water supply systems lecture 2
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Water Supply Systems
Lecture notes 2
dr Patryk Wjtowicz
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Contents
Design considerations - key parameters Water demand calculations:
estimation of base water demand
water demand forecasting
peaking factors
leakage and unaccounted-for water water for fire protection
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Design considerations
The design considerations of water supply systems involve topographicfeatures of terrain and economical parameters (restrictions)
Some essential parameters for network sizing are: the projection of residential, commercial and industrial water
demand per capita water consumption
peak flow factors
minimum and maximum pipe sizes pipe material
system safety and reliability requirements
selection of optimal design periodof a water distribution system
in a pre-decided time horizon
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Water demand
The estimation of water demand for the sizing of any watersupply system or its components is the most important part ofthe design methodology
Water demands (water duties) are generated from:
residential industrial and commercial developments community facilities and services
firefighting demand account for system losses (unaccounted-for water or UFW) periodical flushing
treatment facility water demand
Customerdemand
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Water demand
Water demandis not constant, and is affected by a number of factors:
climate economic and social factors
water pricing, completeness of meterage, system management
land use resort to private supplies population and type of a city
standard of living, extent of sewage system industrialization of the area (size and type)...
A comprehensive study should estimate water demand considering all thesite-specific factors
Variations of water demand are observed in different time horizons (i.e. year,month, day, hour)
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Historical water consumption in Poland
1965-2005
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Historical water consumption in households in
Poland 1953-2005
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Monthly water consumption variations
(for a selected Polish city)
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Example of average daily water consumption
variations throughout a year
(for a selected Polish city)
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Diurnal water variation in water demand
(for a selected Polish city)
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Single FamilyBusinesses
RestaurantFactory
Deman
dMu
ltiplier
Deman
dMu
ltiplier
Deman
dMu
ltiplier
Deman
dMu
ltiplier
Time Time
Time Time
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Water demand forecasting
Forecasting is made for different time horizons: current (actual) water demand - prepared for
existing water networks, based on trends in
historical data average-term forecast
long-term forecast
Average- and long-term forecasts are mainly basedon unit water demands (index method)
Time, year
PeakDayDemand,
MGD
Annual Demand Data
204020302020201020001990198019701960
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
Constant Percent Growth
Growth to Buildout
Economic Downturn
Linear Growth
Different methods for projecting future demands
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Population projection formulas
Arithmetic (recommended for cities up to 20 000):P
f= P
c1+
i + t
100
!"#
$%&
Geometric (recommended for cities up to 20 000):P
f= P
c1+
i
100
!"#
$%&
t
Exponential (recommeded for cities from 20 000):
Pf= P
c+ e
i+t
100
!"#
$%&
Pf - future population
Pc- current population
i - growth rate in %
t - time in years
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Water demand forecasting
To capture variability of water demand there are severalcharacteristic parameters describing water consumption
and usage
Average day water demandQavdexpressed in m3/d:
Maximum day water demandQmaxd(m3/d)
Qavd =Qyear
365, m 3 /d
Qmaxd
= Qavd
! Nd
where: Nd- daily peaking factorMonday 1 December 14
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Daily and hourly peaking factors(Polish regulations)
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Calculation of water demand (cont.)
Peak hour water demandQmaxh(typically expressed in dm3/s or m3/h):Q
maxh = N
h!
Qmaxd
24
where: Nh- hourly peaking factor
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Water demand
The residential forecast of future demandis usually based on house count, census records andpopulation projections
The industrial and commercial facilitieshave a wide range of water demand
This demand can be estimated based on historicaldata from the same or comparable other system
Planning guidelines provided by engineeringbodies, governmental and regulatory agencies
should also be considered
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Water demand
The firefighting demandcan be estimated using equations(Kuichling or Freeman formula) or according to local guidelinesor design codes in national firefighting regulations
Estimation of water lossesis not straightforward anddepends on a number of factors:
age of system minimum prescribed pressure
maximum pressure in the system pipeline material quality of pipeline materials and maintenance works
specific local conditions (mine damages, earthquakes) ...Monday 1 December 14
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Calculation of residential water demand(Polish regulations)
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Typical water duties in USA
T LE 3 3 T ical Rates of Water Use for Various Establishments
T LE 3 2 Typical Water Duties
Land
Use
Low-density residential
Medium-densityresidential
High-density residential
Single-family residential
Multifamily residential
Office commercial
Retail commercial
Light industrial
Heavy industrial
Parks
Schools
Water
Duty,
gal/day/acre)
Low
High verage
400
3300
1670
900 3800 2610
2300
12000
4160
1300 2900 2300
2600 6600 4160
1100
5100
2030
1100 5100 2040
200
4700
1620
200 4800 2270
400
3100 2020
400
2500
1700
Source
Adapted fromMontgomery Watson study of data of 28 western U.S.
cities.
ote
gal X 3.7854 = L.
