Question 1

Preferred location of borrow pits during canal excavation: Where should borrow pits be placed relative to the canal section to minimize bank damage and ensure stability?

Accepted Answer

Introduction / Context: Borrow pits provide additional earth where canal excavation does not supply enough material for embankments. Poor placement of borrow pits can undermine bank stability, cause seepage paths, and promote breaches. Hence, standard practice recommends keeping borrow operations away from canal banks and concentrating them near the center of the section where they do not impair the structural integrity of the banks. Given Data / Assumptions: Earthen canal with banks formed from nearby excavation. Goal: maintain bank stability and reduce seepage/breach risks. Borrow must be convenient yet safe for long-term performance. Concept / Approach: Locating borrow pits in the central part of the canal section (i.e., away from the banks) preserves adequate berm width and prevents steep unsupported faces at or near the embankment toes. It also aids in maintaining a satisfactory saturation gradient and reduces the tendency for piping or erosion near bank toes. Step-by-Step Solution: Identify risk zones: immediately adjacent to banks (especially toes) are critical and should be avoided.Adopt recommended placement: central half width of the section where side slopes remain intact and bank stability is not compromised.Ensure borrow operations respect minimum offsets from the toe and avoid longitudinal borrow trenches parallel to the bank. Verification / Alternative check: Canal design manuals prescribe minimum offsets from bank toes and favour central-section borrowing over edge borrowing. Field practice complements this with spoil placement away from the waterline. Why Other Options Are Wrong: Left only / Right only: Arbitrary side selection does not address stability; the key is distance from banks, not which side. Both sides indiscriminately: May result in pits close to toes, risking erosion and sloughing. At the bank toe: Unsafe; it weakens toe support and invites breaches. Common Pitfalls: Creating continuous longitudinal borrow pits parallel to banks. Ignoring seasonal groundwater conditions that can saturate pit walls near the bank. Final Answer: Preferably within the central half width of the canal section (avoiding banks)

Question 2

Cost of canal lining: If a canal has total length L (in km), perimeter of lining P (in m), and lining cost C (₹ per m²), what is the additional expenditure on providing lining?

Accepted Answer

Introduction / Context: Lining a canal reduces seepage and enhances hydraulic efficiency, but it incurs a capital cost proportional to the area lined. For a prismatic canal, the lined area equals the plan length of the canal multiplied by the wetted perimeter being lined. Converting units consistently is the key to a correct cost estimate. Given Data / Assumptions: Total canal length L is given in kilometres. Perimeter of lining P is given in metres (the wetted perimeter or specified portion to be lined). Lining cost C is given per square metre. Continuous lining along the full length is assumed. Concept / Approach: Area to be lined A = (length in metres) * (perimeter in metres). Since L is in km, convert to metres by multiplying with 1000. Thus A = (1000 * L) * P. Total lining cost = A * C. Step-by-Step Solution: Convert length: L_km → L_m = 1000 * L.Compute area: A = (1000 * L) * P.Compute cost: Cost = A * C = 1000 * L * P * C. Verification / Alternative check: Dimensional check: L (km) → m, so 1000 * L is in metres. Multiplying by P (m) gives area (m²). Multiplying by C (₹/m²) gives ₹, as required. Why Other Options Are Wrong: L * P * C: Misses the km→m conversion factor. (P / L) * C or (L * C) / P: Do not represent an area; wrong dimensions. P * C / 1000: Inverts the conversion; underestimates the cost drastically. Common Pitfalls: Forgetting the unit conversion from km to m. Using wetted perimeter at one depth while costing a different lining extent; ensure P matches the lined profile. Final Answer: 1000 * L * P * C

Question 3

Design rules for a venturi flume (venturi head regulator) on a canal: Which of the following sizing guidelines are appropriate?

