CH-7 Concept of Water Conservation & Rain Water Harvesting

E4-E5 Civil (Technical) Rev date: 20-04-11

BSNL India For Int ernal Circulat ion Only Page: 1

Chapter-7

CONCEPT OF

WATER CONSERVATION

&

RAIN WATER HARVESTING

R.N. Yadav, SDE (BS-C), 9412739253 (M)

E-mail ID: [email protected]



Concept of Water Conservation & Rain Water

Harvesting

• 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

•



• Next to a ir , water is the only o ther resource in the nature which

sustains life on Earth. If we cannot live withou t air fo r more

than a few minute, we cannot live withou t water form more than

a few hours. Life without water is impossible, with scare water

extremely hard and with abundant water a b lessing. In

recognit ion of this fact Natu re has covered two-third o f our

planet with water, but rapid industrializat ion leading to its

indiscr iminate use has a lready made it a scarce commodity which

is gett ing scarcer day by day.

• Indiscriminate mining of water due to rapid industrializat ion as

led to its acute shortage at an alarming rate.

• Although our country has been blessed with an above average

rain fa ll, the availab ilit y of water has become scarcer over the

years.

• Lowering of water tab le leading to drying up of bore wells has

become common occurrence.

• Government of Ind ia has since u ndertaken a number of steps

aimed at p revent ing its excessive mining and harvesting and

conservat ion. Ministry of water resources has vo iced its co ncern

vide his D.O. No. 11-2 -2000-GW-II dated May 17, 2001 address

to secretary department o f telecommunica tion suggest ing var ious

measures o f water harvest ing. 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 direct ion to “- -Take

up roof top rain water harvest ing in our own building in

including resident ial area”, with this single step begin the

journey of a thousand miles in search of water solu tion.

• Rain water harvest ing is the technique o f collection and storage

of rain water of surface o r in sub-surface aquifer by recharging it

fo r future requirement so that it is not lost as surface run-off.

Rain water is the purest form of raw water availab le on the earth.

In fact the tota l freshwater ava ilable on earth is only 3% as

aga inst 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 aqu ifers which is 800 meters below ground and only 12% is

ava ilab le for drinking and other purpose out of which 11% is in



acquires which are up to 800 meters below ground and remaining

1% is ava ilab le in rivers, lakes, ponds and streams

• The so lu t ion of drinking water prob lem of the vast majorit y o f

population in our countr y lies in the appropriate use of Rain

water harvested through roof and from built up catchments where

annual rainfall is sufficient. It has been est imated that the

amount of ra in water that falls on the terrace o f a medium house

3%

97%

Fresh water

saline water

77

11

111

Glaciers

Deep Aquifers>800

Deep Aquifers<800

rivers, ponds, streams



can take care of the drinking-water requirement o f an average

family of four members for one year.

Advantages of Rainwater Harvesting:

• Conservat ion of valuable ground water and enhancing the

ava ilab ilit y.

• Recharge ground water level and improve it .

• Provides suffic ient water for home needs

• Reduction in f looding and drainage problems.

• To arrest seawater ingress.

• Conserve urban water waste.

• Contro ls so il erosion.

• Improves the underground water quality.

• Saves the energy for lifting ground water.

Rainwater Harvesting Systems:

• There are basica lly two main techniques for harvest ing

rainwater :

• Conservat ion by providing storage tank on the ground or

underground and recharge of aquifer . A rain water harvest ing

structu re can incorporate either of these two techniques or a

combinatio n of both depending upon various factors as shown

below.

RAIN WATER

HARVESTING

SYSTEMS

CONSERVATIO

N

GROUND

WATER

RECHARGE

STORAGE

TANK

CHECK

DAMS

LAKES &

PONDS

CONSERVA

TION

&

RECHAR

GE

RECHRGE

TRENCH

RECHARGE

SHAFT

RECHARGE

BORE WELL

DUG

WELL

CAVITY

WELL

HAND

PUMP



Conservat ion of rainwater by storing it on the surface is a trad it iona l

technique and structure used are sto rage tanks, ponds, check dams,

weirs etc. while recharging is a new concept o f rainwater harvesting.

Methods of Rainwater Harvesting:

• In houses and flat complexes ra inwater falls on bo th 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 b roadly be done in two ways:-

1) Direct the terrace rainwater d rain pipes directly into open wells

through a f ilter tank.

