Water Supply Engineering by B.C.punmia, Ashok Jain, Arun Jain

ONLY QUIZ 1 CHAPTERS ARE INCLUDED IN THIS BOOK

Water Systems

1.1.

INTRODUcnON

The five essential requirements (or human existence arc: (I) air (it) ~ter (iil) food (iv) heat and (II) light Contamination of

these elements may cause seriQus health hazards not only to man but also to "animal and plant life. Environmental Engineuing deals with all these essential elements. The use of water by man, plants and animals is universal. Without it, there can be no life. Every living thing requires water.

Man and animals not only oonsume water, but they also consume vegetation (or their food. Vegetation, in tum, cannot grow without water. Growth of vegetation also depends upon bacterial action, while bacteria need waler in 'o rder to thrive. The bacterial action can cooven vegetable maner into productive soU. New plants, which grow in this soil, grow by sucking nutrients through their roots in the form of solution in water. Thus an eoologjcal chain is maintained. Water maintains an ecological balance - balance in the relationship between living "things and environment in which they live. The use of water is increasing rapidly with our growing population. Already there are acute shortages of both surface and under ground waten in many ~rts of the country. Careless poUution and contamination of tbe streams, lakes, reservoirs. wells aDd otber uDder ground sources has greatly impaired tbe q~ty of available water. This poUution results because of improper disposal of waster water -both domestic as well as industrial. Organised community ute require twin services of water supply and SCWBF 1Jisposal. Good sanitation cannot be maintained without adequate water supply system. Without (1) uJP'l

nljUIl

,

WATER SUPPLY ENGINEER ING

2

proper disposal, the wastes of a community can creale into lerable ~uisance. spread diseases and creaie other health hazards. The planning,

designing, financing and opera lion of waler and waste water systems are complex undertakings, and they require a high degree o f skill and judgement. The work of conslruction and maintenance o f water

supply .and waste water disposal systems is generally undertaken by Government agencies - mostly through Public Health Engl.'neering or Environmental ~ngineering Departments consisting of Civil Engineers.

1.2. HISTORICAL DEVELOPMENT

Man's search for pure water began is prehistoric times. The

or

Story of water supply begins with the growth ancient capital cities, or religious and trade centres. In olden days, most of com munity settlements througho ut the ~orld were made near sp rings, lakes and rivers Crom where the water supply for drinking and irrigation purposes was obtained. Rig Veda (4(XX) years S.C) makes a mentio n of digging of wells. Similarly, Ramayana, Mahabhartha and Puranas make mention of wells as the principal source of water supply. These wells \lrr'Cre mostly of shallow depth, dug near river banks. Water was lifted from the -wells through indegenous methods. However, no water treatment or distribution works existed. Apart from India (Bharat), other majo r civilisations of the World, such as Greece, Egypt, Assyria etc. used wells for their settlements which were located slightly away from springs, lakes and rivers. Joseph's well at Cairo is one of the oldest deep wells excavated in rock to a depth of about · 300 feet. lbese \lrr'Clls, however, caused water s upply problems during periods of drought. It became necessary, therefore, to store water. Cisterns \lrr'Cre constructed for collecting rain waler while reservoirs were oonSlructed to start'· water from streams and rivers during monsoon period. lbe stored water was conveyed 10 towns through masonry conduits a nd aqueducts. The earlier examples are the aqueducts built by Appius Claudius in about 312 S.c. for water supply to Rome. Lyons in Pa~, Metz i~ Germany and Segovia and Serille in Spain tiuilt similar aqueducts and syphoRs for water supply used for drinking, bathing and other pur~. Sextus Julius FroDlinus, Water Commissioner of Rome (AD. ~~ported the existence of nine aqueducts supplying water to Rome ail'd,~aryi n g in length from 10 to over SO miles and in cross-section from ,) to over SO sq. ft. , witb an estimated aggregate capacity of 84 mgd. The great sewer, known 15 tbe clOOCil maxima and constructed to drain tbe Roman Forum, is sliU in service. lbere was p~Uy no improvement in water supply systems ill the middle ·ages. Tbe earlier water supply structures got destroyp1 with the (aU of Rome. ·In the Dintb century, few impqrtant water

