CVE 471 WATER RESOURCES ENGINEERING
WATER SUPPLY
Assist. Prof. Dr. Bertuğ Bertuğ Akıntuğ ntuğ Civil Engineering Program Middle East Technical University Northern Cyprus Campus
5 . WATER SUPPLY
Overview
Elements of Municipal Water Supply Systems
Hydraulics and Operation of Gravity Pipelines Design of Transmission Lines
Distribution Reservoirs Pipes Pumps and Valves
Gravity Lines Pumped Lines Mixed Lines
Construction and Maintenance of Municipal Water Supply Systems
5 . WATER SUPPLY
Elements of Municipal Water Supply System
Water is conveyed from a source or combination of sources to community in mainly closed conduits.
pressurized flow is possible pollution control
Possible element of a water transmission system:
canals and flumes grade aqueducts grade tunnels pipelines valves pumps pressure reducing chambers etc…. 1915-19 Winnipeg, Manitoba, Canada http://www.mhs.mb.ca/docs/page http://www.mhs.mb.ca/ docs/pageant/24/win ant/24/winnipegaq nipegaqueduct.shtml ueduct.shtml
5 . WATER SUPPLY
Elements of Municipal Water Supply System
Transmission pipelines
5 . WATER SUPPLY
Elements of Municipal Water Supply System
Typical arrangement of a municipal water supply system
Distribution reservoirs are designed to meet the hourly variations in water demand and to store extra water for fire fighting and emergencies.
5 . WATER SUPPLY
Elements of Municipal Water Supply System
In the main transmission line
In a main feeder Qdesign= Dmh = Dmd x (P.F.)hour
Qdesign= Dmd = Dad x (P.F.)day
OR
Qdesign= Dmh = Dad x (P.F.)hour x (P.F.)day
5 . WATER SUPPLY
Elements of Municipal Water Supply System
A water distribution network is normally composed of pipes, valves, hydrants, and pumps. Distribution of water is possible by
gravity (storage reservoir is required at a sufficient altitude) pump without storage (may be required during any emergency), and pump with storage (the most common way).
Types of distribution systems depends on
street plan topography, location of supply works, level of service dictated.
5 . WATER SUPPLY
Elements of Municipal Water Supply System
Types of distribution systems: a) a branching pattern with dead ends, b) a gridiron pattern, c) a gridiron pattern with central feeder.
A branching pattern with dead ends
A gridiron pattern
suitable for strip-shaped districts where water flow in one direction during any repair downstream of the section cannot take water preferred for flat and wide terrains
A gridiron pattern with a central feeder
preferred as the auxiliary main is in a looped pattern
5 . WATER SUPPLY
Overview
Elements of Municipal Water Supply Systems
Pipes Pumps and Valves
Hydraulics and Operation of Gravity Pipelines Design of Transmission Lines
Distribution Reservoirs
Gravity Lines Pumped Lines Mixed Lines
Construction and Maintenance of Municipal Water Supply Systems
5 . WATER SUPPLY
Elements of Municipal Water Supply System Distribution Reservoirs In large cities (population > 100,000) pumping stations and distribution reservoirs are operated in conjunction with each other. Pumping stations usually pump the average daily demand to distribution reservoirs during the minimum demand hours of the day. Distribution reservoir release the water when the demand is above the average daily demand to meet the fluctuations in use. Location: as close as the center of use as possible. Water Level: high enough to permit gravity flow at satisfactory pressure.
5 . WATER SUPPLY
Elements of Municipal Water Supply System Distribution Reservoirs (con’t) May be located located in critical critical points points in the city city in such a way way that the hydraulic grade line is still above the highest storey buildings. Elevated tanks: circular cross-section (cylinder gives a max. volume). Buried reservoirs: rectangular cross-section (easy to construct)
Small: concrete or stone masonry Large: reinforced concrete with dividing walls
Cylindrical Reservoirs:
reinforces concrete or steel
5 . WATER SUPPLY
Elements of Municipal Water Supply System Distribution Reservoirs (con’t)
A fill layer of about about one meter thick is placed. Lower temperature in summer (better quality and taste)
Buried distribution reservoir
5 . WATER SUPPLY
Elements of Municipal Water Supply System Distribution Reservoirs (con’t)
Buried distribution reservoir
5 . WATER SUPPLY
Elements of Municipal Water Supply System Distribution Reservoirs (con’t) The capacity of a distribution reservoir is determined by the summation of the following components:
Storage to meet hourly fluctuations, Required storage to put out a fire with certain duration (C fire) Storage to meet emergencies
5 . WATER SUPPLY
Overview
Elements of Municipal Water Supply Systems
Distribution Reservoirs
Pipes
Pumps and Valves
Hydraulics and Operation of Gravity Pipelines Design of Transmission Lines
Gravity Lines Pumped Lines Mixed Lines
Construction and Maintenance of Municipal Water Supply Systems
5 . WATER SUPPLY
Elements of Municipal Water Supply System Pipes Pipes materials:
reinforced concrete (no corrosion problem), asbestos cement (limited use cancerous effect of asbestos fibers), ductile iron (corrosion problem interior is coated with cement), steel (good for large diameter and high pressure, pressure, buckling buckling under high negative pressure) plastic (widely used, highly smooth, light, easy to install and remove)
The minimum pipe size required in a distribution network is dictated by the population.
