W4-L1-L2-Raw Water Intakes PDF

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WATER TREATMENT ENGINEERING

PART 2-SURFACE WATER TREATMENT RAW COLLECTION SYSTEM

Lectures Notes Environmental Engineering Program Zewail City Of Science and Technology Associate Prof. Emad S. Elmolla

CONTENTS      

Raw water intake structures Types of intake structures Factors to be considered in the intake-site selection Design considerations-intakes Design considerations-water conveyance system Design Example

Assoc. Prof. Emad S. Elmolla ‘s Lectures Notes

Water Treatment Engineering

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LEARNING OUTCOMES 

To be able to design and plan the raw water abstraction systems for surface water treatment plant.

Assoc. Prof. Emad S. Elmolla ‘s Lectures Notes

Water Treatment Engineering

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SCHEMATIC FOR SURFACE WATER WORKS

Assoc. Prof. Emad S. Elmolla ‘s Lectures Notes

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RAW WATER ABSTRACTION Raw water collection system consists of:  Raw water intake, o o



Inlet structure, Screening, gates and conduits,

Raw water conveyance system o o

Pumping station Transmission pipelines

Assoc. Prof. Emad S. Elmolla ‘s Lectures Notes

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RAW WATER INTAKE STRUCTURES Introduction  



Raw water intake: it consists of structures and equipment that used to control raw water withdrawal from the source. Their primary purpose is to selectively withdraw the best-quality water while excluding fish, floating debris, coarse sediment, and other objectionable suspended matter. These structures may be simple submerged intake pipes or elaborate tower-like structures that house intake gates, screens, control valves, pumps, chemical feeders, flow meters, offices, and machine shops.

Assoc. Prof. Emad S. Elmolla ‘s Lectures Notes

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TYPES OF INTAKE STRUCTURES 

Several different types of intake structures are in common use such as: o o o o o



Open Shore intake, Pipe intake Submerged intake, Tower intake Floating intake,

Selection of intake structure type depends on the nature of the water source (river, canal; wide, narrow, deep) and the quantity and quality of the water being withdrawn.

Assoc. Prof. Emad S. Elmolla ‘s Lectures Notes

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TYPES OF INTAKE STRUCTURES Open Shore-intake  Shore-intake structures are used for    

   

Narrow or wide water stream Deep or shallow shorelines Unpolluted shorelines Variable water level sources.

Example: canals and lakes Typically, they are concrete structure opened on the water side. They are constructed on the bank of the water stream. The structures may be constructed to be integrated with a pump station, Assoc. Prof. Emad S. Elmolla ‘s Lectures Notes

Water Treatment Engineering

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TYPES OF INTAKE STRUCTURES

Water stream Flow direction

Shore-intake

Shore Intake Assoc. Prof. Emad S. Elmolla ‘s Lectures Notes

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TYPES OF INTAKE STRUCTURES      

Pipe Intake The pipe inlet is located several meters away from the shoreline. It is used for wide water streams (Rivers) and when the shore is polluted. The withdrawal pipe discharges either into a sump at the shore or into pumps suction header. The pipes are carried by a fixed steel bridge supported on several piles It is usually used when river is the raw water source Micro strainer could be used at the pipe inlet

Assoc. Prof. Emad S. Elmolla ‘s Lectures Notes

Water Treatment Engineering

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TYPES OF INTAKE STRUCTURES Submerged Intakes  Submerged intakes are used to withdraw water from shallow water streams.  They may consist of a simple concrete box to support the withdrawal pipe.  The withdrawal pipe discharges either into a sump at the shore where pumping equipment is installed or into a gravity conveyance system.  The top opening is covered with mesh grating.  In lakes with heavy siltation, the intake opening is raised about 1-2 m above the bottom.

Assoc. Prof. Emad S. Elmolla ‘s Lectures Notes

Water Treatment Engineering

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TYPES OF INTAKE STRUCTURES 



Intake Towers Tower intakes are used to withdraw water from deep and wide water streams with variable water level ; and when the shore is polluted. Wet-intake towers consist of two wells: o

o

 

Outer well: it is a concrete circular well filled with water up to the water stream level. The purpose of the water-filled outer well is to provide weight needed to balance the buoyant forces when the inner well is dry. Inner well: It is connected to the withdrawal conduit.

