Ideal for a class presentation at High-School and/or UG level for first year students.

1. Rainwater Harvesting -
Needs and Uses
Biology Presentation
By Atrayee Chatterjee

2. Introduction
Rainwater Harvesting:
“Grab hold of water where it falls”
 Rainwater harvesting ( RWH) is a technique of collection and storage
of rainwater into natural reservoirs or tanks, or the infiltration of surface
water into subsurface aquifers (before it is lost as surface runoff).
Rainwater
Harvesting
Roof tops
Local Catchment
Seasonal
floodwater
Watershed
Management
Catchment Type
Catchment Size
Micro-catchment
Macro-catchment

3. Johads of Rajasthan
Earthen or masonry
rainwater harvesting
structure,
for providing water for
domestic use to the
communities.
Tankas of Bikaner,
Rajasthan
Unique underground
structures of various
shapes and sizes to
collect rain water for
drinking purposes
Bamboo drip
irrigation:
200-year-old system.
Used by tribal farmers
of Khasi and Jaintia
hills in Meghalaya.
Bamboos divert water
from perennial springs
on hilltops to the
lower reaches by
gravity

4. Why is RWH needed?
1. To overcome the inadequacy of surface water to meet our demands.
2. To arrest decline in ground water levels.
3. To enhance availability of ground water for sustainable development.
4. To improve ground water quality by dilution.
5. To increase agriculture production.
6. To improve ecology of the area by increase in vegetation cover etc.
7. To mitigate floods.
8. To reduce pressure on other water resources

5. Case Study: Tamil Nadu’s Success
• Chennai gets an average of 1,300 mm of rainfall
every year, which is higher than the national
average of 800 mm. But the rainfall occurs in short
spells of a few days, and nearly 95% of it is lost
due to surface runoff and evaporation.
• The Rain Water Harvesting movement launched in
2001 was the brainchild of the Honourable Chief
Minister. It has had a tremendous impact in
recharging the groundwater table all over Tamil
Nadu.
• To consolidate the gains, various measures have
been taken up for rejuvenation of RWH structures
created already in both public and private
buildings, besides creating new ones.
• There are 1821 water bodies maintained by Town
Panchayats with an extent of 6286.84 acres.
• Over 95 % buildings under Tamil Nadu Town
Panchayats have some form of RWH System.
Villapuram Vellore

6. Potentials And Advantages
Potential Areas:
1. Where ground water
levels are declining on
regular basis.
2. Where substantial
amount of aquifer has to
be de-saturated.
3. Where availability of
ground water is
inadequate in lean
months.
4. Where due to rapid
urbanization, infiltration
of rain water into subsoil
has decreased drastically
and recharging of ground
water has diminished.

7. Rainwater Harvesting Techniques
Two main ways for rainwater harvesting:
1. Storage of rain water on the surface for future use.
2. Recharge of ground water.
Storage Type Recharge Type
Rainwater storage reservoir at
Dholavira (Rann of Kutch) –
Harappan civilization (2500-1900
BC)
Artificial recharge to ground water is a
process by which the ground water reservoir
is augmented at a rate exceeding that under
natural conditions of replenishment.

8. Methods Popular in Urban Regions
• In urban areas, rain water available from roof tops of buildings,
paved and unpaved areas goes waste.
• This water can be recharged to aquifer and can be utilized gainfully
at the time of need.
• The rain water harvesting system needs to be designed in a way
that it does not occupy large space for collection and recharge
system.
Roof Top Rainwater
Harvesting through:
1. Recharge Pit
2. Recharge Trench
3. Tubewells
4. Recharge wells

9. Roof Top Rainwater Harvesting through Recharge Pit
a. In alluvial areas where permeable rocks are
exposed on the land surface or at very shallow
depth, roof top rain water harvesting can be
done through recharge pits.
b. The technique is suitable for buildings having
a roof area of 100 square metres.
c. Recharge Pits may be of any shape and size
which are back filled with boulders (5-20 cm),
gravels (5-10 mm) and coarse sand (1.5-2 mm)
in graded form
d. A mesh should be provided at the roof so that
leaves or any other solid waste/debris is
prevented from entering the pit and a
desalting/collection chamber may also be
provided at the ground to arrest the flow of
finer particles to the recharge pit.
e. The top layer of sand should be cleaned
periodically.