Accepted Answer

Introduction / Context: A venturi flume or venturi head regulator is widely used for discharge measurement and control in canals. Its geometry—throat width, length, and sill level relative to FSL—determines the head–discharge relationship and whether critical flow can be established. Empirical sizing rules are used for safe, accurate performance and to avoid undue head loss. Given Data / Assumptions: Discharge Q and difference in levels d (FSL – sill) are known or prescribed. Throat section must avoid submergence and flow separation. Standard empirical proportions are acceptable for preliminary design. Concept / Approach: To maintain a measurable control, the throat must be wide enough to pass Q with the available head d while not being so narrow that it induces excessive losses or submergence. Minimum geometric limits (like 0.60 m throat) ensure constructability and debris passage. A throat length of ~2.5 times the approach depth helps develop uniform velocity and suppresses abrupt transitions. Step-by-Step Solution: Check minimum width fraction: B_throat ≥ (1/3) * B_canal → avoids overly narrow constrictions.Apply sizing formula: B_throat = Q / (1.2 * d^(3/2)) → ensures capacity with available head.Impose minimum width: B_throat ≥ 0.60 m → practical clearance and maintenance.Set throat length: L_throat ≈ 2.5 * depth_to_FSL → stabilizes velocity distribution. Verification / Alternative check: Prototype designs use gradual converging/diverging transitions (~1:3 to 1:6) to minimize losses—consistent with the above throat rules for a well-behaved control section. Why Other Options Are Wrong: Each individual guideline is part of standard preliminary design; therefore the most complete choice is All the above. Common Pitfalls: Ignoring submergence at downstream levels; submergence corrections may be needed for calibration. Using too short a throat or too sharp transitions, causing separation and unreliable rating. Final Answer: All the above.

Question 4

Canal over natural drainage: What is the correct name of the cross-drainage work when a canal is carried over a natural drain or river?

Accepted Answer

Introduction / Context: Cross-drainage works (CDWs) allow a canal and a natural drainage to cross without interference. The relative elevations of the canal bed level (CBL), canal water level (CWL), and the high flood level (HFL) of the drainage decide the type of CDW used. Given Data / Assumptions: Canal must pass over a natural drain. Canal prism stays above the drainage HFL. Objective is to maintain uninterrupted canal flow and pass drainage floods safely underneath. Concept / Approach: When the canal section is carried physically above the drainage, the structure is called an aqueduct. If the canal is above but has to be dropped below HFL through pressure flow, it becomes a syphon-aqueduct. Conversely, if the drainage is carried over the canal, it is a super-passage. An inverted syphon carries the canal below the drainage through a pressure barrel. Step-by-Step Solution: Identify relative levels: Canal above drainage → open channel flow on top, drainage in a barrel below.Name the CDW: This configuration is an aqueduct. Verification / Alternative check: Design charts list CDW type selection by comparing CBL/CWL with drainage bed level and HFL. Canal over drainage with freeboard clearance corresponds to an aqueduct. Why Other Options Are Wrong: Syphon: Canal below drainage (pressure flow), not applicable here. Super-passage: Drainage over canal, opposite arrangement. Syphon-aqueduct: Used when canal must pass under HFL in pressure; not the case for open canal over drain. Common Pitfalls: Confusing aqueduct with super-passage because both are “over” arrangements; the deciding factor is which flow is on top. Final Answer: Aqueduct

Question 5

River-training spurs: An “attracting groyne” is aligned in which direction relative to the riverbank?

Accepted Answer

Introduction / Context: Groynes (spurs) are transverse structures used in river training to control alignment and protect banks. Their plan orientation determines whether they repel flow away from a bank or attract it along the bank, affecting near-bank velocities and sediment deposition patterns. Given Data / Assumptions: Bank protection and alignment control are desired. Groynes are oriented at a modest angle (often up to ~30°) to the bank alignment. Terminology: “Attracting” vs “Repelling” based on how the spur guides the main current. Concept / Approach: An attracting groyne is skewed downstream, guiding and attaching the current along the bank. A repelling (deflecting) groyne is skewed upstream, pushing the current away from the bank. Normal (perpendicular) groynes neither strongly attract nor repel and are used for local control. Step-by-Step Solution: Match definition to orientation: “Attracting” → inclined downstream.Therefore, choose “Inclined downstream (attracting orientation)”. Verification / Alternative check: River-training manuals depict plan views where downstream-skewed spurs streamline flow along the bank, stabilizing alignment and flushing shoals. Why Other Options Are Wrong: Perpendicular: Neutral orientation; not specifically attracting. Inclined upstream: Repelling, not attracting. Parallel or random: Do not represent standard attracting practice. Common Pitfalls: Using downstream-inclined spurs where bank needs relief from high velocity; an upstream-inclined defensive spur may be preferable. Final Answer: Inclined downstream (attracting orientation)

Question 6

Canal cross-section terminology: Pick the incorrect statement about the positions of banks and the 'dowla' (inspection berm) in a typical irrigation canal cross-section.