Ports are provided at different levels on the outer concrete well and into the inner well. The ports have gates that regulate the flow of water into the well. Water can be withdrawn from any selected level by using the proper port. Assoc. Prof. Emad S. Elmolla ‘s Lectures Notes

Water Treatment Engineering

Wet-intake tower

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TYPES OF INTAKE STRUCTURES Intake Towers  Dry-intake towers- In a dry-intake tower, water enters the tower through gatecontrolled ports.  In the absence of a water-filled outer well, the dry-intake tower must be heavier in construction than a wet-intake tower, to resist the buoyance force.  Water can be withdrawn from any selected level by using the proper port.

Dry-intake tower

Assoc. Prof. Emad S. Elmolla ‘s Lectures Notes

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TYPES OF INTAKE STRUCTURES Floating Intakes  Floating intake structure is suitable for water sources that have unsuitable geological conditions and where relatively little difference in water-surface level over time occurs. 



They consist of a barge-type structure that floats on the water surface and supports pumps, screens, valves, electrical switches, and other equipment. The structure is anchored by at least two mooring piers.



These piers each consist of a steel or concrete column that is embedded in the water source bottom and extends through a specially designed sleeve attached to the structure.



This type of mooring arrangement anchors the structure in place but allows it to freely float on variable water levels. Assoc. Prof. Emad S. Elmolla ‘s Lectures Notes

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TYPES OF INTAKE STRUCTURES Comparison of Types of Intake Structures

Assoc. Prof. Emad S. Elmolla ‘s Lectures Notes

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FACTORS TO BE CONSIDERED IN THE INTAKE-SITE SELECTION Water Quality:  The intake-structure site should selected to yield the best-quality water.  Intakes should not be located in: o

o o

o



Dead areas (areas with little or no water circulation),

1

4

2

5

3

Near wastewater outfalls, In areas susceptible to hazardous chemical spills. Downstream the communities.

It has to be located at straight segment of the water stream to avoid erosion/scoring and silting. Assoc. Prof. Emad S. Elmolla ‘s Lectures Notes

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FACTORS TO BE CONSIDERED IN THE INTAKE-SITE SELECTION Access:  Intakes must be accessible under all weather conditions, to allow operators to inspect and maintain the intake equipment, which includes gates and screens and often pumps. Power Availability :  Electrical power is always required for intake structures, to operate the equipment such as gates and screens and for hazard lighting.  If raw water pumps are not located at the intake, the power load may be small; therefore, electrical power can be provided by an on-site generator. Water Depth:  The design should consider lowest water level (drought season) and the high water level (flood level) in the water stream.

Assoc. Prof. Emad S. Elmolla ‘s Lectures Notes

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FACTORS TO BE CONSIDERED IN THE INTAKE-SITE SELECTION Stream or Current Velocities :  Both the direction and magnitude of current velocities can have an impact on the intakes operation .  Water currents with velocities greater than 0.6 m/s can cause eddy currents (Swirl) that will affect the hydraulic function of the intake.  Water velocity also affects the lateral stability and foundation stability of the structure. Foundation Stability:  Typically, intake structures are tall, narrow structures that often have extreme lateral loads caused by water (water pressure).  Therefore, the foundation must be carefully designed to resist the resulting overturning moments. Assoc. Prof. Emad S. Elmolla ‘s Lectures Notes

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FACTORS TO BE CONSIDERED IN THE INTAKE-SITE SELECTION Proximity To Water Treatment Plant :  The cost of facilities to convey water from the source to the treatment plant is related directly to the distance between the source and WTP  Therefore, during selection of an intake site, the length of the conveyance system must be given serious consideration. Environmental Impact  To minimize the intake pollution, a prohibited area around the intake site of 150 m upstream the intake and 50 m downstream should be considered.  Other environmental issues that must be considered are impacts on wildlife habitats, endangered species  EIA issues must be carefully considered when one is selecting intake sites.  Usually, the greatest impact of raw water intake is on recreational uses in a body of water. Assoc. Prof. Emad S. Elmolla ‘s Lectures Notes

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FACTORS TO BE CONSIDERED IN THE INTAKE-SITE SELECTION Hazard to Navigation:  Floating, submerged, pipe and tower-type intakes are located in the waterway.  In many cases, particularly in major rivers, the water body may also serve as a navigation channel.  In these cases, intake structures must be located and designed so that they do not pose a hazard to navigation.  Particular attention in this regard must be given to submerged intakes, because they may pose a hidden hazard and are more susceptible to accidents.