10. Roof Top Rain Water Harvesting through
Recharge Trench
a. Recharge trenches are suitable for buildings having
roof area of 200-300 sq m and where permeable
strata are available at shallow depths.
b. Trench may be 0.5 to 1 m wide, 1 to 1.5 m deep
and 10 to 20 m long depending upon availability of
water to be recharged.
c. These are back filled with boulders (5-20 cm),
gravels (5-10 mm) and coarse sand (1.5-2 mm) in
graded form
d. A mesh should be provided at the roof so that
leaves or any other solid waste/debris is prevented
from entering the trench
e. By-pass arrangement is provided before the
collection chamber to reject the first showers.
f. The top layer of sand should be cleaned periodically
to maintain the recharge rate.

11. Methods Popular in Rural Regions
• In rural areas, rain water harvesting is taken up considering
watershed as a unit.
• Surface spreading techniques are common since space for such
systems is available in plenty and quantity of recharged water is also
large.
Following techniques may be
adopted to save water going waste:
1. Gully Plug
2. Contour Bund
3. Check Dams
4.Percolation tanks
5. Recharge Shafts
6. Dugwell Recharge

12. Rain water harvesting through
Check Dams
A check dam is generally constructed on small
streams and long gullies formed by the erosive
activity of water. The ideally a check dam is
located in a narrow stream with high banks.
A check dam serves many purposes.
• It cuts off the runoff velocity and reduces
erosive activity
• The water stored improves soil moisture of
the adjoining areas and allows percolation to
recharge the aquifers
• While constructing a series of check dams on
along stream course, the spacing between
two check dams should be beyond their
water spread. The height of the check dam
should be such that even during the highest
flood, water does not spill over the banks.

13. Rain Water Harvesting through
Contour Bund
• Contour bunds are effective method to
conserve soil moisture in watershed for long
duration.
• These are suitable in low rain fall areas where
monsoon run off can be impounded by
constructing bunds on the sloping ground all
along the contour of equal elevation.
• Flowing water is intercepted before it attains
the erosive velocity by keeping suitable
spacing between bunds.
• Spacing between two contour bunds depends
on the slope of the area and the permeability
of the soil. Lesser the permeability of soil, the
close should be spacing of bunds.
• Contour bunding is suitable on lands with
moderate slopes without involving terracing.

14. Comparison With Other Methods
Water Source Setup Cost Running Cost Yield Applicable in
Tubewells Medium Medium Medium Places with
Deep Aquifers
Hand-dug wells Low Medium Low-Medium Places where
water table is
not lower than
six metres
Reverse
Osmosis
High High High Only in Urban
regions
Rainwater
Harvesting
Low-Medium Low-Medium High Only in regions
which receive
moderate-high
rainfall once a
year
Thus one of the main drawbacks of RWH is that is it is economically viable only in regions
receiving regular rainfall of moderate-high level, i.e. around or greater than national average

15. Here are some important laws that’s have been passed:
In Chennai: Rainwater harvesting has been made mandatory in three storied
buildings
In Ahmedabad: In 2002, the Ahmedabad Urban Development Authority (AUDA)
had made rainwater harvesting mandatory for all buildings covering an area of over
1,500 square metres.
In Himachal Pradesh: All commercial and institutional buildings, tourist and
industrial complexes, hotels etc, existing or coming up and having a plinth area of
more than 1000 square metres will have rain water storage facilities
commensurate with the size of roof area.
 It is evident that there is considerable scope for
collection and utilisation of rainwater especially, in
regions where groundwater is :
 deep, inaccessible due to surface
conditions
 Groundwater is salty, acidic or unfit too
use/consume
 Water we actually tap is: 40% of
precipitation

16. Any Questions?
References:
1. http://cgwb.gov.in/documents/case-studies-rwh-ar-may2011.pdf
2. http://www.yourarticlelibrary.com/water/rain-water-harvesting-in-india-
need-methods-and-other-details/20917/
3. http://www.wateraid.org/~/media/Publications/Rainwater-
harvesting.pdf
4. http://www.rainwaterharvesting.org/policy/legislation.htm