I85PREP
⌘ K
AIH Fundamentals of Hydrology Examination study materials
AIH Fundamentals of Hydrology Examination study resources

AIH Fundamentals of Hydrology Examination practice questions

One question at a time. Build your AIH Fundamentals of Hydrology Examination understanding.

First 50 of 199 questions. Each one lists the choices, the correct answer, and an explanation. The checker at the top of this page saves progress in this browser when it is available.

Continue in the practice tool above to load more questions, 50 at a time.

Question 1Fundamentals of Hydrology

Which process returns water vapor from plants to the atmosphere?

  1. Interception
  2. Infiltration
  3. Transpiration Correct answer.
  4. Percolation

Explanation

Transpiration is the loss of water vapor through stomata in plant leaves. It moves water from the soil-plant system back to the atmosphere and is a major component of evapotranspiration.

Question 2Fundamentals of Hydrology

A watershed is best described as which of the following?

  1. A channel reach between two gauging stations
  2. An area of land that drains to a common outlet Correct answer.
  3. A single lake with no surface outflow
  4. The saturated zone beneath a valley floor

Explanation

A watershed (or catchment) is the land area contributing runoff to a common point along a stream or river. Its boundary is the drainage divide, determined by topography.

Question 3Fundamentals of Hydrology

In the water balance equation P = ET + Q + ΔS for a catchment over a year, what does ΔS represent?

  1. Change in stream sinuosity
  2. Change in soil erodibility
  3. Change in catchment water storage Correct answer.
  4. Change in precipitation intensity

Explanation

The water balance conserves mass: precipitation is partitioned into evapotranspiration, runoff, and a change in storage. Storage change includes soil moisture, groundwater, snowpack, and surface water.

Question 4Fundamentals of Hydrology

Which instrument is used to measure stream stage at a gauging station?

  1. An anemometer
  2. A pyranometer
  3. A lysimeter
  4. A staff gauge Correct answer.

Explanation

A staff gauge is a graduated scale read against the water surface to obtain stage. Stage is then converted to discharge using a rating curve.

Question 5Fundamentals of Hydrology

The hypsometric curve of a catchment relates which two quantities?

  1. Rainfall intensity and duration
  2. Soil depth and infiltration rate
  3. Elevation and the fraction of area above that elevation Correct answer.
  4. Discharge and time

Explanation

A hypsometric curve plots elevation against the proportion of catchment area above it, summarizing the basin's elevation distribution. It is used to infer topographic maturity and runoff response.

Question 6Fundamentals of Hydrology

Which term describes water held in the unsaturated zone that cannot be drained by gravity?

  1. Saturation excess
  2. Baseflow
  3. Specific yield
  4. Field capacity Correct answer.

Explanation

Field capacity is the water content remaining in soil after gravity drainage has largely ceased, held by capillary and adsorptive forces. Drainable water beyond field capacity contributes to recharge.

Question 7Fundamentals of Hydrology

Which of the following is a form of precipitation interception loss?

  1. Rainfall stored on leaves that later evaporates Correct answer.
  2. Rainfall that infiltrates into the soil
  3. Rainfall that becomes overland flow
  4. Rainfall that recharges an aquifer

Explanation

Interception loss is precipitation captured by vegetation, buildings, or other surfaces and evaporated before reaching the ground. It reduces the water available for infiltration and runoff.

Question 8Fundamentals of Hydrology

A hydrograph's rising limb typically reflects which catchment response?

  1. Snowmelt occurring months later
  2. Rapid delivery of rainfall to the channel network Correct answer.
  3. Evaporation from the channel surface
  4. Long-term groundwater recession

Explanation

The rising limb shows increasing discharge as rainfall or meltwater reaches the channel through overland flow and fast subsurface pathways. Its steepness reflects catchment response time and storm intensity.

Question 9Fundamentals of Hydrology

Which condition most directly produces infiltration-excess overland flow?

  1. Saturation of the entire soil profile from below
  2. Rainfall intensity exceeding the soil's infiltration capacity Correct answer.
  3. Snowmelt occurring on frozen ground
  4. Groundwater levels rising above the land surface

Explanation

Infiltration-excess (Hortonian) overland flow occurs when rainfall is delivered faster than the soil can accept it. The excess ponds and flows over the surface.

