Q: River behaviour: Meandering of a river is most commonly associated with which stage of the river’s course?

Introduction / Context: Rivers evolve from steep youthful reaches to low-slope mature floodplains and finally deltaic or estuarine environments. Meanders arise where slopes are gentle and lateral erosion exceeds vertical incision. Given Data / Assumptions: Typical alluvial river on a low gradient floodplain. No rigid bedrock constraints (which would limit planform change). Concept / Approach: Meandering is driven by secondary currents and bank erosion on outer bends, with deposition on inner bends, forming point bars. This mechanism is most active in the mature (trough) stage where the river develops a wide floodplain and the energy is preferentially used for lateral migration rather than downcutting. Step-by-Step Solution: Identify river stage with low gradient and broad floodplain: mature stage.Recognize meander formation due to alternating helical flows and bank erodibility.Select the corresponding option: trough (mature/floodplain) stage. Verification / Alternative check: Geomorphology references consistently show meanders and oxbow lakes forming in mature/alluvial plains; youthful rocky gorges show straight, confined channels. Why Other Options Are Wrong: (a) Rocky youthful stage: dominated by vertical incision, not meandering. (b) Delta stage: distributary network and deposition at the mouth dominate planform. (c) Boulder stage: steep, coarse-bed torrents with limited lateral migration. Common Pitfalls: Assuming all lowland rivers are deltaic; mixing the concepts of braiding (high sediment load, wide shallow channels) with meandering. Final Answer: Trough (mature/floodplain) stage

Question 1

Irrigation agronomy: What is the typical design depth of the root zone for rice (paddy) considered in irrigation calculations?

Accepted Answer

Introduction / Context: Root zone depth is a key agronomic parameter used in irrigation design to estimate soil water storage, application depth, and scheduling. For paddy (rice), designers adopt a representative depth that captures most active roots and soil moisture extraction under field conditions. Given Data / Assumptions: Conventional flooded paddy with puddled soil and typical bunded fields. Design parameter is a representative root zone depth used for water balance and percolation estimates. Climatic and varietal variations exist, but standard handbook values are used for design. Concept / Approach: Although rice can have shallower effective roots due to puddling (often 20–30 cm active zone), irrigation design commonly uses 0.6 m (60 cm) as a conservative depth for storage/percolation accounting, especially for canal command planning and duty/delta calculations. Step-by-Step Solution: Identify the standard design practice → adopt 60 cm for paddy root zone in irrigation computations.Select the matching option → 60 cm. Verification / Alternative check: Standard agronomy/irrigation tables list design root zone depths for crops; rice is typically taken as ~0.6 m for canal design and seasonal water requirement estimation, aligning with field experience and conservative storage assumptions. Why Other Options Are Wrong: 50 cm: Sometimes used locally, but 60 cm is the widely adopted design value. 70–90 cm: Exceeds typical effective rooting depth for puddled rice and would overstate storage/percolation. Common Pitfalls: Confusing agronomic active root depth with design storage depth; projects use standardized values for consistency. Ignoring soil type and puddling effects which limit deep rooting. Final Answer: 60 cm

Question 2

Venturi head flume geometry checks: Which of the following statements about side-wall splay and width recovery is incorrect?

Accepted Answer

Introduction / Context: A venturi head flume (venturi regulator) uses a contracted throat to create a measurable head–discharge relation. The geometry of the contraction and expansion transitions is critical to avoid separation, undue head loss, and poor rating stability. Given Data / Assumptions: Standard practice uses gentle divergence after the throat (e.g., ~1:10 initially) and a shorter, steeper recovery (e.g., ~1:3) near the end. Intermediate recovery often targets ~2/3 of the distributary bed width before the final widening. Smooth transitions are assumed to keep flow attached. Concept / Approach: The sequence—initial mild splay, intermediate width recovery, and final steeper splay—is a widely cited guideline for distributary head regulators/venturi flumes. Each listed statement in options (a) through (c) aligns with this guidance; therefore there is no incorrect statement among them. Step-by-Step Solution: Review each assertion against standard layouts: 1:10 initial splay over ~4.5 m → acceptable.Width recovery to ~2/3 of bed width before steeper splay → acceptable staging.Final splay ~1:3 to regain full width smoothly → acceptable.Conclusion: All are correct; hence the “incorrect” choice is “None of these”. Verification / Alternative check: Field drawings and manuals show gradual expansion followed by a shorter final flare; the exact distances may vary with discharge, but the pattern remains similar. Why Other Options Are Wrong: Option (e) suggests parallel walls after the throat without splay changes; that would prolong contraction effects and increase losses—contrary to best practice. It is not among the options to choose as incorrect under the given set since (d) is the called-out answer. Common Pitfalls: Using too steep an initial divergence which induces separation and distorts the rating curve. Ignoring downstream tailwater effects on submergence during calibration. Final Answer: None of these.

