Question 1

Porosity, pellicular water, and yield – groundwater property definitions Choose the statements that correctly define porosity, pellicular water, specific yield, and the relationship between specific yield and specific retention in an unconfined aqui…

Accepted Answer

Introduction / Context: Key groundwater terms quantify how much water is stored and how much can be released. Understanding porosity, specific yield, and specific retention is essential for aquifer evaluation, well design, and groundwater balance studies. Given Data / Assumptions: Unconfined aquifer conditions for yield–retention relationships. Representative volume elements with uniform properties. Gravity drainage considered after full saturation. Concept / Approach: Porosity n = Vvoids / Vtotal.Specific yield Sy = Vdrained by gravity / Vtotal.Specific retention Sr = Vretained against gravity / Vtotal.For unconfined materials, Sy + Sr ≈ n*100% (as percentages). When expressed as percentages of total volume, it is common to say Sy% + Sr% ≈ 100% of the voided water portion for practical teaching; the key idea is that gravity-drainable water plus capillary-retained water partitions the pore space. Step-by-Step Solution: (a) Correct by definition: porosity quantifies the fraction of voids.(b) Correct: pellicular or capillary water clings to grain surfaces by adhesion/cohesion.(c) Correct: specific yield is the drainable portion under gravity.(d) Conceptually correct for unconfined pore water partitioning. Verification / Alternative check: Textbook tables show typical values: sands have higher Sy (20–30%) and lower Sr; clays have low Sy and high Sr due to strong capillarity, yet the sum reflects pore space allocation. Why Other Options Are Wrong: All listed statements are consistent with standard groundwater definitions; hence (e) is correct. Common Pitfalls: Confusing porosity with specific yield; total porosity overestimates the amount of water that can be practically extracted. Final Answer: All the above.

Question 2

Form factor – choose the correct formula The drainage-basin form factor is defined in terms of basin area and axial (maximum) length. Which expression is correct?

Accepted Answer

Introduction / Context: Basin shape indices help anticipate runoff timing. The form factor normalizes area by length scale to compare the “roundness” or elongation of catchments of different sizes. Given Data / Assumptions: Axial length is the maximum straight-line length of the basin. Area and length are measured at consistent map scale. No need for relief corrections for this planimetric index. Concept / Approach: The correct and widely used formula is: form factor Ff = A / L^2, where A is basin area and L is axial length. This yields a dimensionless number because the units cancel, enabling inter-basin comparison. Step-by-Step Solution: Identify required terms: A (area) and L (axial length).Apply the standard definition: Ff = A / L^2.Among the options, only (c) matches the formula. Verification / Alternative check: If two basins have the same A but one has twice the L, the longer one has one-quarter the form factor, reflecting a more elongated shape—exactly what Ff = A / L^2 captures. Why Other Options Are Wrong: (a) and (b) do not square the length, so they do not provide a dimensionless, scale-normalized measure. (d) and (e) include incorrect components and thus are not valid definitions. Common Pitfalls: Using average width or perimeter in place of axial length; different indices (e.g., circularity ratio) use different inputs—do not mix them. Final Answer: Area of the basin divided by the square of the axial length

Question 3

IMD non-recording (Symon’s) rain gauge – common standard specification Which of the following pairs correctly states the most commonly used IMD standard non-recording rain gauge specification (collector aperture and receiving bottle capacity)?

Accepted Answer

Introduction / Context: Standardization of rain gauges ensures inter-comparable measurements across a national network. In India, the Symon’s non-recording gauge is widely deployed with specific dimensions for the collector and receiving bottle. Given Data / Assumptions: Non-recording gauge (manual daily reading). IMD standard configuration commonly issued to stations. Standard measuring cylinder used for reading the collected volume as rainfall depth. Concept / Approach: The collector area determines the conversion from collected volume to rainfall depth (Depth = Volume / Area). A 200 sq. cm orifice paired with a 4 L bottle is the classic IMD non-recording specification, providing adequate storage for heavy rain events before observation time. Step-by-Step Solution: Identify IMD’s widely used non-recording gauge setup.Match the pair to options → 200 sq. cm collector with 4 L bottle. Verification / Alternative check: Hydrology manuals summarizing IMD practice specify a 200 cm² orifice with 4 L capacity as the standard reference for non-recording gauges. Why Other Options Are Wrong: (b) and (d) assign the smaller 100 cm² orifice to large bottle capacities not typical of the standard. (c) 10 L is larger than standard practice for the commonly issued Symon’s gauge. Common Pitfalls: Confusing non-recording Symon’s gauges with tipping-bucket or weighing gauges, which have different specifications and are used for intensity recording. Final Answer: 200 sq. cm collector and 4 litres bottle