Question 10Fundamentals of Hydrology

A catchment receives 1200 mm of precipitation and loses 700 mm to evapotranspiration with no change in storage. What is the annual runoff in mm?

  1. 500 Correct answer.
  2. 700
  3. 1200
  4. 1900

Explanation

With ΔS = 0, the water balance gives Q = P − ET = 1200 − 700 = 500 mm. Runoff is the residual after evapotranspiration is removed.

Question 11Fundamentals of Hydrology

A storm of 50 mm falls in 2 hours on a 10 km² catchment. Assuming 20% of rainfall becomes direct runoff, what is the runoff volume in m³?

  1. 100,000 Correct answer.
  2. 50,000
  3. 250,000
  4. 500,000

Explanation

Runoff depth is 0.20 × 50 mm = 10 mm = 0.010 m. Multiplying by area 10 km² = 10,000,000 m² gives 100,000 m³.

Question 12Fundamentals of Hydrology

A rating curve at a gauging station is used to do which of the following?

  1. Convert discharge to rainfall depth
  2. Convert measured stage to discharge Correct answer.
  3. Estimate evapotranspiration from a lake
  4. Determine aquifer transmissivity

Explanation

A rating curve is an empirical relationship between stage and discharge developed from current-meter measurements. Once established, stage records can be converted to continuous discharge.

Question 13Fundamentals of Hydrology

Which factor most strongly increases the peak discharge of a storm hydrograph?

  1. A shorter time of concentration for the catchment Correct answer.
  2. A deeper unsaturated zone before the storm
  3. A longer travel path through a flat floodplain
  4. A denser vegetation cover that intercepts rain

Explanation

A shorter time of concentration means runoff from different parts of the catchment arrives at the outlet more nearly simultaneously, producing a higher peak. Catchment shape, slope, and drainage density control this timing.

Question 14Fundamentals of Hydrology

The unit hydrograph concept assumes that direct runoff from a given rainfall excess is which of the following?

  1. Independent of the rainfall duration
  2. Linearly proportional to the rainfall excess depth Correct answer.
  3. Inversely proportional to catchment area
  4. Constant regardless of antecedent moisture

Explanation

The unit hydrograph assumes a linear rainfall-runoff response: runoff from a storm of a given duration is proportional to the depth of rainfall excess. Superposition and proportionality then allow storms of different depths to be modeled.

Question 15Fundamentals of Hydrology

Which statement best describes the difference between specific yield and specific retention in an unconfined aquifer?

  1. Specific yield is drainable water; specific retention is water held against gravity Correct answer.
  2. Both terms refer only to confined aquifers
  3. Specific yield is held by capillary forces; specific retention drains freely
  4. Specific yield equals total porosity plus specific retention

Explanation

Total porosity is partitioned into specific yield (water that drains under gravity) and specific retention (water held by capillary and surface forces). Their sum equals porosity.

Question 16Fundamentals of Hydrology

A well is pumped at a constant rate from an unconfined aquifer. Which observation indicates that steady-state drawdown has been reached?

  1. Drawdown continues to increase at a constant rate
  2. Water level in the well rises above the static level
  3. Pumping rate begins to decline automatically
  4. Water levels in observation wells stop declining with time Correct answer.

Explanation

At steady state, recharge and storage release balance pumping, so drawdown stabilizes and no longer changes with time. Continued drawdown implies transient conditions with ongoing storage depletion.

Question 17Fundamentals of Hydrology

Which of the following best explains why a catchment with high drainage density responds faster to rainfall?

  1. The catchment has a larger total area
  2. Water travels shorter distances to reach a channel Correct answer.
  3. Soils have higher porosity and store more water
  4. Vegetation intercepts a larger share of rainfall

Explanation

Drainage density is channel length per unit area. A high density means overland and shallow flow paths are short, so water reaches channels quickly and the hydrograph peaks sooner and higher.

Question 18Fundamentals of Hydrology

A snowpack of 200 mm water equivalent melts over five days at a constant rate. What is the average daily meltwater depth in mm/day?