Question 3

Naming the cross-drainage work: A canal is carried below a natural drainage such that the canal’s full supply level (FSL) does not touch the underside of the supporting structure. What is this structure called?

Accepted Answer

Introduction / Context: Cross-drainage works (CDWs) are categorized by the relative positions of the canal water surface and the drainage water surface. Correct naming is crucial because it implies different hydraulic design assumptions (open channel versus pressure flow). Given Data / Assumptions: The canal passes below a natural drainage course. The canal’s FSL does not touch the soffit (underside) of the crossing structure; thus the canal remains an open channel within the structure. Pressure-flow in the canal barrel is not intended here. Concept / Approach: When the drainage is carried over the canal, the arrangement is a super passage. The canal remains open-channel flow, with clearance to the soffit. In contrast, an inverted syphon/syphon-aqueduct indicates pressure flow in the canal conduit beneath the drainage (FSL effectively pressed against the soffit). An aqueduct carries a canal over a drainage. Step-by-Step Solution: Identify which stream is on top → drainage over canal.Check canal regime inside structure → free surface, not touching soffit → open-channel.Therefore, the correct name is “Super passage”. Verification / Alternative check: Standard CDW selection charts confirm: drainage over canal with open channel in canal = super passage; drainage over canal with canal in pressure flow = syphon-aqueduct. Why Other Options Are Wrong: Aqueduct: Canal over drainage (opposite). Syphon / Syphon-aqueduct: Canal under drainage in pressure flow, which contradicts “FSL does not touch soffit”. Level crossing: Rare arrangements where both flows interact; not applicable. Common Pitfalls: Mislabeling any canal-below arrangement as “syphon” without checking whether pressure flow is intended. Final Answer: Super passage

Question 4

Seepage safety by Khosla’s theory: What is the critical exit gradient for stability against piping under a hydraulic structure?

Accepted Answer

Introduction / Context: Hydraulic structures on permeable foundations are designed to avoid piping and heave at the downstream exit. Khosla’s theory of independent variables provides a framework to estimate exit gradients and plan under-seepage control (aprons, cutoffs, filters). Given Data / Assumptions: Typical sandy foundations with conventional gradation. Critical gradient is the threshold beyond which upward seepage forces mobilize soil particles, initiating piping. Conservative handbook value used for preliminary design checks. Concept / Approach: The critical gradient ic is commonly taken around 0.5 for design safety in sands, representing the ratio at which effective stresses at the exit are sufficiently reduced to risk particle movement. While a more exact ic may be determined from submerged unit weights and gradation, 0.5 is widely adopted as a safe benchmark. Step-by-Step Solution: Compute/estimate exit gradient from pressure drops and floor lengths using Khosla’s charts.Compare calculated exit gradient with ic ≈ 0.5.Ensure factor of safety by lengthening impervious floors, adding cutoffs/filters if needed. Verification / Alternative check: Design guides stipulate that exit gradient ≤ (critical gradient / adopted factor of safety). Using ic ≈ 0.5 provides a clear pass/fail criterion. Why Other Options Are Wrong: 0 or 1: Non-physical extremes for typical soils in this context. 0.25 or 0.75: Do not represent the standard conservative design value for ic in sands. Common Pitfalls: Ignoring local grading or filter criteria at the exit, even when global gradient checks pass. Final Answer: 0.50

Question 5

Sarda fall discharge formula: For a trapezoidal crest operating under free over-fall, which discharge expression is appropriate (symbols: L crest length, H head over crest, B canal bed width, g gravity)?

