CHAPTER 4 Water Treatment Process Water Intake DR
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CHAPTER 4: Water Treatment Process: Water Intake DR. ABDUL HAQI BIN IBRAHIM WATER RESEARCH GROUP (WAREG) SCHOOL OF ENVIRONMENTAL ENGINEERING
WATER INTAKE: GENERAL constructed in or adjacent to lakes, reservoirs, or rivers for the purpose of withdrawing water. consist of an opening with a grate or strainer through which the water enters, and a conduit to conduct the water by gravity to a low-lift pumping station The water is pumped from the low-lift pumping station to the water treatment facility
WATER INTAKE: KEY REQUIREMENT Reliable. Adequate size to provide the required quantity of water Located to obtain the best quality water. Protected from objects that may damage equipment. Easy to inspect and maintain Designed to minimize damage to aquatic life. Located to minimize navigational hazards.
WATER INTAKE: DESIGN ELEMENTS Design Elements Reliability Capacity Location Conduit
DESIGN ELEMENTS: RELIABILITY water supply system ceases to function when the intake system fails Small systems with only one intake structure are particularly vulnerable duplicate intake structures include multiple inlet ports, screens, conduits, and pumping units.
DESIGN ELEMENTS: CAPACITY design life of the intake structures in the range of 20 to 40 years (minimum)
WATER INTAKE: LOCATION Water Quality Water Depth Silt, Sand Treatment Facility Cost • Currents • Wind and wave impacts • comply with surface water regulations • Maximum available • Avoid ice problems • Locate to minimize impact • Minimize conduit length to treatment plant • Minimize consistent with long-term performance • and operation & maintenance requirements
TYPE OF INTAKE CATEGORY DESIGN TYPE Exposed Tower integral with dam Tower in lake Shore inlet Floating or movable Siphon well Sub-merged Plain-end pipe or elbow Screened inlet crib Gravel-packed well(s) Horizontal collection systems
LAKES/RESERVOIR EXPOSED STRUCTURE SUBMERGED STRUCTURE exposed structures are not often coldclimate lakes avoid many of the problems of the exposed systems. Exposed intake structures have been widely used in more warm-climate lakes and in reservoirs significantly more difficult to maintain because of lack of access lack of exposed mechanical parts lowers the amount of maintenance time required
RIVERS Both exposed and submerged are used. In large rivers that are controlled by locks and dams, the variation in flow and consequent variation in water surface elevation are of less concern than in unregulated waterways shore-based systems provide the best combination of access for operation and maintenance and reliable supply special consideration must be given to the impact of floods and droughts on river intakes. river intake structure must be designed to protect the pumps and valves in the transmission system from undue wear from grit.
FLOATING & MOVABLE Inexpansive method of constructing an intake in an existing lake or reservoir. Suitable for water sources that have unsuitable geological conditions
CONDUIT connects the inlet works with the low-lift pump station tunnel or a pipeline may be used tunnels have a high degree of reliability BUT they are expensive may be the more economical choice when both capital and long-term maintenance costs are considered.
DESIGN CRITERIA: DESIGN CAPACITY design flow rate ( Q ) is based on a forecast demand intake structure design are based on the worst case estimate of: - friction loss, - an estimate of potential sand intrusion into the conduit, - the all-time historic low water level, - life expectancy of 60 years
DESIGN CRITERIA: DESIGN CAPACITY ultimate flow to design the hydraulic structures (intake tower or crib, conduit, gates, etc. ) design flow is used to select pumps and motors. Space is provided for additional pumps that will be required to meet the ultimate flow.
DESIGN CRITERIA: DESIGN CAPACITY Flow criteria Design flow Capacity Q Minimum flow Ultimate flow 0. 10 Q to 0. 20 Q 2. 0 Q or higher Remarks Capacity at design life under worst case conditions System specific At life expectancy
DESIGN CRITERIA: LAYOUT Division of the intake system into two or more independent cellular or parallel components The operating deck (also called the operating floor and pump station floor ) that houses the motors, control systems, and so on should be located 1. 5 m or more, depending on: the maximum wave height OR above the high water level of a lake or reservoir OR the 500 -year flood level of a river supply.
DESIGN CRITERIA: INTAKE TOWER located as close to the shore as possible consistent with the variation in water depth
DESIGN CRITERIA: INTAKE PORT Gated ports are provided at various depths to allow for changes in water elevation and changes in water quality
DESIGN CRITERIA: INTAKE PORT The port area may be estimated using the relationship Q =v. A Where Q = flow rate, m 3 /s v = velocity of flow, m/s A = cross-sectional area of flow, m 2
DESIGN CRITERIA: SCREEN COARSE FINE Also known as bar racks placed downstream of the coarse screen prevent large pieces of debris from entering the tower. Collect smaller material that has passed through the coarse screen Bar rack screenings are taken to a landfill. design of the port must take the area occupied by the bars into account