Question 4

Cyclonic precipitation – where is air lifted to produce rain? In the context of cyclonic systems producing precipitation, from which portion of the cyclone is air lifted to generate rainfall most effectively?

Accepted Answer

Introduction / Context: Cyclonic precipitation occurs when large-scale convergence and frontal lifting cause air to ascend, cool, and condense. Recognizing where the strongest ascent is organized within a cyclone helps explain rainfall distribution and intensity patterns. Given Data / Assumptions: Mature, well-developed cyclone at mid-latitudes or a warm-core tropical cyclone. Frontal or eyewall/spiral-band structures organize ascent. Precipitation depends on vertical motion, moisture, and stability. Concept / Approach: In organized cyclonic systems, the strongest and most sustained updrafts occur near the central part of the system—near the low-pressure core in extratropical cyclones and in the eyewall/inner rainbands of tropical cyclones. While ascent occurs along fronts and spiral bands extending outward, the dominant, persistent lifting that drives heavy precipitation is centered near the system’s core. Step-by-Step Solution: Identify typical ascent zones: near the low center and along organized bands.Compare statements: “Outer only” is too restrictive; “entire surface uniformly” ignores organization.Thus, “primarily central portion” best characterizes the dominant lifting zone. Verification / Alternative check: Radar composites of cyclones show strongest reflectivity and sustained vertical velocities near the center or frontal wave, confirming the central dominance in precipitation production. Why Other Options Are Wrong: (a) Outer-only ascent understates core dynamics. (c) Ascent is not uniform; it is organized in bands/fronts with maxima near the center. (d) is invalid because (b) is correct. Common Pitfalls: Assuming convective cells in outer bands dominate totals; over long durations, central and frontal ascent typically contributes the bulk of rainfall. Final Answer: Primarily from the central portion of the cyclone

Question 5

Rain gauge exposure and siting – identify the correct statement Considering siting and exposure effects on rain-gauge catch, which of the following statements is correct for standard field practice?

Accepted Answer

Introduction / Context: Accurate rainfall measurement requires careful gauge siting to avoid wind-induced undercatch and obstruction. Exposure guidelines specify distance from obstacles and mounting height to minimize bias. Given Data / Assumptions: Standard non-recording or recording gauges installed in open terrain. Wind effects increase with height and exposure. Trees and buildings can shelter or obstruct, altering the catch. Concept / Approach: Wind speed increases with height above ground; raindrops are deflected by airflow over the gauge orifice, causing undercatch. Therefore, higher or overly exposed placement typically increases catch deficiency. Good practice places gauges near ground level on level pads, away from obstacles that subtend a small angle (often recommended not exceeding about 30°) at the gauge. Step-by-Step Solution: Evaluate (a): Greater exposure/height → more wind → more undercatch → correct.Evaluate (b): Heavier rain produces larger drops less affected by wind; catch generally improves, so (b) is incorrect.Evaluate (c): Recommended obstruction angle limits are typically stricter (≈ 30°), hence 45° is not standard; (c) is incorrect as stated.Evaluate (d): Forest canopies cause interception and turbulence; not ideal → incorrect. Verification / Alternative check: Exposure correction studies consistently show increased undercatch with height and wind; siting standards prescribe low, open, and level placements away from tall obstructions. Why Other Options Are Wrong: (b) contradicts empirical undercatch behavior with drop size and intensity. (c) uses an overly permissive angle, not aligned with common standards. (d) forests are poor sites due to interception and turbulence. (e) cannot be correct since several statements are false. Common Pitfalls: Mounting gauges on rooftops or hill crests; placing them too close to trees or walls; neglecting wind shielding where appropriate. Final Answer: The higher the gauge is installed (above ground or surroundings), the more deficient the rain catch tends to be due to wind effects.

