Question 1

Power requirement for pumping: motor horsepower expression Let ω be the unit weight of water (N/m^3), Q the discharge (m^3/s), H the total head (m), and η the overall pump–motor efficiency (decimal). What is the required motor horsepower (HP)?

Accepted Answer

Introduction / Context: Determining pump power is central to water-supply and irrigation design. The hydraulic power equals the product of unit weight, discharge, and head. Accounting for efficiency and converting watts to horsepower yields the motor rating required for continuous operation at the design point. Given Data / Assumptions: ω in N/m^3, Q in m^3/s, H in m. η is the overall efficiency (pump + motor + transmission) expressed as a fraction (e.g., 0.7). 1 horsepower (mechanical) ≈ 746 W. Concept / Approach: Hydraulic power P_h = ω * Q * H in watts. The shaft power required is P_shaft = P_h / η. Converting to horsepower uses division by 746. Step-by-Step Solution: Compute P_h = ω * Q * H.Account for efficiency: P_shaft = (ω * Q * H) / η.Convert to HP: HP = P_shaft / 746 = (ω * Q * H) / (η * 746). Verification / Alternative check: Using example values (ω = 9810 N/m^3, Q = 0.05 m^3/s, H = 20 m, η = 0.7) gives HP ≈ (98100.0520)/(0.7*746) ≈ 18.8 HP, consistent with handbook estimates. Why Other Options Are Wrong: (ω * Q * H)/(η * 75): 75 is for metric horsepower (kgf·m/s); the problem defines ω in N/m^3 and requests HP, so 746 is appropriate. Multiplying by η: Would underestimate the motor size; efficiency losses must be divided out. Omitting η: Ignores real losses. Missing ω: Loses unit-weight term, not dimensionally correct. Common Pitfalls: Confusing N/m^3 with kgf/m^3; ensure consistent unit system. Using pump efficiency only and forgetting motor/drive losses. Final Answer: (ω * Q * H) / (η * 746).

Question 2

Vertical soil profile zones in the unsaturated–saturated column A representative soil profile is often described as comprising which of the following vertical zones (from top downward)?

Accepted Answer

Introduction / Context: Understanding vertical partitioning of the subsurface helps interpret infiltration, storage, and flow toward wells and streams. The unsaturated (vadose) zone, capillary fringe, and saturated zone each govern different hydrologic processes and engineering behaviors. Given Data / Assumptions: Soil profile under typical field conditions. Static description without storm transients or perched layers. Concept / Approach: The near-surface soil zone (root zone) experiences strong evapotranspiration and biological activity. Beneath it, the intermediate vadose zone drains toward the water table. Immediately above the water table lies the capillary fringe, where capillary rise maintains near-saturation. Below the water table is the groundwater zone (saturated), where effective stress, permeability, and storage define aquifer behavior. Step-by-Step Solution: Identify four conceptual layers: soil zone, intermediate vadose zone, capillary fringe, saturated groundwater.Relate each zone to dominant processes (root uptake, percolation, capillarity, saturated flow).Conclude that all listed zones are part of the full profile. Verification / Alternative check: Standard hydrology and soil physics texts present this canonical zonation; field logs and piezometer data corroborate the capillary fringe immediately above measured water tables. Why Other Options Are Wrong: Each individual zone represents only part of the profile; only “All the above” is comprehensive. Common Pitfalls: Overlooking perched water tables that can add localized saturated zones in the vadose profile. Assuming capillary fringe thickness is constant; it varies with grain size. Final Answer: All the above.

Question 3

Groundwater contouring terminology: isopiestic (isopiastic) lines In groundwater mapping, “isopiestic lines” on a plan refer to contours drawn to represent which hydraulic quantity?