Assoc. Prof. Emad S. Elmolla ‘s Lectures Notes

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FACTORS TO BE CONSIDERED IN THE INTAKE-SITE SELECTION

What do you think about the suitable intake type for this water stream

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DESIGN CONSIDERATIONS-INTAKES 1- Velocities through the ports:  High intake velocities increase head loss, entrain suspended matter, trap fish and other aquatic animals, and compound ice problems.  However, low velocities require the intake port to be larger and so add to the cost of the structure.  Experience has shown that a velocity below 8.0 cm/s. (0.3 fps) allows fish and other aquatic animals to escape and minimizes the entrainment of suspended matter.  The port should be gated for flow regulation and maintenance.

Assoc. Prof. Emad S. Elmolla ‘s Lectures Notes

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DESIGN CONSIDERATIONS-INTAKES 2- Intake-Ports vertical location:  Lakes and reservoirs tend to be stratified. As a result, water quality in each stratum may vary.  Ideally, the vertical location of ports should be determined by testing of water quality from various depths at the proposed intake site.  In the absence of such testing, intake ports should be provided along the entire height of the structure.  The top intake port should be located not less than 2 m below the normal water surface, so that floating debris will not be drawn into the port.  The bottom port should be located at least 1 m above the bottom to prevent the suspension of bottom sediments

Assoc. Prof. Emad S. Elmolla ‘s Lectures Notes

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DESIGN CONSIDERATIONS-INTAKES 3- Intake Conduit: 

Purpose: To transmit raw water from source to the pumping station.



Design criteria:   

Design flow = Qmax monthly x 1.10 Velocity = 0.6 – 1.5 m/s Number of pipes n ≥ 2

Assoc. Prof. Emad S. Elmolla ‘s Lectures Notes

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DESIGN CONSIDERATIONS-INTAKES 3- Intake Conduit: 

Losses o o o o o

hf L V g F

Flv 2 hf  2 gd = Friction Loss (m) = Length of the conduit (m) = Velocity in the conduit (m/sec) = Gravity Acceleration, m2/sec = Friction Factor=0.02

Assoc. Prof. Emad S. Elmolla ‘s Lectures Notes

Water Treatment Engineering

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DESIGN CONSIDERATIONS-INTAKES 4-Screening   

Screening is a unit operation that removes suspended matter from water. Screens may be classified as coarse, fine, or microstrainer, depending on the size of material removed. Screens may be located at the intake structure, raw water pump station, or water treatment plant.·

Assoc. Prof. Emad S. Elmolla ‘s Lectures Notes

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DESIGN CONSIDERATIONS-INTAKES Coarse Screen or Trash Rack  Intake ports should be equipped with a coarse screen or bar rack to prevent large objects from entering the conveyance system.  These screens consist or" vertical flat bars, or, in some cases, round pipes spaced with 5 to 8 cm of clear opening.  The design should provide access for equipment to remove any debris that does accumulate.  The velocity through the coarse screen is generally less than 8.0 cm/s to minimize the entrainment of fish and suspended matter Assoc. Prof. Emad S. Elmolla ‘s Lectures Notes

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DESIGN CONSIDERATIONS-INTAKES Fine Screen  Fine screens are used to remove smaller objects that may damage pumps or other equipment.  They may be located either at the intake structure or at the raw water pump station.  In the case of gravity conveyance systems, the fine screen may be provided at the water treatment plant.  These screens consist of heavy wire mesh with 0.5 cm square openings or of circular passive screens with similar opening widths.  The screen area efficiency factor is 0.5 to 0.6, and the typical design velocity through the effective area is in the range of 0.20 to 0.30 m/s.  Design velocities are much lower if fish protection is required.

