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

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