What do you do when you can’t find the right tool for the job?

You make it yourself.

When Kyle Strom, an associate professor of civil and environmental engineering, and his research team needed to measure small particle aggregates within the Mississippi River, no equipment existed to accomplish the task.

So to get the data they needed, they built a novel camera, called the FlocARAZI, to provide first-time measurements of flocs, or muddy snowflake-shaped particle aggregates, within the river. The underwater microscope camera can be lowered hundreds of feet below the surface while sending images of what it's observing — particles and organisms in suspension that range in size from 0.01 to 2 millimeters — back up to computers and researchers on survey boats.

But why would someone want to take pictures of muddy flocs? It all has to do with trying to understand where the mud will deposit in and around the Mississippi River and its delta and how this might impact land loss or gain in the area. Knowing where mud from the mighty river eventually goes is difficult because researchers don’t know much about the size of flocs and their settling characteristics.

Flocs form when small mud particles clump together, and they can grow or shrink in size depending on turbulence levels in the flow and the type of sediment in the water. As flocs change in size, the speed at which they settle also changes.

“Where the mud deposits in the river channel, adjacent floodplains, or adjoining bays depends on how fast it settles in the water,” said Strom. “The big problem is that there are no standard tools for measuring these little guys and how they change. And because we don’t have good data on the flocculation state of the mud, we don’t have good models to help us predict where this mud will eventually go. For example, before this study, we didn’t even know for sure if the mud was flocculated in the freshwater reaches of the river.”

The Mississippi River, one of the longest rivers in the world, flows 2,350 miles from Lake Itasca in Minnesota to the Gulf of Mexico, according to the National Park Service. Over the river’s long course, it carries a significant amount of sediment from the land to the sea.

This delivery of sediment by the Mississippi River to the Gulf Coast region has historically resulted in land growth at the coast. However, coastal Louisiana is currently losing land because of subsidence, sea level rise, and a lack of fresh sediment arriving from the Mississippi River — due to new levees constructed for flood protection that effectively cut off the river and its sediment from the surrounding regions.

One possible solution to help offset the region’s land loss is to install engineered diversion structures in the banks and levees of the Mississippi that can be opened at key times to allow water and sediment to flow out into the surrounding bays and marshes. To know how effective such new engineering efforts might be requires accurately predicting how fast the fine muddy sediment will settle. Therefore, it is vital to know if the mud is flocculated and, if so, to be able to predict the size of the flocs under different conditions in the river.

With support from the National Science Foundation and in collaboration with researchers from Texas Tech University, the Virginia Tech team hopped onto a boat and went riding down the Mississippi to collect water samples. The research team, made up of master's, Ph.D., and postdoctoral scientists, took the FlocARAZI out on the lower Mississippi in both the summer and winter seasons to measure how flocs change in size as the river approaches and enters the Gulf of Mexico and the surrounding bays. They collected water samples and sediment samples of the bed at several locations along the river and measured water temperature, salinity, and particle sizes with the FlocARAZI camera system. 

The FlocARAZI before it was dropped into the Mississippi River to collect samples. Photo courtesy of Kyle Strom.

To strengthen their field observations, Strom and his team coupled the field measurements with controlled laboratory experiments both on the banks of the Mississippi and in the Baker Environmental Hydraulics Laboratory, a 3,100-square-foot facility in Hancock Hall that houses research flumes, tanks, and advanced research instrumentation and hydraulic measurement systems. The laboratory experiments relied on mixing tanks that precisely control water chemistry, sediment type, and turbulence.

One of the study’s key findings is that mud in the Mississippi is highly flocculated in the freshwater reaches of the river long before the sediment arrives at the sea or any saltwater intrusion.

“This finding has significant implications for understanding where mud would settle if allowed to pass out through engineered river diversion structures and is in contrast to long-standing assumptions about the state of mud and its transport properties in freshwater systems,” said Strom.

Team members also were able to show how floc sizes change with turbulent energy in the flow, salt levels, and water temperature. They found that flocs were larger during the summer than the winter. Strom suspects that warmer water enhances microbial activity and the production of organic polymers that glue the mud particles together.

Taken together, these results provide a clearer picture of what governs mud movement in the system and what analytic tools are needed to make more accurate predictions of land growth or loss in the area.

Developing the FlocARAZI played a critical role in gaining these insights, and Strom wants to expand the research tool’s reach. According to Strom, most mud studies are limited in their ability to accurately measure the size of mud flocs as they exist within rivers and estuaries.

“I believe the lack of field data has significantly impeded our understanding of mud transport,” he said. “For this reason, we wanted to create the FlocARAZI in a way that would make it easier for others to replicate or improve upon our design so that more field data can be collected.”

To do this, they used off-the-shelf or 3D-printed parts in the design and tried to keep the cost low. The team have made publicly available the camera’s parts list, build and operating instructions, and image processing code that can help researchers extract size information from the images. The FlocARAZI provides unique data that cannot be obtained with any current commercial instrument and is about 1/20 the cost of the instruction that is often used for similar measurements.

“Our hope is that making the instrument assembly procedures available to others, will allow scientists throughout the world to work together in advancing this field of research,” said Strom. 

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