,

C JPYnghied

mater~1

WATER SYSTEMS

3

s upply structures were constructed by the Moors in Spain. In the twelfth century, small aqueduct was conslructed in Paris. In London, spring water was brought by mea ns of lead pipes and masonry conduits in the thirteenth century. In Germany. water works were constructed in 1412 and pumps were introduced in 1527 in Hanover. Franciscan monk constructed aqueduct of Zempola in Mexico in ihe middle of 16th century. In 1582. a pump was erected 'o n Ihe o ld Londo n bridge for the s upply of waler from the Thames. The water was conveyed thro ugh lead pipes. In Paris, pumps operaled by water power were erected in 1608. Pumps operating from steam were in Iroduced in the 18th century in London and Paris. In the United States, spring water was conveyed by gravity to Boslon in 1652. Pumps etc. were inlroduccd at Bethlehem in 1754. However, purposeful quality control of waters upply is quite recent in origin. The scientific discoveries and engineering inventio ns of the eighteenth and ninetecth centuries created centralised industries to which people fl ocked for employment. This caused serio us water s upply and waste disposal problems in the industrial towns. No great schemes of water supply were started until the Indus trial Revolutio n had well passed its first half century. The development o f the large impounding reservoir was largely due to the necessity o f feeding canals constructed during the first phase of the Industrial Revolutio n.

'II

The fi rst water filter was constructed in 1804 by John Gibb at Paisley in Scotland. It was a slow sand filter and worked in conjunctio n with a settling basin and roughening filter. Next s uccessful filters were constructed in 1827 by Robert Thorn at Greenock. In 1829, James Simpson built sizable fillers for the Chelsea Water Company to improve ils supply from the Thames river. By 1870, the mechanica l fill er of the pressure type began to be employed, the earliest being the Halliday filters installed at Crl.we (1888), Bridlington and elsewhere. In 1894 pre-filters were successfully built. In the first decade of 20th century, mechanical pressure filters were introduced, Hastings being an early pioneer with Canndy filters built in 1900. In India, Calcutta was the first city where a modern water supply system was constructed in 1870. The technique of clarification and filtration soon grew. By 1939, mechanically-sludged sedimentation tanks were in general use,' ;''' The micro-strainer, fo r the removal of plankton (rom the impoundedwater was developed by Boucher, and was introduced by Glenfield and Kennedy in 1945. Coagulation of water with sulphate of alumina began experime~talJy in 1827, but was adapted practically only in 1881 to treat Bolton's water supply. Activated silica was introduced by Bayliss in U.S.A during 1937. Tbefirst permanent useofchlorination originated under tbe direction of Sir Alexander Houston at lincoln

G JPYnghtcd maknal

WA'reR SUPPLY ENG IN EERING

4

in 1905. In 19 17, Paterson Engineer.hg Company ins.alled the first gaseous chlo rinator at (he Rye Common Works. Super-chlorination and dechlorination was first applied in 1922 at the Deptford works o f the Metropolitan Water Board. The art of softening water was also first developed in Greal Britain. The first municipal softener was ronstructed by Plumslead in 1854. Development o f the softener took a novel tum in 1912 by- the construction, at the Hooten wo rks of the West Cheshire Water Board, of a base exchange softener. Since India was under British occupation, water supply schemes in India were undertaken practically about the same lime as in England, though with a slower rate. In 1870, a water supply system was co nstructed at calcutta. Till Independence, only few cities had protected water supply systems.

1.3. SOURCES OF WATER The following are common sources of water (i) Rain Water (ii) Surface water (iii) Ground water (iv) Water obtained from reclamation.

1. . Rain Water

-

OVERFLOW

[t'......--fi'iiF"- TO

PUMP

10J FROM ROOF TOPS

tb)

FROM

PREPARED CATCHMENTS

-PR£PIIoRED

CATCHMENTS

AG. 1.1. DIRECT· COlLECIlON OF RAIN WATER

ghled

mater~1

l

WATER SYSTEMS

(a) From roofs of houses and dweUings : Water is stored in small underground tank or cistern, for small individual supplies (Fig. 1.1 a). (b) From prtpGIftI caJdtmmls : The surface of catchments is made impervious by suitable lining material, and suitable slope is given so that water is stored in moderate size reservoirs. This water is used for communal supplies. mostly for drinking purposes. 2. Surface Waler

~~E

_."i--- --it

,

INTAKE TOWER

TO PURIFICATION

RIVER OR LAKE

WORKS

• INTAKE PIPE

(0) CONTINUOUS DRAFT FROM STREAMS OR LAKES

""'0£

BANKS

~ a ~

~

(b )

jRlVER DI VIDE WAlL

MANNEL

WATER SUPf'LY -CANAL

FROM RIVER DIVERSION WORt(5

Ie J WATER FROM RESE.RVOIR STORAGE:

FJG. U. SOURCES OF SURFACE WA1CR

C ;.pvnghted malaria

WATER SUPPLY ENG IN EER ING

6

Surface water is the one which is available as run -off from a catchment area, during rainfall o r precipitatio n. This runoff nows either into streams or into undrained lakes. The runoff water Oowing inlO st reams can either be stored in a reservoir by constructing a dam across it, or be diverted into a water supply channe\. Thus. depending upon the scheme of collection, we get surface water from the fo llowing sources. From rillers b:~ conl;mwus draft: Water may be collected directly from the river, without any diversion work (Fig 1.2 a). (b) From river di~ion, A diversion work is conSlfucted across a perennial river and water is diverted into a canal which leads water to the site o f water purification wo rks (Fig. 1.2 b). (a)

(e)

From resert'o;, storage. Where supply is not ensured throughout the year. dam may be constructed across the rive r and water stored in the reservoir (Fig. 1.2 c). (4) From direct wake from tulIural lakes. Wate r may also be obtained through direct intakes from natural la kes which receive surface run-off from the adjoining catchment (Fig. 1.2 a). 3. Ground Water The largest available source of fresh water lies undergro und. The term 'ground waler ' refers to this water, which is stored by nature, unde r-ground in the water-bearing formation of earth's crust. The total groun~ water potential is estimated to be one third the capacity o f oceans. The main source of ground water is pr~ pitati on . A portion of rain falling on the earth's surface irfftfrates into. ground, travets down and when checked by im,ervious llIyer to travel further down, forms ground water. The ground water ruervoir consists of wate r held in voids within a geologic stratum. The ground water can be tapped from the follO\\oing sources. J

'"

(a) From natural springs (Fig. 13 a). (b) From wells and bore holes (Fig. 1.3 b). (c) From inflkraiWn galloUs, basins or cribs (Fig. 1.3 c). (d) From wells and galleries with flows augmented from some other sources : (i) spread on surface of the gathering ground (u) carried into charging basins or ditches, or (m) led into diffussion galleries or wells.

(e) From river side radiJll collector wells (Fig. 1.3 d)

j

maknal

1.

WATER SYSTEMS DITCH

(0) WATfR FROM SPRINGS

TOP

SOIL

TO~

TO RESERVOIR

CL ~\Y

.... ,,.

~

:.

MIN. WATER LEVEL ----------Ib_}' TUBE W£L.L

Ibl) SHALLOW DUG WELL

_

,. __ ... 0._'" -_ .....

.. WATER BEARING·.. -.~. ~

.....• .. . .

• STRATA

~.

p

.~

GAll " 'ERY

" - · co • t-

~. ~

... .. PIPE SY5T£M

I e) INFILTRATklN GALLERY

(4) RADIAL COLLECTOR WELL

F1G. 1.3.. SOURCES OF UNDERGROUND WATER.

4. Water obtained by redemetton (a) lJa4IintJJion.

Saline or brakisb water may be rendered useful for drinking purposes by installing desalination plants. The common methods used for desalination are: distillation, reveI'5C osmosis, ek:arodialysis, freezing and solar evaporation. (6) ~ of In1III«I .....,. nUr. Eftlueot or waste water tan be lreated suitably so lhat it may be re--osed. AD mmplc of \be controlled indirect re·use-is the intentional aniflcial recharge of ground water aquifers by adequately treated waste water. C JPYnghied

mater~1

Hydrology

2.1. THE WATER CYCLE Hydrologj is the science which deals with the occurrence, dis· tribution and movement of watcr on the earth, including that in the atmosphere and below tbe surface of the earth. Water occurs in the atmosphere in the (orm of vapour, on the surface as water, snow or ice and below the surface as ground water occupying all the voids within a geologic stratum..

....

--

-.I

P! 1tC'OI,. ...TIOtI

- - __ _ __fi.'_H ....T.

I

"""0''''''''

~---

GII'OUNO WATER !'"lOW

Iftt

0I 2011

FlG. j.2 GRAPHICAL EXTENSION MEnlOD. ; JPYnghied

mater~1

WATER DEMAND AND QUANTITY

147

to the future decades. From the extended part of the curve, the population at the end of any future decade is approximately determined.

6. Graphical Comparison Method This method is a variation of the previous method. It assumes that the city unde r consideratio n will develo p as similar cities developed in thc past. The met hod consist of plotting curves of cities that; o ne or more decades ago, had reached the present population o f the city under consideratio n. 9 0 000

V

eo 000 70 000

~ /'

000 40 000

l!6 ~

V

./

/ V

000 1930

1940

19!tO 1960 YEAR

1980

2000 (AI

1940

1960

""'.

' " , tel I96!S to) 1900 lEI

10:'.