Question 6

Pumping test (confined aquifer) – compute soil permeability from observed drawdowns In a constant-discharge pumping test, a discharge of 2.91 litres/s is maintained. Observation wells at r1 = 3 m and r2 = 6.184 m from the pumped well show steady dra…

Accepted Answer

Introduction / Context: Pumping tests allow estimation of aquifer properties by relating discharge, drawdown, and geometry. For confined aquifers under steady conditions, the Thiem equation connects discharge to transmissivity and observed heads (or drawdowns) at different radii. Given Data / Assumptions: Constant discharge Q = 2.91 L/s = 0.00291 m^3/s. Observation radii r1 = 3 m, r2 = 6.184 m. Drawdowns s1 = 2.6 m, s2 = 0.3 m. Confined aquifer of thickness b = 16 m; transmissivity T = k * b. Steady, horizontal, radial flow; Dupuit–Thiem assumptions apply. Concept / Approach: Thiem (confined) equation in natural log form: Q = 2 * π * k * b * (s1 - s2) / ln(r2 / r1). Solve for k and convert to cm/s. The larger drawdown near the well and the logarithmic radial term govern the estimate. Step-by-Step Solution: Compute ln(r2/r1) = ln(6.184 / 3) ≈ ln(2.0613) ≈ 0.724.Compute numerator factor: 2 * π * b * (s1 - s2) = 6.283 * 16 * (2.6 - 0.3) = 6.283 * 16 * 2.3 ≈ 231.2.Rearrange for k: k = Q * ln(r2/r1) / [2 * π * b * (s1 - s2)] = 0.00291 * 0.724 / 231.2 ≈ 9.1 × 10^-6 m/s.Convert to cm/s: 9.1 × 10^-6 m/s × 100 = 9.1 × 10^-4 cm/s ≈ 0.001 cm/s. Verification / Alternative check: Check order of magnitude: Typical sandy aquifers have k from 10^-4 to 10^-2 cm/s; the computed 10^-3 cm/s is plausible for fine sand/silty sand, validating the result. Why Other Options Are Wrong: 0.0005 cm/s and 0.002 cm/s bracket the computed value but do not match the calculation. 0.01 cm/s is an order of magnitude too high for the given drawdown behavior at small radii. Common Pitfalls: Using (s1/s2) instead of (s1 − s2) for confined Thiem, or forgetting to convert litres/s to m^3/s and m/s to cm/s. Final Answer: 0.001 cm/s

Question 7

Atmospheric thermodynamics: A fixed volume of air at constant barometric pressure can be brought to its dew point by which action?

Accepted Answer

Introduction / Context: Dew point is the temperature at which air becomes saturated with water vapor for a given pressure and moisture content. In hydrology and meteorology, understanding dew point helps in estimating condensation, fog formation, and precipitation potential. Given Data / Assumptions: Barometric (ambient) pressure is constant. The air parcel volume is considered, with fixed water vapor mixing ratio before cooling begins. No external moisture is added or removed during the temperature change. Concept / Approach: For a given pressure and actual water vapor content, saturation vapor pressure depends on temperature. Dew point is reached when the actual vapor pressure equals the saturation vapor pressure at the cooled temperature. Therefore, at constant pressure and humidity ratio, the only way to reach saturation is to lower temperature until saturation occurs. Step-by-Step Solution: At constant pressure, saturation vapor pressure e_s(T) decreases as temperature decreases.The actual vapor pressure e_a is fixed by the moisture present.Cooling the air until e_s(T_dew) = e_a yields the dew point temperature T_dew.Therefore, the correct action to achieve dew point is decreasing temperature. Verification / Alternative check: Psychrometric charts show that, for a fixed humidity ratio and pressure, horizontal movement to the left (cooling) reaches the saturation curve; this intersection temperature is the dew point. Why Other Options Are Wrong: Increasing temperature increases e_s(T), moving the state away from saturation.Options “neither” or “both” contradict the thermodynamic definition at constant pressure and constant moisture content. Common Pitfalls: Confusing relative humidity changes with absolute humidity; mixing constant-volume vs. constant-pressure processes; assuming addition of moisture—which is not permitted in this question. Final Answer: Decreasing the temperature.

Question 8

Levees and floodwalls in flood control: identify the incorrect statement (choose the single false option).

