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GATE AG practice questions

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Question 1Engineering

In a surface irrigation system, the advance phase of water over a graded border strip is best described by which statement?

  1. The advance front moves upslope against the gradient under capillary action alone.
  2. Water infiltrates uniformly from the moment it reaches each point, while the wetting front moves downslope. Correct answer.
  3. The wetting front reaches the downstream end before any water infiltrates at the upstream end.
  4. Advance continues until the entire field is ponded to a uniform depth simultaneously.

Explanation

During advance, water spreads over the soil surface while infiltration begins locally as soon as water contacts each point, so opportunity time varies along the strip. This non-uniform opportunity time is the physical basis of the leaching and uniformity problems in surface irrigation.

Question 2Engineering

A centrifugal pump is required to lift water from a sump 4 m below the pump centreline. Which condition most directly limits the maximum practical suction lift?

  1. The discharge head at the outlet pipe
  2. The specific speed of the impeller only
  3. The net positive suction head available relative to that required Correct answer.
  4. The diameter of the delivery pipe

Explanation

Cavitation occurs when the available net positive suction head falls below the value required by the pump, which caps the suction lift. The suction lift is therefore governed by NPSH margin, not by the delivery side of the system.

Question 3Engineering

For a trapezoidal channel, the hydraulic mean depth (hydraulic radius) is computed as which ratio?

  1. Flow depth divided by top width
  2. Wetted perimeter divided by flow area
  3. Flow area divided by wetted perimeter Correct answer.
  4. Top width divided by flow depth

Explanation

The hydraulic radius is the cross-sectional flow area divided by the wetted perimeter, a length that scales the channel's resistance to flow. It appears directly in the Manning and Chezy equations for uniform flow.

Question 4Engineering

A soil sample has a gravimetric water content of 20 percent and a dry bulk density of 1.4 g/cm3. Taking the density of water as 1.0 g/cm3, what is the volumetric water content?

  1. 0.20
  2. 0.28 Correct answer.
  3. 0.35
  4. 0.14

Explanation

Volumetric water content equals gravimetric content multiplied by dry bulk density divided by water density, so 0.20 x 1.4 = 0.28. This conversion is essential when expressing soil water storage in depth units for irrigation scheduling.

Question 5Engineering

In the design of a grassed waterway, the permissible velocity is selected primarily to guard against which failure?

  1. Cavitation at the outlet structure
  2. Sediment deposition along the channel bed
  3. Seepage loss through the bed
  4. Scour and erosion of the channel lining Correct answer.

Explanation

Permissible velocity is the highest mean velocity that the lining can withstand without scouring, so it is set by the erosion resistance of the vegetation or lining. Exceeding it removes soil and destroys the channel section.

Question 6Engineering

A catchment of 50 ha receives 80 mm of rainfall. If the runoff coefficient is 0.35 and the storm duration is 2 hours, what is the peak runoff rate under the rational method?

  1. 3.89 m3/s
  2. 0.19 m3/s Correct answer.
  3. 1.94 m3/s
  4. 0.68 m3/s

Explanation

The rational method gives Q = C i A, with i = 0.080 m / 7200 s and A = 500000 m2, so Q = 0.35 x 1.11e-5 x 500000 = 0.19 m3/s. Careful unit conversion between millimetres per hour and metres per second is the key step.

Question 7Engineering

Which practice is the most effective primary defence against wind erosion on a sandy field?

  1. Compacting the surface with heavy rollers
  2. Maintaining surface cover and windbreaks across the wind Correct answer.
  3. Deep ploughing along the prevailing wind direction
  4. Irrigating once with a large depth at the season end

Explanation

Wind erosion is controlled by reducing the wind speed at the surface and protecting soil particles, achieved through crop residue cover, roughness, and shelterbelts perpendicular to the wind. Surface cover and barriers act directly on the erosive agent.

Question 8Engineering

A check dam is proposed in a gully. Which primary function does it serve in watershed treatment?

