Sand moves in mysterious ways. Predicting its next move is the goal of a Mississippi State research team studying erosion on Deer Island, located just off the coast of Biloxi, Mississippi.
Every year millions of state dollars are spent dredging sand to "nourish" the vanishing shores of Deer Island. In addition to being a popular spot for fishing and recreation, the island helps protect communities along the coast and wetlands in Biloxi Bay during harmful weather events such as hurricanes.
In fact, all of Mississippi's recreational beaches are nourished artificially, a practice that's easily justifiable given the value beaches bring to Mississippi's culture, economy and ecological diversity.
"Beaches are a habitat for many wildlife species, and having sandy beaches on our coastline is a big economic driver," says Anna Linhoss, assistant professor of agricultural and biological engineering at Mississippi State. "If we're investing a lot of money in nourishing our beaches, we need to make sure it's done the best and most cost-effective way possible."
Beaches are not static environments, Linhoss notes. Sand movement is natural and in some cases even beneficial.
MSU researchers completed field work on Deer Island during summer 2016. They started by digging trenches along the shore that corresponded to a sampling grid. At each sampling point, they blended tracer grains with native sand in a cement mixer and shoveled the mixture back into the trench. Over the following weeks, they collected samples at different intervals and brought them back to the MSU lab for testing.
In the early days, scientists used radioactive tracers and Geiger counters to study sand movement. When radioactive substances were banned, they switched to lacing sand with florescent tracers, a practice that produces accurate results but involves extremely time-intensive lab work.
Thankfully MSU discovered a tracer that's not only florescent but also magnetic. A powerful magnet is run over each sample to pick up magnetized grains, which are then weighed. MSU researchers are using results to create a sediment-transport model that will measure the sand's movement over time.
They also installed instruments in the gulf to measure wave height and current patterns around Deer Island. The data will be used to build a wave model that will be linked to their sediment-transport model, providing a multi-dimensional view of the world of activity underwater.
"Once we've modeled the system, we can validate it with the sample data and use it to predict sediment movement," says Linhoss. "We'll be able to apply the model to different scenarios, such as calculating the effect of a storm on sand or seeing what happens when we do sand nourishment at different locations."
MSU researchers also are taking a closer look at activities taking place near Deer Island that may affect sand movement, including dredging operations on the sea floor to create shipping channels.