Question 1

Streamflow velocity measurement – best instrument for discharge gauging For measuring the point velocity profile in natural streams to compute discharge accurately, which instrument is considered the best standard practice?

Accepted Answer

Introduction / Context: Accurate discharge measurements in rivers and canals require reliable velocity observations at multiple depths and laterals. The choice of instrument affects measurement accuracy, repeatability, and suitability across a range of velocities and depths. Given Data / Assumptions: Wading or boat-mounted discharge measurements using standard mid-section or mean-section methods. Velocities typically range from slow to moderate (roughly 0.1 to 3 m/s). Field conditions may include suspended sediment and debris. Concept / Approach: Price’s current meter (cup or rotor type) is a well-established, calibrated instrument designed to measure point velocity at selected depths (e.g., 0.2 and 0.8 of depth) to estimate mean velocity. It is rugged, field-proven, and supported by rating procedures. In contrast, floats provide only surface or near-surface velocities and require empirical correction factors, while pitot tubes are sensitive to alignment and debris in natural channels. Step-by-Step Solution: Identify the instrument that measures point velocity reliably at depth → current meter.Among current meters, Price’s meter is the classic benchmark for stream gauging.Therefore choose option (b). Verification / Alternative check: Hydrometry standards recommend current meters (including electromagnetic/ADCP for advanced surveys). Historical datasets commonly rely on Price’s meters for rating curves. Why Other Options Are Wrong: (a) Pitot tubes are practical in clean pipelines or labs; field use in rivers is cumbersome. (c) Surface floats measure only surface velocity and require uncertain correction to mean velocity. (d) Sub-surface floats are less precise and harder to control than meters. Common Pitfalls: Relying on float methods for precise discharge studies; for robust hydrographs and rating development, point-velocity methods are preferred. Final Answer: Price’s current meter

Question 2

Time of overland flow – key controlling factors Which physical basin characteristics significantly influence the time of overland flow (the travel time of sheet runoff to channels)?

Accepted Answer

Introduction / Context: The time of overland flow is a key component of the basin time of concentration, shaping the peak and timing of hydrographs. Understanding its controls helps in urban drainage design, flood estimation, and stormwater management. Given Data / Assumptions: Overland flow is shallow sheet flow before water concentrates into rills and small channels. Uniform rainfall excess (infiltration already accounted for) is assumed during the effective storm period. Hydraulic roughness reflects land use/land cover and surface condition. Concept / Approach: Flow velocity in sheet flow is governed by hydraulic slope, roughness, and flow depth. Steeper slopes accelerate runoff, smoother/impervious surfaces increase velocity (reducing travel time), while longer path lengths increase travel time. Empirical relations (e.g., kinematic wave or NRCS methods) encode these dependencies. Step-by-Step Solution: Assess slope: greater slope → higher velocity → shorter time of overland flow.Assess ground type: impervious or smooth surfaces → less resistance → shorter time; vegetated/rough surfaces → longer time.Assess path length: longer surface path → greater travel time, all else equal.Therefore all listed factors are controlling variables. Verification / Alternative check: Design nomographs and formulas (e.g., kinematic wave time of concentration) include slope S, Manning’s n (roughness), and flow length L, confirming the multi-factor control. Why Other Options Are Wrong: (a), (b), or (c) alone provide only a partial picture. (e) contradicts established hydrologic practice. Common Pitfalls: Ignoring micro-relief and land use changes that alter roughness; redevelopment can drastically shorten overland flow time and increase peak discharge. Final Answer: All the above.

Question 3

Flood control embankments along rivers – terminology Earthen embankments constructed parallel to river banks at some distance, primarily for flood protection, are commonly called what?