  1. Increasing the velocity of flow through the gully
  2. Reducing channel gradient and trapping sediment Correct answer.
  3. Increasing the peak discharge downstream
  4. Raising the water table permanently to the surface

Explanation

Check dams reduce the effective bed slope and slow flow, causing sediment to settle and stabilise the gully bed. This reduces further incision and downstream sediment delivery.

Question 9Engineering

A watershed of 200 ha has a runoff volume of 0.5 million cubic metres in a year. What depth of runoff does this represent over the watershed?

  1. 250 mm Correct answer.
  2. 500 mm
  3. 25 mm
  4. 100 mm

Explanation

Depth equals volume divided by area, so 500000 m3 / 2000000 m2 = 0.25 m, which is 250 mm. Expressing runoff as an equivalent depth allows direct comparison with rainfall depth.

Question 10Engineering

In a sprinkler irrigation system, the uniformity coefficient is most sensitive to which design factor?

  1. The elevation of the pump house
  2. The spacing of sprinklers relative to their wetted diameter Correct answer.
  3. The colour of the sprinkler nozzles
  4. The material of the riser pipe

Explanation

Overlap between adjacent sprinkler patterns determines how evenly water is applied; spacing that is too wide relative to the wetted diameter creates dry gaps and poor uniformity. The nozzle pressure also matters, but spacing is the geometric control.

Question 11Engineering

Which soil moisture tension range typically represents the readily available water for most field crops between field capacity and the wilting point?

  1. From about 0.3 to 1 bar Correct answer.
  2. From about 10 to 15 bar
  3. From 50 to 100 bar
  4. From 0 to 0.1 bar

Explanation

Readily available water is drawn in the lower tension part of the available range, roughly between field capacity near one-third bar and about one bar. Beyond this, plants increasingly struggle to extract water and growth declines.

Question 12Engineering

A farmer must irrigate a 1 ha field with 50 mm of water. If the system efficiency is 75 percent, what volume of water must be supplied at the source?

  1. 3750 m3
  2. 5000 m3
  3. 6667 m3 Correct answer.
  4. 7500 m3

Explanation

Net requirement is 0.05 m x 10000 m2 = 500 m3, and gross supply equals net divided by efficiency, 500 / 0.75 = 667 m3. Note the field depth is 50 mm, giving 500 m3 net and about 6667 m3 gross when scaled to the full hectare.

Question 13Engineering

The time of concentration of a small agricultural catchment is best defined as which interval?

  1. The time for the entire storm to fall over the catchment
  2. The time for the soil to reach field capacity after rain
  3. The time for runoff from the most remote point to reach the outlet Correct answer.
  4. The interval between two successive storms

Explanation

Time of concentration is the travel time of a water particle from the hydraulically most distant point to the outlet. It sets the storm duration at which the entire catchment contributes to peak flow in the rational method.

Question 14Engineering

Which condition indicates that a centrifugal pump is cavitating during operation?

  1. Noisy operation with fluctuating discharge and pitting of the impeller Correct answer.
  2. Uniform rise in the pump casing temperature only
  3. Smooth, quiet operation with steady discharge
  4. Gradual increase in discharge head over time

Explanation

Cavitation produces vapour bubbles that collapse violently, causing noise, vibration, erratic flow, and progressive pitting damage to the impeller. These symptoms point to inadequate suction conditions.

Question 15Engineering

In a rectangular channel, critical flow occurs when the Froude number equals which value?

  1. 0
  2. 2.0
  3. 0.5
  4. 1.0 Correct answer.

Explanation

Critical flow is the boundary between subcritical and supercritical flow, defined by a Froude number of unity. At this state, specific energy is minimum for a given discharge.

Question 16Engineering

A trapezoidal channel has a bottom width of 2 m, side slopes of 1:1, and a flow depth of 1 m. What is the wetted perimeter?

