Environmental Engineering-I

Prof. Dr. Muhammad Zulfiqar Ali Khan

Engr. Muhammad Aboubakar Farooq

Department of Civil Engineering

The University of Lahore

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Sources of Water

Rain Water

Surface Water

Ground Water

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Quality of Water Sources

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1. Rain Water:

• Generally Satisfactory

• Dissolution of CO2 results in formation of H2CO3.

• Affected by Collection System and Storage Conditions.

Quality of Water Sources

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2. Surface Water: (Rivers, Streams, Lakes)

Generally Soft Water but may contain:

• Significant Load of Suspended Solids (Silt, Clay) from land erosion.

• Color, Odor (Decaying Vegetation)

• Heavy metals, inorganic salts, oils, organic compounds, nutrients, pesticides, pathogens, from municipal, industrial and agricultural runoffs.

Quality of Water Sources

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3. Ground Water:

• Taken from a depth >35m, ground water are generally safe w.r.t. microbial contamination.

• May contain significant amount of TDS

(Saline water at Pattoki, SO4= in DGK water)

• May contain naturally occuring subsoil heavy metals i.e. As, F, Fe, Mn

Quality of Water Sources

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3. Ground Water:

• May be polluted due to Seepage of agricultural chemicals i.e. NO3, Pesticides, Insecticides.

• May be polluted through sanitary landfill leachates.

• Ground Waters are generally Hard Waters.

Quality of Water Sources

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• Surface Waters require elaborate treatment for use as Drinking Water Supplies.

• Ground Waters mostly require Minimal treatment (Disinfection only) for use as Drinking Water.

Collection of Surface Waters

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Intake:

“A water intake is a device or structure placed in a surface water source to permit the withdrawal of water from that source and then discharge into an intake conduit through which it will flow into water works system.”

Intake Structures

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An intake consists of 3 parts:

1. An OPENINIG, or STRAINER or GRATING through which water enters.

2. A CONDUIT with protective works to convey water to sump.

3. A SUMP or WELL (containing Gates & Valves to regulate flow) from where water is pumped to treatment plant.

Why to construct Intake Structures

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Surface Sources of water are subject to wide variations in flow, quality and temperature, and intake structures must be designed so that the required flow can be withdrawn despite these natural fluctuations e.g.

o Impounding Reservoirs are subject to rather wide variations in depth.

o The water at bottom of an impoundment is normally low in DO and high in organic matter.

Types of INTAKE

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Based on No. of Ports:

1. Single Port: To draw water from a CONSTANT/FIXED depth.

2. Multi Ports: For selective draft of VARIOUS depths.

Based on Source:

1. Reservoir Intakes

2. River Intakes

3. Canal Intakes

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Factors affecting Intake type:

• Source of Supply:

Source of Supply Type of Intake

1. River, 2. Canal, 3. Lake

Single Port

Reservoirs Multi Ports

Reservoir Intakes

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These comprise of intake tower(having no water inside) or sump. The interior of tower is made for inspection and operation.

The intake is usually located either along the U/S toe of an earthen dam or within the body of Concrete dam.

There are number of inlets/ports protected by screens and at different levels, to withdraw in clearer water from near surface.

Reservoir Intakes

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River Intake

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Depending on the layout and river conditions, river intake may be of following types:

1. Cross-weir Intake (for no wide fluctuations)

2. Side-weir Intake

3. Floating Pontoon Intake

4. Piled Crib Intake (for static water level)

River Intake

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Side-weir Intake:

• This is in simple form consists of a chamber, sump built in river bank and protected by bar screens to prevent any floating debris from entering the pumps.

• This is simple in cost and easy to construct but requires steep and stable banks.

Side-weir River Intake

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Lake Intake

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Wooden Crib Intake:

Canal Intake

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Canal intake is comparatively a simpler arrangement consisting of a brick-masonry chamber built particularly in canal bank. It has side opening fitted with coarse screen which excludes heavier matter. Silt etc from entering the conduit. The entry of water is controlled by gate valves which is operated from top. Pitching on both U/S & D/S to avoid scouring as it reduces the area and velocity of water is increased.

Canal Intake

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Canal Intake

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Design Considerations of Intakes

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In locating intakes, one must consider anticipated variations in water level, navigation requirements, local currents, and pattern of sediment deposition and scour, variations in water quality:

1. Reliability of Operation

2. Quality of water

3. Structural Strength

4. Economy of Construction

Design Considerations of Intakes

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• The point of intake should be so located as to obtain water of best quality.

• It should be located away from point of source of pollution.

• It should preferably be submerged in river so as not to obstruct any navigation system, to avoid floating debris and further several meters above the bed to prevent entry of silt.

Design Considerations of Intakes

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• Entering velocity in conduit not to exceed 0.15 m/sec to avoid small fish intrusion.

• Intake should be sufficiently heavy so that it may not start floating due to up thrust of water. Also a heavy intake will not be washed away by heavy water currents.

• All the forces which are expected to work on intake should be carefully analyzed and intake should be designed to withstand all these forces.

Design Considerations of Intakes

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• Strainers in the form of wire mesh should be provided on all the intake inlets. This will avoid entry of large floating objects and fishes into the intake.

• Intake should be of such size and so located that sufficient quantity of water can be obtained from the intake in all circumstances.

Water Supply Pipes

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