L10– Rainwater Harvesting System

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M odu le 3 – ( L8 - L1 1 ) : I n t e gr a t e d W a t e r sh e d M a n a ge m e n t I n t r odu ct ion t o I n t e gr a t e d Appr oa ch , I n t e gr a t e d W a t e r Re sou r ce s M a n a ge m e n t , Con j u n ct ive Use of W a t e r Re sou r ce s, Ra in w a t e r

H a r ve st in g; Roof Ca t ch m e n t Syst e m .

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Ra in w a t e r H a r ve st in g Syst e m

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L10

L10– Rainw at er Harvest ing Syst em

L10

Rainw at er Harvest ing Syst em



Topics Cove r e d



I nt roduct ion t o Rainw at er harvest ing syst em ,

Hydrological aspect s Hydro

Hydrological aspect s Hydro geological

geological

Hydrological aspect s, Hydro

Hydrological aspect s, Hydro-- geological

geological

aspect s, Groundw at er recharge, I nt egrat ed

syst em , Case st udy



Keywords:

Rainw at er harvest ing syst em HydroRainw at er harvest ing syst em Hydro--



Keywords:

Rainw at er harvest ing syst em , HydroRainw at er harvest ing syst em , Hydro geology, Groundw at er recharge

geology, Groundw at er recharge

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I nt roduct ion t o Rainwat er Harvest ing

 Ra in W a t e r H a r ve st in g - pr oce ss of colle ct in g, con ve yin g & st or in g w a t e r fr om r a in fa ll in a n a r e a – for be n e ficia l u se.

 St or a ge – in t a n k s r e se r voir s  St or a ge in t a n k s, r e se r voir s,

u n de r gr ou n d st or a ge -gr ou n dw a t e r

N it T l & t i l  N e ce ssit y: Te m por a l & spa t ia l

va r ia t ion of r a in fa ll & w a t e r a va ila bilit y

http://wrmin.nic.in/

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www.medindia.net

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I nt roduct ion t o Rainwat er Harvest ing..

 Rainwat er harvest ing- t echnology used for collect ing &

st oring rainwat er from rooft ops, land surface or cat chm ent s/ w at ersheds using various t echniques cat chm ent s/ w at ersheds using various t echniques such as t anks or check dam s or recharge t o aquifer.

 Most prom ising alt ernat ives for supplying freshw at er

in t he face of increasing wat er scarcit y & escalat ing dem and.

 Basic Com ponent s of RWH:

– Precipit at ion

– Collect ion of w at er from surface cat chm ent

W t t

– Wat er st orage

– Dist ribut ion of w at er

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W h y Ra in w a t e r H a r ve st in g ( RW H ) ?.

 Rainwat er Harvest ing - yield copious am ount s of wat er.

For average rainfall of 1,000m m , approxim at ely four m illion lit ers of rainwat er can be collect ed in a year in m illion lit ers of rainwat er can be collect ed in a year in an acre of land ( 4,047 m 2) , post - evaporat ion.

 As RWH is neit her energy- int ensive nor labor- int ensive,

- a cost - effect ive alt ernat ive t o ot her wat er- accruing m et hods, such as desalinat ion of seawat er & wat er t ransfer.

 Wit h t he wat er t able falling rapidly, & wit h concret e

buildings, paved car parks, business com plexes, & landfill dum ps t aking t he place of wat er bodies landfill dum ps t aking t he place of wat er bodies, RWH is t he m ost reliable solut ion for augm ent ing groundwat er level t o at t ain self- sufficiency in public dist ribut ion of wat er

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Prof. T I Eldho, Department of Civil Engineering, IIT Bombay

dist ribut ion of wat er.