2) Direct these p ipes to percolat ion / absorption pits and wells

constructed specifically for this purpose.

• A similar thing will have to be done for the water fa lling on

the open area around.

A. Perco la tion/Absorptions Pit

A percolation/absorption p it is a hand bore made in the soil with

the he lp o f an augur and filled up with pebb les and river sand on top.

The depth of these p its will be anywhere between 4 and 8 meters

depending on the natu re of the soil if the soil is c laye y the pit has to be

dug to a depth t ill a reasonab ly sand y stratum is reached. These pits

will be 25 cm. (10 in.) A square/ circular collect ion chamber with st il l

arresto r is provided at the top .

B. Perco lation/Absorption Well

These wells are constructed using cement r ings read ily

ava ilab le 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 o f the soil

and the diameter depends on the number o f 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 vehicu lar movement on the ground

C. Perco la tion Well cum Borepit (for clayey so il)

In areas where the soil is likely to be claye y up to say 15ft.and

more, it is advisab le to go in fo r a perco lation 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 ent ire length.

• There are d ifferent structure for rain water harvest ing which

singly or in combinat ion with structures are emplo yed depending

upon var ious factors as described below:

1. Recharge Pit

• It is suitable for areas where sandy fo rmations occur within 1-2m

from the ground surface.

• This is idea lly su ited for small bu ild ings up to 100 sq. m roof top

area.

• It can be circular, square o r rectangu lar in shape.

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

• After excavat ion the pits are refilled with pebbles and boulders.



2. Recharge Trench

• It is suitable when permeab le stra ta of adequate thickness are

ava ilab le 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 depend ing upon the

ava ilab ilit y of water to be recharged.

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

• The recharge trench shou ld be filled with filter media which can

grade from boulders (5-20cm) at the top fo r filtrat ion o f water.

• The s ides of the trench should slope at low angle for stab ilit y.



3 . Recharge Shaft:

• This is the most effic ient and cost effect ive technique to

recharge unconfined aquifer over lain by poorly permeable strata.

• This is like an open well but filled with f ilter med ia.

• Diameter o f the shaft generally var ies from 1-3m depending upon

the availab ility of the water to be recharged.

• It is constructed where the aqu ifer to e recharged is located a t

med ium depth.

• The recharge shaft end in permeab le 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 stab ilit y o f the structure.



4. Dug Well:

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

desilt ing the same.

• A filtrat ion chamber may be constructed so that the water can be

made silt free before entering the dug well.

• The recharge water is gu ided 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 chlorinat ion should be done for controlling the

bacteriological contaminat ions.



5. Recharge/Injection Well:

• This is used to recharge deep aquifer or where mult iple aquifers

are met interspersed with impervious strata.

• In case o f recharge well single d iameter p ipe assembly is used

and it should have the provis io n of s lotted pipes against the

water bearing strata.

• The rainwater is a llowed to pass through the f ilter 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 abstract ion structures act as good recharge structu re.

• The hand pump is su itable for small bu ild ing having roof area up

to 150sqm.

• Water is d iverted from the roof top to the hand pump through

pipe o f 100 mm dia.



7. Cavity Wells:

• Cavit y wells in use also form good recharge structures.

• Cavit y wells are constructed by d rilling boreholes with hand

boring and pipes are driven up to the bo ttom of the clayey bed.

• Cavit y is formed within the underlying sand bed with the he lp of

the high capac ity pumps.

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

is no t closed but kep t open fo r entering water.

• The filtered water is recharged under gravit y through these

wells.

• Cavit y well can be constructed in the areas where overlying

aquifer la yer to be charged is hard and plast ic in nature.

• The recharge capacit y o f the cavit y well is genera lly 5 to 10

liters/Sec.

• It is cheap structure compared to recharge well.

• The water to be recharged should be silt free.

• The cavit y shou ld be developed periodically whenever it is found

that the recharge capacit y is reduced.

• It can be used as pumping well.



8 . Contour Bunds:

• These are suitable in low ra infall areas where mo nsoon runoff

can be impounded by constructing bunds on the slop ing ground

all along the contour of equal elevat ion.

• Flowing water is intercep ted before it atta ins the erosive velocit y

by keeping su itab le spacing between the bunds.

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

the area as well as the permeabilit y o f soil.

