Brae 349 Final Examination Ultimate Study Guide
Domain I: Hydrologic Cycle & Water Budget Analysis
1. Which type of rain gauge provides a continuous digital record of rainfall intensity
over time?
A. Standard non-recording gauge
B. Tipping bucket rain gauge
C. Simple graduated cylinder gauge
D. Manual storage gauge
Correct Answer: B
Rationale: The tipping bucket rain gauge provides a continuous digital record of rainfall by
counting the number of times a small bucket tips (each tip representing a fixed volume, typically
0.01 inch or 0.2 mm of rainfall). This allows measurement of both total rainfall and rainfall
intensity over time. Standard non-recording gauges and manual storage gauges measure only
total accumulated rainfall without temporal resolution, making them unsuitable for intensity
analysis needed in hydrologic modeling and stormwater design.
2. In the hydrologic cycle, the process by which water vapor is released by plants into the
atmosphere is specifically termed:
A. Evaporation
B. Transpiration
C. Sublimation
D. Condensation
Correct Answer: B
Rationale: Transpiration is the specific process by which plants absorb water through their
roots and release it as water vapor through stomata in their leaves. While evaporation refers to
the conversion of liquid water to vapor from surfaces such as lakes, soil, and pavement,
transpiration is biologically mediated. The combined process is called evapotranspiration (ET),
which represents the total water lost to the atmosphere from both sources. Sublimation is the
direct phase change from ice to vapor, and condensation is the reverse process (vapor to liquid).
3. The Penman-Monteith equation for estimating reference evapotranspiration (ET₀)
requires which of the following input variables?
A. Only temperature and wind speed
B. Net radiation, air temperature, wind speed, and vapor pressure deficit
C. Only precipitation and humidity
D. Soil moisture content and leaf area index exclusively
Correct Answer: B
Rationale: The Penman-Monteith equation is a physically based combination method that
requires net radiation (energy available for evaporation), air temperature (affects saturation
vapor pressure and air density), wind speed (controls aerodynamic resistance and turbulent
transfer), and vapor pressure deficit (driving force for evaporation). It also requires
atmospheric pressure data. This comprehensive approach accounts for both energy availability
and aerodynamic transport, making it the FAO-recommended standard for ET estimation.
Simpler methods like Blaney-Criddle use only temperature and day length.
4. Horton's infiltration equation is expressed as: f(t) = fc + (f0 - fc)e^(-kt). In this
equation, f0 represents:
A. The final steady-state infiltration rate
1
, B. The initial infiltration rate at time t = 0
C. The decay constant describing the rate of infiltration decrease
D. The cumulative infiltration depth
Correct Answer: B
Rationale: In Horton's infiltration equation, f0 is the initial infiltration rate at the beginning of
rainfall (t = 0), when the soil is relatively dry and infiltration capacity is highest. The parameter
fc represents the final steady-state infiltration rate (achieved as the soil profile becomes
saturated), and k is the decay constant that describes how quickly infiltration decreases from f0
to fc. The exponential term e^(-kt) causes the infiltration rate to decrease exponentially over
time. Understanding these parameters is essential for modeling rainfallrunoff relationships and
designing stormwater management systems.
5. The SCS Curve Number (CN) method estimates runoff using the equation Q = (P -
0.2S)² / (P + 0.8S). A curve number of 100 indicates:
A. Zero runoff regardless of rainfall
B. A highly permeable sandy soil with minimal runoff potential
C. An impervious surface where all rainfall becomes runoff
D. A moderate infiltration rate typical of loam soils
Correct Answer: C
Rationale: A curve number of 100 represents an impervious surface (such as concrete or
asphalt) where all rainfall becomes direct runoff with no infiltration. The CN scale ranges from
approximately 30 (highly permeable soils with dense vegetation) to 100 (completely
impervious). Higher CN values indicate greater runoff potential and lower infiltration capacity.
The potential maximum retention S = (1000/CN) - 10, so at CN = 100, S = 0, meaning all
rainfall above the initial abstraction becomes runoff. This method is widely used by USDANRCS
for watershed planning and stormwater design.