Accepted Answer

Introduction / Context: Levees and floodwalls are structural countermeasures built along rivers and coasts to prevent overtopping and inundation during high flows or surges. Sound design requires hydraulic, geotechnical, and structural considerations. Given Data / Assumptions: Levees/floodwalls resist hydrostatic and hydrodynamic loads during floods. Design should include safety margins for uncertainties (e.g., debris, waves, settlement). Freeboard is the height added above the design high water level to reduce risk of overtopping. Concept / Approach: Flood-protection structures must safely resist unbalanced lateral water loads. Adequate cross-sections and foundations are adopted to prevent sliding, overturning, piping, and excessive deformation. Freeboard allowances are standard to accommodate waves, wind setup, and forecasting errors. Step-by-Step Solution: Check option (a): Unbalanced water load across the riverward and landward sides is fundamental ⇒ true.Option (b): “Adequate dimensions” (crest width, side slopes, wall thickness) are essential ⇒ true.Option (c): They are indeed flood-control measures ⇒ true.Option (d): Claiming freeboard is never provided contradicts standard practice; freeboard is routinely included ⇒ false. Verification / Alternative check: Most design manuals specify freeboard above design water levels to cover uncertainties and wave run-up; many agencies mandate minimum freeboard values. Why Other Options Are Wrong: Options (a), (b), and (c) reflect accepted engineering practice; they are not incorrect. Common Pitfalls: Assuming crest height equals exactly the computed design level without adding freeboard; ignoring foundation seepage/piping risks while focusing only on wall geometry. Final Answer: They are never provided with freeboard allowances.

Question 9

Hydrograph essentials: select the correct statements about stream hydrographs and peak flow identification.

Accepted Answer

Introduction / Context: Hydrographs are foundational tools in hydrology used to describe how streamflow varies with time at a gauging station. They inform flood estimation, reservoir operation, and watershed management. Given Data / Assumptions: A fixed river cross-section where discharge is measured. Time series of discharge covering a storm event and baseflow recession. Storm variability in intensity, duration, and spatial pattern. Concept / Approach: A hydrograph plots discharge (vertical axis) against time (horizontal axis). It typically has a rising limb, a crest (peak), and a recession limb. The peak flow is the maximum discharge attained during the event and is influenced by rainfall and catchment characteristics. Step-by-Step Solution: Confirm definition: discharge vs time ⇒ hydrograph.Axes convention: time on X-axis, flow on Y-axis ⇒ standard practice.Peak flow definition: maximum event discharge ⇒ correct.Variability: differing storms and antecedent conditions produce different peak flows ⇒ correct. Verification / Alternative check: Comparison with hyetographs (rainfall intensity vs time) and mass curves (cumulative volume vs time) reinforces correct hydrograph interpretation. Why Other Options Are Wrong: Since all four statements are correct, any single choice would be incomplete. The comprehensive answer is “All the above.” Common Pitfalls: Confusing hydrographs with hyetographs; misidentifying the inflection points and timing of the peak relative to rainfall centroid. Final Answer: All the above.

Question 10

Soil–water terminology in irrigation hydrology: choose the correct statements about pellicular water, field capacity, and available moisture.

Accepted Answer

Introduction / Context: In irrigation and soil physics, precise terminology for water held in soils is essential for scheduling irrigation and estimating plant water availability. Terms such as pellicular water, field capacity, and available moisture describe how water is retained and used by crops. Given Data / Assumptions: Soil contains gravitational, capillary (pellicular), and hygroscopic water. Field capacity is the soil water content after free drainage stops (capillary retention dominant). Available moisture is the fraction plants can withdraw between field capacity and permanent wilting point. Concept / Approach: Pellicular water, often synonymous with capillary water films, adheres to soil particles due to molecular forces. Its mobility is influenced by surface tension and capillary potential. After gravitational water drains, the remaining water (largely pellicular) defines field capacity. Plants extract a portion of this until the wilting point is reached. Step-by-Step Solution: (a) Definition aligns with soil physics: thin films on grain surfaces ⇒ correct.(b) Surface tension/capillarity govern movement and retention ⇒ correct.(c) Field capacity correlates to retained capillary (pellicular) water after gravity drainage ⇒ correct in practical agronomic usage.(d) Available moisture refers to extractable water between field capacity and wilting point ⇒ correct. Verification / Alternative check: Soil water characteristic curves and capillary theory support these relationships; irrigation texts use these operational definitions for scheduling. Why Other Options Are Wrong: All listed statements are consistent within standard agronomic conventions; hence the inclusive choice is appropriate. Common Pitfalls: Equating field capacity with a fixed moisture percentage irrespective of soil texture; ignoring that “pellicular” and “capillary” are often used interchangeably in this context. Final Answer: All the above.