Accepted Answer

Introduction / Context: Groundwater maps visualize spatial variations of hydraulic head. The term “isopiestic” (sometimes written “isopiastic”) refers to equal-pressure or equal-head lines. Correct interpretation is essential for inferring flow directions and gradients for well siting, dewatering, and contaminant control. Given Data / Assumptions: Confined conditions are common when using piezometric heads; unconfined cases use water-table contours. Heads are referenced to a common datum (e.g., mean sea level). Concept / Approach: On a plan map, a contour labeled with head values connects points of equal hydraulic head measured in observation wells. These contours are isopiestic lines and represent the projection of the piezometric surface onto the horizontal plane. Step-by-Step Solution: Measure water levels in piezometers/wells and convert to head (elevation + pressure head where applicable).Plot equal-head values to form isopiestic lines on plan view.Infer groundwater flow from high head to low head, perpendicular to isopiestic lines. Verification / Alternative check: Cross-sections reconstruct the 3D piezometric surface, while plan-view isopiestic lines provide 2D visualization consistent with measured heads. Why Other Options Are Wrong: Water-table elevation only: Correct for unconfined aquifers, but the term isopiestic typically emphasizes piezometric head (confined). Piezometric surface itself: That is a 3D surface; the map shows contours of that surface (isopiestic lines). Stream stage contours / None: Not the definition. Common Pitfalls: Mixing water-table (unconfined) and piezometric contours (confined). Using inconsistent datums across wells. Final Answer: Piezometric head (hydraulic head) values.

Question 4

Units of runoff measurement in hydrology When reporting stream runoff or basin outflow as a rate for hydrograph analysis and design, which unit is most commonly used in engineering practice?

Accepted Answer

Introduction / Context: Discharge, or runoff rate, is fundamental for hydrographs, flood routing, and structure sizing. The SI base rate used in most hydrologic and hydraulic design is cubic metres per second, often abbreviated as cumecs. Given Data / Assumptions: Standard SI engineering practice. Focus on discharge rates, not depth-runoff (mm over catchment). Concept / Approach: Discharge Q is volume per unit time. For rivers and design flows, m^3/s provides a consistent scale from baseflow to flood peaks and integrates easily with energy/power calculations. Step-by-Step Solution: Recognize that hydrographs plot Q vs. time; ordinates are most commonly m^3/s.Alternative units (L/s or m^3/min) may appear in water-supply contexts but are less standard for floods. Verification / Alternative check: Design manuals and flood-frequency analyses universally present discharges in m^3/s (or cfs in US customary units). Why Other Options Are Wrong: m^3: Volume, not rate. m^3/min, m^3/h: Usable but not the prevailing convention for hydrologic design hydrographs. L/s: Common for small-supply systems, not river basin flood work. Common Pitfalls: Mixing instantaneous peak with mean daily discharge units. Final Answer: Cubic metres per second (m^3/s).

Question 5

Regional applicability of Dickens’ flood formula Dickens’ empirical formula for high flood estimation is traditionally considered most applicable to catchments located in which broad region of India?

Accepted Answer

Introduction / Context: Historic Indian flood-estimation practice includes regional empirical relations such as Dickens, Ryve’s, and Inglis. Each was developed from data in particular geographic–climatic settings, and their coefficients are intended for those regions absent site-specific gauged records. Given Data / Assumptions: Dickens’ form: Q = C * A^(3/4), with C set from regional experience. Use at reconnaissance/preliminary design level, subject to later refinement. Concept / Approach: Textbook guidance associates Dickens’ formula primarily with Northern India, whereas Ryve’s is often cited for southern regions and Inglis for certain western/Deccan areas. Applying a formula outside its calibration region without recalibrating C risks bias. Step-by-Step Solution: Identify Dickens’ exponent 3/4 and northern provenance.Select Northern India as the most traditional region of applicability. Verification / Alternative check: Handbooks list Dickens for northern catchments; other formulas are flagged for the south/west, supporting the regional mapping. Why Other Options Are Wrong: Southern/Eastern/Western India: Typically linked to other empirical relations or require recalibrated coefficients. Islands: Distinct hydroclimates; Dickens is not specifically intended for them. Common Pitfalls: Using Dickens coefficients unmodified for small urbanized catchments or steep Western Ghats basins. Final Answer: Northern India.

