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Collection & Conveyance of

Systems of Sanitation.Methods of Collection

The sanitation of town or city is done

by two methods:• Conservancy System

• Water-Carriage System

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Conservancy System

• Sometimes this system is also called dry-

System. This system is in practice fromvery ancient times. Actually it is out ofdate system even though it is prevailing

in small towns, villages and undevelopedportions of the large cities. Various typesof refuse and storm water are collected,

conveyed and disposed of separately bydierent methods in this system,therefore, it is called conservancy system.

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• Garbage or dry refuse of a town is collected in dust binsplaced along the roads and streets, from where it is

conveyed by trucs or covered carts once or twice in a dayto the point of disposal.

• All the non-combustible portions of the garbage such assand, dust, clay ashes etc., are used for !lling the low level

areas to reclaim land for further development of the town.

•   The combustible portion of garbage such as dryleaves waste paper bro!en furniture etc. are burnt.The decaying fruit and vegetables grass and other

things are "rst dried and then disposed of by burningor in the manufacturing of Manure.

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• #uman $%creta or ight Soil is collected separately inprivies or conservancy laterins. The li"uid and semi-li"uidwastes are collected in separate drains of the same latrine,

from where they are removed through human agency.

• The night soil is ta!en outside the town in closedanimal drawn carts truc!s or tan!s mounted on the

trailers. The night soil is buried in trenches.

• #n conservancy system the Sullage and Storm waters are also

carried out separately in closed or open drains, upto the pointof disposal, where they are allowed to mi$ with stream, rivers

or sea without any treatment.

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Merits of Conservancy System

•  The following are the merits of %onservancy System

• #t is cheaper in #nitial cost because storm water canpass in open drains and conservancy latrines aremuch economical.

•  The "uantity of sewage reaching at the treatmentplant before disposal is low.

• As the storm water goes in open drains, the sewer

section will be small and will run full for the ma&orportion of the year, due to which there will be nosilting and deposits in sewer-lines.

• #n 'oods if the water level of river rises at the out-fall,

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'emerits Conservancy System

• #t is possible that storm water may go in sewer causing

heavy load on treatment plants, therefore it is to bewatched.

• #n crouded lanes it is very di(cult to lay two sewers orconstruct road side drains, causing great inconvenienceto the tra(c.

• )uildings cannot be designed as compact unit, becauselatrines are to be designed away from the living roomsdue to foul smell, which are also inconvenient.

• #n the presence of conservancy system, the aestheticappearance of the city cannot be increased.

• *ecomposition of sewage causes insanitary conditionswhich are dangerous to public health.

•  This system completely depends on the mercy ofsweepers.

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Water Carriage System

• +ith the development and advantages of the cities,

urgent need was felt to replace conservancy systemwith some more improved types of system in whichhuman agencies should not be used for the collectionand conveyance of the sewage. After a large numberof trials it was found that the water is the only

cheapest substance, which can be easily used forcollection and conveyance of sewage. Therefore it iscalled +ater-%arriage System.

• (n this system the e%cremental matters aremi%ed up in large )uantity of water and aredisposed o* after necessary treatment in asatisfactory manner.

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Collection & Conveyance ofSystems of Sanitation.

Merits & 'emerits of Water Carriage System

erits

• #t is hygienic method, because all the e$cremental matters are collected andconveyed by water only and no human agency is employed for it.

•  There is no nuisance in the street of the town due to oensive matters,because all the sewage goes in closed sewers under the ground. The ris of

epidemic is reduced.

• As only one sewer is laid, therefore it occupies less space in crowded lane.

• *ue to more "uantity of sewage, self-cleansing velocity can be obtained evenat less gradients.

• )uildings can be designed as compact one unit.

•  The land re"uired for the disposal wor is less as compared with conservancy

system in which more area is re"uired.•  The usual water supply is su(cient and no additional water is re"uired in water

carriage system.

•  This system does not depend on the manual labours

• Sewage after proper treatment can be used for various purposes.

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1. SewageIndicates liquid waste from community which includes domestic or industrial

establishments that is carried away in sewers or drains for dumping or for

conversion of a form that is not toxic.

Domestic Sewage Industrial Sewage

• Liquid waste originating

from kitchen sinks, urinals,latrines, bathrooms, wash

 basins etc of the residential,

commercial or institutional

 buildings.

• Extremely foul due to

 presence of human excreta in

it.

• Liquid waste from industrial

 processes like dyeing, papermaking, brewing etc.

• Quality depends upon the

type of industry and

chemicals used.