Accepted Answer

Introduction / Context: Linear flood defences along rivers are used to contain high flows within the channel corridor and protect adjacent land. Understanding the terminology helps in interpreting design reports, environmental impact statements, and floodplain management plans. Given Data / Assumptions: Earthen embankments set back from the river channel. Primary purpose is to reduce floodplain inundation during high stages. No special reference to reinforced concrete walls or sheet-pile systems. Concept / Approach: In many regions, the terms “levee” and “dike” are used interchangeably to describe earthen embankments built for flood control. “Flood wall” typically refers to a rigid wall (often concrete) rather than an earth embankment. “River wall” is less standard and may refer to revetments or quay walls rather than flood retention structures. Step-by-Step Solution: Match description: earthen embankments parallel to rivers → levees/dikes.Select the combined correct terminology → option (e) Both (c) and (d). Verification / Alternative check: Technical literature and flood management agencies routinely use “levees/dikes” for earthen flood barriers, reserving “flood walls” for vertical, engineered wall systems. Why Other Options Are Wrong: (a) Flood walls are rigid walls, not earthen embankments. (b) River walls are bank protection/quays, not necessarily setback flood embankments. (c) or (d) individually are correct but incomplete since both names are accepted. Common Pitfalls: Assuming armoured revetments are levees; revetments protect banks from erosion but do not necessarily provide flood storage or conveyance control like levees/dikes. Final Answer: Both (c) and (d)

Question 4

Rainfall description parameters – what fully characterizes a storm at a location? Which set of parameters is used to describe rainfall at a point for design and analysis purposes?

Accepted Answer

Introduction / Context: Hydrologic design relies on characterizing rainfall using metrics that capture its severity and likelihood. Drainage sizing, detention storage, and flood risk assessments routinely reference intensity, duration, and frequency (IDF) relationships. Given Data / Assumptions: Point rainfall at a site, not areal averages. Design relies on historical IDF curves or intensity-duration-frequency equations. Stationarity over the fitting window is assumed for frequency analysis, unless nonstationary methods are used. Concept / Approach: Intensity describes the rate (e.g., mm/h), duration is the storm length over which intensity is averaged, and frequency quantifies the statistical rarity via return period (e.g., 2-year, 10-year, 100-year). Design storms are specified by pairing duration and return period to read a corresponding intensity from IDF curves. Step-by-Step Solution: Recognize that intensity depends on the averaging duration; they are inseparable in IDF analysis.Frequency encodes exceedance probability, linking design risk to infrastructure class.Therefore, a complete description includes intensity, duration, and frequency together. Verification / Alternative check: Municipal stormwater manuals specify design intensities for multiple durations at prescribed return periods, confirming the IDF triad as standard. Why Other Options Are Wrong: (a), (b), and (c) alone are incomplete descriptors. (e) is false because the combination in (d) is correct and widely used. Common Pitfalls: Using a single-duration intensity across all events; always match the critical duration to the watershed’s time of concentration for conservative design. Final Answer: All the above

Question 5

Open-channel hydrometry: A stream is 10 m deep. Using the two-point method, a current meter records velocities of 0.7 m/s at 2 m below the surface (0.2D) and 0.3 m/s at 8 m below the surface (0.8D). Compute the discharge per unit width (m^3/s per m).

Accepted Answer

Introduction / Context: In hydrometry, the velocity distribution over depth is often estimated with point-velocity measurements. The two-point method (at 0.2D and 0.8D, where D is depth) gives a reliable estimate of the mean velocity in verticals for open-channel flow measurements. Given Data / Assumptions: Total depth D = 10 m. Point velocities: V(0.2D) = 0.7 m/s at 2 m depth; V(0.8D) = 0.3 m/s at 8 m depth. Steady flow and typical velocity profile; negligible secondary currents for this estimation. Concept / Approach: The two-point method estimates the depth-averaged velocity V_avg in a vertical as the arithmetic mean of velocities at 0.2D and 0.8D. Discharge per unit width q is then the product of V_avg and depth D. Step-by-Step Solution: V_avg = (V_0.2D + V_0.8D) / 2 = (0.7 + 0.3) / 2 = 0.5 m/sq = V_avg * D = 0.5 * 10 = 5 m^3/s per metre width Verification / Alternative check: A single-point method (0.6D) typically yields a similar magnitude. Here, the symmetric values around the mean support the average of 0.5 m/s. Why Other Options Are Wrong: 2, 3, 4, and 6 m^3/s per m do not match the calculated q = 5 based on the standard two-point averaging technique. Common Pitfalls: Confusing depth positions (from surface vs. bed) or averaging the depths instead of velocities; forgetting to multiply the mean velocity by the full depth to obtain discharge per unit width. Final Answer: 5.

