Question 1

Scour at a bend by Lacey’s recommendation: If D is the normal regime scour depth in a straight reach, what is the design scour depth in a right-angled river bend?

Accepted Answer

Introduction / Context: River training and hydraulic structure foundations must consider aggravated scour at bends. Lacey provided multipliers over the normal regime scour depth D to account for curvature effects. Designers use these to determine founding levels or protection depths at bends. Given Data / Assumptions: D is the regime (straight-reach) scour depth. Right-angled bend indicates strong curvature. Applicability: alluvial rivers in regime conditions. Concept / Approach: Bends increase secondary currents and attack on the outer bank, deepening the scour hole beyond straight-reach values. Empirical multipliers convert D to a conservative design scour at bends. Step-by-Step Solution: Take base scour depth D from regime equations or measurements.Apply Lacey’s bend factor for a pronounced 90° bend: about 1.5.Design scour = 1.5 D for foundation embedment or apron sizing. Verification / Alternative check: Where data allow, compare with observed thalweg depths during high flows or use numerical modeling. The empirical factor is typically conservative. Why Other Options Are Wrong: 1.25 D and 1.10 D underestimate scour at a sharp bend; 1.75 D and 2.00 D are excessive for a right-angled bend in common practice without special aggravating factors. Common Pitfalls: Ignoring local contraction or pier effects which can further increase scour; using bend multipliers without verifying river planform dynamics. Final Answer: 1.50 D

Question 2

Proportional outlet in canal distribution: An outlet is termed “proportional” when its flexibility (ratio of percentage change in outlet discharge to percentage change in parent channel discharge) is

Accepted Answer

Introduction / Context: In canal irrigation, outlets connect distributaries to watercourses. Their hydraulic behavior is characterized by sensitivity, efficiency, and flexibility. “Proportional” outlets aim to pass a constant proportion of the parent channel discharge, maintaining equity as supplies vary. Given Data / Assumptions: Flexibility = (% change in outlet discharge) / (% change in distributary discharge). Proportionality implies same percentage variation. Backwater and submergence effects are negligible for definition. Concept / Approach: A flexibility value of one means the outlet flow changes one-to-one with changes in the parent channel discharge, i.e., a fixed fraction is drawn off regardless of supply fluctuations, which is the defining characteristic of proportional outlets. Step-by-Step Solution: Write flexibility φ = (Δq/q) / (ΔQ/Q).For proportional behavior, φ must equal 1.Hence, option “Exactly one” is correct. Verification / Alternative check: Design texts describe orifice-type proportional modules calibrated to achieve φ ≈ 1 over a range of heads. Why Other Options Are Wrong: φ < 1 implies a rigid outlet; φ > 1 implies hyper-sensitive outlet; φ = 0 means insensitive; negative is nonsensical for normal operation. Common Pitfalls: Confusing “efficiency” with “flexibility”; overlooking tail-water submergence which can alter actual flexibility in field. Final Answer: Exactly one

Question 3

Type of canal used to divert flood water directly from rivers during high stages (without storage): identify the most appropriate term.

Accepted Answer

Introduction / Context: Canal classification depends on the source and regulation of supply. Some canals tap regulated storage, while others draw water opportunistically during floods. Understanding these distinctions guides planning, command area reliability, and protection works. Given Data / Assumptions: No mention of storage regulation or perennial releases. Water is diverted during flood/high river stages. Direct offtake from river through a head regulator. Concept / Approach: An inundation canal takes water only when the river is in flood or high stage, often without a permanent weir or with a simple diversion structure. Historically common in monsoon-fed rivers, they provide seasonal irrigation and require careful silt management. Step-by-Step Solution: Match description with definitions: “diverting flood water directly” → inundation canal.Exclude other canal types: ridge/contour refer to alignment; perennial implies year-round regulated supply. Verification / Alternative check: Textbook definitions consistently name flood-season canals as “inundation canals”. Why Other Options Are Wrong: Ridge/contour are geometric terms; perennial canals have controlled storage releases; generic “lined supply canal” does not describe flood-only diversion. Common Pitfalls: Confusing alignment-based names with source-based names; assuming all canals with river intakes are perennial. Final Answer: Inundation canal

Question 4

Identify the correct Lacey-type velocity relationship for regime channels (metric form): V as a function of hydraulic mean depth R and bed slope S.