Question 6

Infiltration index concept in hydrology The relation P − Q = φ * t_e is used to estimate the constant infiltration index (φ-index), where P is total storm rainfall depth, Q is direct-runoff depth, and t_e is the duration of rainfall excess. This equ…

Accepted Answer

Introduction / Context: The φ-index is a practical hydrologic tool used to convert a storm's total rainfall into rainfall excess by assuming a constant infiltration rate over the effective duration. This question asks who is credited with the widely used constant-infiltration approach summarized by P − Q = φ * t_e. Given Data / Assumptions: P = total storm rainfall depth. Q = direct runoff (rainfall excess) depth reaching the stream. t_e = duration during which rainfall intensity exceeds infiltration. φ = constant infiltration index to be back-calculated. Concept / Approach: The equation assumes a uniform, constant rate of infiltration during the effective period, allowing direct computation of φ from measured rainfall and runoff. The approach is rooted in early infiltration research and practical runoff separation methods. Step-by-Step Solution: Recognize P − Q as the depth lost to abstractions (primarily infiltration) during the effective period.Assume constant infiltration rate φ over time t_e.Relate them by P − Q = φ * t_e and solve φ = (P − Q) / t_e. Verification / Alternative check: If more detailed infiltration data are available, one may compare the constant φ approximation with Hortonian infiltration-capacity curves i_f(t) that decline exponentially; the φ-index then approximates the time-average of i_f over the effective period. Why Other Options Are Wrong: Horner and Lloyd are not associated with this constant-infiltration runoff separation. Bernard is associated with the distribution (mass) graph of runoff, not the φ-index. Common Pitfalls: Using P (gross rainfall) and Q (direct runoff) from mismatched durations; φ must be based on the effective period only. Also, confusing φ-index with W-index (which additionally accounts for initial losses). Final Answer: Horton

Question 7

Dew formation versus frost formation If the dew point of air is greater than 0°C (i.e., above the freezing point), which form of near-surface condensation will occur on exposed surfaces?

Accepted Answer

Introduction / Context: Dew and frost are products of condensation (or deposition) occurring when surfaces cool at night. Whether liquid droplets (dew) or ice crystals (frost) form depends on the dew point relative to 0°C and the surface temperature. Given Data / Assumptions: Dew point is the temperature at which air becomes saturated (100% relative humidity). Dew point here is specified as greater than 0°C. Exposed surface cools to near the dew point during nighttime radiative cooling. Concept / Approach: If the dew point is above 0°C and a surface cools to that temperature, condensation occurs as liquid water (dew). Frost forms only if the surface temperature is at or below 0°C and the frost point (the dew point below freezing) is reached, leading to direct deposition of ice. Step-by-Step Solution: Check dew point sign: dew point > 0°C implies saturation at a temperature above freezing.If the surface cools to the dew point, phase change is vapour → liquid (condensation), forming dew.No deposition of ice occurs unless temperatures drop to ≤ 0°C with a frost point reached. Verification / Alternative check: Meteorology texts state: when T_surface ≤ T_dew and T_dew > 0°C → dew; when T_surface ≤ 0°C and T_dew ≤ 0°C → frost by deposition. Why Other Options Are Wrong: Frost (b) requires subfreezing conditions and a frost point at or below 0°C. “Water vapour will be formed” (c) is backwards; vapour condenses instead of forming. “Neither” (d) is incorrect when saturation is reached at above-freezing dew point. Simultaneous dew and frost (e) needs mixed conditions not indicated here. Common Pitfalls: Confusing air temperature with dew point; the dew point alone does not guarantee dew unless the surface cools to it. Final Answer: Dew will be formed

Question 8

Rational method for peak discharge estimation Using the Rational formula, the peak discharge is given by Q = 0.278 * C * I * A in SI units, where A is the drainage area (km²), I is design rainfall intensity (mm/h), and C is runoff coefficient. If Po…