Accepted Answer

Introduction / Context: In open-channel irrigation engineering, a canal cross-section is described with reference to its two banks (right and left, defined while facing downstream) and ancillary features that aid operation and maintenance. One such feature is the 'dowla'—a narrow inspection berm or service path provided on a specific bank to facilitate patrol, minor maintenance, and emergency interventions. This question checks familiarity with standard layout conventions used in many canal systems. Given Data / Assumptions: Conventional earthen canal in a distributary or minor system. Right bank and left bank are referenced facing the direction of flow (downstream). The 'dowla' is the inspection berm commonly assigned to one designated bank for uniformity of operations. Concept / Approach: Canals have two banks by definition, one on either side of the waterway. The 'dowla' is not a central feature; it is constructed on a selected bank (commonly the right bank in many standard practices) to give staff safe access and a consistent side for patrolling and silt/debris management. Hence, statements that merely acknowledge the existence of left and right banks are correct, while a statement that misplaces the standard position of the 'dowla' is considered incorrect in the conventional context. Step-by-Step Solution: Identify facts: both right and left banks exist → statements acknowledging either bank alone are not false.Interpret 'dowla': an inspection berm conventionally provided on the right bank in many canal layouts.Therefore, the statement placing the 'dowla' on the left is the incorrect one. Verification / Alternative check: Standard canal drawings and departmental manuals typically show a single inspection berm on the right bank for consistency of field operations. Local practices can vary, but the conventional answer follows the common standard. Why Other Options Are Wrong: A bank on the right / on the left: Both are inherently true (two banks exist). None of these: Incorrect because one statement is indeed wrong. A 'dowla' at bed centreline: Not standard practice; 'dowla' is on a bank, not at the channel centre. Common Pitfalls: Confusing local variations with generalized exam conventions. Assuming the dowla could be on either side without recognizing the widely adopted “right-bank” convention in many texts. Final Answer: A 'dowla' in the cross-section of a canal is provided on the left

Question 7

Canal bank seepage: What saturation gradient (saturation line slope) is generally adopted for ordinary loam soil after a canal has been running for some time?

Accepted Answer

Introduction / Context: When an irrigation canal runs for some time, seepage causes a wetted or saturated zone to develop within the earthen banks. The upper boundary of this zone is commonly called the saturation line (or phreatic line). Designers use an empirical saturation gradient to anticipate how far upward and landward the saturation will extend in typical soils, which influences stability, erosion control, and the placement of berms or toe drains. Given Data / Assumptions: Ordinary loam soil for canal banks and embankments. Canal has been in operation long enough for a representative saturation profile to establish. Saturation gradient is expressed as a horizontal:vertical slope ratio for the phreatic line within the bank. Concept / Approach: Empirical practice in canal engineering adopts a typical saturation gradient for ordinary loam soils of about 4:1 (horizontal:vertical). This provides a practical estimate of how the phreatic line will rise into the bank, guiding checks on stability against sloughing, location of inspection berms ('dowla'), and design of pitching or turfing to protect against erosion. Step-by-Step Solution: Recognize soil type: ordinary loam → use standard empirical saturation gradient.Adopt the conventional practice: saturation gradient ≈ 4 : 1 (H:V).Select the matching option → 4 : 1. Verification / Alternative check: Field observations and guidance in canal manuals corroborate that for loam soils, a 4:1 saturation line offers a reasonable design estimate; clayey soils may show flatter phreatic lines, whereas coarser materials may differ, so designers can refine based on site investigations. Why Other Options Are Wrong: 2 : 1 or 3 : 1: Too steep for ordinary loam; tend to underestimate the horizontal spread of saturation. 5 : 1 or 6 : 1: Flatter than commonly adopted for loam; may overestimate spread, affecting economy. Common Pitfalls: Using the same saturation gradient for all soil types without adjustment based on investigations. Ignoring long-term operation; the phreatic line can shift seasonally with canal levels. Final Answer: 4 : 1

Question 8

Pick up the correct statement from the following

Accepted Answer

Approach of the water line should not be steeper than 30° and departure line not steeper than in a flumed channel section

Question 9

Diversion headworks crest setting in canal design — the crest level primarily depends on multiple hydraulic and operational criteria; identify the most comprehensive choice.

