Intake structures play a crucial role in the collection and transportation of water from surface sources, such as rivers, lakes, and reservoirs, to water treatment plants. These structures are designed to ensure that water is collected efficiently and remains relatively free from pollutants, sand, and floating debris. Generally constructed from masonry or concrete, intake structures provide a vital function in water supply systems, ensuring clean water is available for treatment and distribution.
Site Selection for Intake Structures
Choosing the right location for an intake structure is critical to ensuring a reliable and clean water supply. Several key factors must be considered when selecting the site:
- Water Availability: The intake should be located in an area where water is readily available, even during periods of low flow. It’s essential to ensure that the location can accommodate water demands throughout various seasonal conditions.
- Proximity to the Treatment Plant: The intake structure should be as close to the treatment plant as possible to minimize the distance water has to travel, which reduces the risk of contamination during transport.
- Pollution-Free Zone: The site should be free from pollutants, and locating the intake upstream from any urban areas is preferable. This ensures that the water remains uncontaminated by city waste and other pollutants.
- Avoiding River Traffic: If the intake is located in a river, it should not interfere with any river traffic or navigation routes, ensuring minimal disruptions to transportation and maintaining public safety.
- Good Foundation Conditions: The site should have stable ground to support the intake structure, preventing any structural damage due to soil instability or water movements.
- Protection from Rapid Currents: To ensure the intake remains effective, it should be located in a region where rapid currents are not an issue, preventing the intake from being overwhelmed by strong water flows and potential damage.
Types of Intake Structures
Intake structures come in a variety of types, each suited to different water sources and operational needs. The main types of intake structures include:
1. Submerged Intake Structures
A submerged intake structure is constructed entirely below the water surface. This type of intake is typically used for lakes, where it is essential to draw water from deeper, more stable layers. The submerged design helps ensure the water collected is free from floating debris and surface pollutants, providing a cleaner source for treatment.
2. Exposed Intake Structures
Unlike submerged intakes, exposed intake structures are built above the water surface, often as wells or towers located near the riverbank or other water bodies. These structures are more common due to their ease of operation and maintenance. Exposed intakes are accessible for cleaning and inspection, making them more practical for regular use.
3. Wet Intake Structures
A wet intake structure typically operates with the water level inside the intake tower remaining the same as the water level in the source. This type of structure is commonly referred to as a “Jack well.” Wet intakes are used when it is necessary to maintain a constant water level in the intake chamber to prevent the system from running dry and to keep the operation smooth.
4. Dry Intake Structures
In contrast to wet intake structures, dry intake systems are designed so that the intake tower remains dry at all times. Water enters directly through entry ports into the conveyance pipes, which then transport the water to the treatment plant. Dry intakes are primarily used for regulating valves and controlling water flow, rather than collecting large amounts of water.
5. River Intake Structures
River intake structures are typically located within the riverbed or close to the riverbank, ensuring that water can be collected during all seasons. In cases where water levels are low, an approach channel or a weir may be constructed to raise the water level and direct water to the intake tower. This type of intake is essential for areas relying on rivers for water supply throughout the year.
6. Reservoir Intake Structures
When river flow is not consistent, reservoirs are built by constructing dams across rivers to store water. Intake structures located in reservoirs are positioned near the upstream side of the dam, where the water depth is the highest. These structures are designed to draw water from the reservoir, ensuring a steady supply even in seasons of low river flow. The design of these intakes may vary depending on the type of dam used.
7. Lake Intake Structures
For lake-based water sources, submerged intakes are often preferred. These intake structures are typically constructed as cribs or bell mouths. Cribs are sturdy frameworks made of heavy timber, often filled with rip-rap (large rocks) to protect the intake from wave damage. The top of the crib is often covered with a cast iron or mesh grating to prevent debris from entering the intake and ensure clean water collection.
8. Canal Intake Structures
In certain situations, a small town may rely on water from an irrigation canal. In these cases, an intake structure is built into the canal to collect the water. Canal intake structures typically consist of a masonry or concrete chamber, through which water is drawn using coarse screens to filter out large debris. The chamber may be constructed within the canal banks, ensuring minimal disruption to the water flow. Fine screens are often placed over the outlet pipe to ensure clean water enters the treatment system.
Conclusion
Intake structures are vital components of water supply systems, ensuring that water is collected from surface sources and transported to treatment plants without contamination. The proper selection of intake sites and the choice of appropriate intake structures based on water source and operational needs can significantly impact the efficiency and reliability of a water treatment system. Understanding the different types of intake structures—submerged, exposed, wet, dry, and specific designs for river, reservoir, lake, and canal sources—helps ensure that clean and safe water is available for communities, even in challenging environmental conditions.