DESIGN OF WATER SUPPLY SCHEME

DESIGN OF WATER SUPPLY SCHEME

MAIN PURPOSE

                 The purpose of this project is to design the “Water Distribution Scheme” for a society which includes the Diameter of pipes, Lengths of Pipes, Pressure in pipes, Turbine Motor, Storage Tank and Strainer length.

EXPLANATION:

                 We are provided with a map of a society, in which Pipes are to be laid by using EPANET software. It is a modren society containing flats, appartments, plots, scool and parks along with the treatment and disposal sites, situated near the bank of Jehlum canal. Knowing the importance of the water in the life, and its wide use in the human societies, during the preparation of this report, I have collected  the data from the class notes provided, design data, and from the internet. I also discussed some confusing points with my class fellow in order to get the better idea about the design procedure.
This report gives a detailed description about how to establish a water distribution system for a community. I am Thankful to Allah Almighty for giving me the wisdom and knowledge to complete the water supply scheme assigned by the teacher. I have successfully carried out the design of water supply system of the residential housing society. I am confident that my design will successfully run throughout the design period of the water supply system. I have taken all precautionary measures to make sure that there is no major problem in my system and it will smoothly run throughout its useful life.
Output is attached with this report showing all the necessary data required for designing process. All the pressures are greater than 14m. The Project designed shows that it is an economical project as all the diameters of the pipes are 80mm only a few pipes are of 200mm diameter which are located near the Overhead reservoir.
So this economical project of Water Distribution Scheme is successfully completed and all the results are attached at the end of the report.

Water

  Water is a chemical substance that is composed of hydrogen and oxygen and is vital for all known forms of life.

REQUIREMENTS OF DRINKABLE WATER

                    It is almost impossible to find a source of water that will meet basic requirements for a public water supply without requiring some form of treatment. In general, the requirements for a public water supply may be considered as follows:
1.   That it shall contain no disease-producing organisms.
2. That it be colorless and clear.
3.   That it be good-tasting, free from odors and preferably cool.
4. That it be non-corrosive.
5. That it be free from objectionable gases, such as hydrogen sulfide, and objectionable staining minerals, such as iron and manganese.
6. That it be plentiful and low in cost.

WATER CONSUMPTION

It is the amount of water consumed by a community in one day. Water consumption is expressed as Literes/Capita/Day i.e lpcd

Per Capita Water Consumption

It is that amount of water in Liters/day which a person uses daily on average.  Its average value is 150-600 lpcd.

Average Daily Consumption

It is the average amount of water used by a person/ Community in one day divided by the number of people served.
Average Daily consumption (lpcd) = total water used in one year/(365 or 366 x mid year population)
Avg. Daily consumption = Avg. daily Consumption x population.

 Maximum Daily consumption

It is the maximum water consumption during any one day in the year. It is about 150 to 180 % of the avg. daily consumption.
Maximum Daily consumption =   1.5 x Avg. Daily

 Peak Hourly Consumption

It is the peak consumption during any one hour of the years excluding the fire demand. The peak hourly consumption can be between 150 to 400 percent of the average hourly consumption during a peak day. It is around 150% of the maximum daily consumption.
Peak Hourly demand = 1.5 x Max. Daily Demand  = 2.25 x Avg. Daily Demand.
The different ratios that are widely used by used by Water and Sanitation Authority Lahore are
Average Daily Consumption         :     Maximum Daily Consumption

         1                                    :                                1.5

Average Daily Consumption         :         Peak Hourly Consumption

        1                                    :                                2.25

Maximum Daily Consumption       :     Peak Hour Consumption

        1                                    :                                  1.5

Factors Affecting Water Consumption

The various factors affecting the water consumption are given below

• Climate
• Standard of living
• Extent of sewerage
• Commercial or industrial activity
• Metering or cost of water
• Quality of water
• Availability of private sources
• Distribution system pressure
• Size of city
• Efficiency of the system
• Type of supply (continuous or intermittent)
• Level of service (Stand Post, Yard Connection, Full Plumbing)

PIPES AND THEIR TYPES

Pipes are mainly differentiated on the basis of their material of construction. Different types of water supply pipes are available in the market. While selecting a particular type of pipe, following points must be considered.

• Carrying Capacity
• Durability
• Purchasing Cost
• Maintenance Cost
• Type of water to be conveyed (Corrosive / Normal)

Following are some major types of pipes commonly used in water supply system

• Cast Iron Pipes
• Steel Pipes
• Asbestos Cement Pipes
• PVC Pipes
• Galvanized Iron Pipes

All the above described pipes have their own merits and demerits. A brief Review of the pipes is given below.

