Stream and River Flow Measurement


Maintaining oversight of stream and river flows is important in many applications ranging from water use management in drought-prone or irrigation-intensive areas to early warning in waterways subject to flooding. Real-time monitoring systems continuously measure flow by recording the water level and mean or index velocity of water flowing through channels of known cross-sectional area.

Stream and River Flow

Calculating flow rate is straightforward in a channel with known cross-sectional area. However, some variables need to be accounted for in order to achieve best possible accuracy in total flow calculations.
By physically measuring flow over a range of water levels (stage), a stage-discharge relation can be developed to determine flow based on stage alone.
However, stage-discharge rating curves do not work well in situations where streams or rivers are affected by control structures, backwater or tidal effects.
Furthermore, as river and streambeds are subject to erosion and/or sediment deposits, their changing geometry must be periodically remeasured.
In addition, factors such as the shape, slope, and roughness of the channel can impact velocity and flow rates at various locations throughout the cross-section.
Even with constant geometry, hysteresis effects where the water surface slope changes due to rapidly rising or falling water levels can impact flows.
Modern sensing technology for flow measurement takes all of these factors into account to improve accuracy in continuous monitoring systems.

Typical Stream/River Flow System

The process of establishing a stream or river flow monitoring station normally begins by selecting a suitable site and determining the cross-sectional area of the waterway. This can be done by manual survey but more frequently is performed using an ADCP instrument which can survey both the geometry and velocity profile throughout the channel.

A typical continuous monitoring system takes the information gained from the site survey and combines it with water level and velocity measurements. An instrument such as the Geolux non-contact flow sensor has integrated radar surface velocity and level sensors for accurate measurement with minimal maintenance requirements. Flow outputs directly from the instrument based on user-supplied inputs of cross-sectional geometry and stream/riverbed composition. Since the sensor measures only surface velocity, and the actual velocity varies throughout the stream or river profile due to friction, corrective factors can be applied using established standards (e.g. from USGS) or based on actual measurement data recorded during the site survey.

For real-time data acquisition, the flow sensor is connected to an X3 environmental data logger equipped with 4G LTE cellular or satellite communications. Data transmits to the WQData LIVE web datacenter, which provides remote logger controls as well as a suite of data management and reporting tools. Available features include various data export options, API, alarm notifications and public portal option.

With multiple sensor ports using robust, waterproof connectors, the X3 logger is specifically designed for use in harsh environments. Systems are easily expanded with a range of other sensor types, including rain gauges, multiparameter weather stations, side-looking current profilers, water quality sensors and multiparameter water quality sondes.

Contact a NexSens Applications Engineer today to discuss your stream or river flow monitoring application.

Learning Center Logo
Visit the Fondriest Learning Center to learn more about the fundamentals of environmental measurements.

Case Studies


Tracking Flow For Hydropower

The Northern Indiana Public Service Company (NIPSCO) is a large energy provider in the state of Indiana servicing more than a million customers. Maintaining network reliability depends in part on monitoring flow rates near its hydropower assets. To achieve this, several flow monitoring stations have been installed from bridges on the Tippecanoe River and Wabash River.

Read More

Wetland and Urban Stream Flow Monitoring

Heavy urban development has caused excess stormwater runoff in the Cleveland area. Resulting flash floods in the city’s metroparks can damage aquatic habitat, erode river banks, and carry sediment into Lake Erie. In response, Cleveland Metroparks staff have deployed a monitoring network to study flow and spread of pollution through park streams and wetlands.

Read More

Water Quality and Flow Monitoring

The University of Akron Field Station, located on the Bath Nature Preserve in northeast Ohio, promotes a better understanding of our relationship with the natural environment through research, education, and service. Students, faculty, and Bath community members have been working to gather long-term data, including monitoring with four real-time stream flow sites.

Read More