Accepted Answer

Introduction / Context: Regime theory (Lacey) provides empirical relations for stable alluvial channels carrying their sediment load. A frequently used form expresses mean velocity V as a function of hydraulic mean depth R and bed slope S, with a metric coefficient. Given Data / Assumptions: Alluvial channel in regime conditions. V in m/s, R in m, S dimensionless bed slope. Use standard metric adaptation. Concept / Approach: The velocity formula analogous to Chezy/Manning forms but calibrated for regime channels is V = 10.8 R^{2/3} S^{1/2}. The exponents reflect hydraulic similarity; the coefficient 10.8 is the empirical metric constant used in many design examples. Step-by-Step Solution: Recall Lacey velocity form V ∝ R^{2/3} S^{1/2}.Insert the metric coefficient 10.8 for regimen channels.Therefore V = 10.8 R^{2/3} S^{1/2} is correct. Verification / Alternative check: Comparisons with Chezy or Manning yield similar exponent structure; design charts reproduce the 10.8 coefficient for metric units. Why Other Options Are Wrong: (a), (c), and (d) use incorrect exponents; (e) uses a nonstandard coefficient. Common Pitfalls: Mixing unit systems; confusing Lacey with Manning where coefficients differ and depend on roughness rather than regime conditions. Final Answer: V = 10.8 R^{2/3} S^{1/2}

Question 5

Garnett’s diagrams (graphical aids) are traditionally used to solve the design equations of a canal according to which regime theory?

Accepted Answer

Introduction / Context: Before widespread digital computation, designers relied on graphical tools to solve iterative canal-design equations. Garnett’s diagrams are classic aids connected with one of the two well-known regime design approaches: Kennedy and Lacey. Given Data / Assumptions: Design target is a non-silting, non-scouring canal section. Charts/nomograms attributed to Garnett are referenced. Question asks which theory they support. Concept / Approach: Kennedy’s theory centers on critical velocities to prevent silting/scour and involves interdependent variables (depth, velocity, slope). Garnett produced graphical charts to streamline these computations, allowing designers to read off solutions for given discharge and silt grade. Step-by-Step Solution: Identify the design framework (Kennedy) where critical velocity ratios are used.Recall that Garnett’s diagrams plot relationships to bypass algebraic iteration.Therefore, they are tied to Kennedy’s method. Verification / Alternative check: Many irrigation texts list “Garnett’s diagrams for Kennedy’s design” alongside regime tables. Why Other Options Are Wrong: Lacey’s method uses a different set of empirical relations; Gibb’s and Lindley’s are not the standard attributions for Garnett’s charts. Common Pitfalls: Conflating graphical tools across theories; overlooking that each regime theory has its own calibration and parameters. Final Answer: Kennedy’s theory

Question 6

Relationship between canal systems and drainage systems in an irrigated command: choose the correct comprehensive statement.

Accepted Answer

Introduction / Context: Sustainable irrigation requires not only conveyance of water but also safe removal of excess. Hence, canal (supply) and drainage (disposal) systems must be planned together to avoid waterlogging and salinity, and to maintain infrastructure integrity. Given Data / Assumptions: Irrigated command area with relief features (ridges and valleys). Separate channels convey supply vs. drainage. Hydraulic gradient and gravity dictate alignments. Concept / Approach: Canal systems commonly take ridge alignments to maximize command by gravity; water is then distributed via minors and watercourses. Drainage systems occupy the thalwegs (lowest lines) to collect surface and subsurface flows and discharge to natural streams. Proper integration makes the two systems complementary. Step-by-Step Solution: Check statement (a): Complementarity is fundamental—true.Check statement (b): Ridge alignment enhances gravity command—true.Check statement (c): Drains follow low lines to outfalls—true.Hence, (d) All of the above is correct. Verification / Alternative check: Command design guidelines show paired maps for canals and drains; failures to coordinate cause chronic waterlogging. Why Other Options Are Wrong: Any single statement alone is incomplete; “None” contradicts well-established planning practice. Common Pitfalls: Using canals for dual drainage in flat terrain without checks; underestimating subsurface drainage needs. Final Answer: All of the above