Accepted Answer

Introduction / Context: The crest level of a diversion headworks (weir or barrage) is a keystone decision in canal engineering. It governs how much hydraulic head is available at the canal regulator, the sediment-exclusion efficiency, and the safe passage of floods. Examinations often ask whether crest level should be tied to a single factor or a combination of interdependent design inputs. Given Data / Assumptions: A canal offtakes from a river via a diversion headworks comprising a crest (weir/barrage), undersluices, and a head regulator. Full Supply Level (F.S.L.) of the canal is preselected from command requirements. Pond level (upstream water level) must reliably supply the canal even at low river flow. Design discharge and control needs determine regulator openings and approach conditions. Concept / Approach: The crest level must be high enough to create a dependable pond level above the canal F.S.L., while accommodating ecological flow, sediment management, and flood routing. It is therefore set by simultaneously meeting: (i) canal F.S.L. and head across regulator, (ii) discharge-capacity/control requirements, and (iii) the desired pond level envelope for multiple flow regimes. Step-by-Step Solution: Relate regulator head need → crest level fixes pond level for smooth entry.Check design discharge / gate geometry → adequate head for offtake and sediment control.Confirm pond level range → stable operation over seasonal flow variability. Verification / Alternative check (if short method exists): Carry out a backwater/gradually varied flow analysis to verify that for critical low-flow conditions the pond level still exceeds the canal F.S.L. by the target margin, while flood routing keeps upstream afflux within allowable limits. Why Other Options Are Wrong: Choosing only F.S.L., only discharge parameters, or only pond level neglects key coupled constraints. “None of these” is incorrect because all listed factors do govern crest fixing. Common Pitfalls (misconceptions, mistakes): Designing for a single criterion (e.g., just canal F.S.L.) and ignoring flood afflux or sediment approach; confusing pond level with long-term storage (it is operational pondage, not reservoir storage). Final Answer: all the above

Question 10

Soil alkalinity in waterlogged fields — the topsoil becomes strongly alkaline and infertile when the measured pH reaches approximately which value?

Accepted Answer

Introduction / Context: Waterlogging and poor drainage can drive soluble salts and sodium into the root zone, elevating soil pH. From an irrigation and agronomy perspective, knowing the pH threshold at which soils become markedly alkaline and infertile is critical for reclamation planning (e.g., gypsum application, leaching, and drainage improvements). Given Data / Assumptions: Field prone to waterlogging with capillary rise and evaporative concentration of salts. Soil pH scale from acidic (<7) to alkaline (>7). Question asks for a typical pH value at which the topsoil becomes strongly alkaline and infertile. Concept / Approach: Alkali (sodic) soils commonly exhibit pH above 8.5; as pH approaches ~10, exchangeable sodium percentage and carbonate/bicarbonate hazards are usually severe, degrading soil structure, reducing infiltration, and restricting nutrient availability. This threshold reflects conditions where yields are strongly depressed unless reclamation is undertaken. Step-by-Step Solution: Recognize waterlogging effect → salt and sodium accumulation, rising pH.Interpret agronomic severity → mild: ~8–8.5, strong: ~9–10, very strong: >10.Select representative threshold for ‘‘strongly alkaline and infertile’’ → pH 10. Verification / Alternative check (if short method exists): Cross-check with soil classification: saline-sodic/sodic soils at high pH show dispersion, crusting, poor tilth, and micronutrient deficiencies—consistent with infertility at ~10. Why Other Options Are Wrong: pH 6 is acidic; pH 8–9 indicates alkalinity but not typically the severe infertility implied; pH 11 is extreme and less common as a practical field threshold. pH 10 is the most defensible indicator of strong alkalinity and infertility. Common Pitfalls (misconceptions, mistakes): Equating any pH above 7 with severe infertility; ignoring the role of exchangeable sodium and carbonate equilibria; overlooking drainage as the root cause. Final Answer: pH 10

Question 11

Preferred alignment of irrigation canals — when laying a new canal to minimize cross-drainage works and command both sides, which line is generally followed?