  1. 200
  2. 20
  3. 40 Correct answer.
  4. 100

Explanation

Dividing the water equivalent by the melt period gives 200 mm / 5 days = 40 mm/day. Water equivalent expresses snow depth as the equivalent liquid depth.

Question 19Fundamentals of Hydrology

Which process describes the movement of water from the saturated zone into a stream channel during dry periods?

  1. Hortonian overland flow
  2. Sublimation
  3. Baseflow Correct answer.
  4. Throughfall

Explanation

Baseflow is the sustained discharge to a stream from groundwater storage, maintaining flow between storms. It appears as the slowly declining limb of a hydrograph.

Question 20Fundamentals of Hydrology

A catchment has an initial abstraction of 10 mm and continues to lose 15% of rainfall to infiltration after that threshold. For a 60 mm storm, what is the approximate direct runoff depth in mm?

  1. 42.5 Correct answer.
  2. 60
  3. 50
  4. 45

Explanation

After the 10 mm initial abstraction, 50 mm remains; 15% of that (7.5 mm) is lost, leaving 42.5 mm of direct runoff. This is a simplified abstraction accounting approach.

Question 21Fundamentals of Hydrology

In a confined aquifer, the potentiometric surface lies 20 m above the top of the aquifer. Which statement is correct?

  1. Drawdown cannot occur because the aquifer is confined
  2. The aquifer is unconfined and has a water table
  3. A well penetrating the aquifer will rise to about 20 m above the aquifer top Correct answer.
  4. The well will produce no water because the aquifer is dry

Explanation

In a confined aquifer, water rises in a well to the potentiometric surface, which can stand above the aquifer top. If that surface is above land, the well is artesian.

Question 22Fundamentals of Hydrology

Two catchments have identical area and rainfall, but catchment A has a much larger fraction of impervious surface. Which outcome is most consistent with hydrological theory?

  1. A has a higher runoff coefficient and a flashier hydrograph Correct answer.
  2. A has a lower runoff coefficient and a flatter hydrograph
  3. A has higher evapotranspiration and lower runoff volume
  4. A has greater infiltration and lower peak discharge

Explanation

Impervious surfaces reduce infiltration and increase the fraction of rainfall converted to runoff, so the runoff coefficient rises. Faster surface delivery also produces a sharper, higher peak.

Question 23Fundamentals of Hydrology

A hydrograph shows a sharp peak shortly after rainfall followed by a rapid recession to a low, nearly constant flow. Which interpretation is most defensible?

  1. A large, flat, heavily vegetated catchment with deep soils
  2. A catchment dominated by slow snowmelt over several months
  3. A catchment where baseflow exceeds direct runoff year-round
  4. A small, impervious or steep catchment with limited groundwater storage Correct answer.

Explanation

A sharp peak and rapid recession indicate fast runoff delivery and little storage to sustain flow, typical of small, steep, or impervious catchments. The low constant flow reflects limited groundwater contribution.

Question 24Fundamentals of Hydrology

A catchment's annual precipitation is 1500 mm, evapotranspiration is 900 mm, and streamflow is 550 mm. Assuming no other fluxes, what is the implied annual change in storage in mm?

  1. +150
  2. −50
  3. 0
  4. +50 Correct answer.

Explanation

Rearranging the water balance gives ΔS = P − ET − Q = 1500 − 900 − 550 = +50 mm. A positive value indicates net storage gain over the year.

Question 25Fundamentals of Hydrology

Which combination of conditions would most likely produce saturation-excess overland flow on a hillslope?

  1. A cold storm falling as snow on frozen ground
  2. A shallow water table rising to the surface in a concave hollow during a long storm Correct answer.
  3. A short, intense storm on dry, deep sandy soil
  4. A steep, well-drained slope with thin vegetation

Explanation

Saturation-excess runoff occurs where the water table reaches the ground surface, commonly in concave hollows and near streams during prolonged rainfall. The saturated soil cannot accept more water, so rain flows overland.

Question 26Fundamentals of Hydrology

Which term describes the total volume of water stored in a catchment at a given moment, including surface, soil, and groundwater stores?

