e2-e3: civil chapter-7 rain water conservation & …

E2-E3/Civil Rev date: 01-04-2011

BSNL India For Internal Circulation Only Page: 1

E2-E3: CIVIL

CHAPTER-7

RAIN WATER CONSERVATION &

HARVESTING



Rain Water Conservation & Harvesting

jfgeu ikuh jkf[k;¨] fcu ikuh lCk lwuA ikuh Xk;s u mCkjs] e¨rh ekul PkwuAA

• Rahiman Pani Rakhiyo, Bin Pani Sab Soon

• Paani Gaye Na Ubre, Moti Maanas Choon.

• Rakhiyo – To Protect

• Soon – Empty

• Ubre – Not Survive

• Moti – Pearl

• Manas – Man

•

• Choon – Hydreted Lime



• Next to air, water is the only other resource in the nature which sustains

life on Earth. If we cannot live without air for more than a few minute, we

cannot live without water form more than a few hours. Life without water

is impossible, with scare water extremely hard and with abundant water a

blessing. In recognition of this fact Nature has covered two-third of our

planet with water, but rapid industrialization leading to its indiscriminate

use has already made it a scarce commodity which is getting scarcer day

by day.

• Indiscriminate mining of water due to rapid industrialization as led to its

acute shortage at an alarming rate.

• Although our country has been blessed with an above average rain fall, the

availability of water has become scarcer over the years.

• Lowering of water table leading to drying up of bore wells has become

common occurrence.

• Government of India has since undertaken a number of steps aimed at

preventing its excessive mining and harvesting and conservation. Ministry

of water resources has voiced its concern vide his D.O. No. 11-2-2000-

GW-II dated May 17, 2001 address to secretary department of

telecommunication suggesting various measures of water harvesting. In

pursuance of the same Dr. D.P.S.Seth, the then CMD, vide his D.O. No.

4859/CMD (BSNL)/2001 dated June 21, 2001 issued direction to “- -Take

up roof top rain water harvesting in our own building in including

residential area”, with this single step begin the journey of a thousand

miles in search of water solution.

Rain water harvesting is the technique of collection and storage of rain

water of surface or in sub-surface aquifer by recharging it for future

requirement so that it is not lost as surface run-off. Rain water is the purest

form of raw water available on the earth. In fact the total freshwater

available on earth is only 3% as against 97% saline water in Oceans. Out

of this 3% fresh water, 77% water is in the form of glaciers and icecaps,

11% water is in deep aquifers which is 800 meters below ground and only

12% is available for drinking and other purpose out of which 11% is in

acquires which are up to 800 meters below ground and remaining 1% is

available in rivers, lakes, ponds and streams



The solution of drinking water problem of the vast majority of population

in our country lies in the appropriate use of Rain water harvested through

roof and from built up catchments where annual rainfall is sufficient. It

has been estimated that the amount of rain water that falls on the terrace of

a medium house can take care of the drinking-water requirement of an

average family of four members for one year.

3%

97%

Fresh water

saline water

77%

11%

11%

1%

Glaciers 77%

Deep Aquifers>800 m 11% Deep Aquifers<800 m 11% rivers, ponds, streams 1%



Advantages of Rainwater Harvesting:

• Conservation of valuable ground water and enhancing the availability.

• Recharge ground water level and improve it.

• Provides sufficient water for home needs

• Reduction in flooding and drainage problems.

• To arrest seawater ingress.

• Conserve urban water waste.

• Controls soil erosion.

• Improves the underground water quality.

• Saves the energy for lifting ground water.

Rainwater Harvesting Systems:

• There are basically two main techniques for harvesting rainwater:

• Conservation by providing storage tank on the ground or underground and

recharge of aquifer. A rain water harvesting structure can incorporate

either of these two techniques or a combination of both depending upon

various factors as shown below.

RAIN WATER HARVESTING

SYSTEMS

CONSERVATION GROUND WATER

RECHARGE

STORAGE

TANK

CHECK

DAMS

LAKES &

PONDS

CONSERVATION

& RECHARGE RECHARGE

PIT

RECHRGE

TRENCH

RECHARGE

SHAFT

RECHARGE

BORE WELL

DUG

WELL

CAVITY

WELL

HAND

PUMP



Conservation of rainwater by storing it on the surface is a traditional technique

and structure used are storage tanks, ponds, check dams, weirs etc. while

recharging is a new concept of rainwater harvesting.

Methods of Rainwater Harvesting:

• In houses and flat complexes rainwater falls on both the

• Terrace as well as on the open area all around.

• It is this water which will have to be led into the ground

• wherever possible, this can broadly be done in two ways:-

1) Direct the terrace rainwater drain pipes directly into open wells through a

filter tank.

2) Direct these pipes to percolation / absorption pits and wells constructed

specifically for this purpose.

• A similar thing will have to be done for the water falling on the open

area around.