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  Sources of Sanitary Sewage

. !ater supplied by water authority for domestic usage, after desired use it is

discharged into sewers as sewage.

". !ater supplied to the various industries for various industrial processes by local

authority. #ome quantity of this water after use in different industrial

applications is discharged as wastewater.

$. %he water supplied to the various public places such as, schools, cinema theaters,

hotels, hospitals, and commercial complexes. &art of this water after desired use

 'oins the sewers as wastewater.

(. !ater drawn from wells by individuals to fulfill domestic demand. )fter uses

this water is discharged in to sewers.

*. %he water drawn for various purposes by industries, from individual water

sources such as, wells, tube wells, lake, river, etc. +raction of this water isconverted into wastewater in different industrial rocesses or used for ublic

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2. Storm Drainage / Drainage

• unoff resulting from storms.

• -enerally no treatment required for this

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+. Sewerage%he term sewerage is applied to the art of collecting, treating and disposing of

the sewage

ypes of Sewerage Systems:1. Combined System

!hen drainage is taken along with sewage by

carrying it through the sewers of the sewerage system

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2. Separate System

!hen drainage and sewage are taken independently

of each other through two different sets of conduits

3. Partially Separate System

) part of the drainage water especially that

originating from the roofs or paved courtyards of buildings is allowed to be admitted into the sewers and

sometimes the domestic sewage coming from

residences or institutions etc. is allowed to be admitted

into the drains

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Merits and 'emerits of SeparateSystem

ollowings are the merits of SeparateSystem

•  The sewage 'ows in separate sewer,therefore the "uantity to be treated is

small which results in economical designof treatment wors.

• Separate system is cheaper thancombined system, because only sanitarysewage 'ows in closed sewer and thestorm water which is unfoul in nature canbe taen through open gutter or drains,

whereas both types of sewage is to becarried in closed sewer in case of  

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,ollowings are the demerits of separate

System• Generally self-cleaning velocity is not available,

due to small "uantity of sewage, therefore 'ushingis re"uired at various points.

•  There is always a ris that storm water may enterthe sanitary sewer and cause over 'owing of sewerand heavy load on the treatment plant.

• As two sets of sewer are laid, therefore its

maintenance cost is more.• #n busy lanes laying of two sewers is di(cult which

also causes great inconvenience to the tra(cduring repairs.

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Sewerage System

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Merits and 'emerits of Combined System

Merits of Combined System

•  There is no need of 'ushing, because self-cleansing velocity iseasily available at every place due to more "uantity of sewage.

• ain water dilutes the sewage, therefore it can be easily andeconomically treated.

• /ouse plumbing can be done easily because only one set of pipeswill be re"uired

 'emerits of Combined System

• #nitial cost is high as compared with separate System

• #t is not suitable for areas having rainfall for small period of theyear, because the dry weather 'ow will be small due to which self-cleaning velocities will not be available resulting in silting up ofthe sewers.

• #f the whole sewage is to be disposed o by pumping, it isuneconomical

• *uring heavy rains, the over'owing of sewers will endanger thepublic health.

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Merits and 'emerits of artiallySeparate System

,ollowing are the merits of artially SeparateSystem:

• As it is an improvement over separate System,economical and reasonable si0e of sewers are

re"uired.•  The wor of house-plumbing is reduced, because

the rain water from roof, sullage from bath anditchens etc. can be taen in the same pipe carrying

the discharge from the water closets.• 1o 'ushing is re"uired, because the "uantity of

sewage is increased as small portion of storm wateris allowed to enter in sanitary sewage.

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Merits and 'emerits of artiallySeparate System

,ollowing are demerits of partiallySeparate System

•  The %ost of 2umping is #ncreased at

disposal plants than separate systembecause a portion of storm water is mi$edwith sanitary Sewage.

•  There are possibilities of over'ow, re"uiring

storm over'ows.

• #n dry weather, the self cleaning velocitiesmay not develop.

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Components of Sewerage

System. #ouse sewers/. 0ateral sewers12ranch sewer3

+. Main sewer4. Trun! sewers5. (ntercepting sewer

#omes

Sewage

Treatmentlant

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'i*erent types of Sewers:

ollowing are dierent types of sewers classi!ed on thebasis of wastewater carried by them and their si0e3

Soil pipe

• #t is the pipe carrying sewage from latrine in a housedrainage system. #t is one of the component of a house

drainage systemWaste ipe

• #t is the pipe carrying wastewater from bathrooms sinsand itchens, it is one of the components of house

drainage system0ateral sewer

• #t is sewer receiving domestic wastewater from housesewer. #t is one of the component of sewerage system ofa town or city.

