Artificial Groundwater Recharge for Water Supply of Medium-size Communities in Developing Countries

8/12/2019 Artificial Groundwater Recharge for Water Supply of Medium-size Communities in Developing Countries

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ARTIFICIAL GROUNDWATER RECHARGE

FOR WATER SUPPLY

OF MEDIUM SIZE COMMUNITIES

IN DEVELOPING COUNTRIES

by

E H Hofkes

and

J T Visscher

December 1986

In te rna t iona l Reference Centre

for Community Water Supply and Sani ta t ion

The Hague The Netherlands


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1.

PREFACESUMM RY

INTRODUCTION

CONTENTS

1.1 Groundwater as a source o f water supply1.2 r t i f i c i a l groundwater recharge

2. ARTIFICIAL GROUNDWATER RECHARGE SCHEMESFOR COMMUNITY WATER SUPPLY2.1 Water qua l i t y aspec ts2.2 Storage

2.2.1 Effec t ive poros i ty2.2 .2 Storage capac i ty

2.3 Hydraul ic design of a r t i f i c i a l recharge schemes2.3.1 I n f i l t r a t i o n r a t e2 .3 .2 Reten t ion t ime2.3 .3 Permeabil i ty2 .3 .4 Hydraul ic t ransmiss iv i ty

3. PLANNING ND ORGANIZATIONAL ASPECTS OFARTIFICIAL GROUNDWATER RECHARGE SCHEMES3.1 Planning

4.

3.2 Community involvement3.3 Organizat ional aspec ts3.4 Hygiene educa t ion

TYPES OF ARTIFICIAL GROUNDWATER RECHARGE SCHEMES4.1 I n f i l t r a t i o n d i t ches ponds and bas ins4.2 Induced recharge4.3 Retent ion of r i v e r underflow4.4 Retent ion of r i v e r f lood water4.5 Recovery means

4.5.1 Col lec tor d ra ins4 .5 .2 Dug wells4.5 .3 Boreholes

5. BASIC DESIGN OF ARTIFICIAL GROUNDWATERRECHARGE SCHEMES

6.

5.1 Pr i nc ipa l design parameters5.2 Example design

FIELD EXPERIENCE AND COSTS OFARTIFICIAL RECHARGE SCHEMES6.1 Fie ld experience6 .2 Costs

SELECTED BIBLIOGRAPHY

Appendix C r i t e r i a for smal l - sca le a r t i f i c i a lrecharge schemes

3

678999

1212

3136

18

223252628282930

3233

3637

38

40


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PREFACE

A r t i f i c i a l groundwater recharge schemes have the advantage t ha t they canproduce water t ha t i s hygienica lly safe and f i t for domestic use,without requir ing extensive provisions for water t reatment . This f i t s inthe curren t t rend of el iminating where poss ib le t reatment plantsespecia l ly for medium-size communities in ru ra l areas of developingcount r ies , where the organizat ional inf ras t ruc ture i s of ten weak,supplies of power and chemicals unre l iab le , f inancia l resources l imi ted ,and sk i l l ed s t a f f d i f f i c u l t to obta in . I t i s therefore , appropriate tostudy the potent ia l appl ica t ion of a r t i f + c i a l groundwater recharge forcommunity water supply so t ha t adequate assessment can be made of i t smerits and l imi ta t ions .

This document in tegra tes mater ia l se lec ted from many sources, bothpublished and unpublished. The focus i s on potent ia l appl ica t ion ofa r t i f i c i a l groundwater recharge for water supply of medium-size

communities. Published mater ia l mainly concerns la rge-sca le schemes inthe i ndus t r i a l i zed countr ies of Western Europe and North America, andmost of t h i s information has l i t t l e spec i f i c appl ica t ion for t h i sdocument. However, se lec ted information and per t inent data from thesesources have been incorporated.

The purpose of t h i s document i s to provide planners and engineers withprac t i ca l information to assess the po ten t i a l for appl ica t ion ofa r t i f i c i a l groundwater recharge schemes in rura l water supply programmesor pro jec t s .

The study was carr ied out with f inancial support of the NetherlandsMinistry of Housing, Physical Planning, and Environment. The study wassupported by, and benef i t ted grea t ly from, the comments and suggest ionsof the I n f i l t r a t i o n Committee of Netherlands Testing and ResearchIns t i tu te for the Water Industry KIWA).

We wish to acknowledge with appreciat ion the work of Mr. P. Tollenaarw h o ~ ~ c r r i e dout an extensive l i t e r a t u r e survey, and made the compilation

~ f se lec ted information which served as the bas is for t h i s repor t . Ms-C. van Wijk-Sijbesma i s thanked for her valuable comments andsuggest ions which grea t ly contr ibuted to improvement of the document.


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SUMM RY

A r t i f i c i a l groundwater recharge schemes involve measures fori n f i l t r a t i o n of water i n to pervious underground formations t o augmentthe y ie ld capac i ty o f these formations. The qua l i t y of the i n f i l t r a t e d

water improves in most respec ts and the s to rage capac i ty o f theformation can be used t o ensure a v a i l a b i l i t y o f water co l l ec t ed i n thewet season for use in dry periods. Technical ly a r t i f i c i a l rechargeschemes are l i ke ly to be f ea s ib l e in most areas where aqui fer format ionsare su i t ab l e for recharge and s to rage of wate r.

Recharge schemes are economically a t t r a c t i v e and worth cons idera t ion inru ra l areas o f developing count r ies where they are a viable a l t e rna t iveto t reatment works for medium-size water suppl ies . While the c a p i t a lcos ts of recharge schemes are comparable to those of water t r ea tmentworks the recur ren t cos ts for opera t ion and maintenance are l i k e l y tobe lower.

o data are ava i lab le on the soc i a l and cu l tu ra l accep tab i l i t y ofrecharge schemes to the benef ic ia ry communities and t h e i r s u i t a b i l i t yfor community pa r t i c ipa t ion i n plann ing cons t ruc t ion opera t ion andmaintenance needs to be ascer ta ined .

Tentat ive c r i t e r i a for smal l - sca le a r t i f i c i a l recharge schemes are givenin Appendix I . However such c r i t e r i a need to be val ida ted by f i e l ds tud i e s p i l o t schemes and prac t i ca l exper ience in opera t ion andmaintenance.


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1 . INTRODU TION

1.1 Groundwater as a source of water supply

Groundwater as a source of water supply has grea t advantages over

surface water from streams, r ive r s , or lakes . Due to the long re tent ion

t ime underground, of ten for t en years and longer, groundwater i s

genera l ly hygienical ly safe for drinking,and domestic use, and i t can e

s tored for use in periods when drought condit ions have depleted the

surface sources.

Most groundwater resources receive natura l recharge from i n f i l t r a t i n g

rainwater or surface water. The water slowly flows underground to places

where t i s discharged in to streams, r ive r s , lakes, or d i rec t ly in to the

seas and oceans.

In most areas of the world there i s groundwater avai lab le a t some depth,

but the quant i t ies involved vary widely for d i ff e ren t types of

formations. Sedimentary formations which cons is t of deposi ts of

granular rock fragments and prec ip i t a t e s e .g . , sand, gravel , sandstone,

sha le , l imestone) , can hold l a rge quant i t ies of water in the pores andcrevices between the granular par t i c l e s . Metamorphic f o r m a t i o ~ ssuch as

gneiss , quar tz i te and s l a t e formed out of sedimentary or igneous rocks

by the e ffec t s of heat and pressure can hold only l imited quant i t ies in

the small and unconnected voids and pores in the rocks. However, there

are of ten f rac tures , j o in t s , and bedding planes in these rocks where

groundwater can occur in appreciable quant i t ies . Igneous rocks derived

from cooled magma e .g . , grani te , marble, and c rys t a l l i ne rocks, such as

the African Basement Complex are dense and only small quan t i t i e s ofwater occur in f i ssures and f au l t zones. However, often more water i s

held and t ransmit ted in the weathered and fragmented upper zones.

Thus, the quant i t ies of groundwater found in underground formations are

la rge ly governed by the nature and composition of the formations and by

the natura l recharge. The yie ld capaci ty of d i ff e ren t types of aquifer

var ies widely. In c rys ta l l ine rock, a borehole should not be expected


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to give more than one or two l i t r e s per second, and even depends on

s t r ik ing a water-bearing f i s su re . By con t ra s t , wells and boreholes in

sedimentary formations may have a yie ld of up to severa l hundreds of

l i t r e s per second.