Question 7

Field application method most commonly adopted for cereal crops (e.g., wheat, barley) on moderate slopes and typical soils:

Accepted Answer

Introduction / Context: Application methods must match crop type, field slope, soil intake rate, and water control objectives. Cereals such as wheat and barley are typically grown in closely spaced stands rather than wide rows, favoring surface methods that uniformly wet large land strips. Given Data / Assumptions: Conventional open-channel irrigation setting. Moderate slopes and medium-textured soils common to cereal belts. Aim is uniform coverage with manageable labor and cost. Concept / Approach: Check methods (check-basin or border-check) divide fields into leveled units bounded by low bunds; water is let in to pond or flow uniformly until the target depth is applied. This suits cereals’ close spacing and provides good distribution with simple control structures. Step-by-Step Solution: Match crop geometry: cereals are not typically planted in wide furrows; furrows fit row crops like cotton, sugarcane.Assess control: check method allows precise cut-off and uniform depth.Consider practicality: simpler land preparation than furrow/gravity-drip for large cereal acreage. Verification / Alternative check: Extension manuals commonly recommend border or check-basin irrigation for wheat and similar cereals in surface irrigation systems. Why Other Options Are Wrong: Free flooding causes poor uniformity and high losses; furrow suits row crops; sprinklers/drip are effective but not “most commonly adopted” in traditional cereal areas due to cost and logistics. Common Pitfalls: Ignoring field leveling; oversizing checks leading to non-uniform advance; overirrigation near inlets. Final Answer: Check (check-basin/border-check) method

Question 8

In canal embankments, what is a counter berm? Choose the most accurate definition used in irrigation engineering practice.

Accepted Answer

Introduction / Context: Canal banks (embankments) may suffer from sloughing and instability, especially on the outer slope where seepage and drawdown act. To improve stability and reduce the driving height of the slope, engineers provide counter berms. Given Data / Assumptions: Embanked canal with inner (water side) and outer (country side) slopes. Counter berm is an ancillary earthwork used for stability, drainage, and maintenance access. No numerical calculation is required; this is a definition/identification task. Concept / Approach: A berm is a horizontal bench. A counter berm specifically counteracts slope instability by interrupting the outer slope, shortening the seepage face, and providing a platform to catch minor slips and to drain seepage water safely. Step-by-Step Solution: Identify the slope most vulnerable to instability: outside (country) slope.Define a counter berm as a horizontal bench on that outside slope.Conclude that the correct description is a horizontal benching provided on the outside slope. Verification / Alternative check: Canal manuals illustrate cross-sections showing the counter berm breaking the outer slope, often combined with toe drains to control seepage. Why Other Options Are Wrong: Inside slope benching is typically called a berm or inspection berm but is not a counter berm. “Vertical benching” is self-contradictory; a berm is horizontal. “None of these” is incorrect because a standard definition exists. Common Pitfalls: Confusing inspection berms on the water side with counter berms; assuming any platform is a counter berm without considering location and purpose. Final Answer: a horizontal benching provided on the outside slope

Question 9

Hydraulic jump energy loss: If D1 and D2 are the upstream and downstream conjugate depths of a hydraulic jump, the loss of specific head at the jump equals