6. When delineating a watershed boundary, the divide follows:
A. The stream channel at the lowest elevation
B. The ridge line separating adjacent drainage areas
C. The contour line of highest elevation within the watershed
D. The path of steepest descent from the outlet
Correct Answer: B
Rationale: A watershed boundary (or drainage divide) follows the ridge line or topographic
high point that separates adjacent drainage areas. All precipitation falling within this boundary
drains to the watershed outlet, while precipitation on the other side of the divide drains to a
different outlet. The divide is perpendicular to contour lines at ridge tops and is identified by
tracing the highest elevation points between adjacent streams on a topographic map. The
stream channel is within the watershed (not the boundary), and the path of steepest descent
describes water flow direction within the watershed, not the boundary.
7. The Blaney-Criddle method for estimating consumptive use is expressed as: ET = k × p
× (0.46T + 8.13). This method is considered most reliable for:
A. Humid tropical climates with high rainfall
B. Arid and semi-arid climates for estimating monthly ET
C. Cold climates with freezing temperatures
D. Hourly evapotranspiration estimates for irrigation scheduling
Correct Answer: B
Rationale: The Blaney-Criddle method is a temperature-based approach considered most
reliable for estimating monthly ET in arid and semi-arid climates where temperature is the
primary driver of evapotranspiration. It is less accurate in humid regions where advective
energy and humidity play larger roles. The method provides monthly (not hourly) estimates,
and is not designed for freezing conditions. While simpler than Penman-Monteith, its limited
2
, input requirements (temperature and daylight hours) make it practical for regions lacking
comprehensive weather station data, though at the cost of reduced accuracy.
8. A Class A evaporation pan is used to estimate reference evapotranspiration. The pan
coefficient (Kp) is applied to convert pan evaporation to ET₀ because:
A. Pan evaporation always exactly equals ET₀
B. Pan evaporation overestimates ET₀ due to greater exposure, solar absorption, and advective
effects
C. Pan evaporation underestimates ET₀ in all climates
D. The pan coefficient accounts for precipitation only
Correct Answer: B
Rationale: A Class A pan typically overestimates reference ET₀ because the pan absorbs more
solar radiation than a vegetated surface, has greater advective energy exchange due to its small
size relative to surrounding vegetation, and lacks the stomatal resistance that limits plant
transpiration. The pan coefficient (Kp, typically 0.6-0.8) adjusts for these differences so that
ET₀ = Kp × Epan. Kp values vary with surrounding conditions (fetch, wind, humidity), with
lower values in arid, windy locations and higher values in humid, calm environments. This
method provides a practical, low-cost ET estimation approach.
9. In a water budget analysis, the continuity equation is expressed as: P = ET + R + ΔS.
The term ΔS represents:
A. Precipitation minus evapotranspiration
B. Change in storage within the system (soil moisture, groundwater, reservoirs)
C. Total runoff from the watershed
D. Sublimation of snow and ice
Correct Answer: B
Rationale: In the water budget equation P = ET + R + ΔS, ΔS represents the change in water
storage within the system, including soil moisture, groundwater, surface reservoirs, and
snowpack. A positive ΔS indicates net storage increase (more water entering than leaving),
while a negative ΔS indicates storage depletion. P is precipitation (input), ET is
evapotranspiration, and R is runoff (outputs). Over long periods (years to decades), ΔS
approaches zero in stable watersheds, making the budget P ≈ ET + R. Accurate water budget
analysis is fundamental to water resources planning and management.
10. A weighing-type rain gauge measures rainfall by:
A. Counting electrical pulses from tipping buckets
B. Continuously recording the weight of accumulated precipitation on a chart or data logger
C. Measuring the height of water in a graduated cylinder
D. Detecting the acoustic signal of raindrop impacts
Correct Answer: B
Rationale: A weighing-type rain gauge continuously measures and records the total weight of
accumulated precipitation (rain and snow) on a platform connected to a spring mechanism or
load cell, typically recording on a strip chart or data logger. Unlike tipping bucket gauges,
weighing gauges can measure all forms of precipitation including snow without a heater, and
they record both intensity and total accumulation without the data discretization inherent in
tipping bucket mechanisms. They are particularly valuable in cold climates where freezing
temperatures can affect tipping bucket performance.