Accepted Answer

Introduction / Context: The Rational method estimates peak runoff from small urban catchments. In SI practice, Q (m³/s) = 0.278 * C * I * A, where I is in mm/h and A is in km². If a 1-hour design rainfall Po (mm) is used as I, the formula can be written with Po directly. Given Data / Assumptions: C = runoff coefficient (dimensionless), reflecting land use and slope. I (or Po) = design intensity for a duration at least equal to the time of concentration. A in km², Q in m³/s. Concept / Approach: The numerical factor 0.278 converts mm·km²/h to m³/s because 1 mm over 1 km² in 1 hour equals 1000 m³/h, which is 1000 / 3600 ≈ 0.2778 m³/s. Step-by-Step Solution: Start with Q = 0.278 * C * I * A.Let I = Po (mm/h) for the selected return period and duration of 1 h.Thus Q = 0.278 * C * Po * A (m³/s) when A is in km². Verification / Alternative check: Unit check: (mm/h) * (km²) * 0.278 → m³/s. If A were in hectares or I in cm/h, the factor would differ, hence the need for the 0.278 constant in SI-km²-mm/h form. Why Other Options Are Wrong: (b) omits the unit conversion factor; dimensions do not match m³/s. (c) uses 2.78, an order-of-magnitude error. (d) uses 0.028, also incorrect. (e) inverts C and Po; physically meaningless. Common Pitfalls: Using rainfall depth (mm) for durations different from the time of concentration, or mixing unit systems without adjusting the factor. Final Answer: Q = 0.278 * C * Po * A

Question 9

Interpreting a 5-year return period A storm of 20 cm depth has a recurrence interval (return period) of 5 years at a location. Which interpretation is correct?

Accepted Answer

Introduction / Context: Return period (recurrence interval) is a probabilistic measure used in hydrology to characterize how often a given magnitude event is expected to be equaled or exceeded. Given Data / Assumptions: Return period T = 5 years for a 20 cm storm depth. Events are modeled as independent from year to year for simple interpretation. Concept / Approach: The annual exceedance probability (AEP) is p = 1/T = 1/5 = 0.20 (20%) each year. The process is random; the interval between events varies. Multiple exceedances can occur in short spans, or none may occur over several years. Step-by-Step Solution: Compute AEP: p = 1/5 = 0.20 per year.State interpretation: “average once in 5 years,” not a schedule.Acknowledge randomness: occurrences can cluster or be absent over finite periods. Verification / Alternative check: The probability of at least one exceedance in 5 years is 1 − (1 − p)^5 = 1 − 0.8^5 ≈ 67.23%, not 100%. Why Other Options Are Wrong: (a) treats return period deterministically. (c) forbids clustering, which is possible. (d) imposes a fixed count over 10 years, also incorrect. (e) is unnecessary since (b) is the correct probabilistic framing. Common Pitfalls: Assuming a return period guarantees timing. Design should consider AEP and the chance of multiple events within a project life. Final Answer: The storm will occur about once every 5 years on average, with an annual exceedance probability of 20%

Question 10

Meteorological definition “Humidity” of air refers to which of the following physical properties?

Accepted Answer

Introduction / Context: Humidity is a fundamental atmospheric variable used in weather forecasting, comfort indices, and evaporation estimation. It characterizes how much water vapour is present in air. Given Data / Assumptions: No specific units are provided; humidity can be expressed as absolute humidity, specific humidity, or relative humidity. Concept / Approach: Humidity quantifies the water vapour content. Relative humidity, the most common measure, is the ratio of actual vapour pressure to saturation vapour pressure at the same temperature, expressed as a percentage. Step-by-Step Solution: Identify the property tied to water vapour: moisture content.Select option describing moisture content most directly (option c). Verification / Alternative check: Psychrometric relationships link humidity to wet-bulb/dry-bulb temperatures and dew point; these are all moisture-content indicators. Why Other Options Are Wrong: Temperature, pressure, and volume affect humidity but are not themselves humidity. Density alone does not define vapour content. Common Pitfalls: Confusing relative humidity with absolute moisture content or mixing temperature effects without distinguishing the definition. Final Answer: Moisture content of the air