Another important charac te r i s t i c of water-bearing formations or aqui fers

i s whether they are unconfined or confined. Unconfined aqui fers a re

open to recharge by i n f i l t r a t i n g surface water and the groundwater tab le

wi l l f luc tua te with the amount of r e c h ~ r g ein re l a t ion to the water

outf low from the aqui fer Figure 1.1) . Confined, or ar tes ian aqui fers

are water-bearing formations having an impervious base, mostly bedrock,

and an impervious overlaying formation. The water in a confined aqui fer

i s of ten under pressure Figure 1.2) .

;

. __

:

:

: .

t

UI\}U tJFiNEOf t l J J t i F E ~ . . . ; --: : : :

0 : . : : 0 : : : : ,

40

, . : : : : :. : : : .: :: :0 : : : : . : . : : : : = : : .~ : 0

Figure 1.1: Unconfined aqui fer

r t i f i c i a l recharge of a confined aqui fer by d i rec t i n f i l t r a t i o n ofsurface water i s not poss ib le without specia l provisions, such as a

recharge borehole to penet ra te the impervious overlayer, and therefore

are not considered fur ther here.

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Figure 1.2: Confined aqui fer

1.2 A r t i f i c i a l groundwater recharge

A r t i f i c i a l groundwater recharge involves measures to i n f i l t r t e surface

water i n to pervious underground formations to augment yie ld capac i ty.

These measurers are par t i cu la r ly useful in areas where the-na tura l

recharge of aquifers i s small . There are various types of r t i f i c i l

recharge schemes but only open i n f i l t r t i o n means are considered here.

Attent ion i s given to the potent ia l of r t i f i c i l groundwater recharge

for water supply of medium-size communities of 5000 15 000 inhabi tan ts

in developing count r ies .

While i t m y seem i ne ff i c i en t to i n f i l t r t e water in to undergroundformations and then abs t rac t i t for community water supply the

benef i t s of these operat ions in terms of improved water qual i ty and

assured ava i l ab i l i t y are considerable. Fi r s t ly the process ofr t i f i c i l recharge reduce the number of pathogenic bacter ia and other

micro-organisms in the water; pol lu ted surface water can be converted

in to a groundwater resource which i s sa fe for drinking and domestic

use. Secondly water s tored underground i s la rge ly protected from

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po l lu t ion and evaporat ion, as compared with water storage in open

surface r e se rvo i r s . Thirdly, water taken from sur face sources in the

wet season and i n f i l t r t e d for s torage underground, i s avai lab le for

abs t rac t ion in the dry season. Ava i l ab i l i t y of water throughout the

year i s par t i cu la r ly assured i f deep underground s t r t are used for

r t i f i c i l recharge; shallow groundwater resources are l e s s r e l i a b l e ,

because they may dry up in the dry season.

The main components of an r t i f i c i l ,groundwater recharge scheme are

Figure 1 3) :0

0

0

0

recharge means;

pervious underground formation;

recovery means;

system boundaries , e .g . the impermeable base and confining

impervious l ayers on the s ides of the scheme.

; . .:.- ..

. ;-: > ; - -- ; ~~ ~./;:;Xtq.:>-;-;-:;::,;: ;;/ / / / / / / / / / / / / / / / / / / / / / / / / / / / /

/ / / / / / / / / / / / / / / / / / / / I / /1

Figure 1.3: Main fea tures of r t i f i c i l recharge scheme

To al low for adequate pur i f i ca t ion of the water, r t i f i c i l rechargeschemes must be designed for a water re tent ion t ime of t l eas t th ree

weeks, and preferably one to two months. This i s the period during

which the water t r ave l s underground from the recharge area to the

recovery means which must be t a su ff i c i en t dis tance from the poin t of

recharge, depending on the veloc i ty of water flow through the

underground formation. The degree to which the movement of the

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i n f i l t r t e d water through the recharged formation can be cont ro l led

depends on the system boundaries such as an impermeable base and

confining layers to l imi t water losses from the r t i f i c i l recharge

system.


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2 . ARTIFICIAL GROUNDW TER RECH RGE FOR c o a m N T Y W TER SUPPLY

2.1 Water qual i ty aspects

As already s ta ted , various biologica l , chemical and physical processes

occur in the water during a r t i f i c i a l recharge. In most recharge works

the water i s in open contact with the atmosphere so t ha t i t i s aera ted ,

for absorpt ion of oxygen and re lease ,of carbon dioxide. Some s e t t l i n g

of oxidized organic matter and suspended sol ids occurs , thus forming a

f i l t e r matting of deposited material on the bottom of the recharge

means.

As the water enters the i n f i l t r a t i o n zone impur i t ies a re f i l t e r e d out ,

because a l l par t i c l e s la rger than the s o i l pores are re ta ined . Active

colonies of predatory micro-organisms and bacter ia develop and feed on

the organic matter and other nutr ients present in the i n f i l t r a t i n g

water. Most of the bacter ia and other micro-organisms are removed or

re ta ined in the top few decimeters of the i n f i l t r a t i o n zone, and very

few are carr ied deeper in to the ground than 1 2 m Suspended so l id s are

removed by sedimentation and adsorpt ion on the s o i l par t i c l e s . There i s

act ive oxidat ion of both organic and inorganic compounds. Variousco l lo ida l and dissolved impur i t ies a re re ta ined by adherence on the

surfaces of so i l pa r t i c l e s . The water pur i f i ca t ion processes are more

act ive in the top l ayer of the i n f i l t r a t i o n zone, and in the f i l t e r

matt ing of deposi ted material and microbial l i f e which forms on top of

i t .

After passing the i n f i l t r a t i o n zone, the water percola tes downward in

the underground formation to reach the groundwater t ab l e . I n i t i a l l yoxygen i s avai lab le in the water and fu r the r oxidat ion of organic matter

occurs . Because of the continuing breakdown of organic matter,

accumulation of pol lu tants in the underground should not be a problem

for small-scale a r t i f i c i a l recharge schemes. Die-off of bacter ia and

other micro-organisms continues because most of the su i t ab l e nu t r i en t s

have been removed from the water Table 2.1}.

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Table 2.1: Survival t ime for pathogenic bacter ia andvi ruses i n underground formations

Bacter ia /v i ruses

Faecal col iformsEntamoeba h i s t o l y t i c aEntero vi rusCyst of Ascaris

Source: Fi ld ie r 1983.

Survival time

6 days8 days2 days6 months

Not a l l the chemical and physical processes working in the water during

i t s underground t r ave l produce improvement of the water qual i ty. Some

e ffec t changes which can make the water l e s s su i tab le for drinking and

domestic supply. The water wi l l disso lve various cons t i tuents from the

formation s t r a t a through which i t flows. For example calcium and

manganese carbonates can be taken up by the water espec ia l ly i ~ i t i s

acid ic . Iron and manganese are leached out i f present in the

formation. In formations containing peat or the remains of animal l i f e

organic compounds are l i k e l y t ~ e taken up by the water. In an

anaerobic water environment ammonia sulphides and n i t r i t e s can be

formed by reduct ion processes. Some t reatment of the water such as

aera t ion and f i l t r a t i o n i s then needed to produce drinking water of

acceptable qua l i t y.

2.2 Storage

Storage i s a very important aspect of a r t i f i c i a l recharge schemes

because water can be i n f i l t r a t e d during the wet season and s tored

underground for use n dry periods. Sedimentary formations espec ia l ly

sand and gravel aqui fers general ly have the l a rges t storage capaci ty.As water can only occur in the j o in t s f rac tures and f i s su re s of

consol idated rocks the storage capaci ty of these formations therefore

i s very l imi ted .

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2.2.1 Effec t ive poros i ty

The e ffec t ive poros i ty i s the pore space in a un i t volume of rock in

which the water can move f ree ly. t i s l e s s than the void poros i ty

because the pores a lso conta in water which i s bound by absorpt ion to the

surface of the formation par t i c l e s (Table 2.2) . Apart from the type of

rock, the e ffec t ive poros i ty also depends on the s i ze d i s t r ibu t ion o f

formation par t i c l e s , and how dense the packing of the par t i c l e s i s

(Figure 2.1) .

