Prayas Session: Rain Water Harvesting by Soumalya Nandi

Copyright © technoKrats
Wednesday Work-out session – 21th May 2014
Presented By – Soumalya Nandy
Tenet Systems Pvt. Ltd.
An ISO 9001:2008 Certified Company

o A technique used to collect, store, and use rainwater
for efficient application and conservation
o An effective way of utilizing large amount of water which otherwise goes as
surface runoff.
Traditionally, rainwater harvesting has been practiced in arid and semi-arid areas,
and has provided drinking water, domestic water, water for small irrigation and a
way to replenish ground water level.
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o Industrialization and Urbanization
(a) Increase in per capita utilization
(b) Less peculation area
o In places where rain fed/ irrigation based crops are cultivated through
ground water
o Decrease in surface area of Lakes, Ponds
o Changing of climates
o Deforestation
(i) Less precipitation
(ii) Absence of Barriers
(a) Rain drops checked by leaves of tree
(b) Water slowly descends through twigs & trunk
(c) Humus – acts as reservoir
1 hectare of forest-6-7 Lac ton of water
(after filtering) top layer can hold 1.2 Lac tons of water

We have to find an efficient resource for continuous supply of water. Water should be
purified( non polluted ) so to use it in drinking, domestic or any other purpose.
Quantity of water should meet the basic requirements specially for rural areas.
Rain water
• is the ultimate source of fresh water.
• has potential to meet water demand is tremendous.
• harvesting helps to overcome water scarcity.
• help to conserve aquifers by recharging it with water
Rain water harvesting is the ultimate answer!

Broadly rainwater can be harvested for two purposes:
•Storing rainwater for ready use in containers above or below ground
•Charged into the soil for withdrawal later (groundwater recharging)

This is perhaps one of the most frequently asked question, as to
why one should harvest rainwater. Some of the reasons are
following
o Improvement in
• ground water levels
• water availability in wells/tube-wells
• quality of ground water through dilution
• living condition in rural areas
o Reduction in soil erosion due to reduced surface water runoff
o Conservation of surface water runoff during monsoon
o Outdoor(ex. Watering plants or car wash etc.) or
domestic(bathing animals etc.) purpose use
o Inculcate a culture of water conservation

o RWH - yield copious amounts of water. For an average
rainfall of 1,000mm, approximately four million litters of
rainwater can be collected in a year in an acre of land (4,047
m2), post-evaporation.
o As RWH - neither energy-intensive nor labour-intensive
o It can be a cost-effective alternative to other water-accruing
methods.
o With the water table falling rapidly, & concrete surfaces and
landfill dumps taking the place of water bodies, RWH is the
most reliable solution for augmenting groundwater level to
attain self-sufficiency

“Catch rain where it falls.”- Rainwater harvesting can be harvested from the
following surfaces:
• Rooftop : If buildings with impervious roofs are already in place, the
catchment area is effectively available for free of charge.- Roof rain water
harvesting.
• Paved and unpaved areas : i.e. open fields, parks, roads and pavement and
other open areas can be effectively used to harvest the runoff. The main
advantage is that water can be collected from a larger area. – Land based rain
water harvesting.
•Water bodies : The potential of lakes, tanks and ponds to store rainwater is
immense. The harvested rainwater can not only be used to meet water
requirement of the city, it also recharges ground water aquifers. – Water shed
harvesting.

There are two main techniques of rain water harvestings.
• Storage of rainwater on surface for future use.
• Recharge to ground water.
The storage of rain water on surface is a traditional techniques
and structures used were roof top harvesting , underground
tanks, ponds, check dams, weirs etc.
In case of ground water pits, trenches, dug well, shaft etc.

The illustrative design of the basic components of roof top rainwater
harvesting system is given in the following typical schematic diagram/
The system mainly constitutes of following sub components:
o Catchment
o Transportation
o First flush
o Filter
o Store
Catchment : The surface that receives rainfall directly is the catchment of
rainwater harvesting system. It may be terrace, courtyard, or paved or
unpaved open ground. The terrace may be flat /stone roof or sloping roof.
Therefore the catchment is the area, which actually contributes rainwater to
the harvesting system.

Transportation : It is a process by which rain water flow from roof to
the purification system and then finally to the storage tank by the help
of pipes and valves.
First flush : This is a process of rain water pre filter. Rainwater captured
from rooftops contains significant quantities of plant debris, soil, eroded
roof materials, and other solids that can clog pumps, valves, and pipes.
Very small solid substance collect as sediment at the bottom of storage
tanks, reducing tank storage capacity. Organic solids remain in
suspension and decompose, depleting oxygen and generating hydrogen
sulfide and other noxious by-products. To improve the quality of
rainwater we have to install a “roof washer” or “first-flush diverter”, a
device that discards the initial runoff from a roof before it reaches the
storage tank.

