# Engineering Hydrology Questions and Answers – Streamflow Measurement

This set of Engineering Hydrology Multiple Choice Questions & Answers (MCQs) focuses on “Streamflow Measurement”.

1. What is the main condition required for the use of dilution technique for streamflow measurement?
b) Uniform flow
c) Incompressible flow
d) Irrotational flow

Explanation: The main assumption in the application of dilution technique is that the streamflow should be steady. If the flow is unsteady, the continuity equations used to derive the equations for discharge will not be valid.

2. Identify the technique in which tracer is injected continuously at a given section at a constant rate?
a) Sudden injection
b) Gulp method
c) Integration method
d) Plateau gauging

Explanation: Constant rate injection or plateau gauging is a dilution technique of streamflow measurement in which a tracer of given concentration is injected continuously at a constant rate at a given point on the river.

3. Which of the following is data, other than background tracer concentration and tracer concentration at a downstream section, is required for the use of sudden injection method in streamflow measurement?
a) Concentration of tracer applied
b) Concentration of tracer and rate of application
c) Concentration and volume of applied tracer
d) Time of application of tracer volume

Explanation: In sudden injection method, the streamflow measurement is done by adding a given small quantity of tracer of known concentration at a given point in the river. This tracer is allowed to mix for a sufficient distance and further measurements are made at a suitable point downstream.

4. During a constant rate injection method, it was assumed in calculation that the background tracer concentration was zero. It was later found that there was a significant amount of background concentration at the time of injection. Which of the following is true with regards to the calculated discharge?
a) Calculated discharge is underestimated
b) Calculated discharge is overestimated
c) There is no error in calculated discharge
d) Calculated discharge may be overestimated or underestimated

Explanation: If the background concentration is not considered, the concentration of tracer at a downstream section is overestimated as its value will be lesser when considered from background level. This results is an underestimation of the stream discharge.

5. In plateau gauging, if the concentration of tracer is increased, how does it affect the stream discharge?
a) Increases
b) Decreases
c) Remains unchanged
d) Cannot say

Explanation: Streamflow does not depend on the tracer concentration or the application rate. Any changes in the aforementioned will reflect in the concentration of tracer at a downstream section and ultimately the background concentration.

6. In constant rate injection method, the tracer concentration at some point downstream from the injection point increases from the base value, reaches a peak and then drops down to the base value.
a) True
b) False

Explanation: In plateau gauging, as the tracer is continuously injected at a constant rate, the concentration at a downstream point will reflect as increasing gradually upto a certain value and maintaining that concentration until the tracer is injected.

7. 24g of tracer was added to a river at point. After 30 secs of addition, the tracer concentration at a point 1km downstream started to increase from an initial value of zero. After another 60 secs, the tracer concentration reached a peak of 8 µg/L. After 30 more seconds, the tracer concentration at the point dropped back to zero. Find the discharge of the river (in m3/s).
a) 25
b) 33.33
c) 50
d) 100

Explanation: The discharge of river by sudden injection method is given as,
Q = $$\frac{Mass \, of \, tracer}{(Peak \, concentration-Base \, concentration)*time}=\frac{M}{(C_2-C_0)*(t_2-t_1)}$$
⇒ Q=$$\frac{24 g}{(8 μg/L -0)*((30+60+30)-30)} = \frac{24000 mg}{(8*10^{-3} mg/L)*90 secs}$$
∴ Q = 33333.33 L/s=33.33 m3/s

8. Which of the following is a desirable property of a tracer?
a) May chemically react with water body
b) Toxic substance
c) Should not undergo evaporation
d) Should not be identifiable in smaller concentrations

Explanation: Tracers used in dilution technique should have some desirable properties like inability to react with stream and its surfaces, should not be lost by evaporation or other means, should be non-toxic, should be distinguishable in small concentrations and should be economical.

Sanfoundry Global Education & Learning Series – Engineering Hydrology.

To practice all areas of Engineering Hydrology, here is complete set of 1000+ Multiple Choice Questions and Answers.

More MCQs on Streamflow Measurement:

If you find a mistake in question / option / answer, kindly take a screenshot and email to [email protected]