Question 11

Mechanism of rainfall formation Precipitation that results from buoyant upward motion of warmer, lighter air parcels relative to surrounding air is called:

Accepted Answer

Introduction / Context: Understanding the mechanisms that produce precipitation helps engineers interpret storm intensities used in design. Principal mechanisms include convective, orographic, and cyclonic (frontal) lifting. Given Data / Assumptions: Air parcel is warmer and less dense than its surroundings. Upward motion is driven by positive buoyancy. Concept / Approach: Convective precipitation forms when surface heating creates unstable air that rises, cools adiabatically, and condenses. It is often intense and short-duration, typical of thunderstorms. Orographic precipitation arises from forced ascent over topography. Cyclonic precipitation is associated with fronts and large-scale ascent. Step-by-Step Solution: Identify clue: “warmer air rises due to buoyancy”.Link to mechanism: convective uplift leads to cloud formation and precipitation.Select option (b) as the correct classification. Verification / Alternative check: Convective storms typically show high intensities used for urban drainage design (short time of concentration). Why Other Options Are Wrong: (a) Cyclonic is frontal lifting, not buoyant thermals. (c) Orographic requires terrain-forced ascent. (d) Incorrect by elimination. (e) Not a standard term in this context. Common Pitfalls: Confusing convective showers with stratiform rain from fronts or upslope drizzle produced orographically. Final Answer: Convective precipitation

Question 12

Peak runoff rate from a design storm using a distribution graph An intense storm of uniform intensity 7.5 cm/h lasts 60 minutes over a basin of area 500 hectares. Average infiltration capacity during the storm is 1.5 cm/h. Using a 10-minute peak per…

Accepted Answer

Introduction / Context: Design peak discharge can be estimated from total direct-runoff volume combined with a dimensionless distribution graph (e.g., Bernard-type), which gives the percentage of total runoff occurring in the most intense block (here, the 10-minute peak). Given Data / Assumptions: Storm intensity i = 7.5 cm/h for 60 minutes. Average infiltration capacity f = 1.5 cm/h. Basin area A = 500 ha. 10-minute peak percentage = 16% of total runoff volume. Concept / Approach: Total direct runoff depth equals rainfall depth minus losses by infiltration during the same duration. The peak 10-minute discharge equals the fraction of total runoff volume assigned to the 10-minute peak, divided by 600 seconds. Step-by-Step Solution: Compute rainfall excess intensity: i_e = i − f = 7.5 − 1.5 = 6.0 cm/h.Storm duration = 1 h ⇒ runoff depth D_e = 6.0 cm = 0.06 m.Convert area: 500 ha = 5,000,000 m².Total runoff volume V = A * D_e = 5,000,000 * 0.06 = 300,000 m³.Peak 10-min volume = 0.16 * V = 0.16 * 300,000 = 48,000 m³.Peak discharge Q_p = 48,000 m³ / 600 s = 80 m³/s. Verification / Alternative check: Average discharge over the full hour is V / 3600 ≈ 83.3 m³/s. A 10-min peak at 80 m³/s is reasonable given the distribution shape and chosen peak percentage. Why Other Options Are Wrong: 40 and 60 m³/s underestimate the computed peak given the 16% allocation. 100 and 120 m³/s exceed the physically consistent result from the stated distribution percentage. Common Pitfalls: Mixing cm and m or hectares and km²; misapplying the peak percentage to intensity rather than to total runoff volume; using 10 minutes as 10 seconds by mistake. Final Answer: 80 cumecs

Question 13

Practical uses of water resources Which of the following are everyday or engineering uses for water in practice?