Question 6

Evaporation from open water surfaces: Which set of factors collectively governs evaporation losses from reservoirs, tanks, or lakes?

Accepted Answer

Introduction / Context: Evaporation is the phase change of liquid water to vapor from open water bodies. In hydrology and water resources engineering, accurately estimating evaporation is essential for reservoir operation, irrigation planning, and water-balance studies. Given Data / Assumptions: Climatic influences: temperature, humidity, wind speed, solar radiation. Surface characteristics: area and, indirectly, depth due to heat storage effects. Surroundings: vegetation and precipitation regime affect microclimate and advective transfers. Concept / Approach: Evaporation rate increases with higher temperature and wind speed and decreases with higher humidity. Larger surface areas provide more interface for vapor exchange; depth influences thermal inertia and daily evaporation patterns. Vegetation and precipitation modify boundary-layer conditions and energy balance. Step-by-Step Solution: Identify primary meteorological drivers: temperature, humidity, wind.Account for surface characteristics: area (directly) and depth (via heat storage and temperature profile).Consider environmental modifiers: precipitation regime and vegetative surroundings that can affect fetch, shading, and boundary-layer stability.Therefore, all listed factors contribute materially to evaporation losses. Verification / Alternative check: Formulations such as mass-transfer, energy-budget, or combination methods (e.g., Penman-type) explicitly include these variables through aerodynamic and energy components. Why Other Options Are Wrong: Any single subset (only area/depth, or only humidity/wind, etc.) is incomplete; evaporation is multi-factorial. Common Pitfalls: Assuming only temperature matters; ignoring the strong role of wind and humidity deficit or overlooking surface area effects. Final Answer: All the above.

Question 7

Definition check: In hydrometeorology, “precipitation” includes which of the following forms of water reaching the earth’s surface?

Accepted Answer

Introduction / Context: Precipitation is a key input to the hydrologic cycle, representing all water (liquid or solid) that falls from the atmosphere to the ground. Understanding its forms is fundamental for rainfall-runoff modeling and water resources estimation. Given Data / Assumptions: Common hydrometeor types: rain (liquid), snow (solid ice crystals), hail (larger pellets), sleet, drizzle, etc. All are counted in precipitation totals if they reach the ground. Concept / Approach: Standard meteorological definitions include both liquid and solid hydrometeors as precipitation. Instruments such as rain gauges or snow pillows convert or measure these inputs to water-equivalent depth. Step-by-Step Solution: List precipitation types: rain, snow, hail, among others.Recognize that each listed item is indeed a precipitation form.Conclude that the comprehensive choice is “All of these.” Verification / Alternative check: Meteorological references categorize these as precipitation; hydrologic data often use “precipitation” as a total, with breakdowns by type. Why Other Options Are Wrong: Choosing a single type omits other valid forms and under-defines precipitation. Common Pitfalls: Confusing cloud moisture or fog (suspended) with precipitation (reaching ground), or overlooking solid forms. Final Answer: All of these.

Question 8

Runoff generation concept: Surface runoff from a watershed primarily results from which portion of a storm hyetograph?

Accepted Answer

Introduction / Context: Surface runoff is the portion of rainfall that appears as overland flow and subsequently as streamflow, after satisfying initial losses such as interception, depression storage, and infiltration capacity. Identifying the effective part of rainfall that produces runoff is crucial for unit hydrograph and rainfall–runoff modeling. Given Data / Assumptions: Watershed initially has losses (interception, depression storage, infiltration to capacity). Only rainfall exceeding these losses within the supply interval becomes effective rainfall. Baseflow is considered separate from direct runoff. Concept / Approach: Effective rainfall (also called excess rainfall) equals gross rainfall minus initial abstraction and continuing infiltration (up to infiltration capacity). This effective portion during the net supply interval drives surface runoff and shapes the direct-runoff hydrograph. Step-by-Step Solution: Initial rain often satisfies interception and storage; it seldom contributes immediately to surface runoff.As storm intensity exceeds infiltration capacity and storage, the net (effective) rainfall begins.Thus, surface runoff is linked to rain in this net supply interval, not to initial or residual components that do not exceed losses. Verification / Alternative check: Abstraction models (e.g., phi-index, SCS-CN method) explicitly compute excess rainfall, which when convolved with unit hydrographs reproduces observed runoff. Why Other Options Are Wrong: Initial rain: commonly consumed by abstractions.Residual rain/baseflow: generally not the effective driver of direct runoff.“All the above”: overly broad; only the net supply interval creates overland flow. Common Pitfalls: Assuming any rainfall creates runoff; ignoring infiltration capacity and initial abstractions. Final Answer: Rain in the net supply interval (effective rainfall after initial losses).