A. Percolation/Absorptions Pit

A percolation/absorption pit is a hand bore made in the soil with the help of an

augur and filled up with pebbles and river sand on top. The depth of these pits

will be anywhere between 4 and 8 meters depending on the nature of the soil if

the soil is clayey the pit has to be dug to a depth till a reasonably sandy stratum is

reached. These pits will be 25 cm. (10 in.) A square/ circular collection chamber

with still arrestor is provided at the top.

B. Percolation/Absorption Well

These wells are constructed using cement rings readily available in the market.

The diameter of these rings from 2ft.to 6 ft. the depth to which these wells are dug

depends on the nature of the soil and the diameter depends on the number of roof

top pipes that are likely to be connected to each one of these wells. These wells

are left unfilled and are covered with RCC slabs of suitable thickness to facilitate

free pedestrian and vehicular movement on the ground

C. Percolation Well cum Borepit (for clayey soil)

In areas where the soil is likely to be clayey up to say 15 ft.and more, it is

advisable to go in for a percolation well up to 10 ft or 15 ft. and a hand bore pit

within this well up to a depth of 10 ft to 15 ft. from its bottom. A PVC pipe of 6

in. diameter is inserted into the bore for the entire length.



• There are different structure for rain water harvesting which singly or in

combination with structures are employed depending upon various factors

as described below:

1. Recharge Pit

• It is suitable for areas where sandy formations occur within 1-2m from the

ground surface.

• This is ideally suited for small buildings up to 100 sq. m roof top area.

• It can be circular, square or rectangular in shape.

• These are generally constructed 1-2m wide and 2-3m deep.

• After excavation the pits are refilled with pebbles and boulders.



2. Recharge Trench

• It is suitable when permeable strata of adequate thickness are available at

shallow depth and the roof area of the building is 200-300sqm.

• Recharge trench can be of any dimensions. Generally it is 1-1.5m deep,

0.5-1m wide and of any length depending upon the availability of water to

be recharged.

• Recharge trench can be straight, zig-zag, L-shaped, U shaped.

• The recharge trench should be filled with filter media which can grade

from boulders (5-20cm) at the top for filtration of water.

• The sides of the trench should slope at low angle for stability.



3. Recharge Shaft:

• This is the most efficient and cost effective technique to recharge

unconfined aquifer overlain by poorly permeable strata.

• This is like an open well but filled with filter media.

• Diameter of the shaft generally varies from 1-3m depending upon the

availability of the water to be recharged.

• It is constructed where the aquifer to e recharged is located at medium

depth.

• The recharge shaft end in permeable strata to be recharged. It may not

touch the water table.

• In the upper portion of 1-2m depth, the brick masonry work carried out for

the stability of the structure.



4. Dug Well:

• Dug wells may be utilized as recharge structure after cleaning & desilting

the same.

• A filtration chamber may be constructed so that the water can be made silt

free before entering the dug well.

• The recharge water is guided through a pie to the bottom of the dug well

and it is converted into dug-cum-bore well.

• It is suitable for large buildings preferably having the roof area more than

1000sqm from where the rain water can be diverted and recharged.

• Periodic chlorination should be done for controlling the bacteriological

contaminations.



5. Recharge/Injection Well:

• This is used to recharge deep aquifer or where multiple aquifers are met

interspersed with impervious strata.

• In case of recharge well single diameter pipe assembly is used and it

should have the provision of slotted pipes against the water bearing strata.

• The rainwater is allowed to pass through the filter media before it is

channeled to the well under gravity flow conditions.

• The number of recharging wells depends upon the roof top area and

aquifer characteristics.



6. Abandoned Tube wells/Hands Pumps:

• These water abstraction structures act as good recharge structure.

• The hand pump is suitable for small building having roof area up to

150sqm.

• Water is diverted from the roof top to the hand pump through pipe of 100

mm dia.



7. Cavity Wells:

• Cavity wells in use also form good recharge structures.

• Cavity wells are constructed by drilling boreholes with hand boring and

pipes are driven up to the bottom of the clayey bed.

• Cavity is formed within the underlying sand bed with the help of the high

capacity pumps.

• Filter/screen is not used in these wells and the bottom of the pipe is not

closed but kept open for entering water.

• The filtered water is recharged under gravity through these wells.

• Cavity well can be constructed in the areas where overlying aquifer layer

to be charged is hard and plastic in nature.

• The recharge capacity of the cavity well is generally 5 to 10 liters/Sec.

• It is cheap structure compared to recharge well.

• The water to be recharged should be silt free.

• The cavity should be developed periodically whenever it is found that the

recharge capacity is reduced.

• It can be used as pumping well.



8. Contour Bunds:

• These are suitable in low rainfall areas where monsoon runoff 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 the bunds.

• Spacing between the two contour bunds depends on the slope of the area

as well as the permeability of soil.

• Contour bunds are suitable on lands with moderate slopes without

involving terracing.

• Contour bunds are effective methods to conserve soil moisture in

watershed for long duration.