Accepted Answer

Introduction / Context: Water is a versatile resource in civil and mechanical engineering applications, from power generation and transport to thermal conditioning and industrial processes. Given Data / Assumptions: Standard physical properties of water (high specific heat, incompressibility at low pressures, density ~1000 kg/m³) are leveraged in these uses. Concept / Approach: Hydropower converts potential/kinetic energy of stored or flowing water into electricity. Navigation relies on buoyancy. Steam generation uses phase change to power engines/turbines. Thermal systems exploit water’s heat capacity for heating/cooling. Step-by-Step Solution: Relate each listed option to a known engineering application.Confirm that none of the options contradict physical principles or common practice.Select the comprehensive option that includes all valid uses. Verification / Alternative check: Engineering standards and historical practice (e.g., steam locomotives, district heating, hydropower dams) corroborate each use. Why Other Options Are Wrong: Options a–d are each individually true; therefore the best answer is “All of the above”. Common Pitfalls: Assuming modern electrification eliminated steam usage; it persists in power plants and industry. Final Answer: All of the above

Question 14

Definition of basin yield and runoff terms Pick the correct statement about “yield” of a drainage basin and how runoff is expressed.

Accepted Answer

Introduction / Context: Hydrologists distinguish between instantaneous discharge, event runoff, and long-term yield. Correct terminology prevents confusion in water-resources planning. Given Data / Assumptions: “Yield” refers to a long-term average or accumulated runoff from the basin. Runoff can be expressed as depth, volume, or discharge depending on context. Concept / Approach: Yield typically means the dependable or average quantity of water produced by a basin over a specified period (e.g., annual yield). Instantaneous measures (hydrograph ordinates) do not represent yield. Step-by-Step Solution: Identify “yield” as a long-term metric: option (b).Reject statements that fix units or time scales universally for runoff. Verification / Alternative check: Textbooks define yield as long-term runoff availability; project reports quote annual yield or firm yield based on storage–yield analysis. Why Other Options Are Wrong: (a) confuses yield with instantaneous discharge. (c) overly restricts yield to surface runoff only; baseflow contributes too. (d) imposes a single unit/time scale on runoff, which varies by application. Common Pitfalls: Using peak discharge to represent basin yield; they are different metrics for different design questions. Final Answer: Yield of a drainage basin is the runoff evaluated over long periods (e.g., annual or multi-year totals)

Question 15

Bernard’s distribution (mass) graph Bernard’s distribution graph is plotted with time on the X-axis and which quantity on the Y-axis for a given storm-runoff event?

Accepted Answer

Introduction / Context: Bernard’s distribution graph is a dimensionless way of representing how total surface runoff is distributed through time during a storm. It is useful for estimating peak discharge blocks. Given Data / Assumptions: Time is divided into equal intervals (e.g., 5 or 10 minutes). Each interval’s contribution is expressed as a percentage of the event’s total surface runoff volume. Concept / Approach: Unlike a cumulative mass curve, Bernard’s distribution graph presents the percentage per interval (non-cumulative) so designers can identify the fraction that occurs in the peak block (e.g., “10-minute peak percentage”). Step-by-Step Solution: Place time on the X-axis with uniform bins.For each bin, plot % of the total event runoff contributed in that bin on the Y-axis.Use the identified peak percentage with the total runoff volume to compute a peak block discharge. Verification / Alternative check: This interpretation is consistent with how “10-minute peak percentage” is used to derive peak-rate estimates from total volume. Why Other Options Are Wrong: (a) instantaneous discharge is a hydrograph, not Bernard’s distribution. (b) total volume is a single scalar, not a per-interval percentage. (c) cumulative percentage vs time is a mass curve, not Bernard’s distribution. Common Pitfalls: Confusing Bernard’s interval distribution with cumulative mass curves; ensure you use the correct graph for peak-rate calculations. Final Answer: Percentage of total surface runoff during uniform time intervals on the Y-axis

Question 16

Hydrology – Basin shape metric:\r If the axial length (basin length) of a drainage basin is 35 km and its form factor is 0.2, compute the total catchment area in square kilometres. Use the standard definition: form factor F = A / L^2.