Accepted Answer

Introduction / Context: A hydraulic jump in a rectangular channel converts supercritical flow to subcritical flow, dissipating energy. Designers must quantify the head loss across the jump to size stilling basins and appurtenances. Given Data / Assumptions: D1 = supercritical depth upstream of the jump. D2 = subcritical (sequent) depth downstream. Rectangular prismatic channel, steady flow. Concept / Approach: From the specific energy equation and momentum (sequent depth relation), the loss of specific head h_L across the jump can be expressed purely in terms of D1 and D2. Step-by-Step Solution: Specific energy upstream: E1 = D1 + V1^2/(2g).Specific energy downstream: E2 = D2 + V2^2/(2g).Using continuity and momentum to eliminate velocities yields the standard head loss:h_L = E1 - E2 = (D2 - D1)^3 / (4 * D1 * D2). Verification / Alternative check: Check limiting behavior: If D2 ≈ D1, numerator tends to zero faster than denominator, so h_L → 0, as expected for a vanishing jump. Why Other Options Are Wrong: Squares in numerator (option b) underestimates loss. (D2 + D1)^3 (option c) has wrong dependence and gives nonzero loss even when D2 = D1. Option d lacks the cubic dependence characteristic of jump loss. Common Pitfalls: Using depth difference squared instead of cubed; forgetting the product 4 * D1 * D2 in the denominator. Final Answer: (D2 - D1)^3 / (4 * D1 * D2)

Question 10

Outlet hydraulics: The ratio of the rate of change of discharge of an outlet to the rate of change of water level in the distributary (at normal depth) is called

Accepted Answer

Introduction / Context: Equitable water distribution in irrigation depends on how outlets respond to fluctuations in parent channel levels. Key parameters are efficiency, sensitivity, flexibility, and modular limit. Given Data / Assumptions: Outlet draws water from a distributary into a watercourse. Discharge varies as upstream and downstream levels change. Normal depth conditions in the distributary are referenced. Concept / Approach: Flexibility (F) = (rate of change of outlet discharge) / (rate of change of distributary water level at normal depth). It is a measure of how the outlet discharge tracks the parent channel level. Values near unity indicate proportional behavior; for modular outlets, dependence is minimized. Step-by-Step Solution: Identify the variables: discharge Q_out and water level H_d.Define F = dQ_out / dH_d (evaluated at normal depth).Hence, the named parameter is flexibility. Verification / Alternative check: Textbook definitions list: efficiency (ratio of water delivered to water measured), sensitivity (response to watercourse level), flexibility (response to distributary level), modular limit (head range for module performance). Why Other Options Are Wrong: Efficiency: Involves conveyance/delivery, not level response. Sensitivity: Relates to watercourse/backwater effects. Modular limit: Range of levels preserving modularity. Common Pitfalls: Interchanging flexibility and sensitivity; ignoring the specific reference to distributary level at normal depth. Final Answer: flexibility

Question 11

Lined canal section selection: Which combination best represents commonly recommended sections for small and large lined canals?

Accepted Answer

Introduction / Context: Lining reduces seepage and stabilizes canal sections. Standard practice suggests different economical shapes for different capacities while keeping constructability in mind. Given Data / Assumptions: Small canals: low discharge, narrow beds. Large canals: higher discharge requiring stable, hydraulically efficient shapes. Rounded corners reduce stress concentration and erosion. Concept / Approach: For small lined canals, a triangular section with a circular invert is easy to construct and economical. For larger canals, a trapezoidal section with rounded corners combines hydraulic efficiency with structural stability and ease of formwork. Step-by-Step Solution: Identify recommended small-canal section → triangular with circular bottom.Identify recommended large-canal section → trapezoidal with rounded corners.Therefore, the correct combined choice is options (a) and (b). Verification / Alternative check: Design handbooks list popular linings (concrete, brick, shotcrete) applied to these shapes due to stability and reduced eddies at corners. Why Other Options Are Wrong: Rectangular with rounded corners is sometimes used but is less common for very large canals due to structural and freeboard demands. Single options do not capture the small/large pairing in the question. Common Pitfalls: Assuming a single “best” shape for all capacities; neglecting corner rounding which improves durability. Final Answer: both (a) and (b)

Question 12

Structure identification: In a siphon aqueduct, which relation between canal and drainage is correct?