Question 9

Hydrograph fundamentals: A hydrograph is a plot of which primary variable against time at a given stream section?

Accepted Answer

Introduction / Context: A hydrograph is one of the most important tools in surface-water hydrology. It provides a time history of stream discharge at a gauging station, capturing responses to rainfall, snowmelt, and upstream regulation. Given Data / Assumptions: Single stream cross-section (gauging station). Discharge Q(t) measured or estimated over time. Hydrograph features: rising limb, crest, recession limb, baseflow separation. Concept / Approach: By plotting Q on the vertical axis and time on the horizontal axis, engineers analyze flood peaks, lag times, runoff volumes, and recession constants for design and forecasting. Step-by-Step Solution: Identify variable of interest: discharge (flow rate).Associate with time at a fixed location.Hence, hydrograph = Q(t) at a station. Verification / Alternative check: Hyetograph is rainfall intensity vs time; mass curve is cumulative volume vs time. The hydrograph specifically represents discharge vs time. Why Other Options Are Wrong: Surface runoff (qualitative) and groundwater flow depth are not the standard hydrograph axes; rainfall intensity belongs to hyetographs. Common Pitfalls: Confusing hydrograph (Q–t) with hyetograph (i–t) and mass curves. Final Answer: Stream discharge (flow rate) versus time.

Question 10

Climatological design period: The rainfall cycle period commonly adopted for India (for hydrologic design and analysis) is taken as:

Accepted Answer

Introduction / Context: For regional hydrologic assessments, a representative climatic period is selected to smooth short-term variability while capturing multi-decadal oscillations. In India, a conventional “rainfall cycle period” has been used in various planning documents and texts. Given Data / Assumptions: Objective: choose a period long enough to capture interannual and decadal variability. Uniformity in statistics (mean, variance) over the period is desired for planning norms. Traditional practice informs the adopted cycle length. Concept / Approach: A cycle period on the order of several decades is favored to encompass monsoon variability modes. The widely cited value in Indian practice is 35 years, providing a balance between statistical stability and data availability. Step-by-Step Solution: Evaluate candidate periods 15–35 years.Adopt the conventional period used in Indian hydrologic design references.Select 35 years as the rainfall cycle period. Verification / Alternative check: Many regional analyses and academic references cite 35 years as a typical climatological cycle length for rainfall studies in India. Why Other Options Are Wrong: Shorter spans (15–30) may not sufficiently capture low-frequency monsoon variability and can bias design values. Common Pitfalls: Confusing design storm return period with climatic cycle length; these are different concepts. Final Answer: 35 years.

Question 11

Groundwater hydraulics: The basic equation used to determine the average velocity of groundwater flow (m/day) in a porous medium is known as:

Accepted Answer

Introduction / Context: Calculating groundwater flow through porous media under laminar conditions relies on a linear relationship between specific discharge and hydraulic gradient. This foundational relationship underlies aquifer tests and flow-net analyses. Given Data / Assumptions: Laminar flow through saturated porous media. Hydraulic conductivity K is constant over the path considered. Hydraulic gradient i is known (head drop per length). Concept / Approach: Darcy’s law states that the specific discharge q (also called Darcy velocity) equals K * i. The seepage (pore) velocity v is q / n_e, where n_e is effective porosity. For engineering estimates, velocity in m/day is commonly reported using these relations. Step-by-Step Solution: Use q = K * i (Darcy’s law).If pore velocity is needed: v = q / n_e.These give groundwater velocities in consistent units (e.g., m/day) given K and i (and n_e if required). Verification / Alternative check: Field tests (pumping tests) infer K; flow nets and slug tests also use Darcy’s relationship to interpret velocities and fluxes. Why Other Options Are Wrong: Meinzer/Slichter/Hazen are associated with empirical relationships for permeability or well hydraulics; Darcy’s formula is the fundamental velocity–gradient law. Common Pitfalls: Confusing specific discharge with pore velocity; neglecting porosity correction when estimating actual water particle speeds. Final Answer: Darcy’s formula.