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Ra in w a t e r H a r ve st in g

Ra in w a t e r H a r ve st in g -- Pu r pose s

Pu r pose s

Rainwat er Harvest ing t echniques can serve t he following purposes:

T M j P A i lt l

 Tw o Maj or Purposes: Agricult ural

and hum an consum pt ion

 I ncrease groundwat er recharge

Red e st o m at e dis ha ges ma

urban floods and overloading of sewage t reat m ent plant s  Reduce seawat er ingress in coast al

areas

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Photo A K Singh 2002

Rainw at er Harvest ing

Rainw at er Harvest ing -- Met hodologies

Met hodologies

Photo, A.K. Singh, 2002

Wat er harvest ing - undert aken t hrough a variet y of ways

 Capt uring runoff from rooft ops – Roof wat er harvest  Capt uring runoff from local cat chm ent s – Land harvest  Capt uring seasonal floodwat ers from local st ream s

 Conserving wat er t hrough wat ershed m anagem ent  Conserving wat er t hrough wat ershed m anagem ent 

For Urban & I ndust rial Environm ent

–

 Roof & Land based RWH  Roof & Land based RWH

– Public, Privat e, Office & I ndust rial buildings – Pavem ent s, Lawns, Gardens & ot her open

spaces

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Rainw at er Harvest ing

Rainw at er Harvest ing -- Advant ages

Advant ages

 Provides self- sufficiency t o wat er supply

 Reduces t he cost for pum ping of groundwat er

 Provides high qualit y wat er, soft and low in m inerals  I m proves t he qualit y of ground wat er t hrough dilut ion

when recharged t o groundwat er when recharged t o groundwat er

 Reduces soil erosion in urban areas

 Rooft op rain wat er harvest ing is less expensive p g p

 Rainwat er harvest ing syst em s are sim ple which can be

adopt ed by individuals

R ft i t h t i t t

 Rooft op rain w at er harvest ing syst em s are easy t o

const ruct , operat e and m aint ain.

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Rainwat er Harvest ing

Rainwat er Harvest ing –

– Advant ages…

Advant ages…

 I n hilly t errains, rain wat er harvest ing is preferred  I n saline or coast al areas, rain wat er provides good

qualit y wat er and when recharged t o groundwat er, it reduces salinit y and also helps in m aint aining balance bet ween t he fresh- saline wat er int erface

 I n I slands, due t o lim it ed ext ent of fresh wat er

aquifers, rain wat er harvest ing is t he m ost preferred source of wat er for dom est ic use

source of wat er for dom est ic use

 I n desert , where rain fall is low, rain wat er harvest ing

has been providing relief t o people

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Rainw at er Harvest ing

Rainw at er Harvest ing –

– Technology

Technology

 Type of rainwat er harvest ing st ruct ures depends

Topography

– Topography

– Availabilit y of land – Rainfall – Rooft op harvest ing

– Wells and radiat or wells – Parking lot st orage

– Recreat ional Park pondsRecreat ional Park ponds

 Open areas

– Percolat ion ponds

– I nfilt rat ion galleriesI nfilt rat ion galleries _{Ph t} _{A K Si} _{h 2002} – Com m unit y w ells

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Rainw at er Harvest ing

Rainw at er Harvest ing –

– Pot ent ial

 Wat er y ield from a cat chm ent depends on am ount of

rainfall, w at ershed slope, t ypes of soil and veget at ion and t he evapot ranspirat ion rat io.p p

Veget at ion Managem ent :

 I m proved m anagem ent of veget at ion are m ainly applicable

t o large areasg

 Wat er yield from a grass cover is m ore t han t hat from a

forest cover

Land alt erat ion:

 Alt erat ion of land surface of a cat chm ent ( pervious t o

im pervious)

 Laying of paved surfaces on sloping cat chm ent s along w it h y g p p g g

drains at t heir sides

 Collect ion of cat chm ent runoff in st orage t anks

 Met hod is Preferable w here t he land surface is undulat ing.

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od ab a d u a u du a g

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H ydr ologica l Aspe ct s of RW H

 Rainfall m ain source of wat er



 Hydrological Cycle Hydrological Cycle -- Change in phase in Change in phase in HydrosphereHydrosphere  Balance of wat er on Eart h rem ains fairly const ant over

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RW H – Ra in fa ll t o Ru n off

 Various process and pat hways det erm ine how m uch

and how fast precipit at ion becom es st ream flow.