5 . WATER SUPPLY
Overview
Elements of Municipal Water Supply Systems
Distribution Reservoirs Pipes
Pumps and Valves
Hydraulics and Operation of Gravity Pipelines Design of Transmission Lines
Gravity Lines Pumped Lines Mixed Lines
Construction and Maintenance of Municipal Water Supply Systems
5 . WATER SUPPLY
Elements of Municipal Water Supply System Pumps Pumps: mechanical energy potential energy Types of pumps are named according to the direction of the movement of water from the rotating element of the pump (impeller ). ). The specific speed: n s =
where
N Q 3/ 2 H p
Q: discharge (m3/s) N: rotativ rotative e speed speed of impel impeller ler (rpm) (rpm) Hp: Head (m)
5 . WATER SUPPLY
Elements of Municipal Water Supply System Pumps (con’t) Centrifugal Pumps:
For the requirement of high heads (low Impeller in series having radial flow characteristics are adopted.
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5 . WATER SUPPLY
Elements of Municipal Water Supply System Pumps (con’t) Axial-flow Pumps:
For greater flow rates under low heads (high n ). Having axial flow characteristics with respect to the pump axis.
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5 . WATER SUPPLY
Elements of Municipal Water Supply System Pumps (con’t) Mixed-flow Pumps:
For medium head and discharge (medium n ).
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5 . WATER SUPPLY
Elements of Municipal Water Supply System Pumps (con’t) Power of the pump: P p = where
γ QH p η p
Pp: the power (kW). γ: specific weight of water (kN/m3) Q: discharge (m3/s) Hp: head of the system by the pump (m) η p: the efficiency of the pump
5 . WATER SUPPLY
Elements of Municipal Water Supply System Pumps (con’t) Multiple pump operations are often used to increase the discharge or head.
Pumps in Series: Increase the head Pumps in Parallel: Increase in discharge
5 . WATER SUPPLY
Elements of Municipal Water Supply System Valves
Sluice or gate valves are
used to isolate the flow especially during repair works.
http://en.wikipedia.org/wiki http://en.wikipedia.org/wiki/Gate_valve /Gate_valve
5 . WATER SUPPLY
Elements of Municipal Water Supply System Valves
Butterfly valves are widely
used at the exits of distribution reservoirs for regulation or isolation purposes.
5 . WATER SUPPLY
Elements of Municipal Water Supply System Valves
Check valves are used to
stop flow automatically in the reverse direction.
http://www.checkall.com/valvestyle http://www.checkall.com/valvestyles/un3/un3 s/un3/un3enlarged enlargedphoto.htm photo.htm
http://www.spiraxsarco.com/resources http://www.spiraxsarco.com/resources/steam-engin /steam-engineering-tuto eering-tutorials/pipelin rials/pipeline-ancillaries/ e-ancillaries/check-valves.a check-valves.asp sp http://www.checkvalves.co.uk/
5 . WATER SUPPLY
Elements of Municipal Water Supply System Valves
Hydrants are those appurtenances
used for the withdrawal of pressurized flow from the network for fire fighting.
5 . WATER SUPPLY
Overview
Elements of Municipal Water Supply Systems
Distribution Reservoirs Pipes Pumps and Valves
Hydraulics and Operation of Gravity Pipelines
Design of Transmission Lines
Gravity Lines Pumped Lines Mixed Lines
Construction and Maintenance of Municipal Water Supply Systems
5 . WATER SUPPLY
Hydraulics and Operation of Gravity Pipelines
5 . WATER SUPPLY
Hydraulics and Operation of Gravity Pipelines
when (inflow > Qmax) Q - Qmax spills over the reservoir when (Q0 < inflow < Qmax) 0 < reservoir water level < H max when when (inf (inflo low w < Q0) free surface flow in the pipe (empty reservoir). To prevent free surface flow in the pipe use control valve at the pipe exit The valve dissipates the excess potential energy, H v.
Then flow is pressurized in the pipe and the water level in the reservoir is controlled.