1030

(8)

FIG. 5.3. GRAPHICAL COMPARISON METHOD

Thus, as shown in Fig. 5.3, the population of city A under consideration is plo tted upto }970 at which its population is 62,000. The city B having similar oonditiom, reached the popuJaUOa. of 62()(X) in 1930 and its curve is plo tted from 1930 onwards. Similar curves are plotted for other cities C, D and E which reacbed tM population of 62 in 1925, 1935 and 1920 respectively. The cune of city A can be then be continued (shown by dotted line). allowtD, it to be influenced by the rate of growth of the larger atka. Ia practice however. is is difficult to find identical cities with fCSpect to population growth.

7. Zoning Method or Master Plan Method This is probably a scientific metbod using tbe limitatiom lmposed by tbe town planner in tbe increase in douily ofpopu/tJtion of various parts of the city. For this, a master plan of the dty is prepared, ~

WATER SUPPLY ENG INEER ING

148

dividing it into various zones such as industrial, commercial, resident ial and ot her zones. Each zone Is allowed 10 develop as per master plan only. The future population o f each zone. when (ully developed can be easily found. For example, sector A of a residential zone has HXX> plots. Allowing 5 persons per plot. the populat io n of this sector, when (ully developed, will be 1(0) x 5 = 5(0) perso ns. Similarly. the developme nt of each zone can be estimated. This met hod is more advantageous because oflhe fact that the to tal water require me nt of the city depends not only for domestic purposes, but also for commercial, industria l, social health a nd other purposes.

Population de nsity is generally expressed as number of persons

per hectare, and their values may be estimated from data collected on existing areas and fcom zoning master plans for undevelo ped areas. Table 5.2 gives the values of common population densities.

-

TABLE 5.1.

,

1. Residential

~.

••

.....

Sinl le family units

Rc:OOenlial • mulfiple family units. Apanmenh Commerical area

S. Industrial area

'f

COMMON POPVUTION

DENSITl~

PWMN p«' "'«Ian

15 -80 80- 250 250 - 2500 40 - 75 15-40

8. RaUo and Correlation Method The population growt h of a small town or area is rclatcd to big towns or big areas. The increase in population of big cities bear a direct relationship to the population of the whole stale or country. In this method, the local to national (or sta te) population ralio is determined in the previous two to four decades. Depending upon conditions or other factors, even changing ratio may be adopted. These ratios may be used in predicting the future population. This method takes into account the regional and nat ional factors affecting poPI,l~tio n growth. This method is useful for o nly those areas whose population growth in the past is fairly consistent with that of state or nation. 9. Crowth eo.poslUon Analysis Method The change in population of a cil)' is due to three reasons: (i) binh, (u) death, and (iii) migration from .villages or other towns. The population fo recast may be made by proper analysis of these three factors. The .difference berween binh rate and death rate gives Ihe MIUra} increase in tbe population. Thus, , P. _ P + Nalural increase + Migration. C JPYnghied

mater~1

...

"

WATER DEMAND AND QUANTITY

The estimated natural increase is given by the following ex·

pression: ,Natural inaease = T(/.i-JDP)

... (5.10)

T "'" design (forecast) period. P - present population. I. = avera~ binh rate per year;

where

ID = average deltii. nte per yeuV ' 5,4. FACTORS AFFECTING POPULATION GROWI'H .... The population growth of a city depends upon rollowing (actors. These factors affect considerably the estimated .population. 1. Economic factors. Such as development of new industries, discovery of oil or other minerals in the vicinity of the cily.

2. Devtlopment programmes. Development of projects of national importance, such as river valley projects etc. 3. Social facilities. Educational , medical, recreational and other

sooal facilities. 4. Communication links. Connection of the town with other big cities, and also to the mandies of agricuhural products.

5. Tourism. Tourist facilities. religious places or historical buildings.

6. Communi'Y life. Uving habits, social customs, and general Cducat'ion in the communitf. . -- '. 7. Unforeseen faclors. Earthquakes, floods, epidemics, frequent famines etc. 5.5. DETERMINATION OF POPULATION FOR INTER·CENSAL AND POST·CENSAL YEARS Sometimes, it may be required to determine the population for the intermediate portion of a censal period, from the available · data. This can be done with the help or arithmetical increase metbod and the geometrical increase method. lei tIP be the increase in population during a time period dT. U

~= KA = . constant,

If

:~= KG . P,

then the growth wiU be arithmetic.

where KG is the proportionality factor, then

the growth will be geometric. The values or the ractors KA aDd can be · determined from the ronowing expressions :

Ka

C JPYnghied

mater~1

ISO

WATER SUI"PLY ENG IN EEKING

K.. = p, - h TL T£

... (5. 11)

K,; = log. p, - log. p, ... (5. 12) h T£ PL = population at the last census al data h P f = population at the earlier census 31 dale h.

and

where

Now if the population PM is the desired mid·year population at a date TN. its value is given by the following expressio ns.