Accepted Answer

Introduction / Context: Canal alignment determines hydraulic efficiency, cost of cross-drainage works, and the ability to serve the command area. The classical principle in irrigation planning is to choose an alignment that maximizes gravity command while minimizing structures needed to cross natural drains. Given Data / Assumptions: New gravity canal planned in undulating terrain with natural drainage lines. Goal: provide maximum command on both sides and reduce cross-drainage structures. Standard alternatives: ridge, contour, or valley alignment. Concept / Approach: A ridge-line (watershed) alignment keeps the canal near the drainage divide. From here, the canal can command land on both sides with minimal crossings of streams (since streams usually flow away from the ridge). This cuts costs and hydraulic complications. Contour alignments can be long and sinuous; valley alignments face frequent cross-drainage and flooding risks. Step-by-Step Solution: Identify objective → maximum command + minimum cross drainage.Select watershed alignment → streams fall away on both sides, fewer crossings.Hence the preferred choice → ridge line (watershed). Verification / Alternative check (if short method exists): Preliminary reconnaissance profiles show fewer crossings and shorter structures along ridges compared with valley routing. Why Other Options Are Wrong: Contour lines lead to meandering alignment and longer lengths; valley lines require many cross-drainage works and suffer flood interference; straight or random alignments ignore topography and hydrology. Common Pitfalls (misconceptions, mistakes): Confusing watershed alignment with contour alignment; overlooking future drainage development that favors ridge routing. Final Answer: ridge line (watershed alignment)

Question 12

Waterlogging mitigation — which set of measures directly helps to remove waterlogging from irrigated land?

Accepted Answer

Introduction / Context: Waterlogging occurs when the water table rises into the root zone, degrading soil aeration and crop yields. Engineers address both the inflow (percolation into the aquifer) and the outflow (drainage or pumping) sides of the balance to restore a safe depth to the water table. Given Data / Assumptions: Canal command with high seepage and inadequate drainage. Goal: lower water table and prevent salinization/alkalinization. Standard interventions: reduce percolation; improve outflow. Concept / Approach: Reduction of percolation (canal lining, watercourse lining, improved on-farm irrigation practices) decreases recharge to the groundwater. Simultaneously, increasing outflow (surface/subsurface drains, interceptor drains, pumping) removes excess groundwater. Acting on both terms best accelerates recovery from waterlogging. Step-by-Step Solution: Identify recharge pathways → canals/watercourses percolation.Mitigate recharge → lining, maintenance, efficient delivery.Enhance discharge → drainage systems, pumping, reuse. Verification / Alternative check (if short method exists): Water balance analysis before and after intervention should show reduced recharge and increased discharge, producing declining water table trends. Why Other Options Are Wrong: Only one-side action gives slow or partial relief; “neither” fails to address the cause; ignoring drainage overlooks the need for an exit path for groundwater. Common Pitfalls (misconceptions, mistakes): Assuming canal lining alone cures waterlogging; forgetting field drains and maintenance; neglecting conjunctive use of pumped groundwater. Final Answer: both (a) and (b)

Question 13

River-bed retrogression (degradation) downstream of a weir — identify the principal cause that promotes lowering of the bed level after construction.