Table 2. 2: Poros i ty and e ffec t ive poros i ty of var ious types of rock

Type o f rock

c laysandgrave lsand & gravelsandstonesha lel ime stoneigneous rock

Based on Campbell & Lehr, 1973

c

b

Figure 2.1: Rock poros i ty

Void poros i ty( )

4 - 3535 - 4030 - 402 - 251 - 2

1 11 1

0.001 - 1

e

Effec t ive poros i ty( )

1 - 11 - 3025 - 3015 - 25

5 - 150.5 - 20.5 - 2

negl ig ib le

(a) well-sorted sedimentary depos i t having a high poros i ty ;(b) poorly-sorted sedimentary depos i t having a low poros i ty ;(c) wel l -sor ted sedimentary depos i t s with a very high poros i ty ;(d) sedimentary grave l deposi t with the pores f i l l e d up by sand

p a r t i c l e s , so t h a t poros i ty i s reduced;(e) fragmented rock with unevenly d i s t r ibu ted poros i ty ;( f ) fractured rock having a r e l a t ive ly low poros i ty.

(Source: Meinzer, 1959)

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In unconsol idated formations of granular material which i s nei ther

cemented nor compacted the e ffec t ive poros i ty depends mainly on the

packing of the gra ins which in tu rn depends on the s i ze d i s t r ibu t ion

shape and s tapl ing of the rock par t i c l e s . In consolidated formations

which are dens i ly packed or cemented the e ff ec t ive poros i ty i s

genera l ly very small . These formations have a l imited hydraulic

t ransmiss iv i ty and are general ly unsuitable for a r t i f i c i a l recharge

opera t ions .

2 .2 .2 Storage capac i ty

The s torage capac i ty of an area underground volume of a width B = 4 mand a l ength L 1 m, and an e ffec t ive porosi ty Pe of 20 , to a depth

D = 5 m, i s :

Q ===

PeB.L.D

0 20.400.1000.5

400.000 m3

2.3 Hydraulic design o f a r t i f i c i a l recharge schemes

The hydraulic design of a r t i f i c i a l recharge schemes i s governed by the

following parameters:

i n f i l t r a t i o n r a t e

re tent ion t ime

e ffec t ive poros i ty

permeabil i ty

hydraulic t ransmiss iv i ty

2.3.1 I n f i l t r a t i o n r a t e

The i n f i l t r a t i o n r a t e depends mainly on the ver t i ca l permeabil i ty of the

i n f i l t r a t i o n zone and should be designed to allow the scheme to operate

over a long period a t an acceptable r a t e without excess clogging of the

i n f i l t r a t i o n zone. The design r a t e thus should be l e s s than the maximum

i n f i l t r a t i o n r a t e The i n f i l t r a t i n g water should e la rge ly f ree of

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suspended and col lo ida l matter. Surface water may need to be pre t rea ted

to remove excess t u rb id i ty. Sedimentation basins may be used for t h i s

purpose. I f the t u rb id i ty in the i n f i l t r a t i o n water i s mainly caused by

f ine s i l t and co l lo ida l matter, i t i s genera l ly more effec t ive to use

roughing f i l t r a t i o n t ha t i s f i l t r a t i o n through a gravel bed, for

pre-treatment Figure 2.2) . Al terna t ive , two i n f i l t r a t i o n basins can be

used. While one basin s in use, the other i s drained to allow s i l t

depos i t s on the bottom to dry out . This dry mater ia l can be blown away

by the wind, or i t can e removed m ~ u l l yby loca l workers.

Figure 2.2: Pre-treatment of i n f i l t r a t i o n water by roughing f i l t r a t i o n

he maximum i n f i l t r a t i o n r a t e can be determined by the standard t e s t

with an i n f i l t r ome te r which cons i s t s o f two concentr ic r ings , the inner

r ing of 0.7 m diameter, the outer r ing of 1.0 m diameter, and both 0.4 m

high Figure 2.3) . he r ings a re driven ha l f in the bare s o i l of the

i n f i l t r a t i o n area , and then f i l l e d with water. he t opso i l a t the s i t e

should be removed because of i t s l imi ted i n f i l t r a t i o n capaci ty. he

amount of water i n f i l t r a t i n g s determined by measuring the drop of thewater every quarter-hour or half-hour over a period of several hours.

I n f i l t r a t i o n ra tes for various types of s o i l are given in Table 2.3.

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'

Figure 2.3: Inf i l t rometer

Table 2.3: I n f i l t r a t i o n ra tes for various types of s o i l

Type of so i l I n f i l t r a t i o n r a t e(m3jm2/d)

Fine sand 0.2 0.4Sandstone 0.3 - 0.5Medium-sized sand 1 - 2Coarse sand 4 - 6Gravel 1 - 2

The design f i l t r a t i o n r a t e must allow for a degree of clogging and

should be about 20-30 of the standard t e s t i n f i l t r a t i o n ra te . Lower

design ra tes may be appropr ia te where spec ia l care must e taken to

prevent clogging of the s o i l

2.3 .2 Retention t ime

To ensure hygienic safe ty of the recovered water a r t i f i c i a l recharge

schemes should be designed to provide a re tent ion time of a t l eas t three

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weeks and preferably two months. The time the water remains

underground i s the important c r i t e r i o n not the dis tance over which the

water flows from the recharge area to the recovery means. The re tent ion

time i s cont ro l led mainly by the i n f i l t r t i o n r a t e and the hydraulic

t ransmiss iv i ty of the formation.

2.3.3 Permeabil i ty

The permeabil i ty of a formation s the flow r a t e t which water would

move through i t under a head of one metre across a dis tance of one

metre. The main fac tors affec t ing permeabil i ty are the e ffec t ive

poros i ty and the degree to which the pores in the formation are

interconnected. Table 2.4 gives the permeabil i ty of some types of rock.

Table 2.4: Permeabil i ty of some types of rock

Type of rock Permeabil i ty

f ine sandcoarse sand

grave lmixed sand and gravelsandstoneclayshalel imestonef rac tured or weathered rockso l id rock

Source: Campbell Lehr 1973

2.3 .4 Hydraulic t ransmiss iv i ty

(m/d)

1 - 520 - 100

100 - 100050 - 1000.1 1.0

0.01 - 0.05negl ig ib lenegl ig ib le

0 - 3neg l ig ib l e

The hydraulic t ransmiss iv i ty i s the product of the permeabil i ty and the

wate r- f i l l ed depth of the formation and denotes the water t ransmission

capacity of the formation. With the permeabil i ty k and formation depth

D, the hydraulic t ransmiss iv i ty i s of ten given as the k.D f ac to r

expressed in m3/d per m width.

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3 . PLANIIIHG AND ORGANIZATIONAL ASPECTS OF ARTIFICIAL GROUNDWATERRECHARGE SCHEMES

3.1 Planning

In most count r ies , there i s l i k e l y to be l i t t l e know-how and experience

with the planning, design and organiza t iona l aspects of a r t i f i c i a l

groundwater recharge schemes. Important issues in planning such schemes

are the se l ec t i on of a su i tab le source of water, the loca t ion of the

a r t i f i c i a l recharge area , the geohydrological condi t ions , community

involvement, and cos t . The schemes should be planned in accordance with

the avai lab le technica l s k i l l s manpower and management capab i l i t i e s ,

and the capaci ty and will ingness of the user community to bear thecos ts .

3.2 Community involvement

Active involvement of the benef ic ia ry communities i s increas ing ly being

recognized as of major importance in r u r a l water supply projec ts . This

a lso appl ies to a r t i f i c i a l groundwater recharge schemes. Fullinvolvement means t ha t the loca l populat ion can p r t i c i p ~ ein the

s i t i n g of the scheme, planning and des ign , the choice of recovery means,

and the provisions for operat ion and maintenance Table 3.1) . I t also

means t ha t a t imely and sa t i s f ac to ry ~ g r e e m e n tcan be made on the

cont r ibut ions , the r i gh t s and obl iga t ions of both the community and the

water supply agency.