Cast Iron Pipes

Cast iron pipe when used in water mains is selected on the basis of maximum working pressures and laying conditions. Pipe is available for working pressures as high as 350 Psi. The pipe is subject to corrosion from water; however the initial rate of corrosion is not as great as that of steel. After a few years of exposure, the corrosion rate is little different from that of steel

• Average service life is about 100 years
• No longer manufactured, deteriorates in some soils, reduction in capacity due to tuberculation
• Large Distribution Systems, And old Systems
• Most widely used for city water supply
• Corrosion may reduce the capacity by 70%.
• Must be lined with cement or bitumen

Ductile Pipes

•  Similar to cast iron pipe except with increased ductility.
• Ductile iron is produced by adding a controlled amount of Mg in its molten iron of low Sulphur and Phosphorus content.

Asbestos Cement Pipe

Asbestos cement pipe was widely installed in water distribution system in early ages. They are available generally in 100mm-600mm diameter. It was used for a long time as non corrosive and economical alternative to cast iron. When it was found that a fatal lung disease often resulted from breathing airborne asbestos fibers, severe restrictions were mandated for working with asbestos. Although asbestos cement pipe rarely is installed today, thousands of miles of it remain in water

 systems throughout the country.

• Average life is about 30years
• Immune to action of salts, acids, soil, corrosion
• Less cost of  laying and jointing
• Less pumping cost due to less friction
• Brittle, no longer manufactured
• It was used for a long time as non corrosive and economical alternative to cast iron

 Steel Pipes

Steel is used for water mains because of its high tensile strength , it is particularly advantageous where the distribution system may be subjected to impact pressures from railroad tracks , highways , industrial machinery and such or in areas where the danger of earthquake is great. 

• The primary disadvantage of using steel pipes is high installation costs.
• Average life is about 25-50 years
• Contains less carbon than Cast Iron pipes
• Frequently used in trunk mains
• Difficult to make connection, hence seldom used for water distribution
• Much stronger, cheaper and lighter than Cast Iron
• Cannot withstand vacuum and hence collapse
• More susceptible to corrosion, high maintenance cost.

Reinforced Concrete Pipes

Reinforced concrete pipes are not normally used in the distribution system. However it is used on long conduits and aqueducts, because it is used primarily for transferring large quantities of water.

• Average life is about 75 mm.
• It is generally only available in sizes of 400mm and above.
• Manufactured at or near site and not subjected to corrosion.

Plastic Pipes (PVC) 

Plastic pipe is particularly useful in areas where severe corrosion problems are a possibility Polyvinyl Chloride pipe is not subject to corrosion or builds up from corrosion by products. It is also advantageous in areas subject to earthquake shocks or where the live loading, shifting or movement of the earth is anticipated.

• Life time is about  25 years
• Inexpensive, easy to install, small pumping cost
• Gasoline from soil can pass into pipe. Not available in larger size.
• Only available up to 350mm diameter and mainly used for domestic purposes
• Weak to sustain load and piling

Galvanized iron Pipes

• Produced by dipping Cast Iron pipe in molten Zinc.
• Mainly used for plumbing.
• High durability, weld consistency  and superior finish
• Great resistance to corrosion
• Responsive to rigorous fabrication
• Increased bend ability with Diameter of Pipes:

Design Period

It is the number of years in future for which the proposed facility would meet the demand of the community.  Selection of an appropriate design period for a particular facility / component of water supply system is very important and dependent upon following factors.

• Length or life of structure
• Ease of extension
• First cost
• Rate of interest (design period is shorter)
• Economy of scale
• Lead time

Keeping in view these points the design period of our water supply system is

• For reservoir, the design period is 25-50 years (in our design it for 20years).
• For tube well, design period is 5-years (easy to install).
• For distribution system design period is 25-years (difficult to replace)

Adequate design period in water supply system is provided because

• Too frequent extension in water supply system is not possible
• Reasonable economics of scale are achieved

WATER DISTRIBUTION DESIGN DATA

No of Plots = 281

No of Appartments = 3

No of Flats = 3

Design period = 20 years

POPULATION FORECAST

	Present (2009)	Design (2029)
Persons/plot	7	10
Persons/apartment	400	600
Persons/flat	200	400

LAYOUT OF WATER DISTRIBUTION SCHEME

 

 

 

POPULATION FORECASTING Present Population Pp=  1) 281×7+400×3+200×3 =   3767
Present Population Pp=  2) 281×10+600×3+400×3 = 5810
Annual Growth Rate = 2.1% (For Pakistan, 2008 report)
Design Population Pd
1) Pd = Pp x (1+2/100)20
Pd = 3767x(1+2/100)20    = 5598
Per capita water consumption = 344 lpcd
Average Design flow  = 5810 x 344      =  1998640 Lit/day  =   23.13 Lit/Sec