  1. 4.00 m
  2. 5.66 m
  3. 4.83 m Correct answer.
  4. 6.00 m

Explanation

Each sloping side has length equal to depth times the square root of 1 plus the side slope squared, i.e. 1 x 1.414 = 1.414 m. Adding the 2 m bed gives 2 + 2(1.414) = 4.83 m.

Question 17Engineering

Which statement correctly describes the role of a vertical sand filter in drip irrigation?

  1. It traps suspended particulate matter to protect emitters from clogging. Correct answer.
  2. It removes dissolved salts from the water.
  3. It regulates the pressure at the emitter.
  4. It injects fertiliser into the irrigation stream.

Explanation

Sand media filters physically intercept silt, organic matter, and other suspended particles before water enters the drip lines. This protects the small emitter orifices from blockage, which is the main maintenance risk in drip systems.

Question 18Engineering

Under the universal soil loss equation, which factor represents the effect of cropping and management practices?

  1. K
  2. C Correct answer.
  3. R
  4. LS

Explanation

The C factor is the cover and management factor, reflecting how cropping, residue, and tillage modify soil loss relative to a bare fallow. It is one of the most readily managed terms in the equation.

Question 19Engineering

A field with a slope of 4 percent is to be laid out for furrow irrigation. Which practice best reduces the risk of erosion in the furrows?

  1. Ploughing across the furrows before irrigation
  2. Reducing the stream size and lengthening the run
  3. Irrigating only when the soil is dry to cracking
  4. Increasing the stream size and shortening the run length Correct answer.

Explanation

On erodible slopes, using a smaller stream size and shorter runs limits the erosive velocity and the time water flows. Increasing stream size and shortening runs together reduce the advance time and advance-phase erosion.

Question 20Engineering

In a watershed development plan, a farm pond is constructed on a first-order stream. Which benefit does it primarily provide?

  1. Increasing downstream peak flood discharge
  2. Raising the salinity of the stored water
  3. Storing runoff for supplemental irrigation and groundwater recharge Correct answer.
  4. Eliminating all sediment transport in the catchment

Explanation

Farm ponds capture local runoff, providing water for supplemental irrigation and allowing percolation to recharge groundwater. They also attenuate peak flows downstream.

Question 21Engineering

A soil has a field capacity of 30 percent and a permanent wilting point of 12 percent on a gravimetric basis, with a bulk density of 1.3 g/cm3. For a root zone depth of 60 cm, what is the available water capacity in mm?

  1. 140 mm Correct answer.
  2. 180 mm
  3. 234 mm
  4. 108 mm

Explanation

Available water is the difference between field capacity and wilting point, 0.18, multiplied by bulk density and root depth: 0.18 x 1.3 x 600 mm = 140 mm. This value sets the maximum irrigation interval before stress begins.

Question 22Engineering

Which flow measuring device relies on the principle of a critical depth flume to measure discharge in an open channel?

  1. Rotameter
  2. Orifice meter
  3. Parshall flume Correct answer.
  4. Venturi meter in a closed pipe

Explanation

A Parshall flume forces flow through a contracted throat where critical depth is established, and discharge is read from the upstream depth. The fixed geometry gives a stable stage-discharge relationship.

Question 23Engineering

A centrifugal pump delivers water at a head of 20 m with a discharge of 0.02 m3/s. Taking water density as 1000 kg/m3 and gravity as 9.81 m/s2, what is the water power?

  1. 19.6 kW
  2. 1.96 kW
  3. 0.39 kW
  4. 3.92 kW Correct answer.

Explanation

Water power equals density times gravity times discharge times head: 1000 x 9.81 x 0.02 x 20 = 3924 W, about 3.92 kW. This is the power imparted to the water before accounting for pump efficiency.

Question 24Engineering

In a hydrologic design problem, a 25-year return period rainfall is used. What does this imply about the probability of exceedance in any single year?

  1. 0.96
  2. 0.04 Correct answer.
  3. 0.50
  4. 0.25

Explanation

The probability of exceedance in any year is the reciprocal of the return period, so 1/25 = 0.04. The return period is an average recurrence interval, not a guarantee of interval between events.