A First-Flush Diverter retains the initial runoff from a roof in a length of pipe that
is capped at the end. When the pipe is filled, a ball or flapper shuts off the top of
the pipe so that additional rainfall flows directly into the rainwater storage tank.
The pipe cap has a small-diameter outlet that slowly releases the “first-flush”
water so that by the next rain the pipe is empty and is ready to receive more
water. There are three standard sizes that utilize 3”, 4”, and 12” pipe for water
storage.

Filter : After fill the first flush diverter water comes into filter chamber
which containing with different purification materials like sand, small brick,
charcoal, pebble etc places in separate permeable layer. Water get purified
by going through different layers. Then finally to storage.

Store : After get purified water store in tanks for future use.

o In term of complex constructions or use best quality
of materials there is a requirement for high cost.
o Repairing parts or maintenance will add cost or
expenditure for specific period of time.
o If not maintain properly then it can cause various
problems in term of transport of water to storage.
o If the storage tank did not washed properly with in a
period then it will decrease the quality of water.

Check dams/Nala plugging : It is 1.5 to 2 meters height constructed
across streams with gentle slopes. It consist with impermeable
substances. It will force to change the direction of stream to travel
water in different areas for conservation.

Recharge to ground water is a new concept of rain water harvesting
and the structures generally used are :-
Pits : Recharge pits are constructed for recharging the shallow
aquifer. These are constructed 1 to 2 m, wide and to 3 m. deep
which are back filled with boulders, gravels, coarse sand.
Trenches : These are constructed when the permeable stream is
available at shallow depth. Trench may be 0.5 to 1 m. wide, 1 to
1.5m. deep and 10 to 20 m. long depending up availability of water.
These are back filled with filter materials.

Dug wells : Existing dug wells may be utilized as recharge structure and water
should pass through filter media to remove silts before putting into dug well.
Periodic chlorination required.

Spreading techniques : When permeable strata starts from top then this
technique is used. Spread the water in streams/Nalas by
making check dams, nala bunds, cement plugs, gabion structures or a percolation
pond may be constructed.
Recharge Shafts :- For recharging the shallow aquifer which are located below
clayey surface, recharge shafts of 0.5 to 3 m. diameter and 10 to 15 m. deep are
constructed and back filled with boulders, gravels & coarse sand.
Lateral shafts with bore wells :- For recharging the upper as well as deeper
aquifers lateral shafts of 1.5 to 2 m. wide & 10 to 30 m. long depending upon
availability of water with one or two bore wells are constructed. The lateral shafts
is back filled with boulders, gravels & coarse sand.

Some of them are following :
o It is less expensive and economic resource
o It is sustainable and reliable source of water supply
o It is relatively less vulnerable to pollution
o Needs little treatment before use.
o It has no turbidity and colour
o There is no conveyance losses in ground water based supplies.
o It is key to life in arid and semi-arid regions.
o It is usually universally available
o There is more ground water than surface water

A noble goal – A common responsibility
Ground water exploitation is inevitable In Urban areas. But the ground water potential
is getting reduced due to urbanization resulting in over exploitation. Hence, a strategy
to implement the ground water recharge, in a major way need to be launched with
concerted efforts by various Governmental and Non-Governmental Agencies and
Public at large to build up the water table and make the ground water resource, a
reliable and sustainable source for supplementing water supply needs of the urban
dwellers.
Recharge of ground water through storm run off and roof top water collection,
diversion and collection of run off into dry tanks, play grounds, parks and other vacant
places are to be implemented by Special Village Panchayats/ Municipalities /Municipal
Corporations and other Government Establishments with special efforts.

Tenet Systems Pvt. Ltd.
42, N K Guin Lane, Serampore,
Hooghly – 712201, India.
Call: +919830158077 or
+1-850-745-0414
Web: http://tenetsystems.net
Copyright © technoKrats
Thank you for your time!
technoKrats
43, N K Guin Lane, Serampore,
Hooghly – 712201, India.
Call: +919830158077 or
+1-850-745-0414
Web: http://technokrats.in

Prayas Session: Rain Water Harvesting by Soumalya Nandi

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Prayas Session: Rain Water Harvesting by Soumalya Nandi