Question 12

Meteorologically homogeneous stations: Which statement is correct regarding stations being “meteorologically homogeneous”?

Accepted Answer

Introduction / Context: “Meteorologically homogeneous” implies that stations have similar climatological behavior (e.g., co-varying rainfall patterns) due to comparable controlling factors, not merely identical mean values. Given Data / Assumptions: Homogeneity concerns similarity in distribution and temporal variability. Mean annual precipitation alone is not a sufficient criterion. Other influences: topography, prevailing winds, storm tracks. Concept / Approach: Two sites may have the same mean rainfall but very different variance, seasonality, or synoptic controls. Conversely, truly homogeneous stations can have different means yet show consistent proportional changes (e.g., similar anomalies during wet/dry years). Step-by-Step Solution: Evaluate statement (a): Homogeneous stations need not have exactly the same mean; homogeneity is broader than equality of averages ⇒ false.Evaluate statement (b): Equal means at two places do not imply similar variability or controls ⇒ false.Therefore, the correct choice is “Neither (a) nor (b).” Verification / Alternative check: Correlation analyses and regional frequency studies use statistical similarity (e.g., correlation coefficients, index-flood approach) rather than just mean equality to establish homogeneity. Why Other Options Are Wrong: (d) is wrong because both statements are not true; (e) elevation similarity is neither necessary nor sufficient by itself. Common Pitfalls: Equating “same mean” with “same climate,” or ignoring variability and synoptic regimes. Final Answer: Neither (a) nor (b).

Question 13

Irrigation control meter (canal structure) features: Identify the correct statements about a properly designed control meter used in canals.

Accepted Answer

Introduction / Context: Control meters (e.g., flumes, canal meters) regulate and measure discharge in irrigation canals. Their geometry is tailored to produce critical or supercritical conditions, enabling predictable stage–discharge relations and safe energy transitions. Given Data / Assumptions: Control meter has a converging approach, a throat, and a diverging (expanding) outlet. Subcritical to supercritical transitions may occur; hydraulic jump is harnessed downstream for energy dissipation. Stable bed and sidewalls (rectangular or trapezoidal) are used for constructability and hydraulics. Concept / Approach: A nearly level throat floor preserves critical depth and a stable control section. The expanding outlet requires a suitable slope to recover pressure and accommodate the jump at a designed location, preventing scour and ensuring accurate control. Step-by-Step Solution: (a) Canal sections commonly adopt rectangular/trapezoidal forms for the throat.(b) A level throat maintains a well-defined control depth.(c) A steeper slope in the expanding outlet helps manage transitions and velocities.(d) Properly designed, a hydraulic jump forms where energy must be dissipated. Verification / Alternative check: Standard designs (Parshall flume variants and similar meters) follow these principles to achieve stable rating curves. Why Other Options Are Wrong: Any single statement alone is incomplete; accurate control comes from the combined geometric and hydraulic features. Common Pitfalls: Ignoring energy dissipation needs; misplacing the hydraulic jump; providing adverse floor slopes in the control section. Final Answer: All the above.

Question 14

Field instruments: Rainfall simulators are primarily used to determine which hydrologic parameter in infiltration studies?

