As sediment transport and erosion alters portions of the Maumee and Sandusky rivers in northern Ohio, much of the bathymetric data collected for them has become outdated — by more than 50 years in some cases. A research team under the direction of Wayne State University’s Carol Miller wants to understand how channel processes have shifted these river-bottom landscapes.
The team includes personnel from Wayne State University, the Great Lakes Environmental Center, and the U.S. Army Corps of Engineers. The researchers are using bathymetric survey data and collecting sediment cores to assess river morphology.
The survey is part of the team’s larger effort to estimate the rate of sediment deposition behind the network of dams in the Great Lakes watershed that are tributary to federal harbors, where reservoir sediment problems are an issue.
There are more than 100 federal harbors or federally maintained navigation channels in the Great Lakes, through which almost all of the precipitation falling in the Great Lakes Basin eventually passes. This results in a massive accumulation of sediment and contaminants. The U.S. Army Corps of Engineers spends approximately $40 million removing 2-4 million cubic yards of sediment from these channels annually.
Findings will be compared to historical data to establish predicted future rates of sediment accumulation, as well as remaining storage capacity. The team has collected bathymetry and sediment cores at five locations and plans to study a total of 10 to 15 sites over a three-year period.
“We hope to obtain historical bathymetry for all sites so that we can compare it to the new bathymetry to assist in the estimation of sedimentation rates,” said Adam Lacey, a civil and environmental engineering student at Wayne State. “We are also trying to use sites with USGS sediment gages just upstream of the reservoir. This will allow us to develop sediment rating curves for the sites.”
The research sites are intended to be representative of the overall conditions in the watershed. Selecting the appropriate locations, the researchers noted, is critical to ensuring the resulting findings can be applied to the watershed more generally. Most sites will be agricultural basins. A handful of forested and urbanized areas, however, will be used for comparison.
Dr. Mark Baskaran, geology professor at Wayne State, is in the process of dating the sediment cores to determine sedimentation rates in different areas of the reservoirs.
Additionally, to gather the needed bathymetric data, the team utilized a boat-towable SonTek RiverSurveyor M9 rented from Fondriest Environmental. The acoustic Doppler profiling unit emits ultrasonic acoustic bursts of known frequency to measure bathymetric data as well as information about river discharge.
A 500 kHz vertical beam allows for depth measurement as deep as 80 meters. Additionally, a real-time kinematic (or differential) GPS system records position data within ±3 cm accuracy, allowing bathymetry GIS data.
Bluetooth connectivity provides a wireless link from the M9 to a laptop or smart phone. Bathymetric, GPS, and velocity data is then transmitted and displayed graphically in real time.
“The M9 worked great and was very easy to use,” Lacey said. “The software, RiverSurveyor Live, is very user friendly, and it was easy to export into MATLAB and Excel before it was uploaded into ArcGIS.” Lacey said the graphs generated by RiverSurveyor Live were also useful to the study, both in the field and for post processing.