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T i l t f t f if f
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Range of Flow
User (l/person or unit/day) (gal/person or unit/day)
Airport, per passenger 1020 35
Assembly hall, per seat 610 23
Bowling alley, per alley 60100 1626
Camp
Pioneer type 80120 2132
Childrens, central toilet and bath 160200 4253
Day, no meals 4070 1118
Luxury, private bath 300400 79106
Labor 140200 3753
Trailer with private toilet and bath,
per unit (2 1/2 persons)
500600 132159
Country clubs
Resident type 300600 79159
Transient type serving meals 60100 1626
Dwelling unit, residential
Apartment house on individual well 300400 79106
Apartment house on public water supply,unmetered
300500 79132
Boardinghouse 150220 4058
Hotel 200400 53106
Lodging house and tourist home 120200 3253
Motel 400600 106159
Private dwelling on individual well or
metered supply
200600 53159
Private dwelling on public water
supply, unmetered
400800 106211
Factory, sanitary wastes, per shift 40100 1126
Table extracted from Ysuni, 2000 based on Metcalf and Eddy, 1979
Typical rates of water use for variousestablishments (USA)
Typical rates of water use for various
establishments in USA
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Fairground (based on daily attendance) 26 12
Institution
Average type 400600 106159
Hospital 7001200 185317
Office 4060 1116
Picnic park, with flush toilets 2040 511
Restaurant (including toilet)
Average 2540 711
Kitchen wastes only 1020 35
Short order 1020 35
Short order, paper service 48 12
Bar and cocktail lounge 812 23
Average type, per seat 120180 3248
Average type, 24 h, per seat 160220 4258
Tavern, per seat 60100 1626
Service area, per counter seat (toll road) 10001600 264423
Service area, per table seat (toll road) 600800 159211
School
Day, with cafeteria or lunchroom 4060 1116
Day, with cafeteria and showers 6080 1621
Boarding 200400 53106
Self-service laundry, per machine 10003000 264793
Store
First 7.5 m (25 ft) of frontage 16002000 423528
Each additional 7.5 m of frontage 14001600 370423
Swimming pool and beach, toilet and shower 4060 1116
Theater
Indoor, per seat, two showings per day 1020 35
Outdoor, including food stand, per car
(3 1/3 persons)
1020 35
Range of Flow
User (l/person or unit/day) (gal/person or unit/day)
Table extracted from Ysuni, 2000 based on Metcalf and Eddy, 1979
Typical rates of water use for various establishments
in USA (cont.)
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Unit (average) water demand for industrial facilities
according to the population (Poland)
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Average rates of nonresidential water use from
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Category SIC Code Use Rate(gal/employee/day)
SampleSize
Construction 31 246
General building contractors 15 118 66
Heavy construction 16 20 30
Special trade contractors 17 25 150
Manufacturing 164 2790
Food and kindred products 20 469 252
Textile mill products 22 784 20
Apparel and other textile products 23 26 91
Lumber and wood products 24 49 62
Furniture and fixtures 25 36 83
Paper and allied products 26 2614 93
Printing and publishing 27 37 174
Chemicals and allied products 28 267 211
Petroleum and coal products 29 1045 23
Rubber and miscellaneous plastics products 30 119 116
Leather and leather products 31 148 10
Stone, clay, and glass products 32 202 83
Primary metal industries 33 178 80
Fabricated metal products 34 194 395
Industrial machinery and equipment 35 68 304
Electronic and other electrical equipment 36 95 409
Transportation equipment 37 84 182
Instruments and related products 38 66 147
Miscellaneous manufacturing industries 39 36 55
Transportation and public utilities 50 226
Railroad transportation 40 68 3
Local and interurban passenger transit 41 26 32
Trucking and warehousing 42 85 100
U.S. Postal Service 43 5 1
Water transportation 44 353 10
Transportation by air 45 171 17
Transportation services 47 40 13
Communications 48 55 31
Electric, gas, and sanitary services 49 51 19
Wholesale trade 53 751
Wholesale tradedurable goods 50 46 518Wholesale tradenondurable goods 51 87 233
Table from Dziegielweski, Opitz, and Maidment, 1996
