Question 1

Hydrology and soil physics – name of the property describing a soil’s ability to absorb incoming rainfall In surface-hydrology practice, what is the term used for the capacity of a soil surface to admit water during rainfall and thereby absorb moist…

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Introduction / Context: The question tests the distinction between several soil–water terms used in hydrology and geotechnical engineering. When rain strikes the ground, how much of it enters the soil rather than running off depends on the soil’s ability to admit water at the surface—this is called infiltration, and the limiting rate is the infiltration capacity. Given Data / Assumptions: We are concerned with rainfall reaching a soil surface. We want the soil property governing admission of water at the surface. Steady or time-varying rainfall may occur, but the definition is independent of a specific storm. Concept / Approach: Infiltration capacity = the maximum rate (or shorthand, capacity) at which a given soil, in a given condition, can absorb water through the surface. It depends on texture, structure, antecedent moisture, surface sealing, vegetation, and compaction. It is distinct from porosity (volume fraction of voids) and permeability (hydraulic conductivity governing flow within the saturated/unsaturated medium). Step-by-Step Solution: Identify the phenomenon at the soil surface during rainfall → infiltration.Select the specific term describing that limiting ability → infiltration capacity.Reject related but different bulk properties (porosity, permeability) or vague descriptors (perviousness). Verification / Alternative check: In infiltration models (e.g., Horton, Green–Ampt), the rate i(t) is capped by the infiltration capacity f(t). When rainfall intensity exceeds f(t), excess becomes surface runoff. Why Other Options Are Wrong: Permeability: property controlling internal flow; not specifically the surface admission limit. Porosity: volume fraction of voids; does not directly set instantaneous intake rate. Perviousness: qualitative term; lacks the specific quantitative meaning. Sorptivity: early-time capillary-driven intake parameter, not the general capacity term sought here. Common Pitfalls: Using permeability and infiltration capacity interchangeably; a soil may be highly porous yet have low infiltration due to surface sealing. Final Answer: Infiltration capacity

Question 2

Subsurface water terminology – relating yield, specific yield, and specific retention to porosity Which statements correctly define yield, specific yield, and specific retention, and relate their sum to porosity for a saturated soil mass draining by…

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Introduction / Context: This question checks foundational hydrogeology terms used in well hydraulics and groundwater storage calculations. Understanding how the pore space partitions into drainable water and retained water is essential for aquifer yield estimation. Given Data / Assumptions: Saturated soil or aquifer material undergoing gravity drainage. Porosity n is the total void fraction. Some water drains (specific yield), some remains due to capillary and adsorptive forces (specific retention). Concept / Approach: Specific yield (Sy) = V_drained / V_total.Specific retention (Sr) = V_retained / V_total.Porosity (n) = Sy + Sr (neglecting entrapped air). The total void volume splits into drainable and retained portions under gravity drainage, hence the additive relation. Step-by-Step Solution: Map each statement to standard definitions → all match accepted terminology.Conclude that the combined statement “All the above” is correct. Verification / Alternative check: Textbook water-balance in a representative elemental volume shows V_void = V_drained + V_retained → n = Sy + Sr. Why Other Options Are Wrong: Any single option alone is incomplete; the comprehensive, correct choice is the collection. Common Pitfalls: Confusing “yield” (a volume) with “specific yield” (a ratio); the latter is dimensionless and is what appears in groundwater storage equations. Final Answer: All the above

Question 3

Reservoir capacity components – the term “silt storage” corresponds to which storage category? In reservoir planning, the volume intentionally reserved to accommodate sediment (silt) deposition over the project life is equivalent to:

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Introduction / Context: Reservoir capacity is partitioned into functional zones. Designers assign a portion that can be lost to sedimentation over the project life; understanding where this “silt storage” comes from is key to sustainable yield. Given Data / Assumptions: Sediment accumulates at the bottom and progressively encroaches on lower elevations of storage. Dead (inactive) storage lies below the minimum operating level. Concept / Approach: Because sedimentation begins at the lowest pool levels, the capacity primarily sacrificed is the dead storage. Designers may augment dead storage to accommodate forecast sediment so that live storage (usable for regulation and supply) remains largely intact during the design life. Step-by-Step Solution: Identify the locus of sediment deposition → lowest elevations.Match this with the storage category that cannot be released for use → dead storage. Verification / Alternative check: Operation curves place minimum drawdown level above the dead storage top; sediment surveys track loss primarily within this zone. Why Other Options Are Wrong: Live/effective storage: intended for regulation and should be preserved from long-term siltation as far as practicable. Flood control storage: temporary upper-pool space; not a sediment sink by design. Common Pitfalls: Assuming sedimentation uniformly reduces all zones; in practice, geometry and operation concentrate deposition within dead storage. Final Answer: Dead storage

Question 4

Groundwater basics – where do perched aquifers occur relative to the regional water table? Perched aquifers form when a local impervious lens intercepts percolating water. Relative to the main phreatic surface (regional water table), perched aquifer…

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Introduction / Context: Perched aquifers are frequent in hilly or layered terrains where lens-shaped impervious layers create a local saturated zone separated from the main groundwater body. Recognizing perched conditions prevents misinterpretation of well tests and spring yields. Given Data / Assumptions: A relatively impervious lens (e.g., clay) lies above the regional water table. Percolating water collects above this lens, forming a localized saturated zone. Concept / Approach: The perched water body is hydraulically disconnected from the main aquifer beneath. Its “perched water table” stands at a higher elevation than the regional water table and is sustained by local recharge until it drains laterally. Step-by-Step Solution: Identify the structural control (impervious lens) → causes local saturation above it.Conclude relative position → above the regional water table. Verification / Alternative check: Observation wells penetrating only to the perched zone show static levels higher than those in deeper wells tapping the main aquifer. Why Other Options Are Wrong: Below/same elevation: contradicts the definition of “perched”. “Only within aquicludes” or “only within artesian aquifers”: misuse of terms; an aquiclude does not transmit water, and artesian refers to confined conditions in the main aquifer, not to perched zones. Common Pitfalls: Confusing perched saturation after storms with the persistent regional water table; perched levels can be transient. Final Answer: Above the regional water table

Question 5

Water quality chemistry – identify the incorrect statement about pH and hydrogen-ion concentration Which of the following statements is incorrect regarding the pH scale and hydrogen-ion concentration in water?

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Introduction / Context: pH is a master variable for water treatment, corrosion control, and disinfection. Correct interpretation of pH relative to acidity and alkalinity is fundamental to process decisions. Given Data / Assumptions: pH is defined as pH = −log10[H+], which equals log10(1/[H+]). Neutral water at 25°C has pH ≈ 7. Acidic solutions have pH < 7; alkaline (basic) solutions have pH > 7. Concept / Approach: Because pH is the negative logarithm, an increase of pH by 1 indicates a tenfold decrease in hydrogen-ion concentration. Therefore, statements that connect low pH with alkalinity are incorrect. Step-by-Step Solution: Check (a): pH = log10(1/[H+]) → correct.Check (b): higher pH → lower [H+] → correct.Check (c): lower pH → higher [H+] → correct.Check (d): lower pH gives alkalinity → incorrect; lower pH is acidic. Verification / Alternative check: Example: pH 5 has [H+] 100 times higher than pH 7, confirming acidity increases as pH decreases. Why Other Options Are Wrong: Only (d) conflicts with the pH definition; the others are standard relationships. Common Pitfalls: Equating alkalinity (acid-neutralizing capacity) with pH directly; while correlated, alkalinity is a buffering capacity, not simply pH. Final Answer: Lower pH gives an alkaline solution

Question 6

Siting a pumping station – multi-criteria considerations for reliability and safety Which of the following factors are relevant when selecting the site of a municipal water pumping station?