Assoc. Prof. Emad S. Elmolla ‘s Lectures Notes

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DESIGN CONSIDERATIONS-INTAKES Fine Screen  Screens with small openings will retain a large quantity of material; therefore, they may require automatic cleaning.  The screen assembly consists of a number of screens that move slowly upward on a chain system catching debris.  At the top, a system of water jets removes the debris from each screen before the screen travels back down for a repeat of the cycle.

Band Screen

www.mcilvainecompany.com Assoc. Prof. Emad S. Elmolla ‘s Lectures Notes

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DESIGN CONSIDERATIONS-INTAKES Fine Screen  Passive screening system consists of a circular screen, with small bars spaced at the desired spacing.  Debris is removed from the screen either by air purge or by allowing water to flow backward through the screen. Passive Screen

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DESIGN CONSIDERATIONS-INTAKES Fine Screen  Design Basis Design flow = Qmax monthly x 1.10 o Velocity through screen (V) 0.20-0.30 m/sec o Screen efficiency factor 0.50-0.60 o Critical Water Depth: at minimum water level o Head loss through screen can be calculated as follow : 1 V  v  h   , m (for clean or partly clogged screen) 0.7  2 g  where , o V = the velocity through screen , m/s o v = the velocity upstream the screen , m/s o

2

2

l

Assoc. Prof. Emad S. Elmolla ‘s Lectures Notes

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DESIGN CONSIDERATIONS-RAW WATER CONVEYANCE SYSTEM  

1- Suction Well (sump – wet well) Purpose: Distribute the raw water uniformly on the total number of pumps. Design criteria: o

Design flow = Qmax monthly x 1.10

o

Length is the greater from the following: o

o o o o o

Length = number of pumps x (1.5 – 2.5m).

Width 2 – 5 m. Retention time (T) = 5 minutes Volume (V) = Qdesign x T Area (A) = V/d A=BxL

Assoc. Prof. Emad S. Elmolla ‘s Lectures Notes

Water Treatment Engineering

m3 m2 m2

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DESIGN CONSIDERATIONS-RAW WATER CONVEYANCE SYSTEM 2- Raw water Pumping Station Purpose: To pump the raw water from the source level to water level in the first tank in water treatment plant Design criteria: o o o o o

o o

Design flow = Qmax monthly x 1.10 Number of working pumps not less than 2 Standby pumps 30-50% of working pumps Pumps Head (Htotal )= Hs + hf + hm Hs = static head it is the difference between low water level (LWL) and the water level (W.L) in the first tank in the water treatment plant (W.T.P) ~ 5m above Ground level. Hs = (G.LWTP – L.W.L Water source) + 5 Residual head of 1.0 m could be added.

Assoc. Prof. Emad S. Elmolla ‘s Lectures Notes

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DESIGN CONSIDERATIONS-RAW WATER CONVEYANCE SYSTEM 2- Raw water Pumping Station 

Flv 2 gd

2

o

hf = friction losses

o

Hm = Minor losses = 10 % hf HP =  Q HT / 75 *1 1 = 70-75% mechanical efficiency Electrical power (kw/hr) = HP / 1.34 2 2 = 85-90% electrical efficiency

o o o o

Assoc. Prof. Emad S. Elmolla ‘s Lectures Notes

hf

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DESIGN CONSIDERATIONS-RAW WATER CONVEYANCE SYSTEM 3- Raw Water Transmission pipeline: 

Purpose: To transmit raw water from pumping station to the water treatment plant.



Design criteria:   

Design flow = Qmax monthly x 1.10 Velocity = 0.6 – 1.5 m/s Number of pipes n ≥ 2

Assoc. Prof. Emad S. Elmolla ‘s Lectures Notes

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DESIGN CONSIDERATIONS-RAW WATER CONVEYANCE SYSTEM 3- Raw Water Transmission pipeline: 

Losses o o o o o

hf L V g F

Flv 2 hf  2 gd = Friction Loss (m) = Length of the culvert (m) = Velocity in the conduit (m/sec) = Gravity Acceleration, m2/sec = Friction Factor=0.02

Assoc. Prof. Emad S. Elmolla ‘s Lectures Notes

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SHORE INTAKE-DESIGN EXAMPLE Intake-Design Example Wide and deep navigation water body has the following data: Highest Water Level

HWL

25

m MSL

Average water Level

HWL

23.5

m MSL

Lowest water level

LWL

22

m...