NODAL DISTRIBUTION

NODAL DEMAND

Node No	Plots		Flats		Appartnments		Total Population	Avg Demand (L/Day)	Avg Demand (L/Sec)	Peak demand (L/Sec)
	No	Pop	No	Pop	No	Pop
1	16	160	0	0	0	0	160	55040	0.64	1.44
2	16	160	0.2	80	0	0	240	82560	0.96	2.16
3	16	160	0.7	280	0	0	440	151360	1.75	3.9375
4	15	150	0.6	240	0	0	390	134160	1.55	3.4875
5	12	120	0.7	280	0	0	400	137600	1.59	3.5775
6	5	50	0.8	320	0.4	240	610	209840	2.43	5.4675
7	13	130	0	0	0	0	130	44720	0.52	1.17
8	16	160	0	0	0	0	160	55040	0.64	1.44
9	12	120	0	0	0	0	120	41280	0.48	1.08
10	20	200	0	0	0	0	200	68800	0.8	1.8
11	1	10	0	0	0	0	10	3440	0.04	0.09
12	8	80	0	0	0	0	80	27520	0.32	0.72
13	1	10	0	0	0.4	240	250	86000	1	2.25
14	12	120	0	0	0	0	120	41280	0.48	1.08
15	12	120	0	0	0	0	120	41280	0.48	1.08
16	17	170	0	0	0	0	170	58480	0.68	1.53
17	10	100	0	0	0	0	100	34400	0.4	0.9
18	4	40	0	0	0.6	360	400	137600	1.59	3.5775
19	15	150	0	0	0	0	150	51600	0.6	1.35
20	12	120	0	0	0.55	330	450	154800	1.79	4.0275
21	2	20	0	0	0	0	20	6880	0.08	0.18
22	6	60	0	0	0.6	360	420	144480	1.67	3.7575
23	21	210	0	0	0	0	210	72240	0.84	1.89
24	17	170	0	0	0.45	270	440	151360	1.75	3.9375

Minimum Residual Pressure And Roughness Coefficient

Minimum residual pressure should be 14m and the roughness coefficient used = C = 120

DESIGN OF TANK DIAMETER

Discharge = Q =  23.1 lit/sec = 83160 lit/hr = 83.16 m³/hr
Duration for storage = 8 hrs
Volume of Water for storage = Q x t = 83.16 x 8 = 665.28 m3
and Area = L x W …….So Volume = A.D
Usually D = 8ft to 10 ft
Let D = 3m in our case
Area = Volume /D  = 668.28/3 = 221.76m2
Equivalent Diameter = 1.128 x  = 16.79m = 17m

TUBEWELL DESIGN

Design Head = Depth of water + draw down of water table +losses in pumping chamber +losses in pipe from tube well to O.H.R + difference in elevation between T/W & O.H.R + Height of O.H.R
So H = 30`+30`+10`+hl+20m+20m
Now to make units consistent we have to convert all dimensions in meters.
But first we have to find Head Loss in the pipe.
Hl= (4.f.l.v^2)/(2.g.d)
Here f = 0.0046 and length = 87.3m , velocity is usually from 5ft/sec so convert it in meter we get 1.524m/sec
Hl = (4*0.0046*87.3*(1.524^2))/(2*9.81*d)
Now we don’t have the value of d . We will get d from Q=A.V
Here Q = Max flow = Avg x 1.5
Q= 23.1liter/sec = 0.0231m³/sec x 1.5 = 0.03465m³/sec
0.03465m³/sec = π² x 1.524m/sec
From here we get d = 170mm now the diameters available in the market are in the following sequence
80 mm, 100 mm, 150 mm, 200 mm, 250 mm, 300 mm, 400 mm, 500 mm, 1000 mm
So we round our diameter to 200mm and thus the velocity will also change to v = 1.103m/sec
Now the Head loss comes out to be 0.498m
So the Total head becomes now 9.114 + 9.114 + 3.048 + 0.498 + 20+20 = H = 61.7m

PUMP/MOTOR B.H.P DESIGN

B.H.P = BRAKE HORSE POWER

BHP = Gama*Q*H / 550 * nu (efficiency)
= (62.4*1.2375*201.345)/(550*0.6)
Efficiency of a motor is about 60% and for diesel motors its 50%
B.H.P = 47.17 B.h.p

DESIGN OF STRAINER/WALLSCREEN

Q = A.V
Q = Max flow = 0.03465
V = 0.02 – 0.06 m/sec …..let us take v = 0.04m/sec
0.03465 = π . d. L x 0.04m/sec
Diameter of strainer is usually 10”
So, the Length of Strainer comes out to be 9m

RESULTS FROM EPA.NET

 

 

 

 

Click here to find the Results in a text file generated by Epa.Net

COMMENTS

• The Design of Water Distribution Scheme has been completed successfully and some of the values have been taken from the literature While other have been taken from WASA (Water and Sanitation Authority).
• The Maximum diameter pipes have been provided at the Tank as there will be more pressure.
• The design is economical also as the diameters of the  pipes are those which are minimum in the market (80mm).
• The condition of Pressure greater then 14m is also satisfied as all the pressures are greater then 14m.
•  The HazenWilliam method of finding head loss has been used.