Question 11

Runoff components: In a catchment water budget, “runoff” commonly includes which contributions that eventually appear in the stream?

Accepted Answer

Introduction / Context: Runoff, as observed at a basin outlet, represents the portion of precipitation that ultimately becomes streamflow. It aggregates multiple pathways with different travel times and storages. Given Data / Assumptions: Precipitation is the basin input; not all of it becomes runoff due to abstractions. Direct surface runoff plus subsurface quickflow and groundwater baseflow combine at the outlet. Terminology can vary: some texts reserve “runoff” for the streamflow outcome, inclusive of its components. Concept / Approach: At the outlet, hydrograph discharge equals the sum of direct runoff and baseflow. From a water-budget perspective, runoff is the transformed portion of basin precipitation that exits as streamflow after losses (interception, infiltration, evapotranspiration) and storages are accounted. Step-by-Step Solution: Surface runoff (b) clearly contributes to streamflow.Groundwater flow (c) sustains baseflow and is part of the hydrograph.From a mass-balance viewpoint, runoff originates from precipitation (a); though not all rainfall becomes runoff, the streamflow ultimately derives from the precipitation over the catchment.Hence, the inclusive choice “All the above” is appropriate within a basin water-budget framing. Verification / Alternative check: Hydrograph separation decomposes total discharge into direct runoff and baseflow; long-term water balance links total runoff volume to precipitation minus losses. Why Other Options Are Wrong: Taking only one pathway underestimates total runoff; the outlet discharge is the composite of multiple flow components derived from precipitation. Common Pitfalls: Confusing the input (precipitation) with the output (runoff) without considering losses; misinterpreting definitions where some texts limit “runoff” to the streamflow result while others emphasize contributing components. Final Answer: All the above.

Question 12

Runoff versus surface runoff and stream discharge: pick the single best correct statement.

Accepted Answer

Introduction / Context: Hydrologic terminology distinguishes between pathway components and the total discharge at the outlet. Clarity is essential when interpreting models, data, and design criteria. Given Data / Assumptions: Surface runoff (overland flow) is one component of total runoff. Baseflow (groundwater contribution) is another component of total discharge. Some literature uses “runoff” as shorthand for stream discharge; precision matters. Concept / Approach: Runoff at the outlet equals the sum of various contributions, including surface runoff. Therefore, it certainly includes overland flow. However, equating “runoff” strictly with surface runoff is inaccurate, and calling surface runoff “streamflow” (which includes baseflow) is also imprecise. Step-by-Step Solution: Option (a) is incorrect: runoff is broader than surface runoff.Option (b) is correct: runoff includes surface runoff among other components.Option (c) can be contextually true, but it is ambiguous and not universally precise; usage varies.Option (d) is misleading: surface runoff is only the direct component, not the entire streamflow. Verification / Alternative check: Hydrograph separation confirms that streamflow = direct runoff + baseflow; thus surface runoff is a subset of total discharge. Why Other Options Are Wrong: (a) collapses categories; (c) is semantically variable; (d) incorrectly elevates a component to the total. Common Pitfalls: Using terms interchangeably in reports without definition; misinterpreting model outputs where “runoff” may mean event direct runoff only. Final Answer: Runoff includes the water flowing over the land surface.