Careful appra isa l of loca l needs during the p r e - f e a s i b i l i t y studies for

a r t i f i c i a l recharge schemes wi l l ensure t ha t those communities which

have a f e l t need for, and t rue i n t e r e s t in an improved water supply are

served f i r s t . Subsequent information and consul ta t ion of the community

during the loca l planning stages of the pro jec t makes t possible to

take i n to account the needs of various user ca tegor ies e .g . women

l ives tock owners, lowest-income group) . Where necessary, compromises for

conf l ic t ing i n t e re s t s should be sought , which are acceptable to a l l .

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Table 3.1 : Suggested sequence of t echnica l and community involvementprojec t c t i v i t i e s

Technical c t i v i t i e s

Gee-hydrological i nves t i ga t i ons

Inves t iga t ions on capaci ty andwill ingness for cos t recovery

Si t e inves t iga t ions for scheme

Selec t ion of type of pumping

equipment to be used for waterrecovery

Preparat ions for cons t ruc t ionof scheme

Construct ion of the scheme

Local t ra in ing in operat ion andmaintenance work

Evaluat ion

Source: van Wijk, 1985

Community involvementc t i v i t i e s

Consultat ions with communitymembers on s i t i n g of the scheme

Consultat ions with communityon cos t of scheme, and t h e i rcont r ibut ion

Community involvement in s i t ei nves t i ga t i ons

Par t i c ipa t ion in choice of

pumping technologyespec ia l ly by the women

Hygiene educat ion c t i v i t i e s

Par t i c ipa t ion by provision oflabour

Community e l e c t s candidatesfor t r a in ing in operat ionand maintenance

Par t i c ipa t ion in evaluat ion

Competition over water use and payment problems should be avoided. In

par t i cu la r, the leve l of f inancia l cont r ibut ions of the community to

recur ren t cos ts , and a lso to the c a p i t a l cos t , should be s e t t l e d in

consul ta t ions before the scheme i s constructed.

There are numerous examples of water supply schemes which cannot be used

for pa r t of the year because the water source has dr ied up; such cos t l y

mistakes could have been avoided i f the loca l community had been

involved and consul ted. The loca l knowledge should be used to prevent

schemes being inappropr ia te ly s i t e d . Without pr io r consul ta t ion with

the community water supply schemes have sometimes been s i t ed in

cu l tu ra l ly unacceptable places , for example, in the v ic in i ty of agraveyard, or t a place which i s flooded in the rainy season. Adequate

4


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exchange of information between the community and the water supply

agency i s required for reasoned decision-making. Ensuring t ha t pro j ec t

information also reaches the loca l women, and consult ing them on t he i r

views, i s important because they are the main users of the water supply

for domestic purposes .

Involvement of the communities in construct ion work can reduce the

cons t ruc t ion cos ts . The will ingness to cont r ibu te to construct ion work,

in kind o r money, i s c lose ly r e l a t ed to the benef i t s expected from the

scheme. Digging of i n f i l t r a t i o n channels or bas ins , and recovery wells

and construct ion of simple water in take works, lend themselves

par t i cu la r ly to involvement of the loca l populat ion. t i s necessary to

schedule these a c t i v i t i e s for periods in which the work-load of the

community i s l imi ted , and not in the harves t ing season or s imi la r

periods.

Periodic cleaning of the i n f i l t r a t i o n channels , and of pre- t rea tment

f a c i l i t i e s i f incorporated in the recharge scheme, are maintenance tasks

for which the loca l community can r ead i ly assume r e spons ib i l i t y.

Col lec t ion of f inanc ia l cont r ibu t ions from the community should also be

organized loca l ly, for example by a loca l water committee. For more

d e t a i l s the reader i s re fer red to IRC's forthcoming publicat ion What

Pr ice Water: User Par t i c ipa t i on in Paying for Community-Based Water

Supply .

Consultat ion with the loca l community i s a lso par t i cu la r ly helpful to

f ind the most appropr ia te so lu t ion for spec i f ic l oca l problems. For

example, in the v i l l age of Alto de los Idolos, in Colombia, the surface

water source was ser ious ly pol lu ted by manure of c a t t l e allowed to graze

on the banks and surrounding area . Fencing the area with chicken wire

was suggested by the water supply agency, but the v i l l age water

committee did not consider t h i s the appropriate so lu t ion because of the

high cos t involved and the r i s k t ha t the wire fence would be s to len .

Requiring people to keep t h e i r animals from the water in take area, was

considered not to be compatible with loca l custom and the r i gh t of

access to land. After consul ta t ion , the community understood the need

to protec t the intake area, and came up with t h e i r own solut ion.

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Voluntary labour from a l l user-households was organized to p l an t thorn

bushes to form a natura l fence. The work was quick ly completed, and the

thorn bush fence e ff ec t ive ly kept the graz ing c a t t l e away from the water

in take a rea .

The t echnica l pro j ec t work requ i red f o r an a r t i f i c i a l recharge scheme,

and the community involvement a c t i v i t i e s are both es sen t i a l components

o f the water supply pro j ec t . The sequence of these a c t i v i t i e s should be

planned and implemented for mutual ~ e i n f o r c e m e n t

3.3 Organiza t iona l aspec ts

At the v i l l age l eve l , t i s p re f e r ab l e t o work through an ex i s t i ng

organiza t ion , such as a v i l l age committee. However, i f these committees

may have too many broad r e s p o n s i b i l i t i e s to be e ff ec t ive , then a spec ia l

water committee need to be es t ab l i shed . I t i s important to asce r t a in

through consul ta t ions with the v i l l a g e o r water committee whether i t can

and wi l l accept r e spons ib i l i t y fo r opera t ion and maintenance. Agreement

should be reached on the cont r ibu t ions they wi l l make, and those which

they m y expect from the water supply agency. General assemblies o r

separa te meetings with the d i f f e r e n t populat ion sec t ions , inc lud ing

women m y serve to ascer ta in whether the proposed design and community

cont r ibu t ions in cons t ruc t ion , opera t ion and maintenance of the

a r t i f i c i a l recharge scheme are accep tab le to a l l or whether fu r the r

adapta t ion in necessary.

A c l ea r and r e a l i s t i c d i s t r i bu t ion of r e s p o n s i b i l i t i e s and t a sk s with in

the water supply programme i s requi red t o support the i n s t a l l a t i o n of

a r t i f i c i a l recharge schemes. A poss ib l e d iv i s i on o f r e s p o n s i b i l i t i e s a tthe nat iona l , d i s t r i c t and loca l l eve l i s s e t out in Table 3.2 .

I t must be recognized t h a t the opera t ion and maintenance requirements of

a r t i f i c i a l recharge schemes wi l l place considerable demands on the user

community s organiza t iona l i n f r a s t r u c t u r e and f inancia l capac i ty.

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Table 3.2: Possible div is ion of r e spons ib i l i t i e s within a ru ra l watersupply programme

Level Respons ib i l i t i es

National Overal l planning and organizat ion of thewater supply programmeOveral l al loca t ion of programme fundsProvision of technica l supportProvision of methodology for evaluat ion

D i s t r i c t Implementation of schemesAdminis t ra t ion of programme fundsPromotion of community involvementHealth educat ion

Local

Par t ic ipa t ion in eva lua t ion

Par t ic ipa t ion in loca l planning cont r ibu t ionto construct ionPromotion of acceptance of recharge schemesOperation and maintenance of schemesOrganizat ion and co l l ec t i on of loca lcont r ibu t ionsPar t ic ipa t ion in eva lua t ion

The type of exper t i se and numbers of s t f f required to implement

recharge schemes va r i e s according to the local condit ions. Tasks to be

car r ied out include digging of i n f i l t r t i o n channels or ponds cleaning

and maintenance operat ion of pumping p lan t co l l ec t i on and

adminis t ra t ion of loca l cont r ibut ions and promotion of hygiene

educat ion. Not l l s t f f required can be recru i ted l oca l ly. However

i t wi l l of ten be possible to t t r c t po ten t i a l l y su i t ab l e people and

t r i n them for spec i f i c t a sks . A f i r l y successful approach in several

instances has been to use the cons t ruc t ion stage for t ra in ing of those

w o wi l l af terwards be responsible for maintenance and r epa i r of the

scheme. This provides oppor tun i t ies for the recru i ted s t f f to l ea rn

ow the scheme works and so obta in es sen t i a l information for operat ion

and maintenance.

