Stream Velocity Measurement Exam
2026/2027 | Floats, Current Meters &
ADCP | 100 MCQs with Answer Key
Description:
Master streamflow measurement for 2026/2027. 100 multiple-choice questions on floats,
current meters, ADCP, and mean velocity methods. Full answer explanations included.
Download the complete hydrometry exam paper now and ace your hydrology assessment.
, Hydrometry Exam 2026/2027: 100 MCQs
Section A: Fundamental Concepts & Velocity Measurement Instruments (Questions 1-5)
1. Stream velocity is commonly determined using which of the following?
A. Acoustic profilers and pressure transducers
B. Floats and current meters
C. Weirs and flumes
D. Stage-discharge relationships only
Answer: B
Explanation: Floats provide a basic estimate of surface velocity, while current meters offer a
more detailed and accurate measurement of velocity at specific points within the flow cross-
section.
2. A primary limitation of using float measurements for stream velocity determination is that
they:
A. Are too expensive for routine use.
B. Are not as reliable or accurate as current meter measurements.
C. Require complex mathematical corrections for all applications.
D. Can only be used in artificial channels.
Answer: B
Explanation: Float measurements are subject to errors from wind, turbulence, and variations
in float design, making them generally less precise and reliable than direct measurements
from mechanical or acoustic current meters.
3. For most scientific and engineering applications requiring high precision, the most reliable
instrument for measuring stream flow is a:
A. Surface float
B. Rod float
C. Current meter
D. Subsurface double-float
Answer: C
Explanation: Current meters (including mechanical and Acoustic Doppler types) are
designed to accurately determine velocities at nearly all points within a stream’s cross-section
over a sufficient period, providing data for a reliable discharge calculation.
,4. The use of surface floats is generally limited to measuring velocity in artificial channels
that are:
A. Short, winding, and have a variable cross-section.
B. Long, straight, and have a uniform cross-section.
C. Deep, slow-moving, and have a rock bed.
D. Shallow, fast-moving, and have a vegetated bed.
Answer: B
Explanation: For a float measurement to be valid, the reach must be straight and uniform to
ensure consistent flow, and a known length is required to time the float’s passage accurately.
Artificial channels are often designed to meet these conditions.
5. Which instrument is specifically used to indirectly measure subsurface velocities in natural
streams?
A. Surface floats
B. Rod floats
C. Current meters
D. Velocity rods
Answer: C
Explanation: Current meters are lowered to specific depths (e.g., 0.2 and 0.8 of the depth) to
measure velocity at those points, thereby providing an indirect but systematic measure of the
subsurface velocity profile.
Section B: Floats: Types, Applications, and Limitations (Questions 6-10)
6. Floats are particularly well-suited for all the following applications EXCEPT:
A. Reconnaissance surveys of ungaged streams
B. Determining flood velocities when wading is unsafe
C. Locating potential sites for new gaging stations
D. Establishing a permanent, highly accurate stage-discharge rating curve
Answer: D
Explanation: Permanent rating curves require highly precise discharge measurements over a
range of stages. This level of accuracy is best achieved with current meters or Acoustic
Doppler Current Profilers (ADCPs), not the relatively approximate measurements obtained
with floats.
, 7. A key requirement for any float used in a velocity measurement is that it must be easily:
A. Retrieved and recalibrated
B. Seen and identified from a distance
C. Weighted and submerged
D. Attached to a cable system
Answer: B
Explanation: To time the float’s travel over a measured distance, the observer must be able
to clearly see and identify the float as it passes the upstream and downstream marks on the
channel bank.
8. The simplest and most commonly used type of float is the:
A. Subsurface float
B. Rod float
C. Double float
D. Surface float
Answer: D
Explanation: Surface floats are simple to construct (e.g., a weighted piece of wood or an
orange peel), easy to deploy, and directly measure the movement of the water's surface,
making them the most common type, especially for reconnaissance.
9. When using a surface float, the observed surface velocity must be multiplied by a
coefficient (typically 0.80-0.90) primarily to account for the effects of:
A. Evaporation and water temperature.
B. Wind and cross-currents.
C. Dissolved sediment load.
D. Atmospheric pressure changes.
Answer: B
Explanation: Wind pushes the float independently of the current, and cross-currents move it
laterally. The coefficient is an empirical correction to convert the observed surface velocity to
an estimate of the stream's mean velocity.