Accepted Answer

Introduction / Context: Form factor is a widely used hydrologic shape index that relates a basin’s planform geometry to its hydrologic response. It helps infer flood peaks and runoff concentration time from simple geometric inputs (area and length). This question tests the ability to apply the basic relationship between form factor, basin length, and area. Given Data / Assumptions: Basin length L = 35 km (axial length along the principal flow path). Form factor F = 0.2 (dimensionless). Definition: F = A / L^2, where A is basin area (sq. km) and L is basin length (km). Concept / Approach: Form factor compresses shape information into a single number. For two basins of the same area, a larger F indicates a more circular shape and typically a flashier hydrograph. The computation is a direct substitution into the formula F = A / L^2, rearranged to A = F * L^2. Step-by-Step Solution: Write formula: F = A / L^2.Rearrange: A = F * L^2.Substitute values: A = 0.2 * (35)^2.Compute (35)^2 = 1225.So, A = 0.2 * 1225 = 245 sq. km. Verification / Alternative check: If F were 1.0 (a perfectly compact shape, hypothetical), A would equal L^2 = 1225 sq. km, which is much larger. Since the given F is 0.2, area must be a smaller fraction of 1225, namely 245 sq. km, confirming the calculation is consistent. Why Other Options Are Wrong: 205, 215, 225, 235 sq. km: Each results from using an incorrect factor or arithmetic error; only 245 sq. km satisfies A = 0.2 * 1225. Common Pitfalls: Confusing form factor with elongation ratio or circularity ratio. Using diameter instead of basin length, or mixing units. Forgetting the square on length in A = F * L^2, leading to large errors. Final Answer: 245 sq. km

Question 17

Open-channel measurement – Why prefer a control meter over a weir?\r Identify the most comprehensive reason a control meter is preferred to a weir in field channels, especially when streams are silt-laden and may carry debris.

Accepted Answer

Introduction / Context: In irrigation and drainage engineering, flow-measurement devices must work accurately under real field conditions. Control meters (critical-depth flumes and similar controls) are often preferred over sharp-crested weirs for silt-laden channels that also carry floating debris. This question checks understanding of practical selection criteria. Given Data / Assumptions: Silt-laden flow is common in earthen canals and field distributaries. Debris can accumulate on sharp crests and appurtenances of weirs. A control meter creates and maintains critical flow with a shaped control, not a thin sharp crest. Concept / Approach: Control meters are designed with gradually varied transitions that produce a stable head–discharge relationship under a range of approach conditions. They are less sensitive to floating debris and sediment accumulation than thin-plate weirs, which require clean crests and free nappe aeration for accurate calibration. Step-by-Step Reasoning: Silt issue: A control’s geometry promotes higher approach velocity at the throat, discouraging silt deposition, so measurements remain reliable.Debris issue: Control meters lack a delicate sharp crest; debris is less likely to affect calibration or damage the structure.Field robustness: The head–discharge relation of control meters remains dependable across varying field conditions. Verification / Alternative check: Design manuals specify that flumes (e.g., Parshall, cutthroat) are preferred where sediment and debris are present. They maintain accuracy without the strict crest and aeration requirements of sharp-crested weirs. Why Other Options Are Wrong: Each of (a), (b), and (c) is correct but partial; the comprehensive answer that encapsulates all benefits is (d) All of the above. (e) contradicts established field practice. Common Pitfalls: Selecting weirs for channels that cannot guarantee crest cleanliness or free-flow (submergence) limits. Ignoring sediment transport and maintenance realities in device selection. Final Answer: All of the above

Question 18

Uniform (prismatic) river section:\r A river reach is said to have a uniform section when its cross-section maintains a consistent geometrical shape along the reach. Which of the following standard shapes could represent such a uniform section?