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3.4 Hygiene educat ion

Hygiene educat ion i s an essen t i a l pa r t of any water supply projec t and

i t s importance has been confirmed by many s tudies . Safe water supplied

by an a r t i f i c i a l recharge scheme can be re -pol lu ted by the users i f no

prevent ive measures are taken. Hygiene educat ion can bring the people

understand the need for proper handl ing of the water. ne important

objec t ive i s to explain the need for exclusive use of safe water

al though t h i s wi l l not by i t s e l f ~ su ff i c i en t to achieve the desired

hea l th impact. Improvements in general hygiene such as sani ta ry waste

disposa l hygienic food handl ing and prepara t ion balanced nu t r i t i on

and i n sec t and rodent con t ro l are a l so requi red .

Thus hygiene educat ion should be par t of the promotional and

motivat ional a c t i v i t i e s in every projec t for bu i ld ing a recharge

scheme. Preferably i t should begin in the planning stage but always

before the scheme i s ac tua l ly cons t ruc ted . I t must be recognized t ha t

the hygiene educat ion a c t i v i t y has a cos t which needs to be budgeted for

in the overa l l programme budget .

In some areas the abs t r ac t i on of groundwater to provide a safe supply

for drinking and domestic use may encounter r e se rva t i ons e spec i a l l y

where the loca l populat ion has t r a d i t i o n a l l y used flowing water from

streams or r ive r s . Sometimes people bel ieve t h a t flowing water i s more

wholesome and heal thy than groundwater. Users need to understand why

groundwater i s sa fe r t o use and genera l ly of be t t e r qual i ty. Where water

from ex i s t i ng wells t a s t e s sa l ty t should be explained t ha t the

a r t i f i c i a l recharge scheme wi l l produce water t ha t i s fresh and of a

lower s a l t conten t .

Discussions with a l l loca l groups are usefu l t o i den t i fy pa r t i cu l a r

loca l problems and to ensure t h a t the s i t i n g of the a r t i f i c i a l recharge

scheme and i t s design promote hygienic condit ions and a r e l i ab le supply

of the water. Co-operat ion with community workers in teres ted in hea l th

and hygiene such as dispensary s t a f f school maste rs and adul t

educators should be sought . nowledge of loca l circumstances

behaviour b e l i e f s and cons t r a in t s i s necessary to design an e ff ec t ive

hygiene educat ion programme which should be based on i den t i f i ed heal thhazards and behaviour pa t t e rn s which a f f e c t the t ransmission of

18


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diseases . Dirty l a t r i n e s unwil l ingness to use l a t r i n e s f a i l u re to

wash hands before handling food, inadequate drainage, and unhygiene

disposa l of re fuse , are hea l t h hazards and behaviour to which the

hygiene educat ion programme should be d i r ec t ed . For a more deta i led

discuss ion of planning and implementation of a loca l hygiene educat ion

programme with ac t i ve involvement of the community see Boot, 1985}.

Hygiene educat ion should a l so be e f f e c t i v e l y in tegra ted with the primary

hea l t h programme the provision o f a water supply being an important

element. Even when water supply improvement has to be planned and

implemented as a separa te a c t i v i t y the water supply agency s t a f f must

discuss with the community the ro l e of water in hea l t h improvement.

They should encourage other agencies involved in loca l development to

i n t eg ra t e t h e i r programmes with the water supply pro jec t .

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4 TYPES OF ARTIFICIAL RECH RGE S HEMES

The main types of a r t i f i c i a l groundwater recharge schemes for water

supply of medium-size communities are :

o i n f i l t r a t i o n di tches , ponds and bas ins ;

o induced recharge from r ive r s and streams;

o re tent ion of r ive r bed qpderflow;

o re tent ion of r ive r f lood water.

4.1 I n f i l t r a t i o n di tches , ponds and basins

Ditches, ponds, and basins are used t o i n f i l t r a t e water in to formations

of good permeabil i ty which are not over la in by an impervious l aye r.

Recovery of the water can be provided by co l l ec to r dra ins Figure 4.1) .

Ditches are especia l ly used for a r t i f i c i a l recharge of shallow aqui fers ,

whereas i n f i l t r a t i o n ponds are more sui ted to re la tevely la rge-sca le

recharge of medium-depth formations. For recovery of the water, a

bat te ry of wells surrounding the pond can be used Figure 4.2)

. . . . . : .. . . . . .

; ~ > ; ~ : ; ; : ; ~ > > } ; ; : > ; / - ; />> ~ ; ~ / / / ~/// . ; > / ; ~/ };/ / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / I // / / / / / / / / / / / / / / / / / / / / / / / / / / I

Figure 4.1: A r t i f i c i a l recharge ~ shallow formation

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Ditches and ponds are genera l ly 1-4 m deep which i s enough to prevent

excessive growth of algae or water p lan t s , and shallow enough to prevent

anaerobic condi t ions developing except a t the bottom.

...... . :

:

. .

t

.'. Rr:CLJVER f~ v/EJ..)....

t

I-

. :

. . ...: . .

. ~ :.. I o '

. .. ,, 0.

Figure 4.2: A r t i f i c a l recharge of coarse granular formation

Small-scale a r t i f i c a l recharge schemes using di tches or ponds

Small-scale a r t i f i c i a l recharge schemes using i n f i l t r a t i o n ditches or

ponds can be qu i t e sui tab le for water supply of medium-size communities

i n ru ra l areas . To serve 200 people a t a r a t e of 30 1 /c /d requires a

capac i ty of 6 m3/d only. With a r e t en t i on t ime for underground water

flow of 40 days, a formation with e ff ec t ive poros i ty of 20 would needto be of 1200 m3 water f i l l e d volume. f the wetted depth i s 3 m, the

required surface area would be 400 m2, for example 10 m wide and 40 m

long. This so r t of pervious formation may be r ead i ly found in many

places (Figure 4.3) .

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Figure. 4.3: Small-scale recharge scheme

he appl ica t ion of smal l - sca le a r t i f i c i a l groundwater recharge schemes

i s of considerable i n t e r e s t for ru ra l water supply because these

schemes can produce water for domestic use, without the need to provide

extensive t reatment .

Large-scale a r t i f i c a l recharge schemes using i n f i l t r a t i o n basins

I n f i l t r a t i o n basins for la rge a r t i f i c i a l recharge schemes have been

constructed i n i ndus t r i a l i zed count r ies , but these systems are too

expensive and complicated for medium-size community water suppl ies . he

r ive r water i s pumped to the basins and allowed to inf . i - l t rate; a f t e r

recovery the water i s pumped i n to supply. Pre-treatment of the r ive r

water i s general ly required to prevent accumulation of s i l t deposi ts and

microbial slimes in the t ransmission main Figure 4 .4 ) .

. '

~ : ~ : ~ : : ~. ::. : . ~ ; ;::: ~

Figure 4.4: Large-scale a r t i f i c i a l recharge scheme using spec i a l l yconstructed i n f i l t r a t i o n basins

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Some advantages of t h i s type o f recharge scheme are :

o the formation used for recharge can be a t a distance from the

r ive r ;

o there i s l i t t l e or no clogging o f the recharge basins because

the water i s pre - t r ea t ed ; f a i r l y high i n f i l t r a t i o n ra tes can be

applied;

o the bas ins can be eas i ly emptied for cleaning or repai r ;

o during periods when r ive r water i s of poor qual i ty, intake of

water can be stopped, w h ~ l supply of water continues, using

the l a rge amount o f water stored underground.

4.2 Induced recharge

Induced recharge, or bank i n f i l t r a t i o n occurs when water i s abstracted

from underground formations alongside or near a r ive r or stream

Figure 4.5) . In the or ig ina l s i tua t ion , groundwater flows out in to the

r ive r. s water abs t rac t ion begins, the outflow of water i s reduced,

and a t high abs t rac t ion r a t e s the groundwater t ab l e i s l i ke ly to be

drawn down below the water leve l in the r ive r. s a r e su l t r ive r water

i s induced to enter the formation and supplement the groundwater

resource . he water abstracted i s a mixture o f natura l groundwater and

recharge water from the r ive r.

