JNTU B.Tech III ENVIRONMENTAL ENGINEERING Previous Question Paper (August - 2022 - R16)

A river intake is a hydraulic structure constructed in a river to draw water from the source and convey it to the treatment plant. It serves as the primary gateway for a water supply system, ensuring a continuous and reliable supply of raw water while protecting the intake works from debris, silt, and navigation hazards.

The location of an intake structure on a meandering river is critical to ensure water quality and structural stability. The following factors govern its selection:

• River Morphology and Curvature: Intakes should ideally be located on the concave bank (outer curve) of a river. Due to centrifugal force, the main current flows along the outer bank, which prevents the accumulation of silt and ensures deeper water, whereas the inner bank (convex) is prone to heavy sedimentation.
• Water Quality: The site must be upstream of any point of sewage or industrial waste discharge to prevent contamination. It should also be located away from areas where floating debris or aquatic growth accumulates.
• Stability of Banks: The river bank at the chosen site must be stable and not prone to erosion or shifting. Sudden changes in the river's course could leave the intake structure stranded or cause it to be undermined.
• Availability of Sufficient Depth: The location must provide adequate water depth throughout the year, even during the lowest flow periods, to ensure the intake remains submerged and functional.
• Proximity to Treatment Works: To minimize pumping costs and pipeline length, the intake should be located as close as possible to the treatment plant site, provided the other hydraulic and quality criteria are met.
• Foundation Conditions: The river bed and bank must provide a suitable foundation to support the structural weight of the intake, often requiring geological investigation to avoid soft or unstable soil.
• Navigation and Safety: The intake should not interfere with river navigation, and it must be protected from damage by floating objects or ice flows during extreme weather conditions.

Evaluating the suitability of a water source requires a comprehensive assessment of both the quantity and quality of the available water to ensure it can meet the projected demand while remaining safe for the intended use.

1. Evaluation of Quantity:

1. Estimation of Demand: Calculate the total water requirement based on population projections, per capita consumption, and industrial or agricultural needs over the design period.
2. Hydrological Survey: Analyze historical data of the source (e.g., river flow, groundwater recharge rates, or lake storage capacity) to determine the firm yield.
3. Reliability Analysis: Assess the variability of the source during dry seasons or drought conditions to ensure the minimum required flow is available throughout the year.
4. Sustainability Check: Evaluate the long-term impact of extraction to prevent depletion of aquifers or ecological damage to surface water bodies.

2. Evaluation of Quality:

1. Sampling and Collection: Collect representative water samples from various depths and locations of the source over different seasons to account for temporal variations.
2. Physical Analysis: Measure parameters such as turbidity, color, temperature, odor, and taste to assess aesthetic and physical acceptability.
3. Chemical Analysis: Test for pH, alkalinity, hardness, dissolved solids, chlorides, sulfates, and the presence of heavy metals or toxic substances to ensure they fall within permissible limits for drinking water standards (e.g., IS 10500).
4. Biological/Bacteriological Analysis: Test for the presence of pathogens, specifically coliform bacteria, to determine the level of contamination and the required degree of disinfection.
5. Sanitary Survey: Conduct a field inspection of the catchment area to identify potential sources of pollution such as industrial effluents, agricultural runoff, or sewage discharge.

3. Integration and Decision Making:

Once data is collected, compare the findings against national water quality standards. If the source meets the quantity requirements but fails quality standards, evaluate the feasibility and cost-effectiveness of treatment processes (e.g., sedimentation, filtration, disinfection). A source is deemed suitable only if the combination of extraction, treatment, and distribution is economically viable and capable of consistently providing safe water.