Question 1

Basic laboratory indicators for drinking water quality: identify the correct set of statements about colour, odour, and dissolved solids measurement.

Accepted Answer

Introduction / Context: Rapid field and bench tests provide quick insight into aesthetic and operational qualities of raw and treated waters. Colour, odour, and conductivity are among the simplest indicators used by operators and labs. Given Data / Assumptions: Visual comparison methods remain common for low-intensity colour measurement. Odour is evaluated qualitatively by threshold or intensity descriptors. Conductivity correlates with total dissolved solids (TDS). Concept / Approach: A tintometer (or colour comparator) measures small colour intensities by comparing against known standards. Odour is recorded using standard descriptors/intensity. Nessler tubes enable side-by-side visual comparison for colour or residual tests. Electrical conductivity relates to ionic strength and hence dissolved salt content. Step-by-Step Solution: Match instrument to parameter: tintometer for colour; Nessler tube also aids visual detection.Recognize odour reporting via intensity/threshold terms.Use conductivity to infer TDS trends and salinity issues. Verification / Alternative check: Standard methods texts include these procedures as routine preliminary assessments. Why Other Options Are Wrong: Each statement (a–d) is correct; therefore omitting any would reduce completeness. Hence (e) is the best comprehensive choice. Common Pitfalls: Confusing true colour vs. apparent colour; not filtering/treating samples appropriately before measurement. Final Answer: All of the above

Question 2

Cast iron (spun) water pipes: choose the incorrect nominal internal diameter (mm) from the list of typical standard sizes.

Accepted Answer

Introduction / Context: Standardization of nominal diameters simplifies procurement, inventory, and fittings for cast iron (and ductile iron) pipe networks. Non-standard sizes complicate jointing and spares. Given Data / Assumptions: Typical nominal sizes progress in standard steps (e.g., 80, 100, 150, 200, 250, 300, 350, 400, 450, 500, 600 mm, etc.). Question asks for the incorrect (non-standard) size. Concept / Approach: Identify the odd size that does not belong to the common standardized series used in municipal systems and catalogs for C.I. spun pipes. Step-by-Step Solution: Scan listed sizes and compare with the standard sequence.300, 400, 500, 600 mm are common nominal steps.550 mm does not typically exist as a standard C.I. nominal diameter. Verification / Alternative check: Checking fittings and valves catalogs also reveals the absence of 550 mm as a usual nominal size. Why Other Options Are Wrong: The remaining options correspond to standard sizes commonly available in pipes, valves, and specials. Common Pitfalls: Assuming any intermediate number could be ordered; network components must align with prevailing standard sizes. Final Answer: 550 mm

Question 3

What do carbonates (CO3^2−) and bicarbonates (HCO3^−) in water primarily produce with respect to water-quality characterization?

Accepted Answer

Introduction / Context: Understanding the carbonate system in water is central to treating drinking water and controlling corrosion. Carbonates and bicarbonates influence pH buffering and are measured as alkalinity, affecting coagulant dose and stability. Given Data / Assumptions: Presence of carbonate (CO3^2−), bicarbonate (HCO3^−), and hydroxide (OH^−) species. Alkalinity is expressed as CaCO3 equivalent. Concept / Approach: Alkalinity is the capacity of water to neutralize acids and is predominantly due to bicarbonates, carbonates, and hydroxides. While bicarbonates of calcium/magnesium are associated with temporary hardness, the direct characteristic produced by these anions is alkalinity. Step-by-Step Solution: Recognize carbonate system species in natural waters.Relate these to buffering capacity, hence alkalinity.Distinguish hardness (a cation-driven property) from alkalinity (anion-driven buffering and titration property). Verification / Alternative check: Titration to phenolphthalein and methyl orange endpoints quantifies carbonate and bicarbonate alkalinity. Why Other Options Are Wrong: (a) Temporary hardness refers to Ca/Mg bicarbonates but the question asks what carbonates in water produce primarily—alkalinity is more accurate. (b) Permanent hardness arises from sulphates/chlorides of Ca/Mg. (c) Carbonates do not produce acidity; they buffer against it. Common Pitfalls: Equating bicarbonate presence directly with “temporary hardness” when the more fundamental descriptor for anions is alkalinity. Final Answer: Alkalinity

Question 4

Sectors typically supplied with well-treated potable water in a public water-supply system (Select the most comprehensive correct option.)