 Fact ors effect ing runoff response:  Fact ors effect ing runoff response:

– Precipit at ion form , int ensit y, durat ion, dist ribut ion – St orage ( soil m oist ure, sat urat ed areas)

– Flow pat hway ( e.g., shallow soil layer vs. deeper soil layer, or overland surfaces or subsurface)

Spat ial dist ribut ion & geom orphic feat ures – Spat ial dist ribut ion & geom orphic feat ures

 Met eorological fact ors: Type of precipit at ion ( rain,

snow, et c.) : Rainfall int ensit y - am ount , durat ion; Dist ribut ion of rainfall over t he drainage basin, Direct ion of st orm m ovem ent , Precipit at ion t hat occurred earlier and result ing soil m oist ure.

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occu ed ea e a d esu g so o s u e

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How Much Wat er can be Harvest ed?

 The t ot al am ount of wat er t hat is received in t he form

of rainfall over an area is called t he rainw at er endow m ent of t hat area.

endow m ent of t hat area.

 Out of t his, t he am ount t hat can be effect ively

harvest ed is called t he w at er harvest ing pot ent ial.

h l f ll ( )

 Wat er harvest ing pot ent ial = Rainfall ( m m ) x

Collect ion efficiency.

 The The collect ion efficiencycollect ion efficiency account s for t he fact t hat all account s for t he fact t hat all

rainwat er falling over an area cannot be effect ively harvest ed, because of evaporat ion, spillage et c. Fact ors like runoff coefficient is t o be considered

 Fact ors like runoff coefficient is t o be considered.

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www.cimic-coe.org

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How Much Wat er can be Harvest ed?

 Runoff coefficient - fact or account s t hat all t he rainfall falling

on a cat chm ent cannot be collect ed. Som e rainfall will be lost from t he cat chm ent by evaporat ion & ret ent ion on t he surface it self.

 Ru n off coe fficie n t s for va r iou s su r fa ce s

 Type of Ca t ch m e n t Coe fficie n t s

 Roof Cat chm ent s: Tiles 0.8 – 0.9; - Corrugat ed m et al sheet s 0.7 – 0.9  Ground surface coverings- Concret e 0.6–0.8; Brick pavem ent 0.5–0.6

 Unt reat ed ground cat chm ent s - Soil on slopes less t han 10 per cent

0.0 – 0.3; Rocky nat ural cat chm ent s 0.2 – 0.5

Source: Pacey, Arnold and Cullis, Adrian 1989, Rainw at er Harvest ing: The collect ion of rainfall and runoff in rural areas, I nt erm ediat e Technology Publicat ions, London, pg. 55

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How Much Wat er can be Harvest ed?

Prof. T I Eldho, Department of Civil Engineering, IIT BombayJan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Months

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RWH

RWH –

– Calculat ion?

Calculat ion?

C id b ildi i h fl f 100

 Consider a building w it h a flat t errace area of 100 sq.

m . The average annual rainfall be approxim at ely 900 m m . I t m eans t hat if t he t errace floor is assum ed t o be im perm eable, and all t he rain t hat falls on it is

ret ained, t hen, in one year, t here will be rainwat er on t he t errace floor t o a height of 900 m m .g

Area of plot = 100 sq. m .

Height of rainfall = 0.9 m ( 900 m m )

Volum e of rainfall = Area of plot x Height of rainfall = 100 sq. m . x 0.9 m = 90 cu. m . ( 90,000 lit ers)

Assum ing t hat only 70% of t he t ot al rainfall is effect ively Assum ing t hat only 70% of t he t ot al rainfall is effect ively

harvest ed,

Volum e of wat er harvest ed = 63,000 lit ers ( 90,000 lit 0 7)

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lit res x 0.7) .

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How Much Wat er Can be Collect ed ?

– Colle ct ion Efficie n cy

How efficient ly t he rainfall can be collect ed depends on several considerat ions. Collect ion efficiencies of 80% several considerat ions. Collect ion efficiencies of 80% are oft en used depending on t he specific design.

– Rainfall Reliabilit y.

The m ain st ep is t o det erm ine how m uch wat er would The m ain st ep is t o det erm ine how m uch wat er would be generat ed from t he roof area. Average m onsoon rainfall is used for t his purpose.