Question 13

Aquifer tests: If pumping from two wells at equal distance produces equal drawdown responses in an unconfined aquifer and a confined aquifer, the total thickness H of the confined aquifer is given by

Accepted Answer

Introduction / Context: Interpreting pumping-test data often involves comparing water-table (unconfined) and confined aquifer responses. Equivalent drawdowns at equal radial distances can be used to relate saturated thickness and piezometric changes. Given Data / Assumptions: Two observation wells located at equal distances from their respective pumped wells. Measured effects (drawdowns) are equal for the unconfined and confined cases. Symbols h1 and h2 denote corresponding head or thickness measures as per the setup (water table decline and piezometric decline). Concept / Approach: For unconfined aquifers, transmissivity depends on saturated thickness (~ proportional to head). For confined aquifers, transmissivity is constant with thickness H. Equating comparable responses (with appropriate linearized assumptions) leads to the relationship that the confined aquifer thickness equals the sum of the two representative head terms, giving H = h1 + h2. Step-by-Step Solution: Establish equal drawdown response s at equal r for both aquifers.Relate transmissivity in unconfined case to saturated thickness terms (h1, h2).For the confined case, transmissivity involves constant H.Balancing the influences yields H = h1 + h2. Verification / Alternative check: Linearized Dupuit-type assumptions for unconfined flow produce additive head-thickness terms; matching to confined flow recovers the sum relation for equivalent response. Why Other Options Are Wrong: Differences (h2 − h1 or h1 − h2) do not reflect the physics of transmissivity equivalence; parentheses in option (d) do not change the expression but represent the same as (c). Common Pitfalls: Confusing piezometric head drop with saturated thickness; ignoring that transmissivity varies with head in unconfined aquifers. Final Answer: H = h2 + h1.

Question 14

Mechanisms of rainfall formation: Precipitation formed when moist air is forced to ascend a mountain or topographic barrier is called

Accepted Answer

Introduction / Context: Understanding rainfall mechanisms is vital for hydrologic design because storm type controls intensity, duration, and spatial distribution across catchments. Given Data / Assumptions: Air masses interact with topography, thermal instability, or frontal boundaries. Topographic lifting cools air adiabatically, possibly reaching saturation and condensation. Rainfall type is classified based on the dominant lifting mechanism. Concept / Approach: When moist air encounters a mountain range, it is forced upward along the windward slope, cools, and condenses to produce clouds and precipitation—termed orographic precipitation. Convective precipitation arises from buoyant instability, and cyclonic precipitation from frontal dynamics. Step-by-Step Solution: Identify mechanism: forced ascent by terrain ⇒ orographic lifting.Cooling to dew point causes condensation and rainfall on windward side.Leeward side may experience a rain shadow due to descending, warming air. Verification / Alternative check: Storm climatology in mountainous regions (e.g., Western Ghats, Himalayas) exhibits classic orographic enhancement. Why Other Options Are Wrong: Convective: generated by thermal buoyancy; Cyclonic: driven by fronts/pressure systems; “None of these” does not apply. Common Pitfalls: Confusing local convective storms that happen to occur near hills with true terrain-forced orographic rain. Final Answer: Orographic precipitation.

Question 15

Minor head losses in well piping: if h is the friction loss in the pipe, the combined losses in the strainer and bends may be taken approximately as

Accepted Answer

Introduction / Context: Design of well assemblies and pumping lines requires accounting for both major (friction) and minor (local) head losses. Strainers, screens, and bends contribute additional losses that must be included for accurate drawdown and pump sizing. Given Data / Assumptions: Major loss in the line is represented by h (Darcy–Weisbach or Hazen–Williams–based). Minor losses arise from entrance/exit, screens/strainers, elbows, tees, and fittings. Empirical practice suggests a fraction of h to cover these minor losses in preliminary estimates. Concept / Approach: While detailed design uses K-factors for each fitting (loss = K * V^2 / (2g)), preliminary groundwater design often approximates combined local losses as a percentage of the major loss. A typical allowance of about 20 percent of h is used for strainers and bends together. Step-by-Step Solution: Start with friction loss h computed for the pipeline length.Estimate combined local losses ≈ 0.2 * h for strainer and bends.Total dynamic head then becomes h + 0.2h = 1.2h (plus other components as applicable). Verification / Alternative check: Cross-check with individual K-values for the specific fittings; the sum often lies in the same order as 15–30% of the friction loss for typical well columns and discharge heads. Why Other Options Are Wrong: 0.01h is negligible; 0.45h, 0.25h, 0.30h are larger assumptions suited only to unusually loss-intensive layouts and are not standard quick estimates for screen plus a few bends. Common Pitfalls: Ignoring minor losses entirely; using a blanket percentage without checking unusually numerous fittings or small-diameter/high-velocity cases. Final Answer: 0.20 h.