• Contour bunds are su itable on lands with moderate slopes

withou t involving terrac ing.

• Contour bunds are effect ive 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 -percolat ion pits

at 3 meter interva ls all around the house. Lead the terrace p ipes into

the open well if any, through a 60cm x 60cm x 60cm filter ( f illed with

pebb les) 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 b y provid ing a gutter with perforated lid .

The co llected water can be led through necessary p ip ing arrangements

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



Maintenance of Rain Water Harvesting Systems

The ke y to sat isfactory performance of a RWH system lies in it s

periodic maintenance. If not mainta ined properly, the system may not

only no t work at all but or silt ing o f dra ins etc. which will have to be

tackled on emergent basis. As such a RWHS should be provided onl y

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 est imate for

obtaining A/ A & E/ S.

Simple measure given be low so a long way for a trouble frees service

fo r RWHS.

1. It is desirab le to preclude fir st shower from the RWHS as it as

known a conta in pollutants from the atmosphere and excessive

silt .

2 . All terrace and drains ma y be cleaned before the o nset on the

monsoon.

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

and p laced back. This ma y be before monsoon or more frequently

as per the requirement.

4. Silt collected in the buffer/storage tank o r sedimentat ion tank

may be removed prior to monsoon.

5. Bore well may a lso be developed before monsoon as s ilt and fine

sand present in runoff may c log the grave l and the aquifer

immediate ly surrounding the screen. If development operation is

to be effect ive, it must cause reversa l o f f low through the screen

opening of the formation immediate ly around the well.

Development may be done ever y alternate year befo re 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 tab le should be recorded befo re and after the

monsoon.

Glossary of Terms

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

soil or rack which can yield water.

2. Artific ial recharge: Any man scheme or fac ility that adds water

to an aquifer .

3. Bore well: small diameter wells which are genera lly deeper than

open well.



4. Dug Wells : large d iameter p its 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 su rface after fa lling on the

surface in the form of rain.

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

aquifer.

8. Water Table : The leve l of water within the granu lar pores o f the

soil or f issures o f rock be low which the pores of the host are

saturated.

9. Buffer tank/Storage Tank: Tank used fo r sto ring of rain water.

Storage tanks can be o f any size, shape and capac ity depending

upon requirement.

10. Sedimentat ion tank: A tank is used to sett le down/reta in the

impurities of water.

11.Detent ion Per iod: Period for which the water is reta ined in a

sedimentat ion tank.

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

the natural so il/earth.

13.Rainfall Intensit y: Rainfall intensit y is the rate fa ll measured in

mm per hour in any particular area.

14.Peak ra infall intensit y/Peak flow: The maximum intensit y of ra in

fa ll in any part icular area which lasts for a very short period and

given a peak flow of water.

15.Rain Water Harvest ing Structure: The whole system

fabricated/Constructed for rain water harvest ing is termed as

Rain Water Harvest ing structu re.

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

depends upon the s ize of the voids and uniformity coefficient of

the partic les in the strata.

17.Filter Media : A media consist ing of granular particles, which

retains the impurit ies of water when passed through it .

18.Catchment Area: A small p iece of land which collects the surface

runoff and p roduces a stream flowing through its deepest through

it.

19.Well Screen/ Stra iner : Screens/stra iners are long slotted pipes

fitted at proper elevat ion according to the depth o f 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, ga lvanized iron or steel, various alloys and concrete.



20.Inject ion Well: Used to recharge deep aqu ifer or water mult ip le

aquifers are met.

• Cost of Rain water Harvesting

The cost o f implementat ion of rainwater harvest ing 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 o f the so il. Once put

in place, the harvesting structure does not require any ser ious

maintenance and hence there is no recurring expenditure involved.



QQuueess tt iioonnss :: --

1. What is Rain Water Harvest ing? Please elaborate.

2. Describe various rain water harvest ing systems?

3. List the advantages of ra in water harvest ing.

4. Describe in brief Inject ion Well Method of RWH.

5. What is Aquifer? What are it s character is tics?

6. What do you understand by Run o ff?

7. Describe the ground water recharge systems.

8. Explain the recharge pit.

9 . What is water table?

10. Explain the inject ion well for Rain Water Harvesting system.

CH-7 Concept of Water Conservation & Rain Water Harvesting

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Transcript of CH-7 Concept of Water Conservation & Rain Water Harvesting