– Form ula:

– Tot al quant it y of wat er

t o be collect ed ( cu m ) = Roof Top Area ( Sq m ) t o be collect ed ( cu.m .) = Roof Top Area ( Sq.m .)

x Average Monsoon Rainfall ( m ) x Collect ion efficiency

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Rainfall Dist ribut ion in I ndia

 Because of dist inct ive clim at e

– I nt ense m onsoons followed by prot ract ed drought s

-st orage of rainwat er at st orage of rainwat er at

appropriat e sit es becom es im perat ive.

 Eight y percent of annual Eight y percent of annual

rainfall of 1170 m m is

received during t hree m ont hs period.

ll h

 During rainy season all t he

rain falls in about 200 hours and half of it in 30 – 40 hours. Consequent ly runoff is very

 Consequent ly runoff is very

high. I f it is capt ured and st ored, it can be used

effect ively lat er on.

.

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effect ively lat er on.

.

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Rainfall in Mum bai

• Average t ot al annual rainfall is 2335 m m .g • Average annual t em perat ure is 27.2oC Based on 25 years dat a ( 1982- 2006).

Months Av. Annual Rainfall

( ) Rainy Days o s

(mm) y ys

Jan 1.0 0.0

Feb 0.5 0.1

Mar 0.7 0.1

Apr 0.4 0.0

May 29.6 1.0

Jun 475.1 13.5

Jul 815.9 22.8

Aug 579.3 21.7

Sep 328.4 13.8

Oct 93.7 3.4

Nov 8.2 0.4

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Nov 8.2 0.4

Dec 1.9 0.3

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Hydro- geological Aspect s of RWH

H d l f h

 Hydrogeology of t he area - nat ure

& ext ent of aquifer, soil cover,

t opography, dept h t o wat er levels & chem ical qualit y of ground

w at er.

 Eg Geology of I ndia is as diverse  Eg. Geology of I ndia is as diverse

as it s geography and people. I t cont ains rocks covering alm ost t he ent ire spect rum of t he

t he ent ire spect rum of t he Geological Tim e Scale.

 Eg: Archean, Deccan Trap,

Gondwana Super group,

Vindhyan Super group , The

Tert iary group et c. ht t p: / / cgwb.gov.in

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y g p

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H ydr o- ge ology & W a t e r Re sou r ce s

 Wat er resources- as a result of

Hydrogeology – I m port ant param et ers

 soil t hickness  soil t hickness

 dist ribut ion of rock exposures  pore net works in t he rocks

 wat er recharge areas, discharge

locat ions, and general flow direct ions of groundwat er direct ions of groundwat er

 fluid- flow charact erist ics of m ain

aquifer t ypes, including yield

22  ground feat ures ( eg. lineam ent )

ht t p: / / cgwb.gov.in

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Groundwat er & Recharge

 Groundw at er - m aj or sources for wat er

supply in m any part s of t he w orld.

 Ground wat er collect s in aquifers over  Ground wat er collect s in aquifers over

t housands of years t hrough infilt rat ion & ground w at er flow recharge.

 A part icular am ount of groundw at er is

replenished regularly t hrough rainw at er replenished regularly t hrough rainw at er infilt rat ion.

 Sust ainable use of groundw at er m eans

w it hdraw al of ground wat er at a rat e at g w hich it is replenished t hrough

recharge.

 Fast er w it hdrawal rat es would lead t o

fall in wat er t able & finally deplet ion of

ht t p: / / cgwb.gov.in

fall in wat er t able & finally deplet ion of ground w at er.

 The ground w at er recharge areas need

t o be ident ified so t hat m ax. recharge

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Gr ou n dw a t e r Re ch a r ge

 Groundw at er availabilit y depends on recharge.

 Groundw at er - cont rolled by t he hydro- geological sit uat ion

charact erized by alluvial form at ion & quart zit ic hard rocks.

 Groundw at er quant it y depends- Pot ent ial Areas & availabilit y of Groundw at er quant it y depends Pot ent ial Areas & availabilit y of

unsat urat ed zone for recharge.

 Pre- requisit es for art ificial recharge:

– 1 Favorable hydrological set - up1. Favorable hydrological set up. 2. Developed aquifers.

