Methods of rainwater Harvesting
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.”
ROOF BASED RAINWATER HARVESTING
Rooftops: If buildings with impervious roofs are already in place, Flat & slope roofs, the catchment area is effectively
available free of charge and they supply the point of consumption. This water can be stored by filtering
water, with adequate filtration systems, depending upon the available catchment area. Such has wall-mount
mechanical filters (for independent houses and small apartments),ancient sand bed filtration system with settlement
tanks for Big apartments, commercial complexes, and industries. same can Recharge 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
Runoff
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.
Runoff Co-efficient
Runoff coefficient is the factor that 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
STORAGE STRUCTURE & COLLECTION EFFICIENCY
Calculation of storage/recharge volume based on the average rainfall and collection efficiency:
The storage or Recharge structure capacity can be calculated by the amount of runoff from your roof taking into
consideration of 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 coefficient 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 Evaporation and leakages, etc...Average design Rainfall 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
The following details are available:
(R) Average annual rainfall 970 mm (also called as
height of rainfall 0.97meters) (R)=0.97,
(C) Runoff coefficient = 0.9 Annual rainwater potential=(A)Roof area (in Sq.m) X (R)Annual rainfall
(in mm) (X C)Co-efficient run-off from the 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)
LAND-BASED RAINWATER HARVESTING
Rainwater harvesting techniques to augment groundwater
1. Groundwater recharge in rural areas
A• Gully plugs
B• Contour bund
C• Gabion structure
D• Dug well recharge
E• Bore well recharge
F• Groundwater dams
G• Percolation tank
H• Check dams/cement plugs / nala bunds
I• Recharge shaft
J• Sub-surface dykes
K• Lake
L• Pond
2. Groundwater recharge in urban areas
A• Recharge pit
B• Recharge trench
C• Trench with recharge well
D• Storm water drain recharge
E• Footpaths
F• Landscapes
G• Parks
H• Roads
IJ• Tube wells or Bore well recharge