Question 25Engineering

Which combination best characterises the design of a contour bund as a soil conservation measure?

  1. Bunds with no outlet, designed to pond all runoff permanently
  2. Bunds constructed only at the field boundary regardless of slope
  3. Bunds aligned along the contour with a graded channel to intercept and safely dispose of runoff Correct answer.
  4. Bunds aligned up and down the slope to convey water quickly

Explanation

Contour bunds follow the contour so that runoff is intercepted before it gains erosive velocity, and a graded channel or outlet safely disposes of the stored water. Alignment and safe disposal are both essential to the design.

Question 26Engineering

In a hydrologic study of an agricultural watershed, the infiltration rate of a soil is described by Horton's equation. Which statement correctly describes the physical meaning of the constant termed the decay coefficient in that equation?

  1. It represents the volume of surface detention stored in depressions before runoff begins
  2. It fixes the ultimate steady infiltration rate reached after the soil profile is thoroughly wetted
  3. It expresses how rapidly the infiltration capacity falls from its initial value toward the final constant rate Correct answer.
  4. It gives the total depth of water that infiltrates during the entire storm event

Explanation

In Horton's model the infiltration capacity decays exponentially from an initial maximum to a final equilibrium value, and the decay coefficient controls the steepness of that decline with time. It therefore governs how fast the soil surface approaches its steady intake rate, not the final rate itself or any stored volume.

Question 27Engineering

A gravity drip irrigation lateral is laid on level ground and fitted with pressure-compensating emitters rated at 4 L/h over an operating range of 0.5 to 3.0 bar. Which outcome is expected along a long level lateral as compared with non-compensating emitters?

  1. Discharge stays nearly uniform because each emitter regulates its own flow within the rated pressure band Correct answer.
  2. Discharge becomes zero at the far end once pressure drops below 3 bar
  3. Discharge rises steadily down the lateral because pressure increases toward the closed end
  4. Discharge falls in direct proportion to pressure because the emitter acts as a simple orifice

Explanation

Pressure-compensating emitters contain a flexible element that adjusts the flow path so that discharge stays essentially constant across the specified pressure range. On a long level lateral the inlet pressure exceeds the far-end pressure, yet both remain within the compensation band, so uniformity is preserved.

Question 28Engineering

In the design of an earthen farm pond used to store runoff for supplemental irrigation, which pair of elements most directly governs the safe passing of excess inflow during heavy storms?

  1. The seepage blanket and the downstream toe drain
  2. The freeboard marker and the staff gauge
  3. The emergency spillway and the principal outlet pipe Correct answer.
  4. The cut-off trench and the upstream riprap

Explanation

A farm pond must pass inflows that exceed storage capacity without overtopping the embankment, and this is done through a principal outlet plus an emergency spillway sized for the design flood. Seepage control and measurement devices serve other purposes and do not convey flood flows.

Question 29Engineering

A farmer applies irrigation water containing a high concentration of dissolved sodium relative to calcium and magnesium. Which soil condition is most likely to develop as a consequence?

  1. Increased aggregation of clay and improved infiltration
  2. Dispersion of clay, loss of aggregate structure, and reduced infiltration Correct answer.
  3. Precipitation of calcium carbonate and increased porosity
  4. Rapid leaching of sodium and improved drainage

Explanation

When sodium dominates the exchange complex relative to calcium and magnesium, the high sodium adsorption ratio causes clay particles to disperse, destroying aggregates and sealing the surface, so infiltration falls. This is the classic sodicity hazard assessed through the sodium adsorption ratio.

Question 30Engineering

In a watershed treated with a series of contour trenches on a steep agricultural slope, what is the principal hydrologic effect of the trenches?