Average rates of nonresidential water use from
establishment-level data in USA (according to SIC
code)
(SIC) Standard Industrial Classification
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Retail trade 93 1044Building materials and garden supplies 52 35 56
General merchandise stores 53 45 50
Food stores 54 100 90
Automotive dealers and service stations 55 49 498
Apparel and accessory stores 56 68 48
Furniture and home furnishings stores 57 42 100
Eating and drinking places 58 156 341
Miscellaneous retail 59 132 161
Finance, insurance, and real estate 192 238
Depository institutions 60 62 77
Nondepository institutions 61 361 36
Security and commodity brokers 62 1240 2
Insurance carriers 63 136 9
Insurance agents, brokers, and service 64 89 24
Real estate 65 609 84
Holding and other investment offices 67 290 5
Services 137 1878
Hotels and other lodging places 70 230 197
Personal services 72 462 300
Business services 73 73 243
Auto repair, services, and parking 75 217 108
Miscellaneous repair services 76 69 42
Motion pictures 78 110 40
Amusement and recreation services 79 429 105
Health services 80 91 353
Legal services 81 821 15
Educational services 82 110 300
Social service 83 106 55
Museums, botanical, zoological gardens 84 208 9
Membership organizations 86 212 45
Engineering and management services 87 58 5
Services, NEC 89 73 60
Public administration 106 25
Executive, legislative, and general 91 155 2
Justice, public order, and safety 92 18 4
Administration of human resources 94 87 6
Category SIC CodeUse Rate
(gal/employee/day)
Sample
Size
Environmental quality and housing 95 101 6
Administration of economic programs 96 274 5
National security and international affairs 97 445 2
Table from Dziegielweski, Opitz, and Maidment, 1996
Average rates of nonresidential water use from
establishment-level data (cont.)
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A d d f l d i l f ili i
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Average water demand for selected commercial facilities
(Poland)
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Unaccounted-For Water (UFW)
Ideally, if individual meter readings are taken for every customer,
they should exactly equal the amount of water that is measured
leaving the treatment facility
In practice not all of the outflows are metered. These lostflowsare referred to as unaccounted-for water (UFW)
The most common reasons for discrepancies are: leakage
overflows at tanks
errors in flow measurement (under-register at low flow rates) unmetered water usage (illegal connections, usage of fire
hydrants, blow-offs and other maintenance appurtenances)
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Leakage
Leakage is commonly the largest component of UFW and includes:
distribution losses from supply pipes distribution and trunk mains services up to the meter
connections to tanks
The amount of leakage varies from system to system, but there is a generalcorrelation between the age of a system and the amount of UFW. Projections ofleakage must include special areas (mine damages, earthquakes etc.)
New and well maintained systems may have as little as 5% leakage, while oldersystems may have 40% leakage or even higher
Other factors affecting leakage include: system pressure (the higher the pressure, the more leakage) burst frequencies of mains and service pipes
leakage detection and control policiesMonday 1 December 14
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Estimating water leakage
For existing networks made of traditional materials(cast iron) properly maintained leakage index may beestimated from 0.5 m3/h km to 0.3 m3/h km
For new networks (after renovation), properly built
and maintained leakage index should not be higher
than 0.3 - 0.2 m3/h km
For water demand forecasting leakage should be
between 5% to 10% of average daily water demand
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Estimating water leakage
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Leak Losses for Circular Holes Under Different Pressures*
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Leak Losses for Circular Holes Under Different Pressures*
Diameter
of Hole,
in.