Accepted Answer

Introduction / Context: In open-channel hydraulics, a prismatic (uniform) section means the cross-sectional shape and size remain constant along the flow direction. Natural rivers approximate a range of shapes; artificial channels are often designed as rectangular or trapezoidal. Recognizing that multiple shapes can be uniform clarifies the concept. Given Data / Assumptions: Uniform section = constant shape and dimensions along the reach. Possible shapes include circular segment, parabolic, rectangular, and trapezoidal geometries. Concept / Approach: Uniformity is independent of the specific shape; it relates to invariance along the reach. Any idealized shape can be considered uniform if repeated without change. Designers choose shapes for constructability, stability, and hydraulic efficiency (e.g., trapezoidal earth channels; rectangular lined channels). Step-by-Step Reasoning: Define uniform section: cross-section does not change with longitudinal distance.Evaluate options: each shape listed could be maintained consistently along a reach.Therefore, a, b, c, and d can all represent uniform sections. Verification / Alternative check: Textbook definitions of prismatic channels emphasize constant cross-section and slope; they do not restrict the geometry to one specific shape. Why Other Options Are Wrong: Options a–d are all valid instances of uniform sections; the only fully correct response is the inclusive choice (e). Common Pitfalls: Assuming only man-made shapes (rectangular/trapezoidal) can be uniform. Confusing uniform section with uniform flow (the latter refers to constant depth and velocity along the reach under equilibrium conditions). Final Answer: All of the above

Question 19

Scope of hydrology in civil engineering:\r For which of the following civil engineering applications is hydrologic knowledge fundamentally necessary?

Accepted Answer

Introduction / Context: Hydrology underpins the quantification of precipitation, runoff, infiltration, and streamflow. Civil engineers rely on it to design safe, economical, and resilient water structures. This question highlights the breadth of hydrology’s role in practice. Given Data / Assumptions: Irrigation projects require dependable flow estimates and storage planning. Bridges and culverts must pass design floods and avoid scour. Flood control works require frequency analysis and hydrograph routing. Concept / Approach: Across these applications, engineers must estimate design discharges (return periods), hydrographs, sediment transport tendencies, and backwater effects. Hydrologic and hydraulic models inform sizes, freeboards, and safety factors. Step-by-Step Reasoning: Irrigation: canal capacities and diversion structures rely on reliable flow statistics.Cross-drainage works: bridge waterway, afflux, and scour depend on flood estimates.Flood control: levees, reservoirs, and floodways require design storms and routing. Verification / Alternative check: Codes and manuals explicitly require hydrologic inputs (IDF curves, PMP/PMF where warranted) for these designs. Why Other Options Are Wrong: Since all listed applications need hydrology, the inclusive choice is correct; choosing any single option would omit key domains. Common Pitfalls: Treating hydrology and hydraulics as interchangeable; hydrology delivers boundary inputs for hydraulic design. Ignoring climate variability and land-use change impacts on design discharges. Final Answer: All of the above

Question 20

Atmospheric science – definitions:\r What is the correct name for the pressure exerted by fully saturated air (air at 100% relative humidity at a given temperature)?

Accepted Answer

Introduction / Context: Moist air properties are central to hydrometeorology and evaporation estimates. At a given temperature, there is a maximum pressure that water vapour can exert in equilibrium with liquid water; this concept is crucial for psychrometrics and mass-transfer evaporation formulas. Given Data / Assumptions: Air is saturated (relative humidity = 100%). We seek the standard term for the vapour’s equilibrium pressure at this state. Concept / Approach: When air is fully saturated, the water vapour’s partial pressure reaches its temperature-dependent maximum. This maximum is called saturation vapour pressure, often also referred to simply as saturation pressure (of water vapour) at that temperature. Step-by-Step Reasoning: Partial pressure refers to any constituent’s share of total pressure; for saturated air, the water vapour’s partial pressure equals its saturation value.Therefore the correct technical names in this saturated condition are “saturation vapour pressure” and “saturation pressure”. Verification / Alternative check: Psychrometric charts and Clausius–Clapeyron based tables list saturation vapour pressure versus temperature, confirming established terminology. Why Other Options Are Wrong: “Partial pressure” and “vapour pressure” are generic; they do not specifically emphasize the saturated condition. Only the paired terms explicitly denote the maximum at saturation. Common Pitfalls: Using “vapour pressure” generically when the context is specifically the saturated state. Confusing total atmospheric pressure with the vapour’s partial pressure. Final Answer: Both saturation vapour pressure and saturation pressure

Water Resources Engineering Questions