Question 16

Regional flood estimation: Identify the correct Ryve’s empirical formula In catchment hydrology, Ryve’s formula is used for estimating peak flood discharge (in m^3/s, i.e., cumecs) from drainage area A (in km^2). Which expression correctly represent…

Accepted Answer

Introduction / Context: Empirical regional flood formulas relate peak discharge Q to catchment area A using a coefficient C that embeds climatic, topographic, and catchment-response effects. Ryve’s formula is one such Indian regional relation, historically applied in parts of southern India for preliminary peak flood estimates where stream-gauged data are scarce. Given Data / Assumptions: Q is in m^3/s (cumecs). A is in km^2. C is an empirical coefficient dependent on region/catchment characteristics. Intended for quick, reconnaissance-level estimation, not detailed design without checks. Concept / Approach: Regional flood formulas adopt power laws: Q = C * A^n. The exponent n reflects how catchment size scales with peak discharge. For Ryve’s formula, n is taken as 2/3, distinct from other Indian formulas such as Dickens (3/4) or Inglis (state-specific forms). Correctly recognizing n is essential to avoid systematic over- or underestimation across scales. Step-by-Step Solution: Recall Ryve’s functional form: Q = C * A^(2/3).Confirm dimensional consistency: empirical C adjusts for units and hydrologic regime.Contrast with Dickens: Q = C * A^(3/4) (different exponent and regional use). Verification / Alternative check: Typical hydrology handbooks list major Indian empirical relations and emphasize regional calibration; Ryve’s is consistently quoted with the 2/3 exponent for A (in km^2). Why Other Options Are Wrong: A^(3/4), A^(1/2), A^(1/4), A: These exponents correspond to other forms or unrealistic scaling; they do not represent Ryve’s formula. Common Pitfalls: Using Dickens’ exponent (3/4) in place of Ryve’s (2/3). Mixing units (e.g., converting A but not adjusting C). Final Answer: Q = C * A^(2/3).

Question 17

Critical-depth control meters: recommended throat length for reliable control For efficient operation of a critical-depth control meter (e.g., a long-throated flume), the throat length should be approximately how many times the critical depth to ens…

Accepted Answer

Introduction / Context: Critical-depth flow meters (long-throated or control flumes) establish a control section where flow passes at Froude number approximately 1, enabling discharge to be related to stage. The length of the throat is vital: it provides sufficient distance for flow to adjust and maintain near-critical conditions with minimal disturbance from approach and exit effects. Given Data / Assumptions: Open-channel, subcritical approach flow transitioning to control at the throat. Well-formed approach and smooth, prismatic control section. Critical depth dc is the characteristic depth at the control section. Concept / Approach: A sufficiently long throat relative to dc helps ensure: (1) a uniform velocity distribution at control; (2) diminished influence of local eddies; and (3) robust rating stability. Practical design guidance recommends a multiple of dc rather than a minimal equal length. Step-by-Step Solution: Define dc as the critical depth for the design discharge.Adopt a throat length around 3 * dc to secure a stable control section.Confirm that shorter lengths risk premature flow expansion/contraction, while very long throats increase cost and head loss without proportional benefit. Verification / Alternative check: Empirical and field experience in long-throated flume design supports the 3 * dc guideline as a balance between hydraulic stability and construction economy. Why Other Options Are Wrong: Equal to / 2 * dc: Often too short for stable control in field conditions. 4 * dc or 10 * dc: More conservative than necessary; adds cost/head loss without typical need. Common Pitfalls: Ignoring approach conditions and surface roughness, which can necessitate slightly longer throats. Assuming lab-calibrated minimums apply unchanged to field installations. Final Answer: Three times the critical depth.

Question 18

Definition check: Relative humidity Relative humidity (RH) is defined as the ratio of the actual vapor pressure to the saturation vapor pressure measured under which condition?