Accepted Answer

Introduction / Context: Municipal potable water systems distribute treated water to a variety of consumers. Recognizing the principal use sectors helps in demand assessment and system design. Given Data / Assumptions: Treated water meets drinking-water standards. Distribution covers households, commerce/industry, and public/institutional facilities. Wastewater is collected separately via sewers and is not a consumer of potable supply. Concept / Approach: Water-demand categories in planning include domestic, commercial/industrial, and public (municipal/institutional) components. Wastewater is an output from these uses and is conveyed to treatment, not a supply sector to which potable water is “delivered”. Step-by-Step Reasoning: Identify valid potable-water user classes: domestic, commercial/industrial, public services.Exclude wastewater, which represents effluent to be treated, not a user category.Select the comprehensive answer that includes all legitimate demand sectors and excludes wastewater. Verification / Alternative check: Standard water-works texts categorize demands precisely in these classes for per capita or unit-area projections. Why Other Options Are Wrong: (a), (b), (c) are each partial truths but not comprehensive alone. (d) is incorrect—wastewater is not a “use” sector of treated water. Common Pitfalls: Confusing wastewater (collection and treatment) with water-demand categories; they are different subsystems. Final Answer: All of the above except wastewater

Question 5

Identify the rainfall–runoff empirical relation: Q = P − K[1.8 T + 32], where Q is runoff (cm), P is annual rainfall (cm), T is mean annual temperature (°C), and K is a regional constant.

Accepted Answer

Introduction / Context: Empirical runoff–rainfall relations are used for preliminary water-resources assessments when detailed hydrometric records are sparse. Recognizing common forms helps select suitable starting points for catchment studies. Given Data / Assumptions: Q = P − K[1.8T + 32], units in centimetres for P and Q; T in degrees Celsius. K is a catchment-specific constant. Concept / Approach: The presence of the temperature term modified by 1.8T + 32 (conversion towards Fahrenheit scale) is characteristic of the English formula used historically in hydrology texts for annual runoff estimation. Step-by-Step Identification: Compare the given structure with known empirical forms.Note the explicit temperature component 1.8T + 32, pointing to the English formula.Select the name that matches this expression. Verification / Alternative check: Cross-reference with common lists of empirical relations that include Justin, Khosla, English, and Vermule forms; only the English formula uses this specific temperature conversion factor. Why Other Options Are Wrong: Other named formulas use different variables or structures and do not include the 1.8T + 32 term. Common Pitfalls: Forgetting the temperature component and confusing with simpler Q–P linear relations. Final Answer: English formula

Question 6

Ozonation in drinking-water treatment: select the incorrect statement about the effects of ozone on water quality.

Accepted Answer

Introduction / Context: Ozone is a strong oxidant used in advanced drinking-water treatment for primary disinfection and control of taste-and-odour-causing compounds. It decomposes rapidly, leaving no long-lived residual in distribution. Given Data / Assumptions: Properly applied ozone doses within conventional treatment trains. Downstream filtration and, if needed, a secondary disinfectant (e.g., chloramine) may be applied. Concept / Approach: Ozone effectively inactivates many microbes and oxidizes certain organics, improving taste and odour. However, it does not render water “tasteless”; rather, it removes off-flavours without imparting a chlorine-like taste since it leaves minimal residual. Step-by-Step Assessment: Evaluate each statement against known ozonation effects.(a) and (e): Ozone does not leave a noticeable residual odour or taste.(b): Ozone is effective for microbial inactivation and for oxidizing colour/odour-causing substances.(c): Claiming water becomes “tasteless” is incorrect; water retains natural mineral taste. Verification / Alternative check: Utility practice shows ozonated water is often described as “fresh” without chlorine taste, not “tasteless”. Why Other Options Are Wrong: (a), (b), and (e) are generally true within standard practice. (d) “None of these” is false because (c) is indeed incorrect. Common Pitfalls: Confusing absence of chlorine taste with the notion of tasteless water; minerals and temperature still influence taste. Final Answer: Ozonised water becomes tasteless

Question 7

Site selection for productive wells in groundwater engineering:\r A well is generally considered “good” (high-yielding and reliable) when it is sunk into which type of water-bearing formation?