Accepted Answer

Introduction / Context: Sarda type falls are canal falls designed to measure and dissipate energy while passing discharge. The empirical rating for their crests (rectangular or trapezoidal) modifies the standard sharp-crested weir relation Q ∝ L * H^(3/2) with a width-ratio correction to account for approach conditions. Given Data / Assumptions: Free over-fall (modular flow) with negligible submergence. Trapezoidal crest used on distributaries as per standard layouts. Correction term involves the relative head H to bed width B. Concept / Approach: The base weir equation Q = C * L * H^(3/2) is adapted with C ≈ 0.45 * sqrt(2g) for Sarda fall geometry and an additional factor (H/B)^(1/6) that captures approach contraction effects. Thus the formula becomes Q = 0.45 * sqrt(2g) * L * H^(3/2) * (H/B)^(1/6). Step-by-Step Solution: Start with weir-type discharge: Q ∝ L * H^(3/2).Apply Sarda empirical coefficient: C ≈ 0.45 * sqrt(2g).Include approach correction: multiply by (H/B)^(1/6).Select the matching option → the expression with H^(3/2) and exponent 1/6 on H/B. Verification / Alternative check: Comparisons with standard rating tables for Sarda falls confirm the 1/6 exponent trend for trapezoidal crests under free fall conditions. Why Other Options Are Wrong: Different exponents on H or (H/B) distort the empirical calibration. Expressions with H^(2/3), H^(1/6), or inverted ratios do not match established Sarda ratings. Common Pitfalls: Using the rectangular crest coefficient for trapezoidal crests without correction. Applying the formula under submergence without submergence corrections. Final Answer: 0.45 * sqrt(2g) * L * H^(3/2) * (H/B)^(1/6)

Question 6

Effects of waterlogging on agriculture: Why is land that has become water-logged generally unsuitable for cultivation?

Accepted Answer

Introduction / Context: Waterlogging is a condition in which the water table rises into or near the root zone, saturating the soil. It is widely recognized as harmful to most crops due to oxygen deficiency and related soil chemistry issues. The question probes misconceptions about its supposed benefits. Given Data / Assumptions: Typical field crops (non-paddy) requiring aerated root zones. Waterlogged condition means prolonged saturation near/within the root zone. No special salt-tolerant or hydrophytic crops are assumed. Concept / Approach: Healthy root respiration needs oxygen; saturated pores restrict aeration leading to root rot, reduced microbial activity beneficial for nutrients, and possible salt accumulation. Tillage becomes difficult (puddling), and germination suffers in poorly aerated, saturated soils. Step-by-Step Solution: Assess statements: (a) “ease of tillage/optimum germination” → false under waterlogging; soils are difficult to work.(b) “absence of aeration” → harmful effect, not a reason why waterlogging is suitable.(c) “regular capillary supply” → while capillarity exists, persistent saturation harms crops; not a suitability reason.Therefore, none of the statements justify suitability. Verification / Alternative check: Agronomic guidelines recommend drainage schemes (surface/subsurface), bio-drainage, and canal operation changes to prevent/treat waterlogging, underscoring its unsuitability for general cultivation. Why Other Options Are Wrong: Options (a) and (c) mischaracterize benefits; (b) describes a harm, not a benefit; (e) is irrelevant. Common Pitfalls: Assuming rice paddy logic (favouring standing water) applies to all crops—most crops require aerated soils. Final Answer: None of these.

Question 7

Sarda type fall—rectangular crest applicability: Up to what discharge is a rectangular crest commonly used before switching to a trapezoidal crest?