Accepted Answer

Introduction / Context: When a weir or barrage traps part of the incoming sediment load, the water released downstream can become “clearer” (sediment-deficient). Such flows have excess transport capacity relative to available bed material and therefore pick up sediment from the downstream reach, causing degradation (retrogression). Given Data / Assumptions: Weir or barrage with ponding and sediment interception upstream. Downstream reach initially alluvial and movable. Observation: bed level lowers with time. Concept / Approach: Clear-water scour is a well-known phenomenon: the smaller the percentage of silt in the released flow (relative to its transport capacity), the greater the tendency to erode the bed and banks until a new graded regime is achieved. While strata properties matter, sediment deficit is the primary driver of systematic retrogression. Step-by-Step Solution: Upstream trapping → reduced downstream sediment supply.Transport capacity > supply → bed material is entrained from channel.Net effect → degradation/retrogression of bed level downstream. Verification / Alternative check (if short method exists): Compare pre- and post-project bed profiles; use regime or sediment routing models to show declining bed elevations correlated with reduced suspended load concentration. Why Other Options Are Wrong: Impact/jet action is local near structures; increased bed level implies aggradation (opposite); soil softness influences rate but is not the principal cause without sediment deficit. Common Pitfalls (misconceptions, mistakes): Attributing long-reach degradation only to foundation type; ignoring watershed sediment yield changes; mistaking local scour for systemic retrogression. Final Answer: less percentage of silt (clear-water flow)

Question 14

Relative level of undersluice (scouring sluice) crest — typical depth of undersluice crest below the canal head regulator crest is generally kept about:

Accepted Answer

Introduction / Context: In diversion headworks, undersluices (scouring sluices) are provided near the canal offtake to pass heavy silt and to control the approach flow. Their crest is intentionally kept lower than the canal head regulator crest to preferentially pass sediment-laden lower layers and to maintain a silt-free approach to the regulator. Given Data / Assumptions: Standard layout with a weir/barrage, undersluices near the canal bank, and the canal head regulator. Undersluice crest is lower than the regulator crest by a modest margin. Objective: efficient sediment exclusion and pond control. Concept / Approach: Keeping the undersluice crest about 1.0–1.5 m below the regulator crest promotes flushing of silt-laden bottom layers while sustaining an adequate pond level for canal drawal. A typical examination value used is ~1.2 m, balancing sediment control and operational headlosses. Step-by-Step Solution: Set regulator crest = reference elevation.Select undersluice crest lower by ≈1.2 m → promotes silt exclusion.Therefore choose 1.20 m. Verification / Alternative check (if short method exists): Physical/CFD models of approach flow confirm improved bottom-layer withdrawal and reduced deposition near the regulator with a suitably lower undersluice crest. Why Other Options Are Wrong: 0.20 m is too small to create effective silt withdrawal; 2.20–4.90 m are excessive for typical barrages and may waste head or complicate operation. Common Pitfalls (misconceptions, mistakes): Assuming “the lower the better”; over-lowering can impair pond control and gate operations; site-specific tuning is still needed. Final Answer: 1.20 m

Question 15

Blench curves application — for a given channel discharge, Blench curves relate the head loss (HL) across a fall to which specific energy quantity?

Accepted Answer

Introduction / Context: Falls and transitions on canals are designed to dissipate surplus energy safely. Empirical aids like Blench curves are used to estimate head loss (HL) and downstream conditions for given discharges and approach states, assisting in economical stilling arrangements and protection works. Given Data / Assumptions: Channel with a fall/energy dissipator handling a known discharge. Objective: estimate HL and downstream specific energy for design. Blench curves provide empirical relationships between HL and energy terms. Concept / Approach: The performance of a fall is governed by conditions in the hydraulic jump or turbulent roller downstream. Accordingly, the energy state immediately downstream (specific energy downstream) is central to evaluating head loss and ensuring non-scouring velocities. Blench curves capture this relationship for typical canal geometries and flows. Step-by-Step Solution: Select discharge and geometry → consult Blench curves.Read HL as a function of downstream specific energy/state.Size floor/protections based on predicted HL and tailwater. Verification / Alternative check (if short method exists): Compare curve-based HL with calculations from momentum-based hydraulic jump theory using downstream tailwater rating; reconcile for design safety factors. Why Other Options Are Wrong: Upstream specific energy is less indicative of dissipation demand; critical depth/depth alone ignores velocity head; “none” is incorrect because downstream energy is the key correlate. Common Pitfalls (misconceptions, mistakes): Using approach depth instead of downstream energy; ignoring tailwater variability; applying curves outside their empirical range. Final Answer: specific energy downstream of the structure

Question 16

Culturable Commanded Area (CCA) definition — identify the incorrect deduction when computing CCA from Gross Commanded Area (GCA).

