DEPOSITIONAL PATTERNS AND SEDIMENTATION RATES ASSOCIATED WITH LONGITUDINAL TRAINING WALLS (LTWS) IN THE GRAND RIVER, MICHIGAN (USA)

Longitudinal training walls (LTWs) are engineered structures built within river channels that are oriented approximately parallel to the primary flow direction. The bifurcation creates a primary navigation channel that captures the majority of the water discharge, which can lead to sedimentation and overall channel narrowing within the secondary channel, the primary channel is used for improving navigability. Grand River in Michigan is such a river where LTWs were installed during the 1890’s as an effort to maintain navigation. As the river drains into Lake Michigan, the lower portions of the river experience a backwater effect leading to potential spatial variations in the geomorphic response of the river to these structures. This study examines the depositional patterns and rates of sedimentation within regions directly impacted by the LTWs to help elucidate the effects of LTWs on long term deposition rates. Eight sediment cores were collected from different regions behind LTW structures using a 4-inch vibracore setup. The cores were then logged and sampled at regular intervals for radiometric dating using gamma spectrometry for detection of ²¹⁰Pb and ¹³⁷Cs. The findings from this study provide insights into the importance of spatial distribution of the walls on sediment deposition and channel narrowing which will help to ongoing river restoration and management projects, more specifically, related to the decision making of dam removal and dredging projects that have been proposed for the river.