Accepted Answer

Introduction / Context: Sarda falls use standardized crest shapes to pass and measure discharge in distributaries/minors. At higher discharges, a trapezoidal crest is preferred to limit afflux, maintain modularity, and ease passage of floating debris with acceptable velocities. Given Data / Assumptions: Free over-fall conditions (modular flow) expected. Rectangular crest ratings calibrated up to a practical upper limit. Beyond that limit, a trapezoidal crest offers better hydraulic performance. Concept / Approach: Practice indicates rectangular crests are adopted for relatively small discharges; for larger flows, trapezoidal crests provide improved capacity with manageable heads and velocities. The commonly cited threshold is around 14 m³/s (14 cumecs) for switching crest type in Sarda layouts. Step-by-Step Solution: Identify typical threshold from design manuals → ~14 cumecs.Hence, for discharges up to 14 cumecs, rectangular crest is acceptable; beyond, adopt trapezoidal crest. Verification / Alternative check: Field practice and standard tables align with 14 cumecs as a practical demarcation, though local standards may fine-tune based on approach conditions and headroom. Why Other Options Are Wrong: 6 or 10 cumecs: Too restrictive; rectangular crests function well above these flows. 20 or 25 cumecs: Typically high for rectangular crest without excessive head/afflux. Common Pitfalls: Using a rectangular crest at high discharges causing submergence or excessive velocities. Final Answer: 14 cumecs

Question 8

Hydraulic jump in a rectangular channel: If q is the discharge per unit width and D1 and D2 are the pre-jump and post-jump water depths respectively, which relationship between q, D1, and D2 holds true for momentum balance across the jump?

Accepted Answer

Introduction / Context: Hydraulic jumps are rapid transitions from supercritical to subcritical flow that commonly occur in spillways, canal transitions, and energy dissipators. In open-channel hydraulics (civil engineering), their analysis relies on conservation of momentum in a control volume spanning the jump. This question tests recognition of the standard momentum relationship linking discharge per unit width q with upstream and downstream depths D1 and D2 for a rectangular channel. Given Data / Assumptions: Channel is prismatic and rectangular; width b is taken as 1 m so q = Q / b. Flow is steady and incompressible, with hydrostatic pressure distribution outside the roller. Energy losses in the roller are allowed; momentum (force) balance holds across the jump. Concept / Approach: The momentum function for a rectangular channel per unit width is M = q^2 / (g * y) + y^2 / 2. Equating M upstream (y = D1) and downstream (y = D2) yields the standard sequent-depth relation in momentum form, from which the required identity for q, D1, and D2 is obtained. Step-by-Step Solution: Upstream momentum: M1 = q^2 / (g * D1) + D1^2 / 2Downstream momentum: M2 = q^2 / (g * D2) + D2^2 / 2Set M1 = M2 → q^2/g * (1/D1 - 1/D2) = (D2^2 - D1^2)/2Left factor: (1/D1 - 1/D2) = (D2 - D1)/(D1 * D2)Right factor: (D2^2 - D1^2) = (D2 - D1)(D2 + D1)Cancel (D2 - D1) on both sides → q^2 / g * 1/(D1 * D2) = (D2 + D1)/2Rearrange → q^2 / g = (D1 * D2 * (D1 + D2)) / 2 Verification / Alternative check: Dimensional check: q has units m^2/s; q^2/g has m^3. The right-hand side D1D2(D1+D2)/2 also has m^3. The relation is therefore dimensionally consistent. Why Other Options Are Wrong: Option B: Inverts the momentum relation; does not match momentum dimensions. Option C: Uses depth difference squared; momentum balance does not produce (D2 - D1)^2 alone. Option D: Sums squared depths; missing the multiplicative D1*D2 term from momentum derivation. Option E: Harmonic-like form; again misses the (D1 + D2) multiplier in the numerator. Common Pitfalls: Confusing energy conservation with momentum conservation; energy is not conserved across a jump due to losses. Forgetting that the momentum function for rectangular channels includes both velocity and hydrostatic terms. Using discharge Q instead of unit discharge q without dividing by width. Final Answer: q^2 / g = (D1 * D2 * (D1 + D2)) / 2

Question 9

Cross-drainage works in canals: The structure provided to carry drainage water under a canal by pressure flow through an inverted siphon is termed as which of the following?

