An intake structure is a point of transition when the flow from a source, such as a river, reservoir, or ocean is directed into a conduit, which can be a canal or a pipe.
It receives water from surface supplies such as rivers, lakes, and reservoirs that carriage to the water treatment facility.
It offers generally pure water which is devoid of pollutants, sand, and undesirable floating particles.
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What is Intake Structure?
An intake is a structure installed in a water source to allow water to be drawn from the source and discharged into an intake conduit from which it flows to the treatment facility.
Intake is divided into two halves.
Initially, an intake conduit with a screen at the inlet end and a valve to control water flow.
Secondly, a structure allowing water withdrawal from the source that containing intake conduit, valves, pumps, and so on.
The construction might be made of stone or brick masonry, R.C.C., or concrete blocks.
The construction is built waterproof that withstands water pressures, wave action, wind, floating debris, yearly rainfall, and geological formations.
Site Selection for Intake Structures:
- The site should be chosen in such a way that it can allow water even when the river’s flow is at its lowest. In general, it should be located enough below the coastline.
- The site needs to be as close as possible to the treatment plant.
- It should be placed in an area that is free of pollution, they are preferable to supply intake at the city’s higher stream so that the water is not polluted.
- It must not interfere with river navigation.
- It should be positioned in a location with suitable foundational conditions.
- The intake structure has to be protected from powerful currents.
Construction and Design of Intake Structure:
- An intake should be planned and built with the following considerations in mind:
- A sufficient safety factor should be utilized so that the intake work can withstand external forces such as powerful waves and currents, the impact of floating and submerged bodies, and ice pressures among other things.
- Intake should have enough self-weight to float on the upthrust of the water and swept away by the river. To prevent the intake structure from floating, considerable masonry work must be completed, and the bottom must be filled with broken stones.
- If intake work is built-in navigation channels, it should be shielded from the impacts of moving ships and sailboats by clusters of piling all around.
- Intake foundations should be taken sufficiently deep so that they are not eroded and currently do not overthrow the structure.
- Screens should be installed on the inlets and sidewalls to prevent big and medium-sized items and fish from entering.
- Intake inlets should be large enough to allow the needed amount of water to enter.
- Inlet sites should be such that water may be admitted in all seasons along the surface of the water in which the quality of the water is good.
- The inlets should be entirely submerged in order to prevent air from entering the suction pipe.
Types of Intake Structures:
Intakes are classified under three categories:
1. Submerged Intake:
Intakes that are completely submerged in water are known as submerged intakes, and they are frequently used to draw water from lakes.
2. Exposed Intake:
Exposed intakes take the shape of towers or oil platforms built close to the riverbank, or occasionally even farther out from the bank of the river.
This intake structure is well-liked easy to use.
3. Wet Intake:
In wet intake, the water level of the intake tower is almost identical to the water level of the supply sources.
It is also known as a sump well or a jack well.
4. Dry Intake:
During dry intake, the water tower is completely dry.
The conveying pipes receive water immediately through the port.
The dry tower is utilized for valve operation.
5. River Intake:
The river intake structure is a form of intake that may be positioned enough inside the river to meet water demands throughout the year, or it can be located along the river bank where an adequate depth of water is accessible.
An approach canal is sometimes built and water is directed to the intake tower.
A weir may be constructed to elevate and direct the river’s low water level toward the intake tower.
6. Reservoir Intake:
When the river’s flow cannot be guaranteed throughout the year, a dam is constructed across it, creating a reservoir where water may be stored.
All those are comparable to river intakes, except they are positioned towards the dam’s upstream face, where the highest depth of water is accessible.
The intake structure may differ depending on the kind of dam.
7. Lake Intake:
Submerged intakes are often favored for lake intakes, they are built in the shape of cribs or bell mouths.
The cribs are constructed of sturdy timber frame construction that is partially or entirely filled with rip-rap to protect the intake conduit from damage caused by waves, etc.
The crib’s top is made of cast iron or mesh grating.
8. Canal Intake:
In rare situations, a small town’s water supply may originate from an irrigation canal that runs nearby or through town, then it will be constructed.
It typically consists of a rectangular intake chamber made of masonry or concrete in which water is admitted through a coarse filter.
A fine screen is installed above the outflow pipe’s bell mouth entrance.
If there is no significant barrier to normal flow in the canal, the intake chamber can be built inside the canal bank.
The canal should ideally be lined near the intake chamber.
A mix of moving and stationary water screens, stop logs, grab rakes, barracks, and pumps.
9. Spring Intake:
Spring is a location on the earth’s surface where groundwater spontaneously emerges, an intake Spring intake is a structure built at the spring source to extract water.
Springs are typically found on hill slopes as impermeable layer exposes owing to geological development.
In general, spring water is free of suspended pollutants and dangerous germs.
It might be used to fund a small rural water delivery project, surface water can contaminate springs, particularly after rainstorms.
As a result, a U-shaped surface drainage diversion trench or an earth berm at least 15 meters uphill from the spring must be built to redirect any surface runoff away from the spring.
To minimize contamination by cattle and individuals who are uninformed of the spring’s existence, an area of at least 30 meters in all directions must be gated around the spring box.
Plantation may be performed on the outskirts of the spring source to sustain discharge.
Raw Water Intake Screens for Intake Structures:
Intake structure screening systems deliver clean, debris-free raw water while lowering environmental impact, eliminating maintenance issues, and prolonging service life.
Intake traveling water screens must be fish-friendly and in accordance with EPA.
This implies that fish and other living forms are not harmed by the screen and free to return to their natural home.
The screens treat enormous volumes of water for municipal and/or industrial usage while safeguarding pumps, processing equipment, and condensers, and the sturdy framework can withstand significant differential loads.
Advantages of Intake Structure:
- Intakes are desirable if the amount of water to be diverted exceeds 50% of the amount of water provided.
- If the river’s ground design is curving, intake on the outer curve is particularly advantageous.
- Transportation input is particularly suited for low bed load transport.
Disadvantages of Intake Structure:
- Intakes are less desirable for extremely high to high gradients (I > 10%), since they may induce scouring of the downstream feeder channel.
- As long as there is enough water in the river for flushing and transport, input is less appropriate for heavy bed load transportation.
- If the river’s ground design is straight, intake is less beneficial in conjunction with extra constructions.
- If the river’s ground design is split, intake is unfavourable since it will interfere with the weir’s damming activity.
Also read: Cross Drainage Work | Canal Irrigation | River Training Works
Intake Structures are typically designed to extract water from nearly any source.
The fundamental role is to assist in safely extracting water from the source over predefined pool levels, then discharging this water into the withdrawal conduit which runs up to the water treatment plant.