Accepted Answer

Introduction / Context: Cross-drainage works carry a canal across a natural drain/river. The type depends on relative levels of canal bed/full supply and drainage high flood level (HFL). Given Data / Assumptions: Siphon aqueduct vs aqueduct distinction relies on whether canal water runs under pressure (closed trough) when drainage HFL is high. Terminology: FSL = full supply level; HFL = high flood level. Concept / Approach: In a siphon aqueduct, the canal is carried over the drainage, but the drainage HFL lies above the canal bed. Hence the canal is confined in a trough and may flow under pressure (siphonic action) when flood rises, distinguishing it from a normal aqueduct where the canal remains free-flow. Step-by-Step Solution: Identify who passes over whom: canal over drainage.Check level relation: drainage HFL above canal bed → pressure flow in canal trough.Therefore option (c) correctly describes a siphon aqueduct. Verification / Alternative check: Standard classification charts list: Aqueduct (HFL below canal bed), Siphon Aqueduct (HFL above canal bed), Super passage (drainage over canal), etc. Why Other Options Are Wrong: Options (a) and (b) describe drainage over canal (super passage), not siphon aqueduct. Option (d) is an aqueduct (not siphon) case. Common Pitfalls: Confusing super passage with siphon aqueduct; mixing up FSL, bed level, and HFL definitions. Final Answer: canal passes over drainage and the drainage HFL is above the bottom of the canal trough

Question 13

Velocity measurement: A current meter is used to measure the velocity of flow when held

Accepted Answer

Introduction / Context: River and canal discharge measurements require point velocities. A current meter is a standard instrument for obtaining local velocity values in the wetted section. Given Data / Assumptions: Proper calibration of the current meter is available. Instrument is submerged and aligned with flow. Depth and location can be selected as per measurement scheme. Concept / Approach: By placing the current meter (e.g., cup or propeller type) at specific points in the cross-section, the local velocity is measured. Multiple-point methods (0.2D and 0.8D; or 0.6D single-point) integrate these to obtain mean velocity. Step-by-Step Solution: Position the meter at a defined location (x, y) within the wetted cross-section.Record rotations to infer local velocity via calibration.Repeat at various points to compute the cross-sectional average if discharge is required. Verification / Alternative check: Hydrometry standards specify point, vertical, and area methods; all rely on point measurements taken anywhere within the flowing section. Why Other Options Are Wrong: Surface or bottom only does not capture the velocity distribution. “Outside wetted area” is nonsensical for measuring flow. Only mid-depth on centreline is a special-case estimate, not a general rule. Common Pitfalls: Failing to align with flow; measuring too close to boundaries where instrument error increases. Final Answer: at any chosen point within the cross-section

Question 14

Canal escapes: Which statements about escapes provided in canal systems are correct?

Accepted Answer

Introduction / Context: Escapes are controlled outlets provided in canals to dispose of surplus flows safely during floods, regulator failures, or emergency drawdowns. Given Data / Assumptions: Canal reach subject to occasional surplus. Availability of natural drains or rivers to receive excess water. Design must ensure safe conveyance without overtopping. Concept / Approach: Properly designed escapes protect banks and structures by releasing excess water. Their capacity, alignment, and outfall into natural drainage are integral to system safety. Step-by-Step Solution: Confirm role as safety valves (prevents overtopping).Ensure capacity adequate (not less than canal flow at that reach).Lead discharge to natural drainage; align along favorable contours to minimize excavation and erosion. Verification / Alternative check: Design manuals specify escape capacity comparable to or exceeding canal capacity depending on operational needs and hydrologic risk, and outfalls are set into drains with adequate capacity. Why Other Options Are Wrong: Here, each individual statement is correct; hence “All the above” is the best choice. Common Pitfalls: Providing undersized escapes; discharging onto unprotected ground; poor alignment causing erosion. Final Answer: All the above

Question 15

Kennedy’s critical velocity formula: According to Kennedy, the critical (non-silting, non-scouring) mean velocity V0 (m/s) in a channel of depth D (m) is