Accepted Answer

Introduction / Context: Relative humidity is a basic atmospheric moisture metric used in hydrology, meteorology, HVAC, and environmental engineering. It links the current moisture content to the maximum moisture air can hold at a given temperature, which controls evaporation, condensation, and human thermal comfort. Given Data / Assumptions: Actual vapor pressure e reflects the partial pressure of water vapor present. Saturation vapor pressure es is the maximum vapor pressure air can hold at the same temperature before condensation occurs. RH is usually expressed as a percentage. Concept / Approach: The saturation capacity of air varies strongly with temperature; therefore, RH must compare e and es at the same temperature. Pressure effects are secondary for most surface applications, and “same volume” or “entire atmosphere” are not part of the definition. Step-by-Step Solution: Define RH = (e / es) * 100% at the same temperature.Recognize that when air cools at constant water content, es drops and RH rises, reaching 100% at the dew point.Apply RH in evaporation estimates and comfort indices as a temperature-relative measure. Verification / Alternative check: Psychrometric charts and Clausius–Clapeyron relations emphasize the temperature dependence of es, corroborating the definition. Why Other Options Are Wrong: Same pressure only / same volume: Not the definitional condition for RH. Entire atmosphere / dew-point: Dew-point is where RH is 100%, not the reference condition for defining RH. Common Pitfalls: Confusing absolute humidity or specific humidity with RH. Assuming RH alone determines comfort without considering temperature and air movement. Final Answer: At the same temperature.

Question 19

Estimating evaporation from reservoirs: accepted methods Which of the following methods are used in practice to estimate reservoir evaporation rates for water balance and design?

Accepted Answer

Introduction / Context: Evaporation is a critical loss term in reservoir operation and design. Its assessment affects yield analysis, drought planning, and salinity management. Multiple complementary methods exist, each with different data needs and accuracy levels. Given Data / Assumptions: Site has meteorological records (temperature, humidity, wind, radiation) and storage measurements. Calibration from local pan coefficients or energy balance may be available. Concept / Approach: Pan method uses measured pan evaporation times a pan coefficient to approximate lake evaporation. Empirical formulae estimate evaporation from climate variables. Storage equation uses reservoir water-balance closure (inflows, outflows, storage change, rainfall) to back-calculate evaporation. Energy budget evaluates latent heat flux from the surface energy balance. Step-by-Step Solution: Identify available data and select method(s) accordingly.Apply pan measurements with locally derived coefficients for routine operations.Use storage equation checks to validate seasonal totals.Consider energy budget or combination methods for research-grade accuracy. Verification / Alternative check: Comparing monthly totals from pan-based estimates and storage equation often reveals biases, leading to adjusted coefficients. Why Other Options Are Wrong: Each of (a)–(d) is valid; choosing any single one omits accepted practice. Common Pitfalls: Using pan data without local calibration. Ignoring rainfall on the reservoir surface in storage equation calculations. Final Answer: All the above.

Question 20

Gaining vs losing streams and groundwater interaction Consider a channel–aquifer system. Identify the correct statements about effluent (gaining) and influent (losing) conditions and their relation to relative levels of the water table and stream st…

Accepted Answer

Introduction / Context: Surface water and groundwater are hydraulically connected in many basins. Whether a stream gains or loses water depends on the gradient between the stream stage and adjacent water table, which has major implications for baseflow, ecology, and contaminant transport. Given Data / Assumptions: Unconfined conditions near the stream bank. Hydraulic communication between streambed and aquifer (no impermeable barrier). Steady conceptual description (no transient bank storage considered). Concept / Approach: If the water table stands above stream stage, hydraulic gradient points toward the stream and the stream is effluent. If the stream stage exceeds the water table level, water infiltrates downward and the stream is influent. These relationships are standard hydrologic definitions. Step-by-Step Solution: Assess relative heads (stream stage vs water table).Water flows from higher head to lower head through the streambed sediments.Classify as effluent (gaining) when groundwater discharges to the stream; influent (losing) when stream water recharges aquifer. Verification / Alternative check: Hydrographs showing sustained baseflow in dry periods indicate effluent behavior; abrupt post-storm declines can imply losing reaches. Why Other Options Are Wrong: All statements (a)–(d) correctly reflect the standard definitions; choosing fewer than all is incomplete. Common Pitfalls: Confusing “effluent” with “influent” terminology. Ignoring spatial variability: different reaches can alternate between gaining and losing behavior. Final Answer: All the above.

Water Resources Engineering Questions