5 . WATER SUPPLY
Overview
Elements of Municipal Water Supply Systems
Distribution Reservoirs Pipes Pumps and Valves
Hydraulics and Operation of Gravity Pipelines
Design of Transmission Lines
Gravity Lines
Pumped Lines Mixed Lines
Construction and Maintenance of Municipal Water Supply Systems
5 . WATER SUPPLY
Design of Transmission Lines
The pipe size should be determined to meet future requirements. The system should confirm to the required hydraulic performance:
velocity criteria pressure criteria etc…..
In this section design principles of
gravity lines, pumped lines, and mixed lined
are introduced.
5 . WATER SUPPLY
Design of Transmission Lines Design of Gravity Lines For a gravity pipeline, neglecting operating cost, the optimum diameter minimizes the capital cost of the pipeline.
The optimum diameter minimum diameter which can convey the specified design discharge with the available gravity head. In gravity lines there are several design criterions:
Veloci Velocity: ty: 0.5 – 2.0 m/s Press Pressure ure head head:: 3-5 m – 80 m
5 . WATER SUPPLY
Design of Transmission Lines Design of Gravity Lines (con’t)
Step 1:
Determine the control points (C,E,F) and their topographic elevations z c, zE, zF. Add the minimum required pressure head Pmin/γ to these elevations. Determine the energy grade line slopes (S 1, S2, S3), between the reservoir and the control points and select minimum slope. S min =
H A − ( z c + ( P min / γ ) ) L AC
5 . WATER SUPPLY
Design of Transmission Lines Design of Gravity Lines (con’t)
Step 2:
Compute the pipe diameter diameter for line line A-C. Using Darcy-Weisbach Darcy-Weisbach equation, 1/ 5
Dcom
8 fQ 2 = g π 2 S min
and select the nearest larger commercial co mmercial available diameter, D.
5 . WATER SUPPLY
Design of Transmission Lines Design of Gravity Lines (con’t)
Step 3:
Compute velocity
u=
Q π D
2
/4
If umin < u < umax, the selected diameter, D, is used in the project If u < umin, a booster pump may be installed at the reservoir site to increase the velocity to u min.
5 . WATER SUPPLY
Design of Transmission Lines Design of Gravity Lines (con’t)
Step 3: (con’t)
The additional head supplied by the booster pump, H p, is compute using
If u > umax, reduce the velocity to u max, by increasing the pipe diameter from Since the velocity, and hence headlosses are reduced, install a pressure reduction valve or allow increased pressures along
5 . WATER SUPPLY
Design of Transmission Lines Design of Gravity Lines (con’t)
Step 4:
After determining the diameter for pipe segment segment A-B-C and computing computing the piezometr piezometric ic level level at point point C (H (H C), repeat the above procedure for the remaining segments C-D-E-F. Note that for the above example point E now becomes the control point. Therefore, first the diameter for segment C-D-E, and then the diameter of segment EF are determined.
5 . WATER SUPPLY
Design of Transmission Lines Design of Gravity Lines (con’t)
Step 5:
Install a control control valve at point F, and determine the the necessary headloss at the valve, to maintain pressurized flow at segment E-F.
5 . WATER SUPPLY
Overview
Elements of Municipal Water Supply Systems
Distribution Reservoirs Pipes Pumps and Valves
Hydraulics and Operation of Gravity Pipelines Design of Transmission Lines Gravity Lines
Pumped Lines
Mixed Lines
Construction and Maintenance of Municipal Water Supply Systems
5 . WATER SUPPLY
Design of Transmission Lines Design of Pumped Lines For a pumped line, the economical diameter is the one which minimizes the total cost.
investment cost of pipes (placement and installation costs), cost of pump, energy cost of operation (operation and maintenance costs).
A small diameter reduces initial cost but increases pumping and energy costs. For the most economical diameter:
5 . WATER SUPPLY
Design of Transmission Lines Design of Pumped Lines (con’t) Step 1:
Compute the annual energy cost, C E, to overcome friction and static head:
where
Pp: power of the pump. γ: the specific weight of water (kN/m3). Q: design discharge (m3/s). E: energy cost ($/KWh). t: annual operating hours. η: the pump efficiency. Hp: the required pump head (m). Hp=Hs+hf Hs: the static head between the lower and upper reservoir (m) hf : the friction friction headloss headloss along the pipe connectin connecting g these reservoirs. reservoirs.
5 . WATER SUPPLY
Design of Transmission Lines Design of Pumped Lines (con’t) Step 1: (con’t)
Using Using Darcy-Weisb Darcy-Weisbach ach equation, equation, the annual annual energy cost, cost, C E, can be expressed in terms of diameter D:
5 . WATER SUPPLY
Design of Transmission Lines Design of Pumped Lines (con’t) Step 2:
Pipe cost, CD, per unit length for various diameters is obtained from manufacturers, and converted to annual cost, C P, :
where
i : interest rate. N: economic life of the project in years.