Accepted Answer

Introduction / Context: Kennedy’s method sizes alluvial canals by equating the actual mean velocity to a “critical velocity” that avoids silting and scouring. Given Data / Assumptions: D in metres, V0 in m/s. m = critical velocity ratio accounting for sediment characteristics. Uniform flow and representative sediment. Concept / Approach: Kennedy proposed the empirical relation V0 = 0.55 * m * D^0.64 (SI form). Designers iterate canal dimensions so computed actual velocity matches V0. Step-by-Step Solution: Write V0 as function of depth D: V0 = 0.55 * m * D^0.64.Choose m based on silt character; m ≈ 1 for average silt.Use continuity Q = A * V and geometric relations to size the section accordingly. Verification / Alternative check: For D = 1 m, m = 1 → V0 ≈ 0.55 m/s, a plausible value for non-silting/non-scouring velocity in fine-silt canals. Why Other Options Are Wrong: Option b ignores m, which varies by silt type. Options c and d use wrong coefficients/exponents. Option e inverts dependence contrary to observations. Common Pitfalls: Using wrong units; applying exponent to hydraulic radius rather than depth; forgetting to adjust m. Final Answer: V0 = 0.55 * m * D^0.64

Question 16

Canal system hierarchy: Choose the correct sequence of components in a typical canal irrigation system, from headworks to the smallest conveyance.

Accepted Answer

Introduction / Context: Irrigation networks distribute water from a river diversion or storage to fields through a hierarchical system that progressively branches into smaller channels. Given Data / Assumptions: Standard nomenclature: headworks, main canal, branch canal, distributary, minor (watercourse later beyond minor). Gravity distribution from larger to smaller channels. Concept / Approach: The main canal originates at the headworks. It feeds branch canals, which in turn feed distributaries. Distributaries feed minors (and then watercourses to fields). Step-by-Step Solution: Start: Head works.Primary conveyance: Main canal.Secondary: Branch canal.Tertiary: Distributary.Quaternary: Minor. Verification / Alternative check: Project drawings of major canal systems confirm this descending order of command and capacities. Why Other Options Are Wrong: Options a, c, d, e misorder one or more elements (e.g., placing branch before main). Common Pitfalls: Confusing “distributary” with “minor”; mixing watercourse with minor. Final Answer: Head works – main canal – branch canal – distributary – minor

Question 17

Lane’s weighted creep theory for weir foundations: What relative weightages are assigned to vertical and horizontal creeps when computing the effective percolation path length?

Accepted Answer

Introduction / Context: Lane’s weighted creep theory improves upon Bligh’s creep theory by recognizing that vertical percolation through cutoff walls is more effective in reducing uplift than horizontal percolation along the base. Given Data / Assumptions: Weir/barrage foundation on pervious alluvium. Cutoffs and floor lengths provide percolation path (creep). Design seeks sufficient weighted creep length to ensure safety against piping and uplift. Concept / Approach: Lane assigned different effectiveness factors (weights): vertical creep is given three times the weight of horizontal creep because downward percolation through cutoffs dissipates head more efficiently. Step-by-Step Solution: Define weighted creep length Lw = Lh * 1 + Lv * 3.Compare Lw with required length derived from head and soil properties.Therefore, vertical : horizontal weightage = 3 : 1. Verification / Alternative check: Design examples compute Lw by multiplying vertical cutoff depths by 3 and adding horizontal floor lengths to obtain effective creep length. Why Other Options Are Wrong: Equal or greater weight to horizontal creep contradicts Lane’s central postulate. Doubling horizontal over vertical underestimates the value of cutoffs. Common Pitfalls: Forgetting to multiply vertical components by 3; confusing Lane’s weighting with Khosla’s flow net method (a different approach). Final Answer: triple weightage to vertical, single to horizontal

Question 18

Regime channels (Lacey): Under regime conditions, which statements correctly describe how sediment and forces act in an alluvial channel?