Accepted Answer

Introduction / Context: A “good” well in water resources engineering is one that delivers high discharge with limited drawdown and minimal problems such as turbidity, clogging, or excessive fine migration. The hydrogeologic nature of the aquifer material determines yield, water quality, and long-term performance. This item tests understanding of which sediment type provides the most favorable conditions for a high-yield well. Given Data / Assumptions: The well is a properly designed and developed tube well or dug-cum-bore well. Formation types considered: clay, sand, coarse gravel, silt, and hard rock with joints. Objective is sustainable yield with reasonable drawdown and good water quality. Concept / Approach: Specific capacity of wells is controlled by hydraulic conductivity and effective grain size. Coarse gravels possess very high permeability and transmit water readily, leading to large yields for small drawdowns. Conversely, clays and silts have low permeability, causing poor yield and severe well-loss issues. Clean sands are acceptable but commonly yield less than well-sorted gravels of similar thickness. Step-by-Step Solution: Identify formation with highest hydraulic conductivity: coarse gravel.Relate high conductivity to high specific capacity (Q/s), enabling “good” well performance.Eliminate formations with fine grains (clay, silt) due to low permeability and clogging risk.Recognize sand as acceptable but generally lower-yield than well-sorted coarse gravel. Verification / Alternative check: Empirical well design practice favors screened intakes opposite clean, well-graded sands and gravels; development tests consistently show superior yields in coarse gravels at comparable heads. Why Other Options Are Wrong: Clay and silt: very low permeability; wells are poor-yielding and prone to turbidity. Sand: better than clay/silt, but typically less productive than coarse gravel. Hard rock with joints: yields depend on fracture connectivity and are highly variable. Common Pitfalls: Confusing aquifer thickness with productivity; grain size and sorting strongly control yield. Ignoring well development; even good formations need proper development to achieve design yield. Final Answer: Coarse gravel

Question 8

Gravity conduits in water supply engineering:\r Which statements correctly describe gravity conduits used to carry water by gravity from a source to a service area?

Accepted Answer

Introduction / Context: Gravity conduits are the backbone of many cost-effective water transmission systems. By exploiting elevation head between source and demand nodes, engineers can move large flows with minimal operational energy. This question checks the key attributes and alignments used for gravity aqueducts and pipelines in rugged terrain. Given Data / Assumptions: No pumps are intended; flow is driven by elevation head. Design must maintain a continuous downward hydraulic grade. Topographic obstacles (valleys, ridges) are present along the route. Concept / Approach: To sustain gravity flow, the hydraulic gradient line (HGL) must remain above the pipe centerline (or channel invert) after accounting for head losses. Alignments therefore adapt to terrain using trestles (aqueduct bridges) over valleys and tunnels through ridges to reduce excessive headlosses or negative pressures. The overall aim is to preserve the gravity head and avoid cavitation or air-binding. Step-by-Step Solution: Recognize gravity conduits function without pumping (Option A true).They are laid to match the HGL within practical limits (Option B true).Structural solutions like trestles cross depressions (Option C true).Tunnels are used to pass through high ground efficiently (Option D true).Therefore, “All the above” is correct. Verification / Alternative check: Classical aqueduct systems and modern raw water conduits widely use siphons, bridges, and tunnels to maintain gravity-driven conveyance, validating the statements collectively. Why Other Options Are Wrong: Each single statement is correct but partial; only Option E captures the complete, typical design toolkit for gravity conduits. Common Pitfalls: Confusing HGL with pipe crown level; it is the energy grade that matters. Underestimating headlosses at appurtenances, which can drop the HGL below the conduit. Final Answer: All the above

Question 9

Cause of hardness in water (expressed as CaCO3):\r Hardness of water is primarily caused by which dissolved constituents?