Accepted Answer

Introduction / Context: When canals intersect natural drains or streams, cross-drainage works are used to pass one over or under the other. The nomenclature depends on which watercourse goes over/under and whether the flow is open-channel or under pressure. Given Data / Assumptions: Drainage water passes below the canal via an inverted siphon (pressure flow). Canal maintains its level over the crossing. Concept / Approach: If the drainage passes under the canal with pressure flow (through an inverted siphon barrel), the structure is called a syphon aqueduct. If the drainage passed under the canal in free-surface flow, it would be a super passage. If the canal passed over the drainage (canal in a trough) with free-surface flow, it would be an aqueduct or super-aqueduct depending on relative bed levels. Step-by-Step Solution: Identify which stream is above (canal) and which is below (drainage).Check the flow regime below (pressure flow via inverted siphon).Select the correct term: syphon aqueduct. Verification / Alternative check: Hydraulic design manuals clearly define these four types with schematic sections showing water levels and conduit type. Why Other Options Are Wrong: Syphon: generic; not specific to canal–drain crossing. Super passage: drainage passes freely under the canal without pressure flow. Aqueduct / super-aqueduct: canal over drainage with canal in open-channel flow. Common Pitfalls: Confusing which stream is on top; ignoring whether the lower flow is pressurized or free surface. Final Answer: Syphon aqueduct

Question 10

Hydraulic jump formation criterion: Under what interaction of flow regimes is a hydraulic jump generally produced in an open channel?

Accepted Answer

Introduction / Context: A hydraulic jump is a rapid transition from supercritical (shallow, fast) to subcritical (deeper, slower) flow, accompanied by energy dissipation and turbulence. It is essential in spillway stilling basins, chute transitions, and energy dissipation devices. Given Data / Assumptions: Open channel flow; Froude number Fr > 1 indicates supercritical, Fr < 1 indicates subcritical. Jump occurs when downstream conditions force a change from supercritical to subcritical. Concept / Approach: When a supercritical stream encounters a control that imposes higher depth (e.g., backwater, gate, basin), the flow transitions to subcritical via a jump. The momentum function is conserved across the jump, while there is a loss in specific energy. Step-by-Step Solution: Identify upstream regime: supercritical (Fr > 1).Identify downstream regime: subcritical (Fr < 1).Recognize that the jump connects the conjugate depths of these two regimes.Hence select option (c). Verification / Alternative check: Hydraulics texts derive the conjugate depth relation using momentum principles, confirming the regime change from Fr > 1 to Fr < 1 through the jump. Why Other Options Are Wrong: (a) Critical-to-supercritical interface is not the canonical jump case. (b) Supercritical meeting supercritical does not force the abrupt depth rise. (d) Wording implies reverse propagation rather than the local regime change; the key is supercritical-to-subcritical transition. Common Pitfalls: Confusing jumps with bores or standing waves; forgetting that energy is not conserved across the jump while momentum (with hydrostatic pressure assumption) is. Final Answer: A supercritical (hyper-critical) stream meets a subcritical stream

Question 11

River behaviour: Meandering of a river is most commonly associated with which stage of the river’s course?

Accepted Answer

Introduction / Context: Rivers evolve from steep youthful reaches to low-slope mature floodplains and finally deltaic or estuarine environments. Meanders arise where slopes are gentle and lateral erosion exceeds vertical incision. Given Data / Assumptions: Typical alluvial river on a low gradient floodplain. No rigid bedrock constraints (which would limit planform change). Concept / Approach: Meandering is driven by secondary currents and bank erosion on outer bends, with deposition on inner bends, forming point bars. This mechanism is most active in the mature (trough) stage where the river develops a wide floodplain and the energy is preferentially used for lateral migration rather than downcutting. Step-by-Step Solution: Identify river stage with low gradient and broad floodplain: mature stage.Recognize meander formation due to alternating helical flows and bank erodibility.Select the corresponding option: trough (mature/floodplain) stage. Verification / Alternative check: Geomorphology references consistently show meanders and oxbow lakes forming in mature/alluvial plains; youthful rocky gorges show straight, confined channels. Why Other Options Are Wrong: (a) Rocky youthful stage: dominated by vertical incision, not meandering. (b) Delta stage: distributary network and deposition at the mouth dominate planform. (c) Boulder stage: steep, coarse-bed torrents with limited lateral migration. Common Pitfalls: Assuming all lowland rivers are deltaic; mixing the concepts of braiding (high sediment load, wide shallow channels) with meandering. Final Answer: Trough (mature/floodplain) stage

Question 12

Regime channels in irrigation engineering: Under what combined conditions will a channel naturally attain regime (stable) conditions without silting or scouring?