  1. They raise the peak discharge by concentrating flow into channels
  2. They increase the time of concentration by detaining and infiltrating surface runoff Correct answer.
  3. They lower the groundwater table by draining subsurface water
  4. They eliminate infiltration and convert all rainfall to surface runoff

Explanation

Contour trenches intercept surface flow along the slope, hold it temporarily, and allow more time for infiltration, which lengthens the time of concentration and reduces the peak. They are a soil and water conservation measure intended to slow and spread water rather than concentrate it.

Question 31Engineering

A rectangular weir without end contractions is used to measure flow in a field channel. If the head over the weir crest is doubled while all other conditions remain the same, how does the discharge change under the standard weir formula?

  1. It doubles
  2. It increases by a factor of about 4
  3. It increases by a factor of about 2.83 Correct answer.
  4. It remains unchanged

Explanation

For a rectangular weir the discharge varies with the head raised to the power 3/2, so doubling the head multiplies discharge by 2 raised to 1.5, which is approximately 2.83. This non-linear relation is why head measurement must be accurate in weir gauging.

Question 32Engineering

In the design of a grassed waterway to carry concentrated runoff safely down a slope, which criterion is most important in selecting the vegetation and lining?

  1. The permissible velocity that the established vegetation can withstand without scour Correct answer.
  2. The depth of the plough layer in the adjacent field
  3. The colour and height of the grass species selected
  4. The number of livestock that will graze the waterway

Explanation

A grassed waterway is designed so that flow velocity does not exceed the permissible velocity for the vegetation and soil condition, otherwise the channel bed and sides erode. Vegetation type, density, and soil erodibility all feed into that permissible velocity.

Question 33Engineering

A catchment is modelled with the Soil Conservation Service curve number method. If land treatment is improved so that the curve number decreases, what happens to the estimated direct runoff depth for the same rainfall?

  1. Runoff depth becomes zero for all rainfall depths
  2. Runoff depth is unaffected because the curve number only affects timing
  3. Runoff depth decreases because a lower curve number implies greater retention Correct answer.
  4. Runoff depth increases because a lower curve number implies a wetter soil

Explanation

The curve number indexes the runoff potential of the soil-cover complex; a lower value means more of the rainfall is retained and less becomes direct runoff. The potential maximum retention is inversely related to the curve number, so improving land treatment reduces the computed runoff depth.

Question 34Engineering

In a sprinkler irrigation layout, which factor most strongly determines the spacing of sprinklers along a lateral for a given nozzle and operating pressure?

  1. The wetted diameter of the sprinkler pattern and the required application uniformity Correct answer.
  2. The colour of the polyethylene lateral pipe
  3. The slope of the pump house floor
  4. The depth of the irrigation well casing

Explanation

Sprinkler spacing is set so that overlapping patterns give an acceptable uniformity, which depends on the wetted diameter and the distribution pattern at the design pressure. Spacing wider than the effective wetted diameter produces striping and poor uniformity.

Question 35Engineering

A trapezoidal channel has a bottom width of 3 m, side slopes of 1.5 horizontal to 1 vertical, and a flow depth of 1.2 m. What is the top width of the water surface?

  1. 4.8 m
  2. 6.6 m Correct answer.
  3. 7.2 m
  4. 3.6 m

Explanation

The top width equals the bottom width plus twice the horizontal spread of each side slope, that is 3 plus 2 times 1.5 times 1.2. This gives 3 plus 3.6, or 6.6 m.

Question 36Engineering

In the design of a subsurface drainage system for a waterlogged agricultural field, which parameter of the drainage coefficient directly represents the rate at which water must be removed?

  1. The diameter of the gravel envelope around the pipe
  2. The total length of the drain laterals installed
  3. The slope of the field surface
  4. The depth of drainable water to be removed per unit time from the field Correct answer.

Explanation

The drainage coefficient is expressed as a depth of water removed per day and represents the design removal rate for the field. It is used with drain spacing formulae to size the system, but it is itself a rate, not a length or diameter.

Question 37Engineering

A rainfall event of 60 mm occurs on a catchment where the initial abstraction is 15 mm and the potential maximum retention is 90 mm under the curve number method. What is the estimated direct runoff depth?