Accepted Answer

Introduction / Context: Hardness is a key aesthetic and operational parameter in potable water treatment. It increases soap consumption, promotes scaling in boilers and heaters, and affects corrosion control strategies. Knowing its chemical origin is fundamental to selecting appropriate treatment such as lime-soda softening or ion exchange. Given Data / Assumptions: Total hardness is reported as CaCO3 equivalent. Divalent cations calcium (Ca2+) and magnesium (Mg2+) are the principal contributors. Counter-ions commonly encountered are bicarbonate (temporary hardness) and sulphate/chloride (permanent hardness). Concept / Approach: Temporary hardness is mainly due to bicarbonates of Ca and Mg; permanent hardness arises from their chlorides and sulphates. Sodium and potassium salts do not precipitate soaps and thus do not cause classical hardness problems. Suspended solids (turbidity) are unrelated to chemical hardness. Step-by-Step Solution: Identify causative ions: Ca2+ and Mg2+ combined with HCO3–, SO4^2–, or Cl–.Relate to observed effects: scaling and soap precipitation.Select the option listing these salts explicitly. Verification / Alternative check: Soap titration tests and hardness calculations express results as CaCO3 equivalent precisely because Ca and Mg dominate conventional hardness behavior. Why Other Options Are Wrong: Soap lather is an effect, not a cause. Sodium/potassium salts do not precipitate soaps and rarely form scale under normal conditions. Turbidity is a physical parameter, not chemical hardness. Silica/iron may cause other issues but are not principal hardness agents. Common Pitfalls: Confusing alkalinity (HCO3–) with hardness; alkalinity can exist without hardness and vice versa. Assuming “softening” always means demineralization; many processes exchange Ca/Mg for Na+. Final Answer: Bicarbonates, sulphates, or chlorides of calcium and magnesium

Question 10

Demand variations in urban water supply:\r What is the typical ratio of maximum daily consumption to average daily demand used for design checks?

Accepted Answer

Introduction / Context: Water demand fluctuates hourly, daily, seasonally, and with special events. Designers apply peaking factors to ensure the system can meet short-term high demands without unacceptable pressure drops. One common metric is the ratio of the maximum day to the average day demand. Given Data / Assumptions: Typical medium-to-large city with mixed residential, commercial, and institutional use. Historic practice and textbook design values are acceptable for preliminary sizing. Fire flow is handled as a separate, concurrent check. Concept / Approach: Empirical peaking factors reflect user behavior and climate. Many standards employ a maximum-day-to-average-day factor between 1.6 and 2.0. In numerous exam syllabi and design examples, 1.8 is adopted as a representative value for conservative planning at the concept stage. Step-by-Step Solution: Identify the parameter: Max Day / Average Day.Compare listed ratios to typical guideline range.Select 1.8 as a standard, commonly used design factor in teaching practice. Verification / Alternative check: Utility demand records often show 60–100% increase on peak days relative to annual average, supporting factors near 1.8 for preliminary sizing before detailed modeling. Why Other Options Are Wrong: 1.0 implies no peaking and is unrealistic. 1.2 and 1.4 are low for many climates/behaviors. 1.6 can be used, but 1.8 is more typical for conservative designs in many texts. Common Pitfalls: Confusing maximum day factor with maximum hour factor; the latter is higher. Ignoring concurrent fire flow checks which can govern main sizing even if peaking factors are satisfied. Final Answer: 1.8

Question 11

Water treatment process terminology:\r The process of passing water through beds of granular media (such as sand and anthracite) to remove suspended and colloidal impurities is called