Accepted Answer

Introduction / Context: Rainfall simulators reproduce controlled rainfall intensities on test plots to study soil–water interactions. They are invaluable for infiltration, erosion, and runoff initiation research under reproducible conditions. Given Data / Assumptions: Adjustable rainfall intensity and drop size distribution. Known plot area, slope, and soil condition. Collection of runoff and measurement of infiltration. Concept / Approach: By applying known rainfall rates and measuring surface runoff onset and volume, the infiltration capacity (time-varying infiltration rate) can be derived as rainfall rate minus measured runoff rate, adjusted for storage. Step-by-Step Solution: Apply simulated rainfall of known intensity i(t).Measure runoff R(t) from the plot.Compute infiltration rate f(t) ≈ i(t) − R(t)/A, accounting for initial storage when necessary.In this way, infiltration capacity curves are obtained. Verification / Alternative check: Results often align with infiltration models (e.g., Horton-type f(t) curves) under similar soil conditions, validating simulator-based measurements. Why Other Options Are Wrong: Evaporation and precipitation totals are not directly measured with simulators; runoff is a by-product but the main target is to infer infiltration behavior. Common Pitfalls: Neglecting plot edge effects, splash losses, or nonuniformity of simulated rainfall, which can bias infiltration estimates. Final Answer: Infiltration capacity (infiltration rate).

Question 15

Unit hydrograph terminology and properties for rainfall–runoff analysis In hydrology, consider the standard unit hydrograph framework used for transforming effective rainfall of a specified duration into direct-runoff hydrographs. Identify the corre…

Accepted Answer

Introduction / Context: Unit hydrograph theory is a cornerstone of surface-water hydrology. It provides a linear, time-invariant method to relate a specified duration of effective rainfall (also called excess rainfall) to the basin’s direct runoff response. Understanding the associated terminology and properties ensures correct application in design floods, flood routing, and storm synthesis. Given Data / Assumptions: The unit hydrograph corresponds to a fixed unit duration (for example, 1 hour, 3 hours) and to a unit depth of effective rainfall (commonly 1 cm). The rainfall that results in the unit effective rainfall depth over that duration is referred to as a unit storm. Hydrologic system is assumed approximately linear and time-invariant for the period of analysis. Concept / Approach: Under the linear superposition principle, any complex effective rainfall hyetograph with the same duration increments can be decomposed into scaled and time-shifted unit storms. The resulting direct runoff hydrograph is the sum of scaled and lagged unit hydrographs. Because storms vary endlessly in space and time, many valid unit hydrographs (shapes) can be derived from different events, even for the same unit duration. Step-by-Step Solution: Recognize that the “unit duration” names the fixed time base of the unit hydrograph.Define “unit storm” as the event producing one unit depth of effective rainfall during that duration.State the reuse rule: a unit hydrograph of duration Δt can synthesize runoff from any storm built from Δt blocks.Acknowledge non-uniqueness: observational variability and derivation methods imply infinitely many feasible unit hydrographs for the same basin and duration. Verification / Alternative check: Classical hydrology texts derive multiple unit hydrographs from different storms for the same basin; each differs slightly yet remains applicable within the linear framework. Synthetic unit hydrographs (Snyder, SCS) further show the non-uniqueness. Why Other Options Are Wrong: Options (a), (b), (c), and (d) are all correct statements; selecting any single one would be incomplete. Common Pitfalls: Confusing gross rainfall with effective rainfall; unit hydrographs respond to effective rainfall only. Using a unit hydrograph of one duration to synthesize storms with a different duration without proper conversion. Final Answer: All the above.

Question 16

Unconfined aquifer pumping: ratio of discharges for two drawdowns A well fully penetrating an unconfined aquifer has initial saturated thickness 100 m. Under equilibrium (steady) Dupuit conditions and the same radius of influence, compute the ratio …