9. Rainwater Harvesting in Individual Houses

Dig a number of 3 to 6 meter deep and 30 cm diameter -percolation pits at 3 meter

intervals all around the house. Lead the terrace pipes into the open well if any,

through a 60cm x 60cm x 60cm filter (filled with pebbles) under the ground level.

Rain Water Harvesting Methods



10. Rainwater Harvesting in a Flat Complex (Service Well cum Recharge

Well Method)

Utilize the open well if any within the complex to divert the rainwater from the

terrace into it. If not, construct a well for this purpose. The rainwater falling on

the open space around the complex can be collected near the gate by providing a

gutter with perforated lid. The collected water can be led through necessary

piping arrangements into a recharge well of 1 meter diameter and 5 meter deep.



Maintenance of Rain Water Harvesting Systems

The key to satisfactory performance of a RWH system lies in its periodic

maintenance. If not maintained properly, the system may not only not work at all

but or silting of drains etc. which will have to be tackled on emergent basis. As

such a RWHS should be provided only when its periodic maintenance can be

ensured.

Expenditure on maintenance of RWHS may be booked under maintenance head

as there is no need for submitting the estimate for obtaining A/ A & E/ S.

Simple measure given below so a long way for a trouble free service for RWHS.

1. It is desirable to preclude first shower from the RWHS as it as known a

contain pollutants from the atmosphere and excessive silt.

2. All terrace and drains may be cleaned before the onset on the monsoon.

3. Filter may be removed and washed with clean water in a drum and placed

back. This may be before monsoon or more frequently as per the

requirement.

4. Silt collected in the buffer/storage tank or sedimentation tank may be

removed prior to monsoon.

5. Bore well may also be developed before monsoon as silt and fine sand

present in runoff may clog the gravel and the aquifer immediately

surrounding the screen. If development operation is to be effective, it must

cause reversal of flow through the screen opening of the formation

immediately around the well. Development may be done every alternate

year before monsoon or less frequently as per the need. Date of

development as well as annual maintenance may be displayed on the

parapet of the buffer tank.

6. Reading water table should be recorded before and after the monsoon.

Glossary of Terms

1. Aquifer/Ground water aquifer: Any underground formation of soil or rack

which can yield water.

2. Artificial recharge: Any man scheme or facility that adds water to an

aquifer.

3. Bore well: small diameter wells which are generally deeper than open

well.

4. Dug Wells: large diameter pits excavated in the ground until water table is

reached.



5. Ground Water: The water retained in the inter-granular pores of the soil or

fissures of rock below the water table.

6. Runoff: water that flows away from a surface after falling on the surface

in the form of rain.

7. Recharge: the process of surface water joining the ground water aquifer.

8. Water Table: The level of water within the granular pores of the soil or

fissures of rock below which the pores of the host are saturated.

9. Buffer tank/Storage Tank: Tank used for storing of rain water. Storage

tanks can be of any size, shape and capacity depending upon requirement.

10. Sedimentation tank: A tank is used to settle down/retain the impurities of

water.

11. Detention Period: Period for which the water is retained in a sedimentation

tank.

12. Rate of infiltration: The speed by which the water is absorbed by the

natural soil/earth.

13. Rainfall Intensity: Rainfall intensity is the rate fall measured in mm per

hour in any particular area.

14. Peak rainfall intensity/Peak flow: The maximum intensity of rain fall in

any particular area which lasts for a very short period and given a peak

flow of water.

15. Rain Water Harvesting Structure: The whole system

fabricated/Constructed for rain water harvesting is termed as Rain Water

Harvesting structure.

16. Permeable Strata: A strata through which water can pass. It depends upon

the size of the voids and uniformity coefficient of the particles in the

strata.

17. Filter Media: A media consisting of granular particles, which retains the

impurities of water when passed through it.

18. Catchment Area: A small piece of land which collects the surface runoff

and produces a stream flowing through its deepest through it.

19. Well Screen/ Strainer: Screens/strainers are long slotted pipes fitted at

proper elevation according to the depth of the water bearing strata. They

allow the ground water to enter into the well but not the sand or silt

around. They are made of brass, iron, copper, galvanized iron or steel,

various alloys and concrete.

20. Injection Well: Used to recharge deep aquifer or water multiple aquifers

are met.



• Cost of Rain water Harvesting

The cost of implementation of rainwater harvesting systems in a house/flat

complex will vary from Rs.5000 - Rs.50, 000 depending on the size of the

premises as well the nature of the soil. Once put in place, the harvesting

structure does not require any serious maintenance and hence there is no

recurring expenditure involved.



QQuueessttiioonnss::--

1. What is Rain Water Harvesting? Please elaborate.

2. Describe various rain water harvesting systems?

3. List the advantages of rain water harvesting.

4. Describe in brief Injection Well Method of RWH.

5. What is Aquifer? What are its characteristics?

6. What do you understand by Run off?

7. Describe the ground water recharge systems.

8. Explain the recharge pit.

9. What is water table?

10. Explain the injection well for Rain Water Harvesting system.

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