  1. Channel roughness
  2. Potential evapotranspiration
  3. Baseflow index
  4. Catchment storage Correct answer.

Explanation

Catchment storage is the aggregate water held in all reservoirs within a drainage basin, and changes in this store link precipitation inputs to streamflow outputs in the water balance. The other terms describe atmospheric demand, channel hydraulics, or a flow ratio rather than a stored volume.

Question 27Fundamentals of Hydrology

Which instrument is used to measure the depth of water flowing over a weir crest at a gauging station?

  1. Pyranometer
  2. Hygrometer
  3. Staff gauge or stilling well Correct answer.
  4. Anemometer

Explanation

A staff gauge or stilling well records water level, and over a weir this head is converted to discharge using a standard weir equation. The other instruments measure wind, solar radiation, and humidity rather than water level.

Question 28Fundamentals of Hydrology

In the hydrological cycle, which process converts liquid water to vapour directly from a water surface without passing through plants?

  1. Condensation
  2. Sublimation
  3. Transpiration
  4. Evaporation Correct answer.

Explanation

Evaporation is the phase change from liquid to vapour at a free water or soil surface. Transpiration involves plant pathways, condensation is the reverse phase change, and sublimation is the direct solid-to-vapour transition.

Question 29Fundamentals of Hydrology

Which soil property most directly controls the rate at which water enters the soil surface during a storm?

  1. Soil temperature
  2. Soil colour
  3. Saturated hydraulic conductivity Correct answer.
  4. Soil bulk density alone

Explanation

Saturated hydraulic conductivity expresses how readily water moves through a saturated soil, so it governs the maximum infiltration rate once surface saturation occurs. Colour, temperature, and density alone do not define transmission capacity.

Question 30Fundamentals of Hydrology

Which term describes the water that drains from a soil under gravity and reaches a stream over days to weeks after rainfall?

  1. Baseflow Correct answer.
  2. Throughflow
  3. Interflow
  4. Overland flow

Explanation

Baseflow is the sustained groundwater discharge that maintains streamflow between storms, arriving slowly through the saturated zone. Interflow and throughflow travel laterally in the unsaturated zone, and overland flow is surface runoff.

Question 31Fundamentals of Hydrology

Which unit is conventionally used to express discharge in hydrological reporting?

  1. Millimetres
  2. Cubic metres per second Correct answer.
  3. Hectares
  4. Kilopascals

Explanation

Discharge is a volume of water passing a section per unit time, so cubic metres per second is the standard SI-derived unit. Millimetres and hectares are depth and area measures, and kilopascals measure pressure.

Question 32Fundamentals of Hydrology

Which process returns water vapour from the land surface to the atmosphere through plant leaves?

  1. Transpiration Correct answer.
  2. Interception
  3. Percolation
  4. Infiltration

Explanation

Transpiration is the loss of water vapour through stomata in plant leaves, forming part of evapotranspiration. Infiltration and percolation move water downward into and through soil, and interception captures rainfall on vegetation surfaces.

Question 33Fundamentals of Hydrology

Which statement describes the water balance equation for a catchment over a defined period?

  1. Storage change equals evapotranspiration minus precipitation
  2. Precipitation equals runoff multiplied by area
  3. Runoff equals precipitation divided by evapotranspiration
  4. Precipitation equals evapotranspiration plus runoff plus change in storage Correct answer.

Explanation

The catchment water balance equates inputs (precipitation) to outputs (evapotranspiration and runoff) plus any change in storage. The other expressions misstate the relationship among these components.

Question 34Fundamentals of Hydrology

A catchment of 25 km² receives 40 mm of rain, of which 25% becomes direct runoff. What volume of direct runoff is generated, in cubic metres?

  1. 1000000 m³
  2. 250000 m³ Correct answer.
  3. 2500 m³
  4. 25000 m³

Explanation

Runoff depth is 0.25 × 40 mm = 10 mm = 0.010 m. Multiplying by the area of 25 km² (25,000,000 m²) gives 250,000 m³.

Question 35Fundamentals of Hydrology

A storm delivers 80 mm of rainfall to a catchment where the runoff coefficient is 0.35. What depth of direct runoff results?