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#ouse Sewer

• #n house drainage system the domestic wastewater of ahouse is carried by the house sewer to the municipal

sewer called lateral. /ouse sewer is one of thecomponent of house drainage system.

2ranch Sewer

•  The sewer which receives water from laterals sewers is

called as branch sewer. #t is one of the component ofsewerage system of a city or town.

Main sewer

• A main sewer is the sewer which receives wastewater

from the branch sewers. #t is one of the component of asewerage system of a city or town.

6utfall Sewer

•  The sewer conveying wastewater to the treatment plant

is nown as outfall Sewer.

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Characteristics of Sewage

hysical Chemical 2iological. %urbidity

". olour $. /dour 

(. %emperature

. %otal solid ontent

". p0 1alue$. hloride ontent

(. 2itrogen ontent

*. +at, -rease and oil content

3. #ulphates, sulphides and

0"

# gas

4. 5issolved /xygen

6. hemical oxygen 5emand

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9. :iological /xygen

5emand 7:/58

%he micro;

organisms foundin water 

Ph i l h i i

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Physical characteristics

• %urbidity is a measure of the light;transmitting properties of water• #ewage is normally turbid

•

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? #olids are classified into the following types>

1. otal Solids #S1$% )ll the matter that remains as residue upon evaporation of the

sewage.

•. 5etermined by evaporating a known volume of sewage and weighing the dry

residue left.

   S1 &  mg/'

Chemical characteristics

hemical characteristics help in indicating the stage of sewage

decomposition, the extend and type of treatment required for making itsafe for disposal

1. Solid content ( Sewage & )).)* water + ,.,- to ,.1* solids

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". Suspended solids or on( ilterable solids#S2$% %hose solids which remain floating

in sewage or those solids which are

retained on a filter of µm pores.

• 5etermined by filtering a known volume of sewage through a glass fibre filter apparatus andweighing the dry residue left behind

 S1 &  mg/'

3. ilterable solids #S3$%

• omprises of 5issolved #olids and olloidal #olids

• 5ifference between %otal solids and suspended solids

  S3& S1( S2

!. 0olatile #S!$ and ied #S-$ solids

#uspended solids may be either volatile or fixed @ #uspended solids if burnt and ignited at

about **=° in an electric muffle furnace for about * to "= minutes, the loss of weight due

to ignition will represent the olatile solids #S!8

  +ixed #olids, S- & S2 S!

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5. Settleable solids

• 5etermined using a specially designed conical glass vessel called Imhoff

cone of capacity liter.

• #ewage is allowed to stand in Imhoff cone for " hours and quantity of solids

settled in the bottom of the cone can be directly read out or the liquid fromthe cone can be decanted off and the solids collected at bottom of cone

should be dried and weighed

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2. p4 alue

•  p0 value; 2egative log of 0ydrogen ion concentration present in sewage

• 5etermination of p0 is important because efficiency of certain treatment methods

depends on p0 value

• If p0 A 4 @ #ewage is acidic

 p0 B 4 @ #ewage is alkaline

+resh sewage is generally alkaline. !ith time it turns acidic due to production of acids by

 bacterial action.

3. Chloride Content

•  2ormal chloride content of domestic sewage @ "= mgCL.

7&ermissible chloride content for water supplies; "*=mgCL8

• :ut large chloride content may be found in sewage from certain industries like ice cream plants, meat salting etc.

• &resence of high chloride content indicates industrial waste or infiltration of sea water.

• 5etermined by titrating the waste water with std. silver nitrate solution using potassium

chromate as indicator 7

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!. itrogen Content

• Indicates the presence of organic matter.

• It may occur in the following forms>;

a8 )lbuminoid nitrogen 7/rganic compound8

 b8 +ree ammonia 7ammonia nitrogen8

c8 2itrites

d8 2itrates

#a$ 5lbuminoid itrogen)Indicates quantity of nitrogen present in sewage before decomposition of organic matter

has started)

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Even though nitrates are non ob'ectionable final end products in aerobic treatment of

sewage, its concentration in potable water should be controlled due to the

following>;

 2itrate concentration B (* ppm cause nitrate poisoning in babies; 8lue baby Syndrome

