Accurately measuring streamflow at each visit to the site is critical to streamgaging. The correct equipment for each stream during different seasons ensures the highest quality data are collected each time.
The WY-MT office of the USGS measures streamflows (discharge) that range from a few gallons per minute to several hundreds of thousands of cubic feet per second.
When measuring very small flows, oftentimes a portable flume is used to "gather" all the water through a confined throat. The geometry of the flume enables one to use a chart to know how much flow is moving through based on the height of the water in the flume. This measurement was taken on Dugout Creek in Montana.
Most streamflow (discharge) measurements use a technique where the cross-section of the stream is "cut" into subsections. Depth, width, and velocity are measured in each section to calculate the volume of streamflow (discharge). The streamflows in all sections are then added up to get the total for the stream.
This general principle is used whether measuring the streamflow with a handheld current meter or a meter that is attached to a small boat for remote deployment.
When making a streamflow measurement while wading a stream, the hydrographer determines the depth using the wading rod that is etched with a “ruler”, the width using the tag line strung across the stream, and the velocity of each subsection using a current meter.
The current profiler uses SONAR to measure not only velocity, but also depth and width. The hydrographer pulls the boat across the cross section to allow the profiler to measure stream parameters and calculate the streamflow.
Get the whole picture: From Gage to Page: A Look Into How USGS Helps You Know the Flow
The steps involved in getting the data to your fingertips, generally include:
- Establishing a streamgage
- Measuring the streamflow (explained above)
- Creating a stage-discharge relation
- Transmitting data via satellites to computer systems and onto the web
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Hydro-terms visualized
A picture can be worth a thousand words, so we’ll let the pictures help us do the talking:
Streamgaging Basics
How Streamflow is Measured
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- Science
Hydro-terms visualized
A picture can be worth a thousand words, so we’ll let the pictures help us do the talking:
Streamgaging Basics
A streamgage is a structure installed beside a stream or river that contains equipment that measures and records the water level (called gage height or stage) of the stream. Streamflow (also called discharge) is computed from measured water levels using a site-specific relation (called a stage-discharge rating curve) developed from onsite water level and streamflow measurements made by USGS...How Streamflow is Measured
How can one tell how much water is flowing in a river? Can we simply measure how high the water has risen/fallen? The height of the surface of the water is called the stream stage or gage height. However, the USGS has more accurate ways of determining how much water is flowing in a river. Read on to learn more.