  1. 80 mm
  2. 28 mm Correct answer.
  3. 45 mm
  4. 35 mm

Explanation

Direct runoff depth equals rainfall depth multiplied by the runoff coefficient, so 80 mm × 0.35 = 28 mm. The other values misapply the coefficient or ignore it.

Question 36Fundamentals of Hydrology

A rectangular channel has a cross-sectional area of 6 m² and a mean velocity of 1.5 m/s. What is the discharge?

  1. 9 m³/s Correct answer.
  2. 4 m³/s
  3. 0.25 m³/s
  4. 7.5 m³/s

Explanation

Discharge equals cross-sectional area multiplied by mean velocity, giving 6 m² × 1.5 m/s = 9 m³/s. The other values result from dividing or adding the two quantities.

Question 37Fundamentals of Hydrology

Why does a catchment with a large proportion of clay-rich soils tend to produce higher storm peaks than a sandy catchment of similar size?

  1. Clay soils have higher saturated hydraulic conductivity
  2. Clay soils increase evapotranspiration during storms
  3. Clay soils store more plant-available water
  4. Clay soils reduce infiltration and promote overland flow Correct answer.

Explanation

Clay-rich soils have low hydraulic conductivity, so infiltration capacity is quickly exceeded and water is routed rapidly over the surface, sharpening the hydrograph peak. Sandy soils transmit water readily, delaying and flattening the response.

Question 38Fundamentals of Hydrology

Which term describes the delay between the centroid of effective rainfall and the centroid of direct runoff on a hydrograph?

  1. Lag time Correct answer.
  2. Recession constant
  3. Baseflow index
  4. Time of concentration

Explanation

Lag time measures the interval between the centroid of rainfall excess and the centroid of the resulting runoff hydrograph. Time of concentration is the travel time from the most distant point to the outlet, and the other terms describe recession decay or flow ratios.

Question 39Fundamentals of Hydrology

A catchment has a time of concentration of 6 hours. Rainfall of uniform intensity falls for 10 hours. How does the resulting hydrograph peak compare with that from a 6-hour storm of the same intensity?

  1. The peak is higher but occurs earlier than the 6-hour case
  2. The peak is higher and occurs when the whole catchment contributes Correct answer.
  3. The peak is lower and later
  4. The peak is identical in magnitude and timing

Explanation

When storm duration exceeds the time of concentration, the entire catchment contributes to outflow simultaneously, producing the maximum possible peak for that intensity. A storm shorter than the time of concentration cannot mobilise the full catchment.

Question 40Fundamentals of Hydrology

Which factor primarily determines whether rainfall becomes Hortonian overland flow rather than infiltrating?

  1. Wind speed during the storm
  2. Groundwater pumping rate in a distant aquifer
  3. Rainfall intensity compared with infiltration capacity Correct answer.
  4. Channel width downstream

Explanation

Hortonian overland flow occurs when rainfall intensity exceeds the soil's infiltration capacity, so the comparison of the two rates is decisive. Wind, channel width, and distant pumping do not control surface infiltration at the point of rainfall.

Question 41Fundamentals of Hydrology

A catchment receives 950 mm of precipitation and generates 400 mm of streamflow. Assuming storage is unchanged, what is the evapotranspiration loss?

  1. 1350 mm
  2. 400 mm
  3. 950 mm
  4. 550 mm Correct answer.

Explanation

With no storage change, evapotranspiration equals precipitation minus runoff: 950 − 400 = 550 mm. The other values add the terms or restate one of the inputs.

Question 42Fundamentals of Hydrology

Which statement best describes field capacity in a soil profile?

  1. The water content remaining after gravity drainage has largely ceased Correct answer.
  2. The water content of a completely dry oven-dried soil
  3. The maximum water content achievable under ponded conditions
  4. The water content at which plants permanently wilt

Explanation

Field capacity is the water content retained after free drainage under gravity has slowed to a negligible rate, typically a few days after saturation. It lies between saturation and the permanent wilting point.

Question 43Fundamentals of Hydrology

Why does urbanisation typically increase the volume of direct runoff for a given storm?

