UA team studies small-stream surges
Researchers at the Arkansas Agricultural Experiment Station have developed an economical method to monitor rainwater surges in small streams.
They showed that compact upward-scanning Doppler radar systems designed to monitor man-made waterways can be adapted to monitor stream flows in natural channels of smaller watersheds.
Long-term stream flow data is essential to understand changes in hydrology and trends in natural disturbances like floods and drought, said Brian Haggard, professor of biological and agricultural engineering for the experiment station, the research arm of the University of Arkansas System Division of Agriculture.
Haggard is director of the experiment station’s Arkansas Water Resources Center. He also has a teaching appointment with the University of Arkansas’ College of Engineering.
Fresh water is a small percentage of the Earth’s water supply, but it is vital for human well-being, ecosystem support, economic activity and other purposes, Haggard said. Human activity and natural changes have great influence on available freshwater sources. Monitoring stream flow under extreme conditions caused by drought or stormwater runoff is essential for understanding how these stresses affect freshwater ecosystems.
Stream flow data support municipalities that need to manage storm surge water, Haggard said. State and federal agencies and researchers need the information to build and validate watershed models for the movement of sediments and nutrients and to find and correct nonpoint pollution sources.
Haggard said that most techniques for measuring and recording stream flow data can be costly to install and maintain.
“Installing and operating a typical stream flow monitoring station represents an investment of about $50,000 for the first year and around $25,000 for each subsequent year,” he said.
The instruments are not designed to be portable and are not easily moved to multiple locations, Haggard said.
A three-year study by Abbie Lasater, one of Haggard’s former graduate students, evaluated a low-cost method for remotely monitoring stream flow in smallscale watersheds. Haggard said these are mostly smaller streams that feed into larger watersheds, such as the White River.
Lasater led the study in the upper Poteau River Watershed in western Arkansas and eastern Oklahoma. The U.S. Environmental Protection Agency supported the study with a $415,415 grant administered through the Arkansas Natural Resources Commission.
Lasater used three SonTek-IQ acoustic Doppler instruments, rotating them to 12 research sites to monitor stream flow discharges in the upper watershed, Haggard said. Cables connected the units to battery packs and data ports mounted above the high-water levels of each stream. The team used inexpensive pressure transducers to measure stream depth continuously.
The researchers collected stream depth continuously at each location and storm surge data following rain events, Haggard said. The compact SonTek units provided effective and accurate measurements in the
small stream settings.
Haggard said the SonTek devices are designed for measuring flow through manufactured waterways like stormwater conveyances and irrigation canals where the shape and volume of the channels are known. Central to this research was to see if they could accurately measure flow through the irregular channels of natural streams.
The research team learned some valuable lessons about using the compact devices, Haggard said. For example, it’s essential to anchor the devices securely. One unit was lost when a storm surge overpowered the concrete pad used to hold it in the stream bed. Brad Austin, a research scientist for the Arkansas Water Resources Center, said they now use a steel cable as a safety line to limit how far the units can travel downstream if they break loose from their moorings.
Also, some stream beds can cover the devices with sand, fine gravel or other materials during high flows, obscuring the sensor surfaces.
Even so, Haggard said the water resources lab team continues to use the devices in ongoing research. They are currently using them to study rainwater surges in small streams in the White River basin.
To learn more about Division of Agriculture research, visit the Arkansas Agricultural Experiment Station website: https://aaes.uada.edu/. Follow them on Twitter at @ArkAgResearch and on Instagram at @ArkAgResearch.