Area of
Hole,
in.2
Leak Losses, gpm
Water Pressure, psi
20 40 60 80 100 120 140 160 180 200
0.1 0.007 1.067 1.510 1.850 2.136 2.388 2.616 2.825 3.021 3.204 3.337
0.2 0.031 4.271 6.041 7.399 8.544 9.522 10.464 11.302 12.083 12.816 13.509
0.3 0.070 9.611 13.593 16.648 19.224 21.493 23.544 25.430 27.186 28.835 30.395
0.4 0.125 17.087 24.165 29.597 34.175 38.209 41.856 45.209 48.331 51.263 54.036
0.5 0.196 26.699 37.758 46.245 53.399 59.702 65.400 70.640 75.518 80.098 84.431
0.6 0.282 38.477 54.372 66.593 76.894 85.971 94.176 101.721 108.745 115.341 121.5810.7 0.384 52.331 74.007 90.640 104.662 117.010 128.184 138.454 148.014 156.993 165.485
0.8 0.502 68.350 96.662 118.387 136.701 152.840 167.424 180.839 193.325 205.052 216.144
0.9 0.636 86.506 122.338 149.833 173.012 193.434 211.896 228.874 244.676 259.519 273.557
1.0 0.785 106.798 151.035 184.979 213.596 238.807 261.600 282.561 302.070 320.394 337.725
1.1 0.950 129.225 182.752 223.825 258.451 288.957 316.536 341.898 365.505 387.676 408.647
1.2 1.131 153.789 217.490 266.370 307.578 343.882 376.704 406.887 434.981 461.367 486.323
1.3 1.327 180.488 255.249 312.615 360.977 403.584 442.104 477.527 510.498 541.465 570.755
1.4 1.539 209.324 296.028 362.559 418.648 468.062 512.737 553.819 592.057 627.972 661.941
1.5 1.767 240.295 339.829 416.203 480.590 537.317 588.601 635.762 679.658 720.886 759.880
1.6 2.011 273.402 386.649 473.547 546.805 611.347 669.697 723.355 773.299 820.208 864.575
1.7 2.270 308.646 436.491 534.590 617.292 690.153 756.025 816.600 872.983 925.938 976.024
1.8 2.545 346.025 489.353 599.333 692.050 773.736 847.585 915.496 978.707 1,038.070 1,094.220
1.9 2.836 385.540 545.237 667.776 771.081 862.095 944.378 1,020.040 1,090.470 1,156.620 1,219.180
2.0 3.142 427.191 604.140 739.918 854.383 955.230 1,046.400 1,130.240 1,208.280 1,281.570 1,350.890
* Calculated using Greeleys formula (see equation on following page).
Leak Losses for Joints and Cracks*
Area of Joint
or Crack Leak Losses, gpm
Length, Width, Water Pressure, psiin. in. 20 40 60 80 100 120 140 160 180 200
1.0 132 3.2 4.5 5.5 6.4 7.1 7.8 8.4 9.0 9.6 10.1
1.0 116 6.4 9.0 11.0 12.7 14.2 15.6 16.9 18.0 19.1 20.1
1.0 18 12.7 18.0 22.1 25.5 28.5 31.2 33.7 36.0 38.2 40.3
1.0 14 25.5 36.0 44.1 51.0 57.0 62.4 67.4 72.1 76.5 80.6
* For leaks emitted from joints and cracked service pipes, an orice coefcient of 0.60 is used
in the following equation:
Q= (22.796)(A)( P )
Where: Q=ow, in gpm;A= area, in in.2; P= pressure, in psi
43,767
,Q A P1 440 # #
Where:
! = ow, in gpm
" = the cross-sectional area of the leak, in in.2
# = pressure, in psi
Greeleys formula (used for leakages from pipes orbroken taps, assuming an orifice coefficient of 0.80)
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Fire protection
Fire storageis the amount of stored water requiredto provide a specified fire flow for a specified duration
The rate of flow to be provided for fire flow is typicallydependent on the land use and varies by community
The fire flow criteria are usually given in national orlocal regulations (e.g. fire marshall)
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Fi i d d
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Fire protection water demands(USA and Poland)
Table 4.5 Needed fire flow for residences two stories and less
Distance Between Buildings
(ft)
Fire Flow
(gpm)
More than 100 500
31-100 750
11-30 1,000
Less than 11 1,500
T LE
3 4
TypicalFire
Flow
Requirements
Land
Use
Single-family residential
Multifamilyresidential
Commercial
Industrial
Central business district
Note:
gal X
3.7854
= L.
Fire
Flow
Requirements, gal/m
500-2000
1500-3000
2500-5000
3500-10,000
2500-15,000
Typical fire flow requirements (USA)
Polish fire flow requirements for communities
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Supplementary reading
CH3 Introduction to Water Sources. AlaskaDepartment of Environmetal Conservation.
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