Question

With regard to stream gauging, what for the stage-discharge curve is used?

• A. To measure the width of the stream
• B. To measure the depth of the stream and presence of debris in the stream
• C. To find out change in velocity of the stream
• D. To relate the water level of a stream to its discharge

Hint:

• A stage-discharge curve (rating curve) is an empirical relationship developed for a specific stream gauging site.
• It plots stage (water level) against corresponding discharge (flow rate).
• Its main use is to allow for the estimation of discharge from continuous or periodic measurements of stage, as stage is easier to measure than discharge directly.
• This is crucial for hydrological studies, water resource management, and flood forecasting.

Answer 1

The Correct Option is D

In stream gauging (also known as streamflow measurement), a stage-discharge curve, often called a rating curve, is a fundamental tool.

• Stage (Water Level): This is the height of the water surface in a stream or river above a defined reference point (datum). Stage is relatively easy to measure continuously using various instruments (e.g., staff gauge, pressure transducer, ultrasonic sensor).
• Discharge (Flow Rate): This is the volume of water flowing past a specific point in the stream per unit of time (e.g., cubic meters per second (m$^3$/s) or cubic feet per second (cfs)). Measuring discharge directly is more complex and time-consuming, often involving measurements of stream velocity and cross-sectional area.

A stage-discharge curve (rating curve) is a graphical or mathematical relationship established for a specific stream gauging station. It plots corresponding values of stage and discharge. The primary purpose of a stage-discharge curve is: To relate the water level (stage) of a stream to its discharge (option d). Once this relationship is established (by making a series of simultaneous stage and discharge measurements over a range of flow conditions), hydrologists can then estimate the discharge by simply measuring the stage, which is much easier to do continuously. This allows for the generation of continuous discharge records. Option (a) measuring width, (b) measuring depth/debris, and (c) finding change in velocity are all components or factors that might be considered when initially developing the rating curve (by making direct discharge measurements which involve velocity and area), but the curve itself is then used to relate stage to discharge. \[ \boxed{\text{To relate the water level of a stream to its discharge}} \]