Accepted Answer

Introduction / Context: Surface water treatment trains typically include screening, coagulation-flocculation, sedimentation, filtration, and disinfection. Understanding the distinct purpose of each step helps in proper design and troubleshooting of plants. Given Data / Assumptions: Granular media beds (slow sand, rapid gravity, or dual-media) are employed. Targeted removal: fine suspended solids, floc carryover, and some microorganisms. Pretreatment (coagulation/flocculation) may or may not be present depending on raw water quality. Concept / Approach: Filtration is the passage of water through porous media to retain particles by straining, interception, sedimentation within pores, and to some extent adsorption and biofilm action (particularly in slow sand filters). It complements sedimentation by removing particles that escaped settling. Step-by-Step Solution: Identify the defining feature: flow through granular media bed.Relate to process name: filtration.Eliminate other processes: screening is coarse-bar removal; sedimentation is gravity settling without media. Verification / Alternative check: Pilot studies and plant data show turbidity removal polishing across filters, taking settled water from a few NTU to <0.3 NTU, confirming the function of filtration in the treatment chain. Why Other Options Are Wrong: Screening removes large debris only. Sedimentation removes heavier floc by gravity without media. “Adsorption only” is incomplete; several mechanisms act in filtration. Common Pitfalls: Operating at excessive filtration rates that compromise effluent turbidity and pathogen barrier performance. Skipping coagulation where needed, overloading filters with fine colloids. Final Answer: Filtration

Question 12

Settling velocity from sedimentation tank geometry:\r For a rectangular sedimentation tank of length L, breadth B, depth D and total discharge Q, the design settling velocity v_s is equal to

Accepted Answer

Introduction / Context: In ideal sedimentation theory, particle removal depends on the overflow (surface) rate rather than tank depth. Designers therefore use surface loading rate, equated to a critical settling velocity, to size plan area for a given flow and target removal. Given Data / Assumptions: Rectangular clarifier with length L, breadth B, and water depth D. Steady flow Q and ideal plug-flow behavior (no short-circuiting). Uniform vertical settling behavior without flocculation effects. Concept / Approach: In the idealized Hazen model, removal depends on the ratio of settling velocity v_s to overflow rate Q/A, where A is plan area. The critical condition for removal is v_s ≥ Q/A. Thus, v_s equals Q divided by the surface area; tank depth does not affect the theoretical removal efficiency for discrete settling. Step-by-Step Solution: Compute plan area: A = L * B.Overflow rate (surface loading) = Q / A.Set design settling velocity v_s = Q / (L * B).Note that depth D influences sludge storage and inlet/outlet hydraulics, not the basic Hazen criterion. Verification / Alternative check: Plant performance correlations and tracer studies verify that clarifier depth does not directly change ideal surface-based removal; however, non-idealities (density currents) may necessitate additional depth for hydraulic stability. Why Other Options Are Wrong: Options including D in the denominator or numerator contradict the surface-overflow concept. Q / (L * B * D) is the average velocity through the tank volume, not settling velocity criterion. Common Pitfalls: Assuming deeper tanks always improve clarification; without improving hydraulics, depth alone does not increase ideal removal. Ignoring inlet/outlet design that can create short-circuiting and reduce effective surface area. Final Answer: Q / (L * B)

Question 13

Aquifer storage terms in groundwater hydrology:\r If n is porosity, y is specific yield, and r is specific retention of a soil or rock, which relationship is correct?

Accepted Answer

Introduction / Context: Porosity and its partitions govern how much water an aquifer can store and release. Specific yield and specific retention split porosity into a drainable portion and a portion held by molecular and capillary forces. Recognizing their algebraic relationship is essential for well design and groundwater balance calculations. Given Data / Assumptions: n is total porosity (void volume / total volume). y (specific yield) is the fraction of water that drains by gravity. r (specific retention) is the fraction retained against gravity. Concept / Approach: By definition, total pore water divides into two mutually exclusive parts under gravity drainage: drainable (specific yield) and retained (specific retention). Therefore, their sum equals total porosity. This identity underlies volumetric water budget computations in unconfined aquifers. Step-by-Step Solution: Start with total porosity n.Partition into y (drainable) and r (retained).Thus: y + r = n. Verification / Alternative check: Laboratory drainage curves and field specific yield measurements confirm that the difference between porosity and specific retention equals specific yield for typical granular soils. Why Other Options Are Wrong: Adding n to either side (e.g., n + y + r = 1) mixes dimensional fractions incorrectly. Equations setting n + y = r or n + r = y contradict the basic partition concept. n + r + y = 0 is non-physical since all are positive fractions. Common Pitfalls: Assuming y equals n; fine-grained soils have large r, so y can be much smaller than n. Using porosity instead of specific yield in groundwater storage-change calculations, leading to large overestimates. Final Answer: y + r = n

Question 14

Removal of dissolved gases in water treatment:\r Which process is most effective for removing dissolved carbon dioxide (CO2) from the supply main?

