QUANTIFYING THE GEOMORPHIC CHANGE AFTER LEN SMALL LEVEE BREACHES, DOGTOOTH BEND OF THE MISSISSIPPI RIVER

Author

Tara Lal Giri, Southern Illinois University CarbondaleFollow

Date of Award

8-1-2023

Degree Name

Master of Science

Department

Geography and Environmental Resources

First Advisor

Remo, Jonathan

Abstract

The river-connected floodplain along the Mississippi River (MR)’s Dogtooth Bend has experienced substantial sedimentation over the past decade despite a 75% decrease in the total suspended sediment load between the mid-20th century to present. This large decrease in suspended sediment load has been one of the major drivers of land loss within the MR Delta and is attributed to the trapping of sediment behind large dams within the MR watershed. Recent studies have shown that suspended sediment loads continue to decrease despite no substantial dams being constructed since the 1970s. One possible explanation for the continued decrease in suspended sediment loads along the MR is the transient storage of suspended sediment in the river-connected floodplain. Recent levee breaches along the Dogtooth Bend segment of the MR have opened large, new storage areas (65 km2) where river-transported sediments could be stored. To assess the role this recently reconnected floodplain plays as a potential sediment sink, this study quantifies geomorphic change across Dogtooth Bend and the adjacent river-connected floodplain, using geomorphic change detection (GCD) software employing a pre (2011) and post (2020) levee breach, hi-resolution LiDAR-based digital elevation models (DEMs). The GCD results show that the sediment deposition is unevenly distributed throughout the study area. Greater concentrations of sediment deposition were noted in the vicinity of cutoff channels that are actively forming across the neck of Dogtooth Bend during flood events and along a fluvial terrace that traverses the eastern portion of the Bend. In the batture (the land between the main channel's low-water elevation and the flood mitigation levee), areas with substantial sedimentation are concentrated in the vicinity of large islands downstream of the levee breach. The GCD estimated sediment deposition rates were 41±4 and 39±2 mm/yr for Dogtooth Bend and Batture, respectively. The net sediment volume deposited across Dogtooth Bend and the adjacent batture were 27.9±3.0 and 34.3±1.6 Mt, respectively. The net deposition of 67.7 Mt over this 10-year study period equates to 6.8 Mt/year of sediment being deposited along this river segment which is ~8% of the river's annual average suspended load (~81 Mt/year). These results show this river segment is a substantial sink for river-transported sediments and opening once levee-protected areas can have a substantial impact on the sediment load of the MR.