3. Availabilit y of unpollut ed surface wat er. 4. Ground wat er dependent com m unit y.

 Nat ural Recharge

 Nat urally occurring wat er added t o an aquifer

 Nat ural recharge com es from precipit at ion or st orm runoff

A t ifi i l R h

 Art ificial Recharge

 St ore surplus surface wat er underground

 Put t ing surface wat er in basins, furrows, dit ches, or ot her facilit ies

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Artificial Recharge Techniques

 D ir e ct su r fa ce t e ch n iqu e sq

 Flooding

 Basins or percolat ion t anks

 Com bin a t ion su r fa ce –

 Basin or percolat ion

t anks wit h pit shaft or

 Recharge pit s and shaft s

 I nduced recharge from

surface wat er source.

 Aquifer m odificat ion.  Recharge pit s and shaft s

 Dug well recharge  Bore hole flooding

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g

 Nat ural openings, cavit y

fillings

.

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Rainwat er Harvest ing St ruct ures

• St orage of rain wat er on surface for fut ure use

• Recharge t o groundwat er • Pit s

• Trenches • Dug wells • Hand pum ps • Recharge wells • Recharge wells • Recharge shaft s

• Lat eral shaft s wit h bore wells • Spreading t echniques

• Spreading t echniques

( Source: ht t p: / / rainwat erharvest ing.org)

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( p / / g g)

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Est im at ion of Groundw at er

Recharge

 Soil wat er balance m et hod  Soil wat er balance m et hod

 Ground wat er level fluct uat ion m et hod

 Ground wat er balance m et hod

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Design Considerat ions of RWH

 Requirem ent Direct use St orage & needs  Requirem ent – Direct use – St orage & needs

 Recharge t o im prove groundw at er availabilit y

 Hydrogeology of t he area - nat ure & ext ent of aquifer, soil

t h d t h t t l l & h i l lit

cover, t opography, dept h t o w at er levels & chem ical qualit y of ground w at er

 Area cont ribut ing for runoff i.e. how m uch area & land use

pat t ern, w het her indust rial, resident ial or green belt s and general built up pat t ern of t he area

 Hydro- m et eorological charact ers viz. rainfall durat ion,

general pat t ern & int ensit y of rainfall

• Recharge st ruct ures should be designed based on

availabilit y of space, availabilit y of runoff, dept h t o wat er t able & lit hology of t he area.

 Runoff should be accurat ely est im at ed.

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I nt egrat ed RWH Met hodology

 Based on: Geology, Topography, dem and, w at er availabilit y,

infilt rat ion rat e econom ic st at us of t he users

( Source: ht t p: / / rainwat erharvest ing.org)

infilt rat ion rat e, econom ic st at us of t he users.

 I nt egrat ed Rainw at er harvest ing syst em designed

 Com binat ion of Rainw at er Harvest ing st ruct ures like recharge

t renches sum p percolat ion pond et c t renches, sum p, percolat ion pond et c.

 Rainw at er harvest ing in t he st udy area m ay be div ided int o

t w o

– ( i) from built up areas

– ( ii) from non- built up areas

– ( iii) w at ershed based approach.( ) pp

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Flow ch a r t for I n t e gr a t e d RW H in a n Ar e a

Rainwater Harvesting

Non Built up Areas Built up Areas

Direct use To recharge the aquifer

Check dam/ Percolation pond

G d t Sumps Excess Recharge _Pit/

Trenches

Groundwater Recharge & Future

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Case St udy: RWH in Jhabua Wat ershed

 Highly undulat ing, sparsely dist ribut ed

forest cover.

 57% arable land including cult ivable

f ll & 18% t ifi d f t l d

0 50 100

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec PE AE P

fallow & 18% not ified as forest land.

 Average rainfall ~ 750 m m per annum .

 20- 30 event s during June- Sept em ber

Cl ifi d d ht i

 Classified as drought prone region.

 Moist ure deficit during January t o May

Ref: Singh, A.K., T.I. Eldho, D. Prinz (2002)

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Case St udy: RWH in Jhabua Wat ershed

 RWH Measures - Tot al num ber of reservoirs = 144

 St orage capacit y = 81.3 x 106 m 3

Wat er conservat ion and groundw at er recharge t echniques

 Wat er conservat ion and groundw at er recharge t echniques

 Wat er harvest ing cum supplem ent ary irrigat ion t echniques

 Rainw at er harvest ing int ervent ions includes cont our

t renches, gully plugging, veget at ive and field bunding, check dam s, percolat ion t anks et c.

a

Photo A K Singh 2002

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Case St udy: RWH - I m pact s

• About 2- 4 m et er wat er level increase is observed in select ed wells.

select ed wells.