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Introduction / Context: Pumping stations are critical infrastructure. Site selection must balance water quality protection, flood safety, constructability, O&M access, and future growth, ensuring continuous service over decades. Given Data / Assumptions: Urban water-supply context. Station near a water source (river/reservoir) exposed to floods and pollution risks. Long asset life with expected demand growth. Concept / Approach: Robust siting addresses public-health protection (adequate offset from pollution), resilience (above HFL with freeboard), expandability (space/utilities), and logistics (transport connectivity for equipment and chemicals). Ignoring any of these can compromise reliability or increase life-cycle costs. Step-by-Step Solution: Confirm each factor’s relevance → all four are legitimate siting criteria.Therefore, choose “All the above”. Verification / Alternative check: Design manuals list sanitary control, flood protection, power access, and transportation as standard siting requirements. Why Other Options Are Wrong: Single-factor choices are incomplete; station siting is inherently multi-criteria. Common Pitfalls: Focusing solely on hydraulic proximity to source while neglecting flood levels and contamination setbacks. Final Answer: All the above

Question 7

Crossing beneath a channel – terminology for a pressure conduit laid below a stream/canal A closed conduit carrying water under pressure beneath a natural stream or irrigation canal is commonly termed:

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Introduction / Context: Water-supply and irrigation networks often need to cross valleys or existing waterways. When the carrier pipe dips below the obstacle and runs full under pressure, several synonymous field terms are used. Given Data / Assumptions: Closed pipe flowing full under pressure below an obstruction. Entry and exit connected to the distribution main or canal. Concept / Approach: The term “inverted syphon” is standard. The same arrangement is also called a depressed pipe or sag pipe in practice, reflecting its profile. Because all listed terms refer to the same configuration, the inclusive option is correct. Step-by-Step Solution: Match the description (pressure conduit below obstacle) → inverted syphon.Recognize common synonyms → depressed pipe, sag pipe.Therefore, select “All the above”. Verification / Alternative check: Design drawings and specifications often annotate the same crossing with any of these synonyms depending on regional practice. Why Other Options Are Wrong: Each single term is correct but incomplete relative to the question’s inclusive phrasing; the comprehensive choice is “All the above”. Common Pitfalls: Confusing an inverted syphon with a culvert; a culvert conveys external drainage and usually runs partially full, not as a pressurized carrier for the supply line. Final Answer: All the above

Question 8

Design of riveted steel pressure mains – estimate plate thickness with joint efficiency and corrosion allowance A pressure main (diameter = 1.0 m) experiences a static head difference of 180 m, and a water-hammer rise of 7.5 kg/cm^2. Riveted joint e…

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Introduction / Context: Pressure pipelines are often designed using the thin-cylinder hoop-stress approach with allowances for joint efficiency and corrosion. Riveted joints reduce effective strength; water hammer adds to static pressure. This problem consolidates those considerations. Given Data / Assumptions: Diameter D = 1.0 m = 100 cm. Static head = 180 m of water ≈ 180 * 0.1 kg/cm^2 ≈ 18 kg/cm^2 (more precisely ≈ 17.7–18.0). Water-hammer increment = 7.5 kg/cm^2. Joint efficiency η = 0.6. Corrosion allowance c = 3 mm = 0.3 cm. Adopt a typical allowable hoop stress for plate material, f_allow ≈ 1000 kg/cm^2 for working-stress design of riveted steel plates (representative of older practice). Concept / Approach: Use thin-cylinder hoop-stress relation including joint efficiency: t_req = (p_total * D) / (2 * f_allow * η) where p_total is the maximum operating pressure including surge. Add the corrosion allowance afterwards: t = t_req + c. Step-by-Step Solution: Compute total pressure: p_total ≈ 18 + 7.5 = 25.5 kg/cm^2.Compute required thickness without corrosion: t_req = (25.5 * 100) / (2 * 1000 * 0.6) = 2550 / 1200 ≈ 2.125 cm.Add corrosion allowance: t ≈ 2.125 + 0.3 = 2.425 cm ≈ 24.3 mm.Adopt nearest standard thickness → 25 mm. Verification / Alternative check: Using a slightly more precise static head conversion (≈17.7 kg/cm^2) yields t in the same vicinity; standardization still leads to 25 mm plates. Why Other Options Are Wrong: 10–20 mm: insufficient given high combined pressure and reduced joint efficiency. 30 mm: conservative beyond typical need for the given assumptions. Common Pitfalls: Omitting water-hammer allowance or forgetting to divide by joint efficiency significantly underestimates thickness. Final Answer: 25 mm

Water Supply Engineering Questions