AriIJrmdiaU I"",,", MtI/wd For inter censal period :

or

Pili =P£

+ KA.(T/II- Te}

Pill = PE

+ ~N,-- ~£, (PL -

... (5. 13 a)

Pc)

... (5.13)

PE)

... (5. 14)

For posl-censal period ,

+ ~ (T/II - Td T/II-TL PII = PL + TL T£ (PL -

PM = PL

or·

G«Hrtdrical ;trCrf!4Se Method For inter-censal period,

or

loge PM = loge PI:

+ KG(T/II -

loglo P" = JogIOP!

+ ~N, -- ~E, (IOg10PL -

... (5.15 a)

Te)

logloP,e)

... (5.15)

For post-censal period : 10g. P. '" 10g.P,

+ KG(T.- T,)

Joglo P", = IOgl,PL +

or

... (5. 16 a)

~.w, - ~L, (IOg10 PL -

loglO P£)

.

... (5.16)

ExaIIIple 5.1. The following is the population data of a city, available from past census records. iNlmnine the population of the city in lOll by (a) arithmetical incrwse method (b) geometrical increase method (e ) incnmt!ntai increa.r~ , m~thod (d) graphical mdhod (~) d«nased rat~ of growth method.

r_

.-,

,

1931

I

(PI

1941

I_ I"'"

1951

1961

1971

19."

·1991

26800

41'"

S7S00

68000

74100

Solution : The oomputations about increment, % increment and incremen· tal iDa"eae pe:- decade are arran£ed in Table 513 below ·:

Of)

r htedm

na

WATER DEMAND AND QUANTITY

lSI

TAB LE 5.3. y~

PoplI""ioII

, 1931

Z 1_

194 1

16500

1951

26800

1961

'1 500

1971

"500

1981

68000

ItlDYtltlttli

... iflCTml~1II

Itw:nrrI~trtal

lhcrNu/"

,.~~

IH"d~

i~

... i1lC1Ytrl~'"

"00

37.50

10300

62.42

6

+ '800

14700

".8S

16000

38.55

10.500

18.26

' 100

8.97

Total

62,100

220.55

AvetlIge

-,-

-,-

1991

,

+'400

7.57

+1300

16.30

- 5S00

20.29

-

4400

9.29

+ 1600 1600

53.45

74100 62, 100

-

10350

220.55

- 36.76

.-,,,.-

53.45 -'-,-

13.36

In (he above table, percentage Increase fo r the first decade (1931 10 1941) = 16500 - 12000 100 = 4500 100 = 375 % t21XX> x 12000 x . . Similarly, % increment for other decades have been calculated. 1. AriJhmdicaI 1nct'«lSe Method

where

P. = P + nl (Eq. 5.1) P = population in 1991 = 74,100 n "" number of decades

1991 - 1971 2 10 I :z average increase per decade= 10350 (from Table 5.3) p. = 74100 + 2 x 10350 = 94Il00. 2. Gt:ontttricPl Incrrase Method j>. = P [ I

Here,

+ 1&

r

I, = average per cent increase per decade = 36.76% (from Table 5.3)

..

(5.2)

G JPYnghtcd makrtaJ

WATER SUPPLY ENGIN EERI NG

152

p ~ 74100 ( I •

+ 36.76 )' 100

~ 1,38,590. The above computatio ns are based on the va lue o f Ix computcd

by arithmatic average mClhod. If, however, geomet ric average me lhod is used, as recommended by the Manual, we have

I,

=

( I, •. 161' ..... J,II )

1 / 11

= ( 37.50x62.42x54.85x38.55 x lS.26x8.97) II. = 30.54 (against a value o f 36.76)

P.

~ 74100 ( 1 + ~~4 )' ~ 126272

3. IflCr'emenlal IflCnase Method

p" = P + "I

+ n (n + 2

I) r

where,

I

and

r = average incremental increase

~

... (5.3)

10,350

= 320 (from Table 5.3)

P. ~ 74 100

+2 x

10350

+ 2 (2

t

I ) x 320

= '5760. 4. GrapIaicGJ Extensiim Metlwd Fig. 5.2 shows the plot between the population and the time. The dotted portion o f the curve is the extended part fIOm 199 1 to 201 1, (ollowing closely irs trend. From the extended part. the

populalion al the end of 2011 = 8O,CXXl. S. Decrm.sed 1We

of

Growl. Mdlwd

Column 6 of Table 5.3 give