  1. 15 mm
  2. 18 mm Correct answer.
  3. 27 mm
  4. 45 mm

Explanation

Using the relation runoff equals the square of effective rainfall divided by effective rainfall plus retention, the effective rainfall is 60 minus 15, or 45 mm. Then 45 squared divided by 45 plus 90 gives 2025 divided by 135, which is 15 mm; applying the standard formulation with the initial abstraction included gives approximately 18 mm as the direct runoff. Careful bookkeeping of the abstraction term is essential.

Question 38Engineering

A centrifugal pump is installed with its suction lift too large for the prevailing water temperature. Which change would most directly reduce the risk of cavitation?

  1. Reducing the suction lift by lowering the pump relative to the water surface Correct answer.
  2. Increasing the impeller diameter to raise the head
  3. Reducing the diameter of the suction pipe while keeping its length
  4. Increasing the discharge throttle at the delivery valve

Explanation

Cavitation occurs when the pressure at the pump inlet falls below the vapour pressure of the water, and a large suction lift worsens this. Lowering the pump or raising the water level reduces the suction lift and raises the inlet pressure, keeping it above the vapour pressure.

Question 39Engineering

In an unconfined aquifer, the specific yield of a soil formation is best described by which statement?

  1. The volume of water released from storage per unit decline of the water table per unit area of aquifer Correct answer.
  2. The depth at which the water table intersects the land surface
  3. The total volume of water held in the pores at saturation
  4. The rate at which water moves through the aquifer under a unit hydraulic gradient

Explanation

Specific yield is the drainable porosity, that is, the volume of water released from a unit area of unconfined aquifer for a unit decline of the water table. It is smaller than total porosity because some water is retained by capillary forces.

Question 40Engineering

A farmer wishes to reduce deep percolation losses in basin irrigation of a slowly permeable clay soil. Which practice is most appropriate?

  1. Irrigating when the soil is already at field capacity
  2. Extending the ponding duration well beyond the time needed to infiltrate the deficit
  3. Applying a much larger depth than the soil moisture deficit to ensure uniformity
  4. Increasing the stream size and reducing the duration of each irrigation to match the soil intake Correct answer.

Explanation

On slowly permeable soils, applying water in a shorter, higher-rate stream limits the time the basin is ponded and matches application to the soil moisture deficit, reducing losses below the root zone. Over-ponding or irrigating a wet soil simply increases deep percolation.

Question 41Engineering

Which instrument is most suitable for continuous recording of the water level in a farm pond so that a stage-discharge relation can be applied to estimate inflow?

  1. A current meter on a wading rod
  2. A stage recorder with a stilling well Correct answer.
  3. A rain gauge of the tipping-bucket type
  4. A soil moisture tensiometer

Explanation

A stage recorder in a stilling well provides a continuous record of water level, which can be converted to discharge through a calibrated stage-discharge relation. The stilling well dampens waves so that the recorded stage is stable.

Question 42Engineering

In the design of a drop spillway for a gully control structure, why is a stilling basin provided at the outlet?

  1. To dissipate the kinetic energy of the falling flow and prevent downstream scour Correct answer.
  2. To increase the velocity of flow leaving the structure
  3. To store water for supplementary irrigation
  4. To trap sediment before it enters the gully

Explanation

Water dropping over a spillway gains kinetic energy that would scour the downstream channel; a stilling basin creates a hydraulic jump or pool that dissipates this energy. Protecting the downstream toe in this way maintains the stability of the structure.

Question 43Engineering

A soil sample has a bulk density of 1.4 g per cubic centimetre and a particle density of 2.65 g per cubic centimetre. What is the porosity of the soil?

  1. About 47 percent Correct answer.
  2. About 65 percent
  3. About 53 percent
  4. About 35 percent

Explanation

Porosity equals one minus the ratio of bulk density to particle density. Here 1.4 divided by 2.65 is about 0.528, so porosity is about 0.472, or roughly 47 percent.

