Design Norms for Rain Water Harvesting
Generally accepted norms to design an effective Rainwater Harvesting system
Rain Water Harvesting Design Norms
| 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 |