128-16 Sediment Movement in the Mackinaw River

Abstract:

River channels change size and shape in response to their sediment load and streamflow. The rates of erosion and deposition can cause a river to deviate from its equilibrium state, in which it maintains its longitudinal profile and shape over time through processes like bed scour and erosion. Sediment transport and deposition affect many aspects of the ecosystem; excessive sediment can lead to poor water quality, algal blooms, and deposition build-up. Insufficient sediment can lead to channel incision, bank erosion, and changes in the particle-size composition of the channel bed. Understanding erosional and depositional processes throughout medium-gradient rivers is essential for effective sediment management and related habitat management, and for supporting ongoing conservation and understanding impacts on larger rivers. Our research aims to understand erosion and sediment transport in the Mackinaw River system, which flows through glaciated areas of central Illinois. This river is categorized as a medium-gradient river, meaning it has a slope between 0.51 and 2.0% and transports sediments from the Wisconsinan, Illinoian, and Pre-Illinoian glaciations to the Illinois River.

We will track coarse bedload sediment movement through a straight section and a bend in the river. By placing radio-frequency identification (RFID) tags in 100 sediment samples at each location. When we return to the field sites after increased flow events, we will use an antenna to detect the tags and record the identification number and location to track the samples' movements over time. We will measure cross-sections throughout the study to monitor changes in the riverbank and channel bed.

We will investigate the relationship between sediment mass and distance traveled. Masses of samples placed in the river range from 27.89g to 3600g. We expect the mass and distance traveled by the sediment in the Mackinaw River to be independent of each other due to the distribution of sizes across the river channel. We anticipate the cross sections to show little change in the channel bed due to the continuous availability of sediment input from glacial till. Greater change may occur along the riverbanks associated with bank undercutting and collapse or sediment accumulation along bars.

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