EP003-0005
CHANNEL BED CHANGES ALONG A LARGE ALLUVIAL RIVER ENTERING THE NORTHERN GULF OF MEXICO

Monday, 7 December 2020
Poster
Ming Tang, East China Normal University, State Key Laboratory of Estuarine and Coastal Research, Shanghai, China; Louisiana State University, Baton Rouge, United States, Yi-Jun Xu, Louisiana State University, School of Renewable Natural Resources, Baton Rouge, LA, United States, Bo Wang, Louisiana State University, Baton Rouge, LA, United States, Wei Xu, East China Normal University, Shanghai, China and Heqin Cheng, East China Normal University, State Key Labortary of Esturarine and Coastal Research, Shang Hai, China
Abstract:
Many world’s large rivers have experienced significant sediment reduction in the past century. However, channel aggradation near the mouth of these rivers may be still occurring and/or even accelerating, as evidenced by a recent study on the Lowermost Mississippi River. This study was organized to focus on two major questions: (1) What is the pattern of riverbed erosion and deposition throughout the Lower Atchafalaya River in recent decades? (2) What changes have occurred in the hydraulic head for the 174-km river reach? We collected bathymetric survey records in 1977 and 2006 from the U.S. Army Corps of Engineers to analyze riverbed deformation. We utilized river discharge and stage records at the main hydrological gauging stations to determine the change in the hydraulic head of the Lower Atchafalaya River. Geospatial techniques were used to develop channel bed Digital Elevation Models which were used to identify deformation of the 174-km channel bed of the Lower Atchafalaya River. We found a cumulative bed erosion of 6.34 ×107 m3 and a cumulative deposition of 8.79×107 m3, resulting in a net sediment deposition of 2.45 ×107 m3 over the entire 30-year study period. Channel aggradation occurred mainly in the mainstem channel of upstream reach with a rate of 0.37×105 m3·km-1y-1. The changes in riverbed elevation and the channel cross-sectional area are different along the Lower Atchafalaya. Specifically, on average, riverbed elevation in the upper 98 river kilometers (i.e. from RK64 to RK162) decreased by 1.47 m, while the channel cross-sectional area increased by 10,000 m2. The average riverbed elevation increased by 0.19 m and the average channel cross-sectional area deceased by 150,000m2 in the final reach. Additionally, we found that the river stage in the first 36-km reach (i.e., from Krotz Springs to Butte La Rose) decreased by 3.17 m, while the river stage in the final 35 kilometers increased by 0.25 m. These findings showed that channel erosion in the Lower Atchafalaya River mainly occurred upstream, while the downstream channels experienced aggradation. The channel erosion of the Lower Atchafalaya River in its upstream reach will likely continue with the river discharge projected to increase, and deposition in the downstream reach may accelerate because of sea level rise.
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