Upper Mississippi River Restoration Program Long Term Resource Monitoring

Abstract

Net sedimentation rates were obtained for backwaters of the Upper Mississippi River in Pools 4, 8, and 13 by measuring annual bed elevation changes along transects between 1997 and 2001. Average sedimentation rates (cmּyr^­1) during the 5-yr period were lower than most previously reported rates in backwaters of the River, with means of –0.08 (standard error [SE] = 0.18) in Pool 4, 0.21 (SE = 0.10) in Pool 8, and 0.47 (SE = 0.26) in Pool 13. Poolwide estimated mean sedimentation rates in the terrestrial areas adjacent to backwaters appeared higher, ranging from 0.32 (SE = 0.14) to 0.78 (SE = 0.25) cmּyr^­1, but were not significantly different than rates in aquatic areas. When averaged over the study period, sedimentation rates were correlated with bed elevation, but the relations differed in aquatic and terrestrial areas. On an annual basis, the correlation between annual sedimentation rates and bed elevation was similar across aquatic and terrestrial areas, with annual river discharge explaining some of the variability. During the high discharge year of 2001, a positive correlation between sedimentation and bed elevation was observed, whereas in low discharge years, such as 2000, there was a negative correlation. This correlation is reflected in poolwide mean rates for backwaters, that in some pools were significantly higher during low discharge years than in high discharge years. The above inferences suggest there is an opportunity to predict future conditions in a reasonable manner. These predictions would be of value when planning management actions to maintain the viability of the diverse ecosystem of the Upper Mississippi River.

Key words:  Backwaters; erosion; Mississippi River; sediment transport; sedimentation