Design a sewer collection system incorporating flow rates, pipe sizes and pipe slopes for the proposed residential development shown in the attached drawing. In your design, locate suitable sewer alignments, manhole positions and other sewer appurtenances. Clearly point out in the layout diagram which properties are served by which section of the sewer.
The local approving authority accepts sewer alignments that service adjoining properties, i.e. a common line that drains two adjacent properties. Contours indicating the reduced levels are illustrated in Figure 1. You may derive intermediate levels by interpolation wherever necessary. The development consists of residential allotments, a proposed primary school for 500 pupils, a child care facility for 100 children, a church and local park. There are 4 equivalent person (EP) for each residential allotment. The strength of waste discharged from church and local park can be assumed to have an average of 1.2 kg BOD/day and 2.4 kg BOD/day respectively. BOD of an equivalent person can be considered to be 60 g/EP/day.
The sewer size must be capable of carrying the maximum flow at the appropriate gradient and flowing not deeper than three-quarters pipe diameter. Inflow/Infiltration (I/I) may be derived from lengths of contributing pipes or catchment areas whichever is greater.
Use the following design data
ADWF, (L/c.d) 260
I/I, (L/s.ha) 0.8
I/I, (m3/d.km) 28
Primary school, EP/pupil 0.25
Child care, EP/child 0.25
Manning's n 0.013
Use peaking factors shown in Fig. 6.6 of the study book
Wastewater flows from the development is to connect the proposed sewer main at manhole M1. The manhole M1 also accepts upstream future flows from a catchment of 10 hectares and 500 EP. Include calculations for a satisfactory sewer main and gradient between M1 and M2. The limiting upstream invert level at manhole M1 for the upstream flows is 38 m. Manhole M1 surface RL is 40 m. Surface levels at other manholes may be assumed to be 50 mm or more below the nearest calculated reduced levels.
Show clearly the steps taken in your design with accompanying detail working of your calculations and present your design in a format as shown in Example 6.3 and Table 6.7 of the study book. Marks will be allocated for documentation and clarity of design. Provide relevant checks and comment on them.
Prepare and tabulate the design aid for partial flow as per the equations for interpolation of velocity and diameter for corresponding flows.
Attachment:- Assignment2.rar