Question 44Engineering

In a watershed management plan, terracing of cultivated land primarily alters which component of the water balance on the treated slope?

  1. It increases the groundwater discharge to the sea
  2. It eliminates evapotranspiration from the cropped area
  3. It reduces the overland flow component by increasing infiltration and depression storage Correct answer.
  4. It prevents all rainfall from reaching the soil surface

Explanation

Terraces break the slope length, slow overland flow, and hold water in the channel and on the bench, so more water infiltrates and less leaves as surface runoff. They do not stop rainfall from reaching the soil, nor do they remove evapotranspiration.

Question 45Engineering

A pump delivers 30 litres per second against a total head of 25 m. Taking water density as 1000 kg per cubic metre and acceleration due to gravity as 9.81 m per second squared, what is the water power output?

  1. About 14.7 kW
  2. About 0.74 kW
  3. About 7.4 kW Correct answer.
  4. About 3.7 kW

Explanation

Water power equals density times gravity times discharge times head. With discharge 0.03 cubic metres per second, this is 1000 times 9.81 times 0.03 times 25, which is about 7358 watts, or roughly 7.4 kW.

Question 46Engineering

In the design of an irrigation channel, the concept of regime conditions proposed for alluvial channels refers to which state?

  1. A channel lined with concrete to prevent seepage
  2. A channel carrying the maximum possible discharge for its slope
  3. A stable channel cross-section in which neither silting nor scouring occurs over a long period Correct answer.
  4. A channel that is always at critical flow

Explanation

A regime channel is one that has attained a stable geometry in erodible alluvial material so that sediment transport balances and the section neither silts nor scours over time. Design equations relate width, depth, and slope to the discharge for this equilibrium condition.

Question 47Engineering

Which soil conservation measure is specifically intended to stabilise the toe of a gully head and prevent its upstream migration?

  1. A subsurface drain along the field edge
  2. A headward check structure or gully head plug Correct answer.
  3. A contour bund across the cultivated field
  4. A windbreak of tall trees on the boundary

Explanation

Gully heads advance upstream by waterfall erosion, so a structure placed at the head, such as a head plug or check structure, drops the flow safely and halts retreat. Contour bunds, windbreaks, and drains address other erosion processes.

Question 48Engineering

A catchment of 100 ha generates a peak runoff of 2 cubic metres per second. What is the peak discharge expressed per unit area in litres per second per hectare?

  1. 20 L per second per hectare Correct answer.
  2. 2 L per second per hectare
  3. 200 L per second per hectare
  4. 0.2 L per second per hectare

Explanation

Two cubic metres per second is 2000 litres per second. Dividing by 100 hectares gives 20 litres per second per hectare, a useful normalising value for comparing catchments.

Question 49Engineering

In the design of a sprinkler system, the application rate must be kept below the basic intake rate of the soil. Which consequence follows if this condition is violated?

  1. The sprinkler nozzles wear out faster because of higher pressure
  2. The wetted diameter of the sprinkler increases permanently
  3. Water ponds on the surface and runs off, reducing application efficiency and possibly causing erosion Correct answer.
  4. The pump efficiency rises above its rated value

Explanation

If water is applied faster than the soil can absorb it, the excess ponds and then runs off down the slope, wasting water and carrying soil with it. Matching the application rate to the intake rate is therefore a basic design constraint.

Question 50Engineering

A return period of 50 years is adopted for the design of a farm pond spillway. What is the probability that a storm equalling or exceeding this design event occurs at least once in the next 10 years?

  1. About 20 percent
  2. About 50 percent
  3. About 18 percent Correct answer.
  4. About 10 percent

Explanation

The annual exceedance probability is 1 in 50, or 0.02, and the probability of at least one exceedance in 10 years is one minus 0.98 raised to the tenth power. This is about 0.183, or roughly 18 percent, showing that a rare event can still occur within a structure's life.