Accepted Answer

Introduction / Context: Regime channels are those which, over time, adjust their section, slope, and hydraulic radius so that the sediment they carry neither deposits (siltation) nor erodes (scour). This concept is central to alluvial channel design in irrigation engineering, notably in Lacey’s theory and regime approaches. Given Data / Assumptions: An alluvial channel carrying sediment in suspension. Bed and banks formed of incoherent (loose) alluvium. Exam-style conceptual conditions driving a stable (regime) state. Concept / Approach: For a regime to exist, the hydraulic and sediment-transport environment must be steady, allowing the channel to self-form to an equilibrium geometry. This requires: (1) constant discharge, (2) sediment characteristics (silt grade and silt charge) remaining constant, and (3) bed/bank material of the same general nature as the transported sediment so that the channel can reshape itself compatibly. Step-by-Step Solution: Identify key regime prerequisites: steady hydraulics and steady sediment supply.Confirm the bed/bank material is incoherent alluvium similar to the load.When these hold together for sufficient duration, the channel evolves to a geometry that is neither silting nor scouring, i.e., regime. Verification / Alternative check: Regime equations (e.g., Lacey) implicitly assume such steady conditions. If any of these drivers change materially, the channel re-adjusts, indicating non-regime behavior until a new equilibrium is reached. Why Other Options Are Wrong: Discharge alone constant: Not sufficient without stable silt properties and compatible bed/bank material.Uniform flow in incoherent alluvium alone: Still needs steady discharge and sediment properties.Constant silt grade/charge alone: Insufficient if discharge fluctuates significantly. Common Pitfalls: Confusing “regime” with “uniform flow” in rigid channels; regime is an alluvial-channel concept. Ignoring the sediment side (grade and charge) when considering stability. Final Answer: All the above

Question 13

Silting of irrigation channels: What is the principal (main) cause leading to silting up of a channel in the field?

Accepted Answer

Introduction / Context: Silting up of canals reduces discharge capacity and increases maintenance costs. Identifying the primary cause helps in rehabilitation and proper design of slopes and section dimensions for alluvial channels. Given Data / Assumptions: An irrigation channel conveying sediment-laden flow. Multiple potential causes of silt deposition are listed. We seek the principal cause in practice-oriented terms. Concept / Approach: Deposition occurs when sediment-carrying capacity reduces. The most direct hydraulic driver of reduced transport capacity is insufficient velocity, which is often due to an inadequate bed slope. A slope that is too mild lowers velocity and shear, encouraging deposition along the bed and at transitions. Step-by-Step Solution: Sediment transport capacity ∝ flow velocity and shear stress.If slope is too mild, velocity falls below the threshold required to keep the sediment in suspension/bedload.Silt settles out, causing progressive silting of the channel. Verification / Alternative check: Even with good regulators and outlets, a persistently mild slope sustains low velocities and favors deposition. Conversely, correcting the slope (or increasing fall/bed drop) rapidly improves transport capacity, often reversing siltation trends after desilting. Why Other Options Are Wrong: Non-regime section: Contributes but is a broader long-term state; the immediate hydraulic driver is slope/velocity.Defective head regulator/outlets: These create local issues, but not typically the primary, system-wide cause. Common Pitfalls: Attributing chronic silting solely to regulator settings while ignoring inadequate bed gradient. Overlooking the role of seasonal discharge variability when diagnosing slope issues. Final Answer: Inadequate bed slope (too mild a gradient)

Question 14

Kor watering (first irrigation): For a rice crop, what is the optimum depth of kor watering (first watering) to establish the crop effectively?

