas – 0.6 | ||
| Rooftop Areas – 0.8 | ||
| 4 | RWH structure capacity to be created for a catchment i.e. the Dimensions of the Rainwater Harvesting structure (in cu.m.) | = Hourly Rainwater Runoff retention capacity (in cu.m.). |
| Hence structure must be able to hold all the runoff generated by a catchment in an hour assuming average hourly rainfall. | ||
| 5 | Procedure for working out RWH Structure Dimensions | Structure(s) internal holding capacity + infiltration rate of the borewell > or = hourly runoff of catchment |
| i.e. = (Infiltration rate of borewell X no. of borewells) + Effective volume of Recharge trench | ||
| 6 | Infiltration rate of borewell | 40% of pumping yield of tube well in that area. |
| For pumping yield of tube well – reference is CGWB map for the area | ||
| 7 | Volume of filter media | Total 0.5 meter of filter media comprising of: |
| – 2 layers of 0.2 m each – pea gravel (0.1-5mm) and boulders (5-15cm) | ||
| 8 | Parameters for choice of site for RWH | Clear Space available – > 1.5 X trench size |
| Distance from nearest working borewell > 10m | ||
| Distance from nearest building foundation / basement – > 5 m |
About Rainwater Harvesting
Rainwater Harvesting merely means – ‘Catching and Storing Rain where it falls’.
Frequently Asked Questions
Some frequently asked questions on rain water harvesting
Per Capita Per Day Rainfall
Average rainfall per person per day – State-wise & District wise
Baseline of Water Conservation Assets
baseline to estimate the extent of rain water harvesting in your area…
Want to calculate how much water you saved by doing rainwater harvesting in your house / locality / institution?
Visit jalrakshak.org to calculate
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