Accepted Answer

Introduction / Context: For unconfined aquifers, the steady pumping discharge from a fully penetrating well depends on the difference of squares of the piezometric head (measured above an impervious base) at two radii. This is a standard application of the Dupuit–Thiem equation and illustrates how discharge grows nonlinearly with drawdown because the saturated thickness reduces as the water table falls. Given Data / Assumptions: Unconfined aquifer with initial saturated thickness b = 100 m. Steady (equilibrium) flow; homogeneous, isotropic aquifer. Same radius of influence for both cases; well fully penetrating. Drawdowns at the well: s1 = 20 m, s2 = 40 m. Concept / Approach: Dupuit–Thiem for unconfined conditions gives (ignoring constants common to both cases): Q ∝ (H_R^2 − h_w^2), where H_R is head at the radius of influence (approximately the original water table height), and h_w is head at the well. With initial thickness b, take H_R = b. For a drawdown s, the head at the well is h_w = b − s, so the driving term becomes b^2 − (b − s)^2. Step-by-Step Solution: Let b = 100 m.For s1 = 20 m: Q1 ∝ b^2 − (b − s1)^2 = 100^2 − 80^2 = (100 − 80)(100 + 80) = 20 * 180 = 3600.For s2 = 40 m: Q2 ∝ 100^2 − 60^2 = (100 − 60)(100 + 60) = 40 * 160 = 6400.Hence the discharge ratio is Q1 / Q2 = 3600 / 6400 = 9 / 16. Verification / Alternative check: Using the equivalent expression b^2 − (b − s)^2 = 2 b s − s^2 yields 210020 − 20^2 = 3600 and 210040 − 40^2 = 6400, confirming the same ratio 9/16. Why Other Options Are Wrong: 3/4, 1/2, 4/9, 5/4: These ignore the squared-thickness dependence in unconfined flow; only 9/16 matches the correct difference-of-squares relationship. Common Pitfalls: Treating the problem as confined flow (where Q is proportional to drawdown, not to head-squared difference). Using b − s instead of b^2 − (b − s)^2 in the numerator of the discharge relation. Final Answer: 9/16.

Question 17

Aquifer terminology and common groundwater well types Select the correct set of statements about aquifers, aquicludes, artesian versus non-artesian conditions, and ordinary gravity (water-table) wells.

Accepted Answer

Introduction / Context: Groundwater terminology distinguishes between formations that transmit water and those that do not. Correct use of terms like aquifer, aquiclude, and water-table well is essential for hydrogeologic mapping, well design, and yield estimation. Given Data / Assumptions: Standard hydrogeologic definitions are used. Statements relate to common near-surface formations and typical well practice. Concept / Approach: An aquifer is a geologic formation that is both permeable and saturated enough to yield useful water. An aquiclude (or aquitard/aquifuge depending on degree) has very low permeability and confines an underlying aquifer. A non-artesian (unconfined) aquifer has a free water surface (water table). A water-table well draws from this unconfined zone and responds to seasonal fluctuations of the water table. Step-by-Step Solution: (a) Correct: An aquiclude is an impermeable or nearly impermeable layer that can overlie or underlie an aquifer and act as a confining bed.(b) Correct: A non-artesian aquifer has a free surface; it is the uppermost water-bearing layer open to atmospheric pressure.(c) Correct: Water-table (gravity) wells tap the unconfined aquifer directly.(d) Correct: Definition of an aquifer is a permeable formation yielding appreciable groundwater. Verification / Alternative check: Introductory groundwater texts (hydrogeology) define these terms consistently; field practice labels wells by whether they are confined (artesian) or unconfined (water-table). Why Other Options Are Wrong: Since (a)–(d) are all true, choosing only one is incomplete; therefore “All the above” is the only comprehensive selection. Common Pitfalls: Confusing aquiclude (essentially impermeable) with aquitard (low permeability but not zero). Assuming any top layer is non-artesian without confirming the presence of a free water surface. Final Answer: All the above.

Question 18

Measuring plant water use: What does the phytometer method determine? In hydrological investigations, the phytometer (potted-plant) method is typically used to measure which component of the hydrologic cycle?

Accepted Answer

Introduction / Context: Separating evaporation and transpiration is important for water balance studies, irrigation planning, and ecohydrology. The phytometer, which uses living plants in controlled containers, provides a direct way to quantify plant water use. Given Data / Assumptions: Plants are grown in pots (lysimeters or phytometers) with known soil and drainage conditions. Weight or volume changes reflect water consumption by plants, after accounting for precipitation and percolation. Environmental factors (radiation, humidity, wind) are recorded to interpret results. Concept / Approach: Transpiration is the flux of water vapor from plant stomata. In a phytometer, changes in mass (or water balance) over time indicate the water transpired by the plant. With proper controls (bare-soil pots), researchers may also separate soil evaporation to estimate evapotranspiration partitioning. Step-by-Step Solution: Set up potted plants with controlled soil volume and drainage measurement.Measure inflows (irrigation/precipitation) and outflows (drainage) during a period Δt.Calculate water loss from the pot. After subtracting soil evaporation (from control pots) the remainder represents transpiration by the plant. Verification / Alternative check: Comparisons with porometer or sap-flow techniques often align in trends, validating the phytometer as a classical method for transpiration quantification. Why Other Options Are Wrong: Interception: Measured with canopy collectors or throughfall gauges, not phytometers. Evaporation from open water: Determined by pan evaporimeters or energy balance over water bodies. Infiltration capacity: Estimated with infiltrometers or infiltration tests in soil. None of these: Incorrect because phytometers target plant transpiration. Common Pitfalls: Neglecting drainage or percolation losses, which biases transpiration estimates. Failing to use bare-soil control pots to separate soil evaporation from plant transpiration. Final Answer: Transpiration from vegetation.