• Sufficient wat er for dom est ic and agricult ural purposes • One farm ing per year 2 t o 3 farm ing of various crops

No wat er scarcit y even in drought period

 No wat er scarcit y even in drought period.  Agricult ural yield increased by 30- 60%  I m provem ent in % of forest landI m provem ent in % of forest land

 Overall econom ic & social uplift m ent of t he people  People part icipat ion in t he RWH schem es.

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Re fe r e n ce s

 CGWB, ht t p: / / cgwb.gov.in/ groundwat er

• J.V.S Murt hy ( 1991) , Wat ershed Managem ent , New Age y ( ) , g , g

int ernat ional Publicat ions

• Ghanshyam Das ( 2000) , Hydrology and soil conservat ion

engineering, Prent ice Hall of I ndiag g,

• Pat el and Shah ( 2008) , Wat er Managem ent , New Age

int ernat ional Publicat ions

 www rainwat erharvest ing org

 w w w .rainwat erharvest ing.org

 w w w .cseindia.org

 www.fao.org

 ht t p: / / forest .m t u.edu/

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Tu t or ia ls - Qu e st ion !.?.



D e scr ibe t h e t r a dit ion a l w a t e r

h a r ve st in g syst e m a dopt e d in I n dia .



( Ref:

ht t p: / / cgw b.gov.in;

w ww.rainwat erharvest ing.org; www.cseindia.org)



 I llust rat e t he syst em s used for roof rain wat er I llust rat e t he syst em s used for roof rain wat er

harvest ing. harvest ing.



 I llust rat e t he various schem es used for Groundwat er I llust rat e t he various schem es used for Groundwat er 

 I llust rat e t he various schem es used for Groundwat er I llust rat e t he various schem es used for Groundwat er

recharge schem es recharge schem es



 Discuss various t echniques adopt ed at various Discuss various t echniques adopt ed at various

l t i

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Se lf Eva lu a t ion - Qu e st ion s!.

Q



Discuss t he necessit y & purposes of RWH.

Wh t

t h

d

t

f

RWH?



What are t he advant ages of RWH?.



Discuss t he hydrological aspect s of RWH.

I ll

h i

f h d

l

i

l



I llust rat e t he im port ance of hydro- geological

aspect s of RWH.

What are t he im port ant design



What are t he im port ant design

considerat ions of RWH?.

P f T I Eldh D t t f Ci il E i i IIT B b

36 36

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Assign m e n t - Qu e st ion s?.

g

Q



I llust rat e various RWH m et hodologies for

various locat ions

various locat ions.



How t o assess RWH pot ent ial for an area?.

Discuss various t echniques of art ificial



Discuss various t echniques of art ificial

groundwat er recharge.



What is int egrat ed RWH m et hodology?



What is int egrat ed RWH m et hodology?.

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Un solve d Pr oble m !.



 For your Wat ershed area, prepare an int egrat ed plan For your Wat ershed area, prepare an int egrat ed plan

of Rainwat er Harvest ing Schem e considering wat er of Rainwat er Harvest ing Schem e considering wat er st orage & recharge.

– Design an int egrat ed RWH schem e including Design an int egrat ed RWH schem e including groundw at er recharge.

groundw at er recharge.

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Dr. T. I. Eldho Dr. T. I. Eldho Professor,

Professor,

Department of Civil Engineering, Department of Civil Engineering, pp gg gg

Indian Institute of Technology Bombay, Indian Institute of Technology Bombay, Mumbai, India, 400 076.

Mumbai, India, 400 076.

Email:

Email: eldho@iitb.ac.ineldho@iitb.ac.in

39 39

Email:

Email: eldho@iitb.ac.ineldho@iitb.ac.in

Phone: (022)

Phone: (022) –– 25767339; Fax: 2576730225767339; Fax: 25767302

http://www.