Accepted Answer

Introduction / Context: Dissolved gases such as CO2, H2S, and volatile organics can affect taste, odor, corrosivity, and downstream treatment processes. Understanding which unit process targets these gases helps optimize plant performance and corrosion control. Given Data / Assumptions: Water contains dissolved carbon dioxide at levels affecting pH and corrosivity. Treatment options include physical (aeration), chemical (chlorination, coagulation), and physical-chemical (sedimentation) processes. Concept / Approach: Aeration promotes mass transfer of dissolved gases from water to air by increasing interfacial area and turbulence. Packed towers, cascade aerators, and diffused aeration are standard configurations. CO2 stripping raises pH and reduces corrosivity, aiding subsequent lime softening or stabilization steps. Step-by-Step Solution: Identify target: dissolved CO2 (a gas), not particulates or pathogens.Match process: gas removal is achieved by aeration via gas–liquid mass transfer.Select Aeration as the correct process. Verification / Alternative check: Design equations for packed-tower aeration use transfer coefficients to predict CO2 removal; field plants routinely deploy aeration before corrosion control, validating effectiveness. Why Other Options Are Wrong: Sedimentation removes settleable solids, not dissolved gases. Chlorination disinfects and oxidizes but does not strip CO2. Coagulation destabilizes colloids; it does not remove dissolved gases. Common Pitfalls: Confusing pH adjustment by chemical addition with gas stripping; both can raise pH but by different mechanisms. Under-designing aeration contact time or surface area, leading to incomplete CO2 removal. Final Answer: Aeration

Question 15

Why circular-section gravity aqueducts are generally not preferred:\r Identify the main practical reason a circular gravity aqueduct is avoided for open-channel conveyance on ground supports.

Accepted Answer

Introduction / Context: Section shape heavily influences both hydraulic performance and constructability of aqueducts and channels. While a circular section has attractive hydraulic properties for closed conduits under pressure, it is not the go-to shape for gravity aqueducts laid on ground or supported spans. Given Data / Assumptions: “Circular gravity aqueduct” here denotes a conduit intended to flow partly full by gravity, supported on ground or piers. Structural and construction considerations are as important as hydraulics. Alternatives include rectangular, trapezoidal, horseshoe, and elliptical sections. Concept / Approach: A circular cross-section lacks a flat bearing surface, complicating stable support and anchorage as an open channel on ground or trestles. For open-channel conditions, shapes with flat or gently curved inverts (e.g., horseshoe or rectangular) are easier to seat, line, and maintain. Although circles have favorable area-to-wetted-perimeter ratios when flowing full, they are not optimal when partially full and when structural seating dominates design. Step-by-Step Solution: Compare hydraulic versus structural needs for gravity (part-full) operation.Note circular invert provides poor bearing; cradle supports become complex and costly.Hence, difficulty of providing proper support is the practical reason for avoidance. Verification / Alternative check: Historic and modern aqueducts commonly adopt horseshoe or rectangular sections; where circular pipes are used, they usually operate pressurized or are encased with cradles and saddles, reflecting the support concern. Why Other Options Are Wrong: Hydraulic mean depth and wetted perimeter claims (A and B) favor circles when flowing full, not against them. Cost (C) depends on materials and supports; not inherently “always most expensive.” Statement (E) is too absolute; circular conduits can carry sediment-laden flows with proper velocities. Common Pitfalls: Assuming the best pressure-pipe shape is also best for open-channel conveyance. Ignoring maintenance access and seating when selecting section geometry. Final Answer: Difficulty in providing proper support on the ground (unstable bearing geometry)

Question 16

Hydrogeology terminology – what is an aquiclude? In groundwater engineering, identify the most accurate definition of an aquiclude from the choices below. Your answer should reflect standard usage in civil and environmental engineering.