ORiGiN L SiTU JTiON LOW fiBSTR CTIOtl ~ T

Figure 4.5: Induced recharge o f formation

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The design of induced recharge schemes i s mainly governed)by the water

a bs t r ac t i on r a t e the hydraul ic t r ansmis s iv i t y o f the formation ad jacen t

to the r i v e r and the dis tance the recharge water flows underground to

the recovery means Figure 4.6) .

'

.: =: . .kD...:: .~ : : : :. . ~ . . . . . . .. . . .. . . . . . .... .... _ ~ : : : : . : . : . : : : : : . : : ~ . . . . . ~ # ~ : ... . / / . / ./ / ; > / ; , / / / . / / / ;. / / / / / / / / / / / / / / / /./ / 1 / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / /

1 / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / // / / / / / / ~ / / / / / / / / / / / / / / 1 / / / / // / /

/ / / / / / / / / / / / / . / / , / / / , / / / / , , , . / / / / , '

Fig . 4.6: Design parameters fo r induced recharge schemes

Induced recharge improves water q u a l i t y through r i v e r bank

i n f i l t r a t i o n . These schemes a r e p a r t i c u l a r l y e ff ec t i ve where there are

good permeable underground format ions a longs ide a r i v e r f o r example,

sedimentary depos i t s in a r i v e r va l l ey.

In induced recharge schemes some clogging of the r i v e r bed genera l ly

occurs , and as a r e s u l t an i n f i l t r a t i o n head wi l l develop

Figure 4.7) . Clogging wi l l not genera l ly be a problem in r i v e r s where

f lood flows are s t rong enough t o scour the r i v e r bed and wash away the

depos i ted mate r i a l s . In r i v e r s with cont ro l led flow, the scour ing o fthe r i v e r bed may be too weak to preven t clogging.

24


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Figure 4.7: n f i l t r a t i o n head due to clogging of r ive r bed

4.3 Retention of r i v e r underflow

A poten t i a l source of water fo r recharge schemes f requent ly overlooked,

s r i v e r bed underflow, t h a t s t he flow o f water underneath the r ive r

bed in sedimentary formations. This underflow may be in tercepted by

bui ld ing a sub-surface d m across the r ive r bed, and down to the

impervious base bedrock). This wi l l ra i se the groundwater level and

thus increase the y ie ld of the aquifer See Figure 4.8) .

_.,,

- .. -1

Figure 4.8: Sub-surface d m in the r ive r bed

Often formations underneath a r i v e r bed have a high hydraulic

t ransmiss ivi ty, and considerable amounts of water can be re ta ined for

abs t r ac t ion even in the dry season.

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Construct ion mater ia l s used for sub-sur face dams include br ick and stone

masonry, compacted c lay, and concre te . Lateral seepage o f water around

the dam or flow through cracks or f i s su re s underneath t may cause

cons iderab le leakage, and even may undermine the s t ruc tu re of the dam

i t s e l f Preferably, the dam base should be anchored f i rmly onto the

bedrock. I f t h i s i s not f eas ib l e , a dra in may be l a id a t the upstream

foo t o f the dam for pressure r e l i e f Slot ted pipe with gravel packing

has been used for t h i s purpose.

4.4 Retent ion of r ive r flood water

River f lood flows can be re ta ined by bui ld ing sand- f i l l ed dams, of ten

ca l l ed sand dams see Figure 4 .9 ) . These dams are p a r t i c u l a r l y worth

considering i n a r id areas where water evaporat ion r a t e s are very high.

Water col lec ted in the ra iny season can be s tored within the body of

deposi ted sand. Even during extended drought per iods water wi l l be

avai lab le from these dams.

Figure 4.9: Sand dam

o bui ld a sand dam, a t rench i s dug across the r i v e r bed and down to

the impervious base bedrock) and f i l l e d with c lay or other impervious

mater ia l . Sandy or grave l r iver-bedshaving a gradient of 1.5 to 4.9

are genera l ly the most su i t ab le for sand dams.

26


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Sand dams are b u i l t in s tages . To ensure t ha t the dam reservoi r s

f i l l e d only with coarse sand and loose gravel , s i l t and f ine sand

sediments have be car r ied over the dam by the flood waters . In

semi-ar id a reas ra in- fed r i v e r floods of ten come in shor t in tens ive

burs t s and flood water ca r r i e s a high sediment load because there s

l i t t l e vegeta t ion to prevent s o i l erosion. Thus, considerable amounts

of coarse sand and gravel are deposi ted behind the dam during each

f lood. To ensure t ha t the overflow water c a r r i e s the f ine sand and s i l t

over the dam, the f i r s t s tage o f , t h e dam should not be more than about

2 m above the r ive r bed. When coarse sand and gravel depos i t s have

accumulated to the f i r s t s tage l e v e l , another s tage can be added, which

s usua l ly done during the dry season. Bui l t in s tages , the dam wi l l

reach i t s f u l l height of about 6-12 m within 4-5 years Figure 4.10}.

~

r J ~ ~ ~ . _ : : ; ~ = = 7 ~~~ = _ _ _

-- -

' l\'' '

Figure 4.10: Sand dam b u i l t in s tages

n a l t e rna t ive to r i s ing the dam in s tages s to use an ou t l e t opening

in the dam c res t which i s f i l l e d up stage by s tage t the beginning of

each ra iny season.

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4.5 Recovery means

Water co l l ec t ion means used for recovery inc lude : co l l ec to r drains

ga l l e r i e s ) , dug wells and boreholes.

4.5.1 Collector drains

Collector dra ins , or ga l l e r i e s , are only economical for recovery of

shallow groundwater, not more t ~ 6-8 m below the sur face , because of

the excavation cos t s . The dra in i s cons t ruc ted of s lo t t ed o r porous

pipes or pipes l a id with open j o in t s Figure 4.11).

In f ine sand aqui fers , s lo t t ed dra ins and dra ins with open j o in t s should

be packed in one or more l ayers of grave l to prevent f ine sand from

entering the dra in . The top of the grave l pack should be a t l eas t 0.5 m

below the lowest groundwater l eve l , and deeper i f i ron and manganese a re

present in the water. Collector drains are also used in r ive r beds,

across or alongside the stream channel , for withdrawal of r ive r water

i n f i l t r a t e

_ 4 _ .. = ___ ------.. .--- A

. ; .. .::.

Figure 4.11: Collector dra in

28

. . ...

--

0

. .

. :_ :.: :t:: :: :: : : ..


34/46

4. 5. 2 Dug wells

Dug wells are mostly used to withdraw water from shallow or medium-depth

aqui fers of considerable th ickness . The depth to which a well can be

dug la rge ly depends on the groundwater l eve l ; depths of 10-30 m are

common but deeper wells have been dug. The well diameter usua l ly i s

1.5-3.0 m; 1.3 m i s the minimum to allow enough space for the well to be

dug Figure 4.12).

- -

o ',: o o o f I

...

:

. , . . ..

.. . . . . . . .

Figure 4.12: Dug well

. . I : : :

:

.:. .

0

:

The types o f geological formations t h a t are sui tab le for dug wells ,

include sand, grave l , s o f t sandstone, and sof t f rac tured l imestone.

Except in very s t ab l e formations, a l l dug wells must be l ined withs tones , masonry, concrete cas t i n s i t u precas t concrete r ings , o r

s imi la r mater ia l s . The l in ing protec ts the well from caving and

collapse, and from being f i l l e d with crumbling s o i l . In unconsol idated

formations, the well should be l ined over i t s en t i r e depth, with a

perforated, open-jointed, or porous sect ion facing the aqui fer, whereas

in consol idated formations, i t may be su ff i c i en t to l i ne the upper pa r t

of the well only. In f ine sand aqui fers , the l in ing i s of ten extended

29


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over the whole depth o f the well without any perfora t ions , openings, or

porous sec t ion . Water can then en te r the well only through the bottom

which i s covered with severa l l ayers of grave l t o keep the f ine sand o f

the formation in place .

4.5 .3 Boreholes

Boreholes are more su i t ab l e for groundwater withdrawal from grea t e r

depths, but are sometimes a lso u ~ e for recovery of shallow groundwater

see Figure 4.13) . The capac i ty of boreholes va r i e s from l e s s than

1 1 / s for small-diameter wel ls in f ine sand aqui fers t o more than

100 1 / s f o r l a rge diameter wel l s in coarse sand o r grave l depos i t s .