Accepted Answer

Introduction / Context: Planning an irrigation project requires distinguishing the land actually cultivable under a canal system. Culturable Commanded Area (CCA) is derived from the Gross Commanded Area (GCA) by excluding permanently unculturable categories, not land that is simply left uncropped in a given season (fallow). Given Data / Assumptions: GCA includes all land topographically commanded by the project. We remove areas that are intrinsically not cultivable. Fallow land is considered potentially cultivable (culturable). Concept / Approach: CCA = GCA − (permanently unculturable lands such as settlements, roads, forests, rocky patches, water bodies, alkaline wastelands). Seasonal fallow remains within CCA because it can be cultivated when water and agronomy permit. Hence subtracting fallow is incorrect. Step-by-Step Solution: List unculturable lands → settlements, forests, rocky waste, saline-alkaline hard pans, water bodies.Retain fallow as culturable → do not subtract.Therefore the incorrect deduction is “Subtract fallow land.” Verification / Alternative check (if short method exists): Check project planning manuals: CCA serves as the basis for cropping intensity and water duty; fallow is part of the rotation within CCA. Why Other Options Are Wrong: Options A, B, C, and E correctly identify unculturable deductions. Only D conflicts with standard definitions. Common Pitfalls (misconceptions, mistakes): Confusing “fallow” with “unculturable”; miscounting double-cropped area as additional CCA (it affects cropping intensity, not CCA). Final Answer: Subtract fallow land.

Question 17

Sinuosity of a meandering river — choose the correct definition of sinuosity as used in fluvial geomorphology.

Accepted Answer

Introduction / Context: Sinuosity quantifies how much a river meanders relative to the valley or chord line. It is fundamental for river training, navigation, and predicting migration hazards near canals and headworks. Given Data / Assumptions: Two points along a river reach are identified. Curved length is measured along the channel centerline (thalweg). Straight distance is the valley-line or chord between the same two points. Concept / Approach: Sinuosity = (curved channel length) / (straight-line distance). A value greater than 1 indicates meandering; values near 1 indicate near-straight channels. This metric supports decisions on cutoffs, bank protection, and floodplain management. Step-by-Step Solution: Measure curved length along thalweg between points A and B.Measure straight-line distance AB.Compute sinuosity = L_curved / L_straight and interpret > 1 as meandering. Verification / Alternative check (if short method exists): GIS tools can compute centerline length and chord distance directly for rapid sinuosity mapping. Why Other Options Are Wrong: Options A and B confuse belt width/river width with the standard definition; E is not the accepted metric; D is incorrect because C is the standard definition. Common Pitfalls (misconceptions, mistakes): Using bankline length instead of thalweg; mixing meander-belt width metrics with sinuosity; failing to fix the same endpoints. Final Answer: ratio of curved thalweg length to the straight-line distance between the same points

Question 18

Components at a canal–drain level crossing — identify the correct set of provisions typically adopted in a level crossing arrangement.

Accepted Answer

Introduction / Context: When a canal and a natural drain intersect at approximately the same bed level, a level crossing is adopted. Proper appurtenances are required to manage relative water levels and prevent undesirable backflows or sediment entry, while maintaining canal supply reliability. Given Data / Assumptions: Canal and drain cross at similar elevations. No superpassage or aqueduct (i.e., no vertical separation). Operational need to control flows on both channels near the junction. Concept / Approach: Standard practice provides (i) a crest/weir in the drain upstream of the junction to maintain adequate water level for controlled exchange, (ii) a regulator in the drain downstream to modulate outflows and prevent drawdown issues, and (iii) a cross-regulator on the canal downstream of the crossing to maintain canal F.S.L. and safeguard distribution. Step-by-Step Solution: At the drain upstream → install crest to stabilize approach level.At the drain downstream → regulator for controlled release and level management.On the canal downstream → cross-regulator to hold canal F.S.L. through the crossing. Verification / Alternative check (if short method exists): Operational simulations show that absence of any one element can cause level instability, reverse flows, or sediment ingress; the trio ensures robust control. Why Other Options Are Wrong: Any subset omits an essential control element; therefore, only “All the above” reflects the complete, typical provision set. Common Pitfalls (misconceptions, mistakes): Confusing level crossing with superpassage/aqueduct; forgetting the canal cross-regulator below the junction; ignoring sediment management after events. Final Answer: All the above

Question 19

Canal cross-drainage works: In a canal syphon (inverted syphon), what is the nature of flow through the barrel(s)?