/ 9ethaemoglobinemia

#c$ itrates  Indicates the presence of fully decomposed organic matter    2itrates is the most stable form of nitrogenous matter, thus indicating well

oxidied and treated sewage

Estimated using colour matching methods 7olour is developed by adding phenol;

di;sulphonilic acid and potassium hydroxide8 %he colour is then compared with the std. colour of known concentrations

- ats ;reases and "il Content

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-. ats: ;reases and "il Content

• +orm scum on top of the sedimentation tanks and clog the filtering media

  5etermination >

• #ewage sample is first evaporated

• esidual solids are mixed with ether 7hexane8; /ils and greses are soluble in

ether 

• #olution is then poured off and evaporated leaving behind fats and greases as

residue which can be weighed

< Sulphide: Sulphates and 4ydrogen Sulphide gas Content

• #ulphide, sulphates and 0"# are formed due to decomposition of sulphur

containing materials

• In aerobic digestion of sewage aerobic bacteria oxidise the sulphur and its

components to form sulphide which ultimately breakdown to form sulphateions.

• In anaerobic digestion of sewage aerobic bacteria oxidise the sulphur and its

components to form sulphide and 0"# gas. )long with methane and /"

= Di l d "

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=. Dissoled "ygen

• ;   ) solution of sewage and a strong oxidant like potassium dichromate 7D " r " /48

or potassium permangnate 7D

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). 8iological "ygen Demand

  Total organic matter

2iologically7ctive or 2io-'egradable

2iologically (nactive

or on 2io-'egradable

• C6' gives total organic matter

• (n order to "nd biologically active organicmatter 2iological 6%ygen demand is to be foundout by 26' testing

• The std demand is ta!en as 26' of waste waterduring 5 days at /8

C  26' or 26'5 9 ;< of total demand

  26'8  9 =8< of total demand

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 26'5 in ppm 9 6%ygen consumed in the test bythe diluted sample

>

'ilution ,actor

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opulation $)uivalent 9

• (ndicates the strength of wastewater for

estimating the treatment re)uired attreatment plant

• #elp in assessment of the realistic

charges for the treatment to be chargedfrom an industry instead of charging byvolume of sewage

i S i i

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?elatie Stability• he term is defined as the ratio of oygen aailable in the effluent

#as D": nitrite or nitrate$ to the ratio of oygen re@uired to

satisfy its first stage 8"D demand.• It is epressed as percentage of total oygen re@uired.

• ?elatie Stability& S& 1,,A 1( #,.=)!$Bt2, 

  & 1,,A 1( #,.

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8acteriological Characteristics

• 'ue to the presence of micro-organismswhich include bacteria algae fungi

proto?oa etc.

• Micro-organisms mostly originates fromhuman feces

• 2acteria are of / !inds:. on athogenic: #armless and

sometimes bene"cial to human beings/. athogenic: May cause diseases

•. 'epending upon their o%ygenre)uirement bacteria may be classi"edbased as:

. 7erobic

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'esign of pipes and sewers are similare%cept for the following:-

• Sewage contain some amount of solidparticles also some in suspension andsome which may settle

#ence a self cleansing velocity is to beprovided at di*erent possible discharges

The sewer material must resist wear andtear

• The sewer pipes carry sewage as gravityconduits and not under pressure.

#ence it must be laid at a continuous

gradient

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Minimum self cleansing velocity: for removing thedeposition in sewer@enerally ta!en as 8.;mAs

Ma%imum velocity 10imiting or on ScouringBelocity3: 'epends upon the material of sewer

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rovision of freeboards:

•

To account for any large scale in"ltration ofstorm water due to wrong or illegal connection

• 0ow estimates of the average and ma% owsmade due to some wrong data

• Dnforeseen increase in population or waterconsumption and the conse)uent increase insewage production

For sewer pipes of diameter < 0.4m - design forrunning half full 

For sewer pipes of diameter > 0.4m - design for

running rd or full at max discharges

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'esign eriod:

%he future period for which the provision is made in designing the capacities of

the various components of the sewerage scheme is known as design period.

%he design period depends upon the following>

Hseful life of the component structures 7material and equipment8.

Ease and difficulty in expansion )mount and availability of investment, )nticipated rate of population growth, including shifts in communities,

industries and commercial investments 0ydraulic constraints of the systems designed

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ollowing design period can be considered for different components ofsewerage scheme.

