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Updated: Aug 27

There are various methods of rainwater harvesting, each designed to suit different needs, space constraints, and local conditions. Here are some common methods of rainwater harvesting:

Some common methods of rainwater harvesting:

Combining different methods or customizing them to suit specific situations can lead to effective rainwater harvesting systems that benefit both individuals and the environment.


Rooftops: If buildings with impervious roofs are already in place, Flat & slope roof,the catchment area is effectively

available free of charge and they provide a supply at the point of consumption. This water can store by filtering

water, with adequate filtration systems,depending upon the available catchment area. Such has wall mount

mechanical filters (for independent house and small apartments),ancient sand bed filtration system with settlement

tank for Big apartment, commercial complex’s and industries.same can Recharge the the earth or Bore well.

Catchment Area Characteristics

The characteristics of the catchment area determine the storage conditions. All calculations relating to the performance of rainwater catchment systems involve the use of runoff coefficient to account for losses due to

spillage, leakage,infiltration, catchment surface wetting and evaporation, which will all, contribute to reducing the

amount of runoff. (Runoff coefficient for any catchment is the ratio of the volume of water that runs off a surface to

the volume of rainfall that falls on the surface).

Water harvesting potential = Rainfall (mm) x Area of catchment x Runoff coefficient Or

Water harvesting potential = Rainfall (mm) x Collection efficiency

Run off

Runoff is the term applied to the water that flows away from a catchment after falling on its surface in the form of

rain. Runoff can be generated from both paved and unpaved catchment areas of buildings.

Run off Co-efficiant

Runoff coefficient is the factor which accounts for the fact that all the rainfall falling on a catchment cannot be

collected.Some rainfall will be lost from the catchment by evaporation and retention on the surface itself. ( for runoff

coefficient).Rainwater yield varies with the size and texture of the catchment area



Calculation of storage / recharge volume based on the average rain fall and collection efficiency:

The storage or Recharge structure capacity can be calculated by the amount of runoff from your roof taking into

consideration the losses due to evaporation, leakages etc...

The optimum storage = Roof Area in Sq M x Runoff Co-Efficient(0.9) x Average Rainfall in mm,Runoff co-efficient is the percentage of water from the roof that comes down in the rainwater pipes which is taken as 90% for RCC roofs, as about 10% will be lost by Evapration and leakages etc...Average design Rain fall of Bangalore can be taken as 32mm (970mm/30days).

Eg: If the roof area of a building is 1200Sqf(30'x40') 112Sqm,then the storage or recharge structure

capacity will be 112 x 0.9 x 32=3225Liters.

We shall first calculate the maximum amount of

rainfall that can be harvested from the RCC rooftop

following details are available:

(R) Average annual rainfall 970 mm (also call it as

height of rain fall 0.97meters) (R)=0.97,

(C) Runoff coefficient = 0.9 Annual rain water potential=(A)Roof area (in Sq.m) X (R)Annual rain fall

(in mm) (X C)Co-efficient run-off from roof) X Annual water harvesting potential from 112 Sq.m.(1200Sqf)

Roof = AXRXC = 112 x 0.97 x 0.9= 97.7 cu.m. (97776 liters)


Rain water harvesting techniques to augment ground water

1.Ground water recharge in rural areas

A• Gully plug

B• Contour bund

C• Gabion structure

D• Dug well recharge

E• Bore well recharge

F• Ground water dams

G• Percolation tank

H• Check dams / cement plugs / nala bunds

I• Recharge shaft

J• Sub-surface dykes

K• Lake

L• Pond

2. Ground water recharge in urban areas

A• Recharge pit

B• Recharge trench

C• Trench with recharge well

D• Storm water drain recharge

E• Foot paths

F• Land scapes

G• Parks

H• Roads

IJ• Tube wells or Bore well recharge

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