lec 2(design of sewer system).pptx
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Step of Design of Sewer
System
Lecture 2
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Steps
1. Preliminary Investigations
2. Design Criteria Considerations
3. Actual Design. Preparation of Drawing and !"#
$. Su%se&uent 'odi(cation
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1.Preliminary Investigation
• "%tain maps and drawings t)at furnis)information of t)e area
1. Population Density
2. *ater consumption3. Soil c)aracteristics + ,atural slope
•. 'aps s)ould also )ig)lig)t t)e location ofstreets- pars - %uildings etc.
Note: Sewerage systems are operatedunder gravity where as water supplysystems are operated under pressure
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• If a map or needed information is notavaila%le conduct a detailed survey of t)e
area to do t)e needful• /sta%lis) !enc) 'ars t)roug)out t)e area
and mae contours pro(les and crosssections
• 0se a dierent scales e.g 11444 to13444 for maing map5
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• Soil conditions s)ould %e investigated for
t)e type of stratum
• Location of water ta%le
• Presence of any underground roc
• Collection of rainfall and runo data.
• Study of natural slopes of t)e area and
selection of a suita%le disposal point.
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2.Design CriteriaConsideration
15Design 6low 7 Calculation of avg. sewage 8ow ont)e %asis of water consumption and t)e population
at t)e end of design period
a5Sanitary Sewer
# design9 Pea sewage 8ow : In(ltration
%5 Partially Com%ined Sewer
# design9 Pea sewage 8ow :Storm 8ow:
In(ltration
*ASA Criteria (Peak sewage fow = Storm fow)
# design9 2 ; Pea sewage 8ow : In(ltration
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25 Design /&uation
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35'inimum Self cleansing velocity
• Sewage s)ould 8ow at all times wit)
suBcient velocity to preventsettlement of solid matter in t)esewer
• Sel cleansing velocity is minimumvelocity t)at ensures non
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5'a;imum >elocity
S)ould not %e greater t)an 2!m"s
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Fa%le Commercially availa%le diameters of sewer in mm
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5 'inimum cover.
< 'inimum 1 m eart) cover on sewer crown toavoid damage from live loads
E5'an)oles
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6ig 'an)ole
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5 Direction of Sewer lines
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J5 # d@# f ?atio
• # d9 Design 6low
• # f 9 6low w)en sewer is 8owing fullIn order to provide air space in t)e upper portionof sewers for ventilation purposes *ASA
recommends to maintain t)e following ratios orsanitary sewer
Sewer SiGe
22$
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3. Actual Design of Sewer
• SiGe of sewer 0sing #9A> for thecalculation of diameter
• Slope of sewer 0sing manningformula
> 9 1@n ?2@3 S1@2
used for either calculation of slope or checkingvelocity
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. Preparation of drawings and
!"#s
• +ypical drawing includes
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6ig Sewer Pro(le
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-ill o.uantity
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F)an Mou