1. Coursework guidelines
Water Resources Engineering
M3H124594
(Semester A -2017)
Coursework guidelines
Mini project: Design of sewer system

2. Aim
To gain knowledge on design of sewer system through practical application.
Objectives
To interpret data requirement for designing urban drainage systems and to analyze factors affecting urban drainage
To determine quantity of storm water and wastewater originating from urban environments as a basis for the design of separate sewer system
To identify components of urban drainage systems and produce system layout
To illustrate the sanitary and storm water systems design method

3. Given data Urban layout (mainly residential)
Elevation at axis of street (in m)
Population by residence ( 2+ last digit of student number)
Growth rate of 2% and design period of 25 years
Domestic water consumption per head L = (two last digit of student number) liter/head/day and Infiltration I = 1%.
Uniform coefficient of impermeability C =0.5
Time of entry is Te =6 min

4. Sewer system specification
Separate system: design of two parallel systems storm and foul
The sewer system is designed for “gravity flow”. Pumping stations should be avoided as much as possible.
Circular pipe and made of concrete.
Sewer mains shall be aligned in streets. Manholes are provided at heads of runs, at locations where there is changes in direction, changes in gradient, changes in size, at major junctions with other sewers and at every 90 meter intervals.
The sewers are of commercially available sizes (150; 200; 250; 300; ….)

5. Preliminary horizontal layout
A tracing paper is required
Step 1: identify outfall of the sewer system; it is the lowest point on the plan
Step 2: locate pipes so all potential users can readily connect into the system

6. Preliminary horizontal layout
Step 3: Follow natural drainage and show direction of flow (using an arrow in the layout)
Step 4: Locate manholes as per specifications
manhole

8. Preliminary Breakdown in section
Give name to each section (pipe) using nomenclature FS1, FS2, … and to each manhole M1
Indicate head and end of run using Manhole name
Calculate gradient
Prepare tabulation form to record the data and steps in the compilations for each section of sewer between Manholes.

9. Tabulation for section characteristics
Table 1 : Section characteristics
Section
Head of run
End of run
Length (m)
Ground surface elevation
Gradient
(%)
Upper end (m)
Lower end (m)
FS1
 M1
M2 
...
Length of the pipe from plan is converted to scale and given in m
Natural slope is taken to minimize excavation = (Upper- Lower)/Length *100 (given in %)
If slope is not matching specification, take slope 1.3 %
Minimum slope = 1/125 =0.8 %
Maximum slope 1/25 = 4 %

10. Estimation of quantities of wastewater generated
Section
Number of residence connected
Actual population
Future population
DWF
(l/d)
Maximum flow
(m3/s)
FS1

11. Design of storm sewer
Demarcate and name catchment area drained by each section. Calculate area referring to the given scale on the map.
Table 4 : section and catchment area
Section
Length
(m)
Catchment area name
Area
(ha)
SS1

12. Example

13. Estimation of runoff flows
For each catchment area, flow should be determined using rational method. Impermeability coefficient C is taken 0.5. Entry time to the pipe is the same for all section Te= 6 min.
Table 5: Runoff flows
Section
Length L
(m)
Watershed area A
(ha)
Time of flow Tf
(s)
Time of concentration Tc
(min)
Average rainfall intensity i
(mm/hr)
Flow Q
(m3/s)
SS1

14. Vertical profile of pipe
Plot ground surface elevations, working backwards on graph sheet
Sketch invert and crown
Line 1: Locate the invert of the upper end of the pipe
Upper Invert Elevation=Ground surface – depth of cover – pipe wall thickness – pipe diameter.
Lower Invert Elevation= Upper Invert Elevation-(Slope of sewer)x(Length of sewer)
Check: Depth of Cover Adequate/ Not adequate?

15. Marking scheme Introduction, Role and importance of urban drainage
5 marks
Requirement for sewer system and Sewer appurtenances
10 marks
Foul sewer system design
30 marks
Storm sewer system design
Conclusion and Recommendation
3 marks
References
2 marks
Total
80 marks

16. Foul sewer Design
Foul Sewer Design
Mark
Criteria
Smart network design 5
Optimization of manholes number…
Horizontal layout
Flow direction
House connection shown
Manholes and pipe nomenclature
Identification of outfall
Breaking down in section 6
Table 1: Section characteristics
Estimation of quantities of Wastewater generated
Table 2:Wastewater production
Hydraulic design 8
Table 3: Design computation for foul sewer system
Full layout should be drawn, only five consecutive pipes should be designed

17. Storm Sewer Design
Storm Sewer Design
Mark
Criteria
Smart network design 5
Optimization of manholes number…
Horizontal layout
Flow direction
Delineation of watershed,
Catchment area, Manholes and pipe nomenclature
Identification of outfall
Breaking down in section
Table 4: Section and catchment area
Estimation of runoff flows
Table 5: Runoff flows
Hydraulic design 7
Table 6 : Design computation for Storm sewer system
Vertical Profile of pipe 3
Graph and calculation
Full layout should be drawn, only five consecutive pipes should be designed
Only three successive pipes will be selected for Vertical profile

18. Guidelines for the report
Students have different data. Data used should be highlighted in the report.
Report should contain list of contents, list of tables and figures, nomenclature.
Tables and Figures should be with Captions and References.
Layouts prepared by student should be attached in the report in the appropriate part. Urban layout plan should be attached in the appendix
One sample calculation should be written and explained clearly in the report. Results of calculation should be summarized in tables given above accordingly.