Domain II: Soil-Water-Plant Relationships
11. A soil sample contains 40% sand, 40% silt, and 20% clay. Using the USDA soil
textural triangle, this soil is classified as:
3
Domain I: Hydrologic Cycle & Water Budget Analysis
1. Which type of rain gauge provides a continuous digital record of rainfall intensity
over time?
A. Standard non-recording gauge
B. Tipping bucket rain gauge
C. Simple graduated cylinder gauge
D. Manual storage gauge
Correct Answer: B
Rationale: The tipping bucket rain gauge provides a continuous digital record of rainfall by
counting the number of times a small bucket tips (each tip representing a fixed volume, typically
0.01 inch or 0.2 mm of rainfall). This allows measurement of both total rainfall and rainfall
intensity over time. Standard non-recording gauges and manual storage gauges measure only
total accumulated rainfall without temporal resolution, making them unsuitable for intensity
analysis needed in hydrologic modeling and stormwater design.
2. In the hydrologic cycle, the process by which water vapor is released by plants into the
atmosphere is specifically termed:
A. Evaporation
B. Transpiration
C. Sublimation
D. Condensation
Correct Answer: B
Rationale: Transpiration is the specific process by which plants absorb water through their
roots and release it as water vapor through stomata in their leaves. While evaporation refers to
the conversion of liquid water to vapor from surfaces such as lakes, soil, and pavement,
transpiration is biologically mediated. The combined process is called evapotranspiration (ET),
which represents the total water lost to the atmosphere from both sources. Sublimation is the
direct phase change from ice to vapor, and condensation is the reverse process (vapor to liquid).
3. The Penman-Monteith equation for estimating reference evapotranspiration (ET₀)
requires which of the following input variables?
A. Only temperature and wind speed
B. Net radiation, air temperature, wind speed, and vapor pressure deficit
C. Only precipitation and humidity
D. Soil moisture content and leaf area index exclusively
Correct Answer: B
Rationale: The Penman-Monteith equation is a physically based combination method that
requires net radiation (energy available for evaporation), air temperature (affects saturation
vapor pressure and air density), wind speed (controls aerodynamic resistance and turbulent
transfer), and vapor pressure deficit (driving force for evaporation). It also requires
atmospheric pressure data. This comprehensive approach accounts for both energy availability
and aerodynamic transport, making it the FAO-recommended standard for ET estimation.
Simpler methods like Blaney-Criddle use only temperature and day length.
4. Horton's infiltration equation is expressed as: f(t) = fc + (f0 - fc)e^(-kt). In this
equation, f0 represents:
A. The final steady-state infiltration rate
1
, B. The initial infiltration rate at time t = 0
C. The decay constant describing the rate of infiltration decrease
D. The cumulative infiltration depth
Correct Answer: B
Rationale: In Horton's infiltration equation, f0 is the initial infiltration rate at the beginning of
rainfall (t = 0), when the soil is relatively dry and infiltration capacity is highest. The parameter
fc represents the final steady-state infiltration rate (achieved as the soil profile becomes
saturated), and k is the decay constant that describes how quickly infiltration decreases from f0
to fc. The exponential term e^(-kt) causes the infiltration rate to decrease exponentially over
time. Understanding these parameters is essential for modeling rainfallrunoff relationships and
designing stormwater management systems.
5. The SCS Curve Number (CN) method estimates runoff using the equation Q = (P -
0.2S)² / (P + 0.8S). A curve number of 100 indicates:
A. Zero runoff regardless of rainfall
B. A highly permeable sandy soil with minimal runoff potential
C. An impervious surface where all rainfall becomes runoff
D. A moderate infiltration rate typical of loam soils
Correct Answer: C
Rationale: A curve number of 100 represents an impervious surface (such as concrete or
asphalt) where all rainfall becomes direct runoff with no infiltration. The CN scale ranges from
approximately 30 (highly permeable soils with dense vegetation) to 100 (completely
impervious). Higher CN values indicate greater runoff potential and lower infiltration capacity.
The potential maximum retention S = (1000/CN) - 10, so at CN = 100, S = 0, meaning all
rainfall above the initial abstraction becomes runoff. This method is widely used by USDANRCS
for watershed planning and stormwater design.