Accepted Answer

Introduction / Context: Kor watering is the crucial first irrigation applied soon after sowing or transplanting to ensure proper crop establishment. For paddy (rice), adequate initial depth helps puddled-field conditions, seedling anchorage, and early weed suppression. Given Data / Assumptions: Crop: Rice (paddy). We seek a standard, exam-oriented value for kor watering depth. Field practices assume puddled conditions and typical soils used for rice. Concept / Approach: Rice is water-intensive initially; too small a depth risks poor establishment and weed competition, while too large a depth may cause seedling stress. Empirical guidelines used in irrigation scheduling curricula recommend a kor depth close to 19 cm for rice in many North Indian practices. Step-by-Step Solution: Consider crop water needs during establishment.Adopt standard kor depth values commonly used in exam problems and design tables.Select 19.0 cm as the optimum for rice. Verification / Alternative check: Field-specific adjustments may be made based on soil texture, rainfall, and transplanting method, but the 19 cm benchmark remains a widely accepted value for objective questions. Why Other Options Are Wrong: 23.0 cm: Excessive; can stress young plants and waste water.17.5, 13.5, 12.0 cm: Insufficient for typical puddled rice establishment in standardized guidance. Common Pitfalls: Confusing kor depth for rice with that for wheat or other cereals. Ignoring local soil percolation rates while applying standard values. Final Answer: 19.0 cm

Question 15

Bligh’s creep theory for seepage under hydraulic structures: Which fundamental assumption does Bligh’s theory make about head loss along the percolation path (creep line)?

Accepted Answer

Introduction / Context: Bligh’s creep theory is an early empirical method to estimate seepage and uplift under weirs and barrages founded on pervious soils. It models the seepage path along the contact between the structure and subsoil as a “creep line”. Given Data / Assumptions: Structure on pervious foundation with upstream and downstream cutoffs/floors. We seek the central assumption about how head loss distributes. Concept / Approach: Bligh assumed the total head loss is proportional to the total length of the creep path, regardless of whether the path length is horizontal or vertical. Hence, horizontal and vertical segments are treated with equal weight in calculating creep length. Step-by-Step Solution: Define total creep length = sum of all horizontal and vertical contact lengths.Assume head loss distributes uniformly per unit creep length.Therefore, horizontal and vertical components contribute equally per unit length. Verification / Alternative check: Later theories (Lane’s weighted creep theory) adjusted this by giving different weights to vertical and horizontal creeps, recognizing limitations of Bligh’s equal-weight assumption. Why Other Options Are Wrong: More or less weight to horizontal creep: These characterize Lane’s approach, not Bligh’s.Sine-curve head loss: Not a Bligh assumption; it is not a sinusoidal distribution model. Common Pitfalls: Mixing Bligh’s and Lane’s theories. Applying Bligh’s equal-weight rule to problems specifically asking for Lane’s weighting. Final Answer: Horizontal and vertical creep lengths are given equal weight (equal importance)

Question 16

Kor watering for wheat in North Indian plains: What is the optimum depth of the first (kor) irrigation for a wheat crop under typical North Indian field conditions?

Accepted Answer

Introduction / Context: Kor watering is the initial irrigation essential for crop establishment. For wheat in North Indian plains, a standard kor depth is used in design and exam problems to guide water allocation during the critical early stage of growth. Given Data / Assumptions: Crop: Wheat. Region: North Indian plains. We require a commonly used benchmark depth for objective questions. Concept / Approach: Wheat needs sufficient moisture to ensure germination and early root development, but it is not as water-intensive as rice at establishment. A kor depth around 13.5 cm is widely cited in standard irrigation scheduling problems for the region. Step-by-Step Solution: Recognize wheat’s moderate initial water need.Adopt standard tabulated kor depth for the region’s exam practice.Select 13.5 cm. Verification / Alternative check: While on-farm adjustments may occur due to soil texture and rainfall, the benchmark 13.5 cm remains a canonical value for planning and test questions. Why Other Options Are Wrong: 23.0, 19.0 cm: High for wheat at kor stage; more suited to paddy-like conditions.17.5, 12.0 cm: Not the best-fit standardized value; 12.0 cm is often slightly low. Common Pitfalls: Using rice kor depths for wheat. Not adjusting for very light/sandy soils where percolation is high (field judgment still required). Final Answer: 13.5 cm

Question 17

Irrigation duty–delta–base period relation: If Δ is the depth of water (metres), B is the base period (days), and D is the duty (hectare per cumec), which relation correctly connects these quantities?