Accepted Answer

Introduction / Context: An understanding of subsurface units—aquifers, aquitards, and aquicludes—is fundamental for groundwater exploration, well design, and pollution control. Mislabeling these units can lead to wrong inferences about yield and contaminant migration. Given Data / Assumptions: Standard hydrogeologic definitions are used. Flow through the geologic unit described as an aquiclude is negligible for engineering purposes. Adjacent water-bearing units are termed aquifers. Concept / Approach: An aquifer transmits water readily; an aquitard transmits water slowly; an aquiclude is effectively impermeable (transmission ~ zero) but may still contain water. Aquicludes commonly act as confining beds between two aquifers and control vertical leakage and artesian conditions. Step-by-Step Solution: Identify the keyword “aquiclude” → unit of very low permeability (nearly impervious).Relate to its position → typically lies between aquifers and acts as a confining bed.Select the option explicitly describing a confined, impervious bed between aquifers. Verification / Alternative check: Groundwater texts define aquiclude as a formation that can store water but does not transmit it appreciably; it serves as a confining layer creating artesian conditions in adjacent aquifers. Why Other Options Are Wrong: (a) and (b) describe aquifers (unconfined and confined) that do transmit water. (d) is vague and ignores permeability. (e) is incorrect because a precise definition is provided in (c). Common Pitfalls: Confusing aquiclude with aquitard; the latter transmits slowly but not negligibly. Also, assuming an aquiclude is dry—many are saturated but non-transmitting. Final Answer: A confined bed of essentially impervious material situated between aquifers

Question 17

Runoff and basin yield terminology – identify the incorrect statement Read each statement about runoff components and drainage-basin yield. Choose the single statement that is incorrect.

Accepted Answer

Introduction / Context: Hydrology uses precise terminology for components of streamflow and for how catchment performance is summarized. Examinations often test whether a learner can discriminate between correct and subtly incorrect definitions. Given Data / Assumptions: Standard surface-water hydrology definitions. Annual (or seasonal) runoff can be reported as volume or as depth over the basin. Base flow refers to the delayed groundwater contribution to streams. Concept / Approach: All four domain statements (a–d) align with accepted definitions. If each is correct, the only consistent choice for “incorrect statement” is “None of these,” meaning none of the listed statements are wrong. Step-by-Step Solution: Check (a): Surface runoff indeed denotes net flow reaching surface channels from precipitation excess.Check (b): Base flow is the sustained contribution from groundwater storage to streams.Check (c): Yield is frequently reported as an equivalent depth (cm or mm) over the basin.Check (d): Volume = Depth * Area is the standard conversion.Therefore, choose “None of these.” Verification / Alternative check: Hydrology manuals consistently define runoff depth and yield in this manner and convert to volume using basin area. Why Other Options Are Wrong: Picking any of (a)–(d) would contradict textbook definitions. Common Pitfalls: Confusing base flow with interflow; base flow is groundwater-fed and most persistent, whereas interflow is shallower subsurface flow with shorter response time. Final Answer: None of these

Question 18

Confined (artesian) aquifer pumping test – time–distance equivalence In an artesian aquifer, drawdown at r = 100 m equals the drawdown at r = 200 m after x hours. If the first equality occurs at t = 1 hour at 100 m, find x (hours) for the 200 m well…