5 . WATER SUPPLY
Design of Transmission Lines Design of Pumped Lines (con’t) Step 3:
Initial pump cost, C pi, is normally expressed in terms of monetary units per kW of installed power. The power of the pump in kW units is
where
: the specific weight of water (kN/m3). Q: the discharge (m3/s) γ
The annual pump cost:
5 . WATER SUPPLY
Design of Transmission Lines Design of Pumped Lines (con’t) Step 4:
Ignoring annual operation and maintenance costs, the economic diameter is obtained as the value corresponding to the minimum total annual cost. Cp : annual cost of pipe CE: annual energy cost Cpump: pump cost CT: total cost
5 . WATER SUPPLY
Overview
Elements of Municipal Water Supply Systems
Distribution Reservoirs Pipes Pumps and Valves
Hydraulics and Operation of Gravity Pipelines Design of Transmission Lines Gravity Lines Pumped Lines
Mixed Lines
Construction and Maintenance of Municipal Water Supply Systems
5 . WATER SUPPLY
Design of Transmission Lines Design of Mixed Lines A pipeline having both
gravitational and pumped flow rates.
Topographic elevation of point C is higher than the reservoir level. In such a case it is convenient to build a small reservoir at C. The pump may be
located at reservoir site A or located as a booster pump along the line.
Topographic elevation of point C is higher than the reservoir level.
5 . WATER SUPPLY
Design of Transmission Lines Design of Mixed Lines (con’t) If the pump is located at reservoir site A, A, the economic pipe diameter can be computed considering line ABC as a pump discharge line The required pump head:
The diameter of line CD is then determined as a gravity pipeline.
5 . WATER SUPPLY
Design of Transmission Lines Design of Mixed Lines (con’t) If a booster pump is selected, then its location, X, along BC can be determined as follows:
Flow will be transmitted until the booster pump by gravity. Use any available diameters, that keep velocity within the limits (umin < u < umax). The location of booster pump (LBX, zX)
Required Pump Head:
Then the economic pipe diameter for section X-C can be determined as that of a pumped discharge line.
5 . WATER SUPPLY
Design of Transmission Lines Design of Mixed Lines (con’t) If a small diameter is used until the buster pump,
the initial cost will be less the energy cost will be high (the pump will be in at a lower elevation)
Note that for the booster pump applications the followings must also be considered:
cost of energy line transportation, and cost of employment of guards, etc…
5 . WATER SUPPLY
Overview
Elements of Municipal Water Supply Systems
Hydraulics and Operation of Gravity Pipelines Design of Transmission Lines
Distribution Reservoirs Pipes Pumps and Valves
Gravity Lines Pumped Lines Mixed Lines
Construction and Maintenance of Municipal Water Supply Systems
5 . WATER SUPPLY
Construction and Maintenance of Municipal Water Supply Systems
The selection of suitable route for a pipeline has an important bearing on the capital cost and operation cost. A pipeline route is selected from
aerial photos topographic and cadastral plans on-site inspections, and other data available on the terrain, obstacle, and local services.
For suitable route Jointly consider Cost and Practicality. The general level of pipeline route should be as close to hydraulic grade line as possible to minimize pressures and hence pipe costs.
5 . WATER SUPPLY
Construction and Maintenance of Municipal Water Supply Systems
If a pipeline is laid parallel to the natural ground, then it will have many peaks and depressions as the natural ground surface. Air released from water and trapped at peaks
reduces the opening of the waterway, increases energy loss, may interrupt flow.
In this case, air valves are required. In order to minimize the number of air valves the pipeline can be laid
on a more straight profile deeper in the ground, close to the ground surface with a nearly straight profile and covered with earth-fill in depression along the route.
5 . WATER SUPPLY
Construction and Maintenance of Municipal Water Supply Systems
The selection of profile is achieved by cost evaluations. In setting up the alternative profiles:
In order to minimize air entrainment problems: (pipe slope) > 0.005 On very straight ground ground surfaces the minimum minimum slope can be droped to 0.002. No upper limit for the maximum slope.
In long supply lines
frequent changes in direction should be avoided in order to conserve head and pressure. sharp bends should also be avoided to reduce the dynamic impact of the water thrust.
The bends should be blocked with concrete to take the dynamic action.
5 . WATER SUPPLY
Construction and Maintenance of Municipal Water Supply Systems
Laying of pipes:
excavation of trenches, transportation and handling of pipes and appurtenances, backfilling and repaving.
Pipes should be laid on firm beds in order to prevent the problems due to settlement. The dept of burial of pipes may be governed by
the depth of frost line the external loads acting on the pipe
5 . WATER SUPPLY
Construction and Maintenance of Municipal Water Supply Systems