Question 19

Effect of increasing grain size on aquifer properties and well yield When the representative grain size of a granular soil increases (with similar packing), how do surface area, specific retention, specific yield, and expected well yield change?

Accepted Answer

Introduction / Context: Grain-size characteristics strongly influence groundwater storage and transmission. Coarser soils like sands and gravels typically offer higher permeability and different storage components than fine-textured silts and clays. Understanding these trends helps in siting wells and predicting aquifer performance. Given Data / Assumptions: Grains are assumed mineralogically similar; only size changes. Packing and sorting are broadly comparable between the two soils. Hydraulic gradient and boundary conditions for yield comparison are similar. Concept / Approach: As grain size increases, the specific surface area per unit volume decreases, reducing adsorptive water held by capillarity. Consequently, specific retention (water retained against gravity) decreases, while specific yield (drainable water under gravity) increases. Larger pores in coarse media also raise hydraulic conductivity, which supports higher well discharge for a given drawdown. Step-by-Step Solution: Increase grain size ⇒ pore throats widen.Wider pores reduce capillary rise and adsorptive films ⇒ lower specific retention.Lower retention and better connectivity ⇒ higher specific yield.Higher conductivity (K) ⇒ larger transmissivity (T = K * saturated thickness) ⇒ greater well yield for similar conditions. Verification / Alternative check: Empirical relations (e.g., Hazen, Kozeny–Carman) show K increases with effective grain size and decreases with tortuosity and specific surface, consistent with the stated trends. Why Other Options Are Wrong: Options (a)–(d) each state a correct partial effect; omitting any would be incomplete. The comprehensive answer is therefore “All the above.” Common Pitfalls: Confusing porosity (which may not change dramatically with size) with permeability (which is highly size-dependent). Assuming clayey soils yield more water because of higher total water content; much of it is retained and not drainable. Final Answer: All the above.

Question 20

Scope of hydrology as a discipline Hydrology is best described as the science dealing with which category of water on and below the Earth’s surface?

Accepted Answer

Introduction / Context: Hydrology investigates the occurrence, distribution, movement, and quality of water throughout the hydrologic cycle. It encompasses meteorological inputs, surface processes, subsurface storage and flow, as well as interactions with landforms and ecosystems. Given Data / Assumptions: The term “hydrology” is used in the standard engineering sense (surface-water and groundwater hydrology). Oceanography is treated as a related but distinct discipline focusing on ocean waters. Concept / Approach: Hydrology spans precipitation, interception, infiltration, runoff generation, streamflow, lake and reservoir processes, vadose-zone flow, groundwater recharge, aquifer flow, and discharge to springs or streams. Floods and droughts are special regimes within this broad field, not the entirety of it. Step-by-Step Solution: Identify the core domain: water on the land surface (rivers, lakes, reservoirs) and below it (soil moisture, aquifers).Differentiate from oceanography which emphasizes marine systems.Conclude that the comprehensive option is surface and underground water. Verification / Alternative check: Standard engineering hydrology texts define the discipline as the study of water over and beneath the Earth’s surface, inclusive of rainfall-runoff transformation and groundwater mechanics. Why Other Options Are Wrong: Rain water only / river water only / flood water only: Each is a subset of hydrologic phenomena. Sea water only: Oceanography domain, not the primary scope of engineering hydrology. Common Pitfalls: Equating hydrology solely with streamflow measurement; groundwater and near-surface processes are equally essential. Final Answer: Surface water and underground (ground) water.

Water Resources Engineering Questions