6. When delineating a watershed boundary, the divide follows:
A. The stream channel at the lowest elevation
B. The ridge line separating adjacent drainage areas
C. The contour line of highest elevation within the watershed
D. The path of steepest descent from the outlet
Correct Answer: B
Rationale: A watershed boundary (or drainage divide) follows the ridge line or topographic
high point that separates adjacent drainage areas. All precipitation falling within this boundary
drains to the watershed outlet, while precipitation on the other side of the divide drains to a
different outlet. The divide is perpendicular to contour lines at ridge tops and is identified by
tracing the highest elevation points between adjacent streams on a topographic map. The
stream channel is within the watershed (not the boundary), and the path of steepest descent
describes water flow direction within the watershed, not the boundary.
7. The Blaney-Criddle method for estimating consumptive use is expressed as: ET = k × p
× (0.46T + 8.13). This method is considered most reliable for:
A. Humid tropical climates with high rainfall
B. Arid and semi-arid climates for estimating monthly ET
C. Cold climates with freezing temperatures
D. Hourly evapotranspiration estimates for irrigation scheduling
Correct Answer: B
Rationale: The Blaney-Criddle method is a temperature-based approach considered most
reliable for estimating monthly ET in arid and semi-arid climates where temperature is the
primary driver of evapotranspiration. It is less accurate in humid regions where advective
energy and humidity play larger roles. The method provides monthly (not hourly) estimates,
and is not designed for freezing conditions. While simpler than Penman-Monteith, its limited
2
, input requirements (temperature and daylight hours) make it practical for regions lacking
comprehensive weather station data, though at the cost of reduced accuracy.
8. A Class A evaporation pan is used to estimate reference evapotranspiration. The pan
coefficient (Kp) is applied to convert pan evaporation to ET₀ because:
A. Pan evaporation always exactly equals ET₀
B. Pan evaporation overestimates ET₀ due to greater exposure, solar absorption, and advective
effects
C. Pan evaporation underestimates ET₀ in all climates
D. The pan coefficient accounts for precipitation only
Correct Answer: B
Rationale: A Class A pan typically overestimates reference ET₀ because the pan absorbs more
solar radiation than a vegetated surface, has greater advective energy exchange due to its small
size relative to surrounding vegetation, and lacks the stomatal resistance that limits plant
transpiration. The pan coefficient (Kp, typically 0.6-0.8) adjusts for these differences so that
ET₀ = Kp × Epan. Kp values vary with surrounding conditions (fetch, wind, humidity), with
lower values in arid, windy locations and higher values in humid, calm environments. This
method provides a practical, low-cost ET estimation approach.
9. In a water budget analysis, the continuity equation is expressed as: P = ET + R + ΔS.
The term ΔS represents:
A. Precipitation minus evapotranspiration
B. Change in storage within the system (soil moisture, groundwater, reservoirs)
C. Total runoff from the watershed
D. Sublimation of snow and ice
Correct Answer: B
Rationale: In the water budget equation P = ET + R + ΔS, ΔS represents the change in water
storage within the system, including soil moisture, groundwater, surface reservoirs, and
snowpack. A positive ΔS indicates net storage increase (more water entering than leaving),
while a negative ΔS indicates storage depletion. P is precipitation (input), ET is
evapotranspiration, and R is runoff (outputs). Over long periods (years to decades), ΔS
approaches zero in stable watersheds, making the budget P ≈ ET + R. Accurate water budget
analysis is fundamental to water resources planning and management.
10. A weighing-type rain gauge measures rainfall by:
A. Counting electrical pulses from tipping buckets
B. Continuously recording the weight of accumulated precipitation on a chart or data logger
C. Measuring the height of water in a graduated cylinder
D. Detecting the acoustic signal of raindrop impacts
Correct Answer: B
Rationale: A weighing-type rain gauge continuously measures and records the total weight of
accumulated precipitation (rain and snow) on a platform connected to a spring mechanism or
load cell, typically recording on a strip chart or data logger. Unlike tipping bucket gauges,
weighing gauges can measure all forms of precipitation including snow without a heater, and
they record both intensity and total accumulation without the data discretization inherent in
tipping bucket mechanisms. They are particularly valuable in cold climates where freezing
temperatures can affect tipping bucket performance.
Domain II: Soil-Water-Plant Relationships
11. A soil sample contains 40% sand, 40% silt, and 20% clay. Using the USDA soil
textural triangle, this soil is classified as:
3