Accepted Answer

Introduction / Context: Pumping-test interpretation in confined (artesian) aquifers often uses similarity via the Theis solution. Equal drawdown at two radii occurs when a particular nondimensional group is the same at the two observation wells. Given Data / Assumptions: Confined aquifer; constant-rate pumping. Drawdown s is compared at r1 = 100 m after t1 = 1 hour, and at r2 = 200 m after t2 = x hours. Same aquifer properties (transmissivity T and storage S) and same pumping rate Q. Concept / Approach: The Theis variable u = r^2 S / (4 T t). For equal drawdown, u must be equal. Hence r1^2 / t1 = r2^2 / t2 when S and T cancel. Therefore, t ∝ r^2. Step-by-Step Solution: Use similarity: r1^2 / t1 = r2^2 / t2.Rearrange: t2 = t1 * (r2^2 / r1^2).Substitute: t2 = 1 hour * (200^2 / 100^2) = 1 * (40000 / 10000) = 4 hours. Verification / Alternative check: Since t scales with r^2, doubling r requires four times the duration for the same drawdown; result matches 4 hours. Why Other Options Are Wrong: 2 hours underestimates; 9 and 16 hours overestimate given the r^2 proportionality. Common Pitfalls: Applying steady-state Thiem assumptions to early-time transient data; or forgetting that equality of drawdown requires the same u value, not the same r/t ratio. Final Answer: 4 hours

Question 19

Reciprocating pumps – choose the most appropriate limitation for water supply use Which single statement best describes a commonly cited limitation of reciprocating pumps for potable water service?

Accepted Answer

Introduction / Context: Reciprocating pumps are positive-displacement devices used for small to moderate discharges against high heads. In municipal practice, they are selected carefully because certain water qualities and operating conditions cause rapid wear or undesirable hydraulics. Given Data / Assumptions: Potable water duty, not viscous chemicals. Typical reciprocating pump with valves and plungers. Focus on the most general limitation relevant to raw/treated water conveyance. Concept / Approach: Suspended grit and sand abrade valves, seats, and cylinders of reciprocating pumps, increasing maintenance and reducing reliability. Therefore such pumps are avoided for sediment-laden flows unless special protection is provided. Cost ratios (e.g., 4×) are not fixed, and pulsation is inherent rather than “perfectly steady.” Suitability for variable head depends on controls and is not an absolute limitation. Step-by-Step Solution: Identify what most directly limits service → sensitivity to sediment and abrasives.Reject exaggerated or non-general claims (fixed cost multiples, “perfectly steady” flow).Select the statement about unsuitability for sediment-bearing water. Verification / Alternative check: Manufacturer manuals recommend adequate straining/clarification ahead of reciprocating pumps and note accelerated wear with solids. Why Other Options Are Wrong: (a) Not universally true; positive-displacement units can handle head variations with relief/bypass. (b) Cost factor is not a standard constant. (d) Opposite is true; flow is pulsating unless smoothed by air vessels. (e) Inapplicable because (c) is valid. Common Pitfalls: Ignoring the need for air vessels and surge control; using such pumps upstream of grit removal. Final Answer: They are not suitable for pumping water containing sediments

Question 20

Well hydraulics – definition used in many Indian texts In water-supply practice, the “specific yield of a well” is commonly taken to mean which of the following?

Accepted Answer

Introduction / Context: Two similarly named terms often cause confusion: “specific yield” in aquifer storage (a volumetric property) and “specific capacity/yield of a well” in well hydraulics. Many competitive-exam texts in water-supply engineering use the latter meaning for operational well performance. Given Data / Assumptions: Operational definition in water-supply design problems. Drawdown measured at the well under quasi-steady pumping. Concept / Approach: Specific capacity (sometimes called specific yield of a well) is defined as Q / s, where Q is discharge and s is drawdown at the well. It is used to compare wells and to extrapolate performance with different pumping rates. Step-by-Step Solution: Recognize context refers to well performance, not aquifer storage.Recall definition: specific capacity = discharge per unit drawdown.Choose the option that states “quantity of water per unit time per unit drawdown.” Verification / Alternative check: Field pumping tests routinely plot Q versus s; the slope near operating range gives specific capacity (units, e.g., L/s per m). Why Other Options Are Wrong: (a) and (c) are storage quantities, not rates per drawdown. (b) is discharge only; drawdown dependence is missing. (e) is incorrect because (d) is the accepted performance metric. Common Pitfalls: Confusing aquifer “specific yield” (storage parameter) with well “specific capacity.” Always check context. Final Answer: Quantity of water per unit time per unit drawdown at the well (discharge per unit drawdown)

Water Supply Engineering Questions