Accepted Answer

Introduction / Context: Lacey’s regime theory explains how alluvial channels (with mobile beds and banks) naturally attain stable shapes. In regime, the channel adjusts its width, depth, and slope so that neither silting nor scouring predominates. This question probes core qualitative statements behind Lacey’s assumptions. Given Data / Assumptions: Alluvial channel with uniform sediment supply and steady flow. “Regime” means long-term equilibrium: no net aggradation or degradation. We compare two qualitative statements about turbulence and shaping forces. Concept / Approach: According to Lacey, turbulence contains vertical components that help keep silt in suspension. Simultaneously, the channel perimeter experiences normal forces that mold it into a self-formed section. When these processes balance transport capacity with sediment load, a stable geometry develops. Step-by-Step Solution: Recognize that vertical eddies help maintain fine sediment in motion (supports statement a).Acknowledge that bed and banks are shaped by pressure/normal forces around the wetted perimeter (supports statement b).Therefore, both statements a and b reflect regime behavior. Verification / Alternative check: Classic regime literature cites vertical turbulence for suspension and self-formed sections governed by boundary-normal forces. Modern texts echo these qualitative foundations even when using updated resistance or sediment transport formulas. Why Other Options Are Wrong: (a) or (b) alone is incomplete; both processes act together in regime. (d) contradicts regime theory’s fundamentals. (e) omits the perimeter-shaping aspect. Common Pitfalls: Assuming regime implies no turbulence or that only bed shear matters; overlooking the role of bank shaping and three-dimensional turbulence. Final Answer: Both (a) and (b).

Question 19

River behavior types: Which combination correctly matches aggrading, degrading, and meandering rivers?

Accepted Answer

Introduction / Context: Fluvial morphology classifies rivers by how their beds evolve and how the planform looks. Recognizing aggrading, degrading, and meandering behaviors helps in river training, hydraulic design, and sediment management. Given Data / Assumptions: Aggrading: river deposits exceed transport → bed rises. Degrading: transport exceeds supply → bed lowers. Meandering: planform exhibits sinuous curves due to bank erosion/deposition. Concept / Approach: Aggradation tends to occur where energy decreases or sediment supply increases (e.g., after slope reduction). Degradation occurs where energy rises or sediment supply drops. Meandering develops from flow curvature, secondary currents, and bank erodibility, producing alternating pools and point bars. Step-by-Step Solution: Check each statement against standard definitions.Aggrading builds bed (true); degrading cuts bed (true); meandering is sinuous (true).Therefore, all statements are correct. Verification / Alternative check: Geomorphology texts confirm these definitions, with many rivers showing mixed behavior over time, yet the given statements are canonical descriptions. Why Other Options Are Wrong: Any single choice omits the others, although all are correct. “None” contradicts well-established definitions. Common Pitfalls: Confusing meandering with braided; assuming aggradation/degradation are permanent rather than reach-specific and time-dependent. Final Answer: All of the above.

Question 20

Soil–water relations: Field capacity of a soil primarily depends on which factors?

Accepted Answer

Introduction / Context: Field capacity is the moisture content held in the soil after excess gravity water has drained away and downward movement becomes negligible. It is central to irrigation scheduling and estimating plant-available water. Given Data / Assumptions: Soils with different textures exhibit different pore-size distributions. Surface tension and capillary forces govern water retention post-drainage. Concept / Approach: Field capacity is controlled by the soil’s ability to hold water against gravity—largely a function of pore geometry (porosity and pore-size distribution) and capillary tension. Finer soils (clays) retain more water at higher tensions than sands because of smaller pores and larger surface area. Step-by-Step Solution: Identify controlling factors: capillary tension and porosity/pore sizes.Relate finer textures to higher field capacity; coarser textures to lower field capacity.Select “Both (a) and (b).” Verification / Alternative check: Soil water retention curves directly show dependence on capillary pressure and pore structure, confirming both factors as primary controls. Why Other Options Are Wrong: (a) or (b) alone: incomplete—both act together. (d) ignores well-known physics of unsaturated flow. (e) Soil color is not a primary determinant. Common Pitfalls: Equating total porosity with available water (pore-size distribution matters); neglecting structure and organic matter. Final Answer: Both (a) and (b)

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