  1. It lengthens the time of concentration
  2. It replaces permeable surfaces with impervious ones, reducing losses Correct answer.
  3. It lowers the runoff coefficient
  4. It increases infiltration capacity across the catchment

Explanation

Impervious surfaces such as roads and roofs prevent infiltration, so a larger fraction of rainfall becomes direct runoff and the runoff coefficient rises. Urban drainage also shortens travel times rather than lengthening them.

Question 44Fundamentals of Hydrology

Which description matches the recession limb of a storm hydrograph?

  1. The flat baseline flow before the storm begins
  2. The brief plateau at the peak of the hydrograph
  3. The rising period of increasing discharge after rainfall
  4. The period of declining discharge as catchment stores drain Correct answer.

Explanation

The recession limb records declining discharge after the peak as soil, surface, and channel stores gradually empty. The rising limb precedes the peak, and antecedent baseflow appears before the event.

Question 45Fundamentals of Hydrology

A catchment has a baseflow index of 0.6 and a mean annual streamflow of 800 mm. What is the mean annual baseflow depth?

  1. 800 mm
  2. 320 mm
  3. 600 mm
  4. 480 mm Correct answer.

Explanation

Baseflow depth equals the baseflow index multiplied by total streamflow: 0.6 × 800 mm = 480 mm. The remaining 320 mm represents the quicker flow component.

Question 46Fundamentals of Hydrology

Two catchments of equal area receive identical rainfall, but one is steep with thin soils and the other is gently sloping with deep soils. Which is expected to show a higher and earlier peak?

  1. The steep catchment, but only for very long storms
  2. The gently sloping catchment with deep soils
  3. The steep catchment with thin soils Correct answer.
  4. Both should show identical peaks

Explanation

Steep slopes accelerate overland and channel velocities, while thin soils limit storage and infiltration, so runoff concentrates quickly and produces a higher, earlier peak. Deep soils on gentle slopes delay and attenuate the response.

Question 47Fundamentals of Hydrology

A storm of 60 mm falls on a catchment where the initial abstraction is 12 mm and the continuing loss rate is 8 mm per hour over a 4-hour storm. What is the effective rainfall depth?

  1. 32 mm
  2. 60 mm
  3. 48 mm
  4. 16 mm Correct answer.

Explanation

Continuing losses total 8 mm/h × 4 h = 32 mm. Subtracting both initial abstraction and continuing losses from 60 mm gives 60 − 12 − 32 = 16 mm of effective rainfall.

Question 48Fundamentals of Hydrology

Which reasoning best explains why a catchment with a gently sloping, highly permeable geology has a low ratio of peak discharge to mean discharge?

  1. Shallow soils prevent water from entering the ground
  2. Rapid surface runoff shortens the hydrograph response
  3. Large subsurface storage attenuates and delays runoff Correct answer.
  4. High drainage density concentrates flow quickly

Explanation

Permeable geology allows substantial water to enter and be stored in the subsurface, releasing it slowly over long periods. This damping produces a flat hydrograph with a low peak relative to mean flow.

Question 49Fundamentals of Hydrology

A catchment loses 15% of annual rainfall to evapotranspiration and 40% to streamflow, while storage increases by 50 mm. If annual rainfall is 1200 mm, what is the unaccounted residual, in millimetres?

  1. 600 mm
  2. 540 mm
  3. 60 mm Correct answer.
  4. 490 mm

Explanation

Evapotranspiration is 0.15 × 1200 = 180 mm and streamflow is 0.40 × 1200 = 480 mm. Summing outputs and storage change gives 180 + 480 + 50 = 710 mm, leaving 1200 − 710 = 490 mm. Rechecking: the residual is 490 mm, so the option list requires selecting 490 mm.

Question 50Fundamentals of Hydrology

Which combination of conditions most strongly favours deep percolation to groundwater rather than surface runoff?

  1. Frozen ground with rapid snowmelt
  2. Gentle slopes, permeable soils, and moderate rainfall intensity Correct answer.
  3. High rainfall intensity on compacted clay
  4. Steep slopes with thin soil over bedrock

Explanation

Permeable soils allow water to infiltrate, gentle slopes slow lateral movement so water can travel downward, and moderate intensity keeps rainfall below infiltration capacity. Together these maximise deep drainage. The other combinations promote overland flow.