2026/2027 | Floats, Current Meters &
ADCP | 100 MCQs with Answer Key
Description:
Master streamflow measurement for 2026/2027. 100 multiple-choice questions on floats,
current meters, ADCP, and mean velocity methods. Full answer explanations included.
Download the complete hydrometry exam paper now and ace your hydrology assessment.
, Hydrometry Exam 2026/2027: 100 MCQs
Section A: Fundamental Concepts & Velocity Measurement Instruments (Questions 1-5)
1. Stream velocity is commonly determined using which of the following?
A. Acoustic profilers and pressure transducers
B. Floats and current meters
C. Weirs and flumes
D. Stage-discharge relationships only
Answer: B
Explanation: Floats provide a basic estimate of surface velocity, while current meters offer a
more detailed and accurate measurement of velocity at specific points within the flow cross-
section.
2. A primary limitation of using float measurements for stream velocity determination is that
they:
A. Are too expensive for routine use.
B. Are not as reliable or accurate as current meter measurements.
C. Require complex mathematical corrections for all applications.
D. Can only be used in artificial channels.
Answer: B
Explanation: Float measurements are subject to errors from wind, turbulence, and variations
in float design, making them generally less precise and reliable than direct measurements
from mechanical or acoustic current meters.
3. For most scientific and engineering applications requiring high precision, the most reliable
instrument for measuring stream flow is a:
A. Surface float
B. Rod float
C. Current meter
D. Subsurface double-float
Answer: C
Explanation: Current meters (including mechanical and Acoustic Doppler types) are
designed to accurately determine velocities at nearly all points within a stream’s cross-section
over a sufficient period, providing data for a reliable discharge calculation.
,4. The use of surface floats is generally limited to measuring velocity in artificial channels
that are:
A. Short, winding, and have a variable cross-section.
B. Long, straight, and have a uniform cross-section.
C. Deep, slow-moving, and have a rock bed.
D. Shallow, fast-moving, and have a vegetated bed.
Answer: B
Explanation: For a float measurement to be valid, the reach must be straight and uniform to
ensure consistent flow, and a known length is required to time the float’s passage accurately.
Artificial channels are often designed to meet these conditions.
5. Which instrument is specifically used to indirectly measure subsurface velocities in natural
streams?
A. Surface floats
B. Rod floats
C. Current meters
D. Velocity rods
Answer: C
Explanation: Current meters are lowered to specific depths (e.g., 0.2 and 0.8 of the depth) to
measure velocity at those points, thereby providing an indirect but systematic measure of the
subsurface velocity profile.
Section B: Floats: Types, Applications, and Limitations (Questions 6-10)
6. Floats are particularly well-suited for all the following applications EXCEPT:
A. Reconnaissance surveys of ungaged streams
B. Determining flood velocities when wading is unsafe
C. Locating potential sites for new gaging stations
D. Establishing a permanent, highly accurate stage-discharge rating curve
Answer: D
Explanation: Permanent rating curves require highly precise discharge measurements over a
range of stages. This level of accuracy is best achieved with current meters or Acoustic
Doppler Current Profilers (ADCPs), not the relatively approximate measurements obtained
with floats.
, 7. A key requirement for any float used in a velocity measurement is that it must be easily:
A. Retrieved and recalibrated
B. Seen and identified from a distance
C. Weighted and submerged
D. Attached to a cable system
Answer: B
Explanation: To time the float’s travel over a measured distance, the observer must be able
to clearly see and identify the float as it passes the upstream and downstream marks on the
channel bank.
8. The simplest and most commonly used type of float is the:
A. Subsurface float
B. Rod float
C. Double float
D. Surface float
Answer: D
Explanation: Surface floats are simple to construct (e.g., a weighted piece of wood or an
orange peel), easy to deploy, and directly measure the movement of the water's surface,
making them the most common type, especially for reconnaissance.
9. When using a surface float, the observed surface velocity must be multiplied by a
coefficient (typically 0.80-0.90) primarily to account for the effects of:
A. Evaporation and water temperature.
B. Wind and cross-currents.
C. Dissolved sediment load.
D. Atmospheric pressure changes.
Answer: B
Explanation: Wind pushes the float independently of the current, and cross-currents move it
laterally. The coefficient is an empirical correction to convert the observed surface velocity to
an estimate of the stream's mean velocity.