There are various well d r i l l i n g methods inc lud ing auger boring, well

dr iv ing , well j e t t i n g percussion cable- tool ) d r i l l i n g ro t a ry

d r i l l i n g and down-the-hole hammer d r i l l i n g . For each loca t ion or area ,

t he most su i t ab l e method should be ca re fu l ly se l ec t ed Table 4.1) .

PL TFoRn

Figure 4.13: Borehole

3

. .0

. .. ;


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Table 4.1: Charac ter i s t ics of various well d r i l l i n g methods

Type ofwell d r i l l i n gmethod

Boring withauger handoperated)

Driving

J e t t i n g

Percussioncable- too l )

d r i l l i n g

Hydraul icro t a ry -d r i l l i ng

with d r i l l i n gf l u idc i rcu la t ion)

Down-thehole a i r

hammer d r i l -l ing

Maximumprac t i ca ldepth m)

25-30

15-20

30-40

300

300

200

Typicaldiameter

em)

10-25

5- 8

5-20

10-30

10-50

10-30

Sui tab le for : Unsui table for :

Type of rock

c lay, s i l t sand,chalk, grave l ,a l luv i a l depos i t sin r i ve r f loodpla ins

c lay, s i l t sand,f ine grave lso f t sandstone

c lay, s i l t sand,f ine gravel

c lay, s i l t sand,grave l , cementedgrave l , boulders

in firm bedding) ,sandstone,

l imestone, andigneous rock

c lay, s i l t sand,grave l ,cemented gravel ,sandstone,l imestone, andigneous rock

pa r t i cu l a r lysu i tab le for :

dolomite,basa l t s ,methamorphicrocks

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consol idatedformations,unstable formations

a l l consol idatedformations,e spec i a l l y whenboulders a represent

a l l consol idatedformat ions ,espec ia l ly whenboulders arepresent

unstableformat ions ,loose sand

unstable formations;loose sand;problems in a l lformat ions , whereboulders are p re se n t

loose sandgrave l , c lay,

s i l t sandstone


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5 BASIC DESIGN PROCEDURE FOR ARTIFICIAL GROUNDWATER RECHARGE SCHEMES

5.1 Pr inc ipa l design parameters

The pr inc ipa l design parameters for a r t i f i c i a l recharge schemes are:

design i n f i l t r a t i o n r a t e v i toge ther with the width w of the

recharge area g ives the i n f i l t r a t i o n capac i ty per un i t length

quhead between the water l eve l i n t h e recharge works and the

groundwater t ab l e when t he scheme i s in opera t ion ~

the e f f e c t i v e po ros i t y Pe the permeabi l i ty k o f the aqui fe r

formation, and i t s wetted depth, D

t h e d i s t ance L between the recharge works and the recovery

means see Figure 5 .1 ) .

Figure 5.1: Pr inc ipa l des ign parameters for a r t i f i c i a l recharge schemes

The water flow through the aqu i f e r format ion in an a r t i f i c i a l recharge

scheme may be ca lcu la ted with a s impl i f ied form of t h e Darcy equa t ion

used for groundwater flow:

q i = kD sL

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where:

q i = i n f i l t r a t i o n capac i ty per un i t l eng th m3/m/d)k = permeabil i ty m/d)D = wetted depth of format ion (m)s = head of water between the recharge works and the groundwater

t a b l e , when scheme i s in operat ion (m)

L = hor izonta l d i s tance between -recharge works and recoverymeans (m)

5 .2 Example design

Consider an a r t i f i c i a l groundwater recharge scheme which uses an aqui fe r

formation of sand. The wetted depth D of the aqui fe r i s 9 m. Channels

with a bottom width W of 4 m a r e to be constructed as recharge works.

Basic design procedure i s as fol lows:

1) Inf i l t rometer t e s t s conducted on s i t e ind ica te an i n f i l t r a t i o n

r a t e ve of 5-6 m3;m2/d, and t h e design i n f i l t r a t i o n r a t e i s f ixed

a t Vi 3 m3/m2/d.

2) The i n f i l t r a t i o n capaci ty per un i t length of recharge channel i s :

q i 1 /2 .v i .w

1 / 2 3 4 6 m3 m d

3) The e ffec t ive poros i ty Pe o f the formation i s determined by t e s t s

on undisturbed samples, and found to be 20 ; based on a pumping

t e s t or f i e l d experience in s imi l a r schemes in the area , thepermeabil i ty k i s f ixed a t 12 m/d.

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3Q = 2.q . B = 2.6.50 = 6 m /d

8) I f the requi red capac i ty of the recharge scheme i s 12 m3/d,

thentwo

i n f i l t r a t i o n channels should be used.

9) Thus the prel iminary design for the a r t i f i c i a l recharge scheme

cons is t s of two i n f i l t r a t i o n channels constructed in p a r a l l e l

50 m long and 160m apar t wi th the recovery means placed a t a

distance o f 80 m on each s ide . The t o t a l aqui fer area used for

the scheme i s thus 50 m x 32 m

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6 . FIELD EXPERIENCE ND COSTS OF ARTIFICIAL RECH RGE SCHEMES

6.1 Fie ld experience

Most a r t i f i c i a l recharge schemes for which f i e ld experience and cos t

da ta have been reported are in the i ndus t r i a l i zed count r ies ; v i r t u a l l y

no descr ip t ive mater ia l concerning s avai lab le for such schemes in

developing count r ies .

Most problems of operat ion of recharge schemes are r e l a t ed to clogging

of the i n f i l t r a t i o n works because of excessive amounts of suspended

s o l i d s co l lo ida l and organic mat te r in the recharge water. In many

cases occasional drainage of the i n f i l t r a t i o n works followed by drying

out and simple t i l l i n g or harrowing of the bottom appears t o solve the

problem. In some ins tances however i n t e r rup t ion of the recharge

operat ion for cleaning of the recharge works s frequenty requi red .

Pre-treatment of the incoming water then i s needed or expansion of the

i n f i l t r a t i o n area to reduce the i n f i l t r a t i o n r a t e . Research in to the

optimal combination of i n f i l t r a t i o n area and i n f i l t r a t i o n r a t e under

d i ff e r ing condit ions would be very useful .

Excessive algae growth and disturbance of the i n f i l t r a t i o n process by

decaying organic matter can be a ser ious problem when the i n f i l t r a t i o n

water i s r ich in nu t r i en t s e i the r from natura l sources or from upstream

discharges of domestic waste w t e r ~ s imi lar problem i s excessive

growth of water p lan t s e .g . water hyacinth.

The storage capaci ty in the underground formation allows i n t e rmi t t en t

operat ion of a r t i f i c i a l recharge schemes. This i s a major advantage ofthese schemes because i t al lows drainage of the recharge works a t

regular i n t e rva l s to e l imina te any excessive algae growth or water

p lan t s . I t a l so w i l l i n t e r rup t any breeding of mosquitoes or sna i l s .

Aftre digging out s i l t deposi ts and organic matter can be removed by

manual labour and in some ins tances t should be poss ib le t o re ly on

wind blowing away the dr ied-out depos i t s .

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6.2 Costs

Very few cos t da ta are avai lab le and most are for l a rge a r t i f i c i a l

recharge schemes i n i ndus t r i a l i zed count r ies . Often, data include the

cos t of pre- t rea tment works, t ransmission mains and water d i s t r ibu t ion

systems, and thus t i s d i f f i c u l t separa te the cos t of the recharge

works. However t has been est imated t h a t the cos t of the schemes

va r i e s from US 7 to 100 per m3 of da i ly i n f i l t r a t i o n capac i ty. A

comparison of the investment o s ~ sof equiva len t recharge schemes and

t reatment works i s given in Table 6.1.

