U. G SEWERAGE



GIDELINES FOR PREPARATION OF DPR FOR UNDER GROUND SEWERAGE SCHEME

Sl.No.

GUIDELINES

References

1.

Conducting topographical survey of the project area for which DPR is to be prepared and preparing contour plan 1m interval.

 

2.

Soil Investigation to be conducted at proposed WDS site and also for 10% of network length of project area along the roads

 

3.

Preparation of Base Map with Ground levels marking all the major roads, canals, rivers , monuments , TBM in Auto CAD format.

 

4.

Labelling junction points, roads meeting end points as Node numbers and roads as pipe numbers in the base Map. The node to node distance is also marked.

 

5.

Population Projection The population projection for the entire project areas is done based on the following methods recommended by CPHEEO.

  1. Arithmetical increase
  2. Geometrical progression
  3. Incremental increase method
  4. Method of Least square method
  5. Decreasing rate of Growth method
  6. Graphical Method
  7. Logistic Method
  8. Method of Density
  9. City Development Plan (CDP) growth rate (Generally CDP Growth rate is adopted)

 As per the details collected from census department (At least three decade population is required) for projection of population for Base year, intermediate year and Ultimate year.

Base year is the year at which the designed system of the project area is put in to use.

(generally 4 years 6 months from the present year (preparation and approval DPR – 12months + tender process – 6 months + implementations – 21/2 years + effecting house service connections – 6 months).

Intermediate year is 15 years from base Year. Usually, the pumps are designed for intermediate year.

Ultimate year is 30 years from the base year. This usually forms the design year of the system.

Population is projected for 30 years which is the design period. 

CPHEEO, manual on Sewerage and Sewerage Treatment Systems , November 2013,

 

Pg.No. 2-9, 2-10

Chapter 2,

CI. 2.6.1

 

6

Zoning of project area is done in accordance with the density of population, topography and manhole depth restricted to 4.50m (or decided by the authorities) physical barrier like canals/railways major roads/Highways etc.

Decision has to be taken by the concern Chief Engineers, with regards to limitations on max depth of man hole to 4.5m

7

Design norms

Per capita waste water generation considered for design of water supply is 120 lpcd as per CPHEEO norms.

i.e. (80% of 150LPCD)

CPHEEO, Manual on Sewerage Treatment Systems, December 1993, Pg.No. 39, Chapter 3, CI. 3.2.4

8.

Infiltration

 

Estimate of flow in sanitary sewers may include flows due to infiltration of ground water through joints

Ground Water infiltration

                                         Min           Max

Litres/ha/day                5,000         50,000

Litres/km/day                 500           5,000

Litres/day/manhole      250               500

 

Design infiltration value shall be limited to as max of 10% of the design value sewage flow

CPHEEO, Manual on Sewerage Treatment Systems, November 2013, Pg.No. 3 - 4, Chapter 3, CI. 3.6

9

Peak factor

Up to 20,000                          - 3.00

 

Above 20,001 to 50,000       - 2.50

Above 50,001 to 7,50,000    - 2.25

Above 7,50,001                      - 2.00

CPHEEO, Manual on Sewerage and Sewerage Treatment Systems, November 2013,

 

Pg.No. 3 - 3,

Chapter 3,

CI. 3.2

10.

Material of the pipe

DWC/CI

  1. Up to 300mm dia pipe and up to 3.0m depth DWC pipes area used
  2. Above 3.0m depth and size above 350m dia CI pipes are used.

Decision has to be taken by the concerned Chief Engineer’s

11.

COLLECTION SYSTEM

 

 

 

Formula : Manning’s Formula

V= (1/n)xR23 S1/2

For circular conduits

V= (1/n)x(3.968 x 10x2) D2S1/2

Q = (1/n) x (3 .118 x 10x2) D2.67 S1/2

Q = Discharge in l/s

S: Slope of hydraulic gradient

D: Internal diameter of pipe line in mm

R: Hydraulic radius in m

V: Velocity in m/s

N: Manning’s coefficient of roughness

 

A

Minimum size of sewer  200m

CPHEEO,

November 2013,

Pg.No. 3-25,

Chapter 3

B

Minimum velocity (Present peak flow)     : 0.6m/s

Minimum velocity (Ultimate peak flow)  : 0.8m/s

Maximum velocity                                        : 3m/s

CPHEEO,

November 2013

Pg.No. 3-26

Chapter 3, CI.315.1

C

Design Depth of flow

(d/D ratio ) less than or equal to 0.8 full at ultimate flow

D= Dia of Pipe

D+ depth of flow

CPHEEo,

November 2013,

Chief Engineers of

CMWSSB held on 06.07.2017

 

Manhole

 

Size of Manhole :

Brick work Manhole                           : From 1.0m & up to 1.5m        

(SRC cement)                                         average depth range

RCC precast Manholes                      : From 2.0m & upto 2.5m  

                                                                average depth range

RCC Cast in situ manholes               :  From 3.0m & above

                                                                 average depth range.

Spacing of Manhole                            :  30m

Size of manhole door                          : 60mm

Decision has to be taken by the Concerned Chief Engineer’s

12.

HSC

No.of House service connections : 6 No.s per manhole

Decision has to be taken by the Concerned Chief Engineer’s

13.

PUMPING STATION

 

A

GRIT WELL

 

 

  1. Minimum diameter of well           -  3m
  2. Volume of Grit generated             - 0.05 to 0.15 cu.m/ML
  3. Volume of grit storage required  - Min of 2 days
  4. Depth of well below the invert    - Should be

on incoming sewer in gift well       provided taking

                                                            into considered  

                                                            to accommodate  

                                                            volume of grit    

                                                            for 2 days.

  1. Screen angle of inclination         - 45 to 60 deg.

 

B

SUCTION WELL

 

 

1)  Detention time in suction well     - 5 minute of peak flow of ultimate stage (min)

10 mins for smaller pump capacities but 15 minutes is describe

 

2) Minimum dia of well  - 3m

3) Maximum dia of well  - 8m

4) No.of starts per hour    - 6

 

Depth of well below the invert of incoming sewer suction well: height of submersible pump plus depth required for storage of 5 min detention time for ultimate peak flow.

CPHEEO,

November 2013,

Pg.No. 4 -10

Chapter 4, CI.4.6.5

C

PUMPING SETS

1. Submersible pump

2. No.of pumps :

    For SPS : 1 ADF – 3 Nos(Qipf/3)

                                     (out of 3. 1 act as stand by)

   For LS: 1 ADF – 2 Nos (Qipf /1) (1 Standby)

Decision has to be taken by the Concerned Chief Engineer’s

 

PUMPING MAIN

  1. Size decided based on economical dia calculation and velocity criteria.
  2. Class pipe decided based on Surge pressure calculation.
  3. Minimum dia pumping main – 100mm
  4. Maximum velocity at peak conditions <= 3m/s
  5. Minimum velocity not less than 0.8m/s

CPHEEO,

November 2013

Pg.No. 4 -10

Chapter 4, CI 4.6.6

 

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