. Laterals less than * cm diameter 7equirements change faster8 > +ull

development

". %runk or main sewers 75ifficult and costly to enlarge8> (= to *= years

$. %reatment Hnits > * to "= years

(. &umping plant 7Installation of additional pumps is easy and less timeconsuming8 > * to = years

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Fstimating Sewage Discharge

•

%he quantity of sewage is to be properly estimated before design ofsewerage system

• %heoretically,

%he quantity of water supplied

to the contributing area%he quantity of sewage likely

to enter the municipal sewers 5

• :ut apart from accounted water supplied by water authority that will be

converted to wastewater, following quantities are considered while

estimating the sewage quantity>

1. Addition due to unaccounted private water supplies2. Addition due to infiltration

3. Subtraction due to water losses

4. Subtraction due to water not entering the sewerage system

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• Generally net quantity of sewage produced is considered

as ! to "# $ of the accounted water supply from waterwor%s

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'ry weather ow is the ow that occurs in

sewers in separate sewerage system orthe ow that occurs during dry seasons incombined system. This ow indicates theow of sanitary sewage.

This depends upon the rate of watersupply type of area served economicconditions of the people weather

conditions and in"ltration of groundwaterin the sewers if sewers are laid belowgroundwater table.

B i ti i S ,l

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Bariation in Sewage ,low

+luctuation in flow occurs from hour to hour and from season to season

Typical hourly variations in sewage ow

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or estimating design discharge following relation can be considered%

9aimum daily flow & 2 times the aerage daily flow

#representing seasonal ariations$

9aimum hourly flow & 1.- times the maimum daily flow

#accounting hourly ariations$.

& hree times the annual aerage

daily flow

9inimum daily flow & 2/3 5nnual aerage daily

flow

9inimum hourly flow & G minimum daily flow

  & 1/3 5nnual aerage daily

flow

Storm Hater low

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Storm Hater low

• he part of the rainfall after infiltration or percolation flows

oer land depending upon the permeability of ground: its

surface slope etc.

• his water which flows oer the ground surface: paements:

house roofs etc. is called runoff or storm water.

Storm water flow depends upon the following factors%(

1. Catchment area

2. ;round slope

3. Permeability of the ground!. Ftend of imperious area

-. Ftend of egetation growth

. Climatic conditions liEe wind: humidity: temperature etc.

ime of Concentration #tc$

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c

• It is the time re@uired for the flood discharge to reach to the maimum

limit or the time re@uired from the beginning of rainfall to the one

corresponding to the achieement of maimum rate of runoff

• It is the period after which the entire area will start contributing to the

runoff.

• The runo* will bema%imum when theduration of rainfall ise)ual to the time ofconcentration and iscalled as critical rainfallduration.

• The time of concentrationis e)ual to sum of inlettime and time of travel.

t +

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• tc & i + t

 i   Inlet time or ime of entry or "erland flow time

The time re)uired for the rain in falling on the most remotepoint of the tributary area to ow across the groundsurface along the natural drains or gutters up to inlet ofsewer is called inlet time

The inlet time ETiF can be estimated using relationshipssimilar to following. These coeGcients will have di*erentvalues for di*erent catchments.

Ti 9 H8.;;5 0+ A#I8.+;5 

Where Ti 9 Time of inlet in minutes0 9 0ength of overland ow in Jilometer from critical

point to mouth of drain# 9 Total fall of level from the critical point to mouth

of drain meter

Tt - Time of ,low or Time of Travel or channel ow

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Tt - Time of ,low or Time of Travel or channel owtime or gutter ow time

The time re)uired by the water to ow in the

drain channel from the mouth to the point underconsideration or the point of concentration iscalled as time of travel.

Time of Travel 1Tt3 9 0ength of drainA velocity in

drain

Fstimation of Storm Hater low 

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#i$ ?ational 9ethod()sed when area draining the water into sewer is small #J

!,, hectares$  K & . CI5

where, K( ?unoff in cumecsC( Coefficient of runoff 

5( Catchment area in hectares

I( Intensity of rainfall in mm/hour for a duratoion e@ual to time of c

concentration

6K

L 9 8./; C.(.7Where L is m+ AsecN ( is mmAhour and 7 isarea in s)uare !ilometer

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#ii$ Fmperical 9ethod

$mpirical formulae are used for determination of runo*

from very large area. Barious empirical relationships aredeveloped based on the past observations on speci"csite conditions suiting a particular region. Theseempirical formulae can be used for prediction of stormwater runo* for that particular catchment.

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Empirical formulae for rainfallintensities

 These relationships between rainfall intensityand duration are developed based on longterm e$perience in !eld under #ndianconditions, intensity of rainfall in design is

usually in the range 67 mm8h to 79 mm8h. #ngeneral the following empirical relationshipsare used3

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L

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