Accepted Answer

Introduction / Context: A canal syphon—often called an inverted syphon—is a cross-drainage work used when a canal must pass beneath a natural drain/river or an obstruction, while maintaining discharge continuity. The canal is conveyed through one or more closed barrels running full, which changes the flow regime from open-channel to pressure (pipe) flow. Given Data / Assumptions: The structure is a canal syphon (inverted syphon), not an aqueduct or super-passage. The barrel is closed and designed to run full. Approach and exit transitions convert between open-channel flow in the canal and pressure flow in the barrel. Concept / Approach: In an inverted syphon the water surface is not free to adjust to atmospheric pressure within the barrel. Instead, the conduit runs full, and energy grade line calculations use head losses (entrance, friction, exit, bends) typical of pressure flow. The hydraulic grade line and piezometric head determine the capacity and required barrel diameter(s). Step-by-Step Solution: Identify structure type → inverted syphon (closed barrel).Recognize flow regime → pressure flow through the barrel (pipe hydraulics apply).Therefore, the correct description is “pipe flow”. Verification / Alternative check: Design methods (e.g., Darcy–Weisbach/Hazen–Williams, entrance/exit loss coefficients) are applied, confirming pressure-flow behavior. Open-channel formulas (Manning, critical depth) are not applicable inside the running-full barrel. Why Other Options Are Wrong: Under atmospheric pressure: That describes open-channel flow, not valid inside the closed, full barrel. Critical velocity: A specific open-channel control condition, not representative of syphon barrels. Under negative pressure: Properly designed syphons avoid sub-atmospheric pressures that risk cavitation/air binding. Mixed regime: Within a given barrel, the regime is pressure; the regime change occurs only in transitions. Common Pitfalls: Confusing inverted syphons (pressure flow) with aqueducts/super-passages (open channel). Ignoring entrance/exit losses and bend losses, which leads to undersized barrels. Final Answer: Pipe flow (pressure flow through closed barrel)

Question 20

Canal alignment along watersheds: Under which circumstances is a watershed (ridge) alignment abandoned when planning an irrigation canal?

Accepted Answer

Introduction / Context: A watershed (ridge) alignment is generally preferred for main canals because it minimizes cross-drainage structures and seepage into adjacent commands. However, field constraints often force deviations from the ridge alignment to balance constructability, hydraulics, and social impacts. Given Data / Assumptions: Candidate canal alignment follows the watershed where feasible. Practical constraints include terrain geometry, river offtake conditions, and habitation corridors. Objective is to ensure hydraulic efficiency and reduce costs/risks. Concept / Approach: Watershed alignment is abandoned if it introduces excessive curvature (sharp loops), conflicts with mandatory offtake geometry from the source river, or intersects dense settlement corridors. Each of these can increase length, create unsafe embankments, or raise resettlement/land acquisition burdens. Step-by-Step Solution: Check terrain: sharp ridge loops → excessive length and hydraulic losses → avoid.Check river offtake: approach cross-section and silt-free offtake may not coincide with ridge → shift alignment.Check habitations: towns/villages on ridge → social and safety constraints → adopt alternate alignment. Verification / Alternative check: Feasibility reports compare alternatives with counts of cross-drainage works, excavation/embankment quantities, land impacts, and hydraulic losses; often these justify abandoning strict ridge alignment. Why Other Options Are Wrong: None of the above is incorrect because all listed conditions are valid reasons to shift alignment. Common Pitfalls: Over-valuing ridge alignment despite prohibitive bends or offtake problems. Ignoring long-term operation/maintenance costs of overly sinuous alignments. Final Answer: All the above.

Irrigation Questions