Assignment:
Water supply system
Special instructions:
Information provided is generally adequate; if any assumptions are made, these should be clearly stated giving your reasons.
A small coastal town in Queensland is subjected to an increasing permanent population and also a transient influx of tourists during the summer period. Council is already receiving complaints of poor water supply. The water supply system components comprise a trunk main from source to the service reservoir, the service reservoir and service mains to the consumption areas. Two consumption areas A and B at different elevations are gravity supplied from the service reservoir C. The service reservoir has a useable capacity of 6 ML and is gravity fed from a source D located 10 km away. Source D can provide 1000 ML per annum. All other information is shown in the sketch below.
Ductile iron pipes are used and have the following dimensions.
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Nominal Size, mm
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Mean internal diameter, mm
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Pipe wall roughness, mm
|
|
200
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215.4
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0.08
|
|
250
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268.0
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0.08
|
|
300
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326.4
|
0.08
|
|
375
|
401.0
|
0.08
|
|
450
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480.0
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0.08
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You are provided with data on the population and consumption as follows:
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Population (persons)
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Area A
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Area B
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Present maximum population (Dec-Mar)
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4500
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2000
|
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Design maximum population (Dec-Mar)
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6000
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3000
|
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Design maximum population (Apr-Nov)
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3000
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1500
|
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Consumption (litres/person per day)
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|
Average daily demand (Apr - Nov. i.e. 245 days) 240
Average daily demand (Dec - Mar. i.e. 120 days) 600
MDMM = 1.5 times average daily demand
Peak daily demand (Dec-Mar) 1350
Peak hour demand (Dec-Mar) based on L/person per day 2700
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A Determine if the existing source D is adequate to meet the projected average demand at the end of the design period. Substantiate with calculations.
B The ground elevations at area A vary between 25 RL and 48 RL, and that in area B vary between 10 m RL and 28 m RL. The Queensland Guidelines for Planning and Design of Urban Water Supply Schemes require that the minimum allowable pressure in reticulation or service mains should be 22 m head. Other provisions of the Guidelines referred to in the study materials are also to be considered.
You are required to investigate and report to Council what populations are adequately serviced for each component of the existing system (i.e. check the capacity of the present system against the design population). Minor loss in the service mains is estimated to be 1.5 times the velocity head.
Assume that the service reservoir operating storage is 30% of the peak daily demand; the required fire storage is 20 L/s for 4 hours and the breakdown provision is 1 peak daily demand. Assume that the council requires that the service reservoir capacity must meet the following criteria (based on the local knowledge):
- 3(PD-MDMM) demand
- must not empty at 3 days consecutive peak day demand
- At average daily demand, the system should have a capacity to refill from empty to full within 6 days of consecutive operation at this demand
C Based on the results of your investigation suggest some effective immediate and long term measures that may be considered to satisfy present demands and that at the end of the design period. Support your proposals with the relevant calculations.
You should summarise the results for each system components supported with detailed calculations in an appendix. Refer to the marking scheme for assignment sheet for the details. Marks will also be apportioned for documentation and clarity.