Table 6.1: Comparison o f the l eve l of cap i t a l cos ts for equivalent

recharge schemes and t reatment works

Cost i tem

Land acquis i t ionExcavationPumping plantCivi l worksMechanical equipmentPower supply

r t i f i c i a l recharge scheme

highhighmediumlowlowlow

Treatment works

lowlowlowhighhighmedium

The cap i t a l cos ts of a r t i f i c i a l recharge schemes are comparable with

those of treatment works for surface water for drinking water supply,

but costs of opera t ion and maintenance in recharge schemes are l i k e l y to

be l e s s . Estimates of opera t ion and maintenance costs for a r t i f i c i a l

recharge schemes vary from of 0.05 to 0.30 per m3 of water through

put Table 6.2) .

Table 6.2: Comparison of opera t ion and maintenance costs for a r t i f i c i a lrecharge schemes and equivalent water treatment works

Cost i tem

Ski l led opera torsUnskilled labourPowerChemicals

r t i f i c i a l recharge scheme

Maintenance opera t ions

lowhighlownonelow

7

Treatment works

highmediummediumhighhigh


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SELECTED BIBLIOGRAPHY

Andreini , J . C . , and Bourguet, L. (1984). Les barrages souter ra ins :condi t ions d app l i ca t i on au Sahel . Par i s , France , Burgeap.

Basmaci, Y. (1983). Undergound dams for groundwater development. In:Groundwater, 1983, 21, 4, 552.

BCEOM (1978). Les barrages sou t e r r a ine s . Par i s , France , Ministere de l aCooperat ion.

Bize, J . Bourguet, L. , and Lemoin7, J . (1972). L a l imen t a ti ona r t i f i c i e l l e des nappes souter ra ines . Par i s , France, Masson & Cie.

Boot, M.T. (1984). Making the l i nks : guide l ines for hygiene educat ionin community water supply and s a n i t a t i o n (Occasional Paper No. 5 ) . TheHague, The Netherlands, In t e rna t i ona l Reference Centre for CommunityWater Supply and Sani ta t ion .

Davis, S.N. , De Wiest, R.J.M. (1966). Hydrogeology. New York, USA, JohnWiley.

Engman, C.A. (1983). Surface water i n f i l t r a t i o n systems.

F i l d i e r F. (1983). La r e - a l imen t a t i on des nappes Etude technique desynthese. Par i s , France, Associat ion Francaise pour l E tude des Eaux.

Helweg, O.J . , and Smith, G. (1978). Appropriate technology fora r t i f i c i a l recharge of aqu i f e r s . Groundwater, 1978, 16, 3, 144-148.

Huisman, L. (1964). A r t i f i c i a l recharge . Proceedings of SixthIn t e rna t i ona l Water Supply Congress. London, UK, In t e rna t i ona l WaterSupply Associat ion.

Huisman, L. , and Olsthoorn, T.N. (1981). A r t i f i c i a l groundwaterrecharge. London, UK, Pitman Books.

ASH (1968). A r t i f i c i a l recharge and management of aqui fers . Report ofsymposium held in J a i f a I s r a e l June 1967. ( ASH Publ ica t ion No.72).0t tawa, Canada, In t e rna t i ona l Assoc ia t ion of S c i e n t i f i c Hydrology.

Meinzer, R. (1946). General pr inc ip l e s of a r t i f i c i a l groundwaterrecharge . Economic Geology, 1946, 191-201.

Muckel, D.C. (1959). Replenishment of groundwater suppl ies bya r t i f i c i a l means U.S (Technical Bul l e t i n No. 1195). Washington DC, USA,Department of Ar t i cu l tu re .

Nilsson, A. (1984). Groundwater dams for ru ra l water supply indeveloping coun t r i e s . Stockholm, Sweden, Royal I n s t i t u t e of Technology.

Pettyjohn, W.A. (1978). I n t roduc t i on to a r t i f i c i a l groundwaterrecharge. Worthington Ohio, USA, National Water Well Assoc ia t ion .

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Robaux, A. 1954). Les bar rages sou t e r r a ine s . Terres e t Eaux, 6 , 23,23-27.

Sche t t l e r, U. 1980). r t i f i c i a l recharge. Proceedings of I n t e rna t i ona lSeminar on Development and Management of Groundwater Resources , held5-20 November 1979 a t Roorkee, I nd i a , School o f Hydrology.

Todd, O.K. 1980). Groundwater hydrology. New York, USA John Wiley.

Van Tun, Nguyen 1979). Subterranean dams. Ouagadougou, Burkina Faso,I n t e r - A f r i c a in Committee fo r Water Studies .

U 1975). Groundwater s to rage anQ a r t i f i c i a l recharge NaturalResources Water Series No. 2/ST/ESA/L3). New York, USA UnitedNations.

White , A.T. 1981). Community pa r t i c ipa t i on in water supply andsan i t a t i on : concepts , s t r a t e g i e s and methods Technical Paper No. 17) .The Hague, The Nether lands, In t e rna t i ona l Reference Centre fo r CommunityWater Supply and San i t a t i on .

Wijk-Sijbesma, C. van 1985) . Par t i c ipa t i on of women in water supplyand san i t a t i on : r o l e s and r e a l i t i e s Technical Paper No. 22) . The Hague,The Nether lands, I n t e rna t i ona l Reference Centre for Community WaterSupply and San i t a t i on .

Wijk-Sijbesma, c. van. What p r i ce water : user pa r t i c ipa t i on in payingfo r community-based water supply Occasional Paper No. 10) . The Hague,The Nether lands, I n t e rna t i ona l Reference Centre fo r Community WaterSupply and San i t a t i on . i n prepara t ion)

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APPENDIX

CRITERIA FOR SMALL-SCALE ARTIFICIAL RECHARGE SCHEMES

The information and data col lec ted by l i t e r t u r e survey, and synthesized

n the present document, are ne i the r adequate nor r e l i ab le enough to

al low the establ ishment of firm c r i t e r i t ha t could be applied n

smal l - sca le r t i f i c i l recharge schemes for ru ra l water supply.

However, on the bas is of the f ind ings and r e su l t s of the knowledge

synthesis study, the following t en ta t ive c r i t e r i may be presented .

A. Technical geohydrological c r i t e r i

Charac t e r i s t i c s of recharge formation

Water- f i l led th ickness

Effec t ive poros i ty

Permeabil i ty Kh)

Composition

Impervious cover

System boundaries

t l eas t 5 m, preferably more, 25-30m

not l e s s than 10

grea t e r than 10 m/d

preferably sedimentary, granularmate r i a l , with wel l - in te rconnec tedpores ; no f i s su res o r f r ac tu red zones;prac t i ca l ly f r ee of i ron and manganese;no peat or s imi l a r organic mat te r ; nosu lphur-conta in ing layers .

i f impervious subsoi l (e .g . clay)present , overlaying the rechargeformation, then not th icker than 4-5 m,in order to allow excavation ofi n f i l t r t i o n channels (or ponds) downto the water-bearing formation.

presence of natura l system boundariese .g . bedrock in r i ve r-va l l eys i s agrea t advantage for r t i f i c i l rechargesystems.

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B. Organizat ional and i n s t i t u t i o n a l requirements

Local organizat ion

Community involvement

Support from watersupply agency

Capabi l i t i es and s k i l l smanpower)

Pumping equipment and plant

Construct ion mater ia l s andequipment

c. Costs and f inancing

Capital cost

Recurrent cos ts

Financing

loca l committee or o ther loca lorganizat ion ava i l ab l e which i s ableand wil l ing to assume r e spons ib i l i t yfor operat ion and maintenance and fororganizat ion and co l l ec t i on of loca lcont r ibut ions .

su ff i c i en t i n t e r e s t and support forconstruct ion and management of thea r t i f i c i a l recharge scheme.

water supply agency involved andadequately organized to provide t ech-nica l support for planning design andcons t ruc t ion as well as technicalbackstopping for operat ion andmaintenance.

some t echnica l background s k i l l s andexperience with the type o f workinvolved such as control of waterflow excavat ion of ground andconstruct ion of s t ruc tures .

s k i l l s t echnica l support supplies o fspare pa r t s and fue l .

loca l mater ia l s such as c lay br ickscement avai lab le for construct ion;

too ls for excavat ion work.

genera l ly l e s s than for watert reatment works of same outputcapaci ty.

l i k e l y to be far less than for watert reatment works of same outputcapaci ty.

programme funds to cover cap i t a l cos tof recharge schemes.

Artificial Groundwater Recharge for Water Supply of Medium-size Communities in Developing Countries

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