Accepted Answer

Introduction / Context: The classical irrigation relationship links duty (area irrigated per unit discharge), base period (time), and delta (seasonal depth of water). Correct unit handling is essential in canal capacity design and crop-water calculations. Given Data / Assumptions: Δ in metres of water depth. B in days (base period). D in hectare per cumec (ha per m^3/s). Concept / Approach: One cumec flowing for 1 day delivers 86,400 m^3. Spread over 1 hectare (10,000 m^2), this equals 8.64 m depth. Hence, 1 cumec for B days supplies 8.64 * B m over 1 hectare. Generalizing to D hectare per cumec, the delivered depth is (8.64 * B) / D, which by definition equals Δ. Step-by-Step Solution: Volume from 1 cumec in B days = 86,400 * B m^3.Depth over 1 ha = (86,400 * B) / 10,000 = 8.64 * B m.For D ha per cumec, Δ = (8.64 * B) / D ⇒ rearrange to D = 8.64 * B / Δ. Verification / Alternative check: Dimensional check: D has units ha per cumec, while the right side has (m * day) / m, but the factor 8.64 embeds unit conversions (86,400/10,000) yielding correct practical units for the standard irrigation identity. Why Other Options Are Wrong: Other rearrangements either invert the relation or misplace variables, except Δ = 8.64 * B / D which is equivalent but not the form asked (we asked “which relation correctly connects,” and the canonical answer chosen is D = 8.64 * B / Δ). Common Pitfalls: Confusing hectares with square metres in conversions. Dropping the 8.64 factor (86,400/10,000). Final Answer: D = 8.64 * B / Δ

Question 18

Canal classification by source: Canals taking off from ice-fed perennial rivers (with dependable year-round supply) are termed as what type of canals?

Accepted Answer

Introduction / Context: Canals are classified by their source and operating characteristics. Ice-fed Himalayan rivers typically provide sustained flows throughout the year, enabling a certain canal type with year-round supplies and headworks control. Given Data / Assumptions: Source: Ice/snow-fed perennial river. Headworks present for diversion and control. Supply is dependable year-round. Concept / Approach: Perennial canals are designed to run throughout the year, supported by perennial rivers or storage. In contrast, inundation canals draw water primarily during floods and lack reliable flow in lean seasons. Ridge canals describe alignment rather than source, and “ice canals” is not a standard term. Step-by-Step Solution: Identify river as perennial (snow/ice melt maintained).Match with canal type that supplies year-round: perennial canal.Exclude inundation (flood-dependent) and ridge (topographic alignment) definitions. Verification / Alternative check: Historical projects on Himalayan rivers (e.g., Upper Ganga Canal) are classic cases of perennial canals fed by perennial rivers with substantial control structures. Why Other Options Are Wrong: Permanent canals: Vague; not a precise hydrologic classification.Ridge canals: Alignment term; may be perennial or not.Inundation canals: Flow mainly in floods.Ice canals: Not standard terminology. Common Pitfalls: Confusing inundation with perennial due to both being river-fed. Assuming “permanent” equals “perennial.” Final Answer: Perennial canals

Question 19

Consumptive use (evapotranspiration) of water by a crop: Which statements correctly describe consumptive use for irrigation planning?

Accepted Answer

Introduction / Context: Consumptive use (evapotranspiration) is the total water used by the crop for transpiration and soil evaporation. It is core to water requirement estimation and canal capacity planning in irrigation engineering. Given Data / Assumptions: Agronomic and hydrologic perspectives are both acceptable. We consider units and sources of supply. Concept / Approach: Consumptive use can be communicated either as a depth (mm or cm) over a field or as a volume per unit area (m^3/ha). Effective rainfall contributes to consumptive use, reducing irrigation demand; the balance is provided by irrigation application and possibly stored soil moisture. Step-by-Step Solution: Recognize that ET can be represented in multiple equivalent forms (depth or volume/area).Acknowledge that rainfall offsets part of the irrigation requirement.Thus, all listed descriptions are correct. Verification / Alternative check: Water balance methods (e.g., FAO-56) compute ET as a depth, then convert to volumes by multiplying by area; effective rainfall explicitly enters the balance. Why Other Options Are Wrong: Each individual statement is correct; therefore the combined option “All the above” is the best. Common Pitfalls: Confusing gross irrigation depth with consumptive use; gross depth includes application and conveyance losses. Ignoring effective rainfall, leading to overestimation of required canal discharge. Final Answer: All the above

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