Causes for the decline of suspended‐sediment discharge in the Mississippi River system, 1940–2007

Abstract

Abstract:Before 1900, the Missouri-Mississippi River system transported an estimated 400 million metric tons per year of sediment from the interior of the United States to coastal Louisiana. During the last two decades (1987)(1988)(1989)(1990)(1991)(1992)(1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006), this transport has averaged 145 million metric tons per year. The cause for this substantial decrease in sediment has been attributed to the trapping characteristics of dams constructed on the muddy part of the Missouri River during the 1950s. However, reexamination of more than 60 years of water-and sediment-discharge data indicates that the dams alone are not the sole cause. These dams trap about 100-150 million metric tons per year, which represent about half the decrease in sediment discharge near the mouth of the Mississippi. Changes in relations between water discharge and suspended-sediment concentration suggest that the Missouri-Mississippi has been transformed from a transport-limited to a supply-limited system. Thus, other engineering activities such as meander cutoffs, river-training structures, and bank revetments as well as soil erosion controls have trapped sediment, eliminated sediment sources, or protected sediment that was once available for transport episodically throughout the year. Removing major engineering structures such as dams probably would not restore sediment discharges to pre-1900 state, mainly because of the numerous smaller engineering structures and other soil-retention works throughout the Missouri-Mississippi system. Published in

A comparative study of the flux and fate of the Mississippi and Yangtze river sediments

“…1) are the largest rivers in North America and Asia, respectively. Their geological and hydrological conditions and geomorphological evolution have previously been reported for the Mississippi River (Meade et al, 1995;Colman et al, 1998;Roberts, 1998;Day et al, 2007;Bianchi & Allison, 2009;Blum & Roberts, 2009;Horowitz, 2009;Meade & Moody, 2010;Allison et al, 2012) and the Yangtze River (Chen et al, 2001;Yang et al, 2002;Xu et al, 2006;Yang et al, 2006;Xu & Milliman, 2009;Yang et al, 2011). However, only a few papers have directly compared these two rivers (Xu et al, 2007;Bianchi & Allison, 2009).…”

“…Despite the increased water discharge, sediment discharge of the Mississippi has decreased by over 50% since the early 1950s due to impoundments and other engineering activities, such as meander cut-offs, bank revetments and soil erosion controls ( Fig. 3; Meade & Moody, 2010). The declining sediment discharge is mainly related to construction of the Fort Randall ( Fig.…”

Spatial, Temporal, and Human-Induced Variations in Suspended Sediment Concentration in the Surface Waters of the Yangtze Estuary and Adjacent Coastal Areas

“…In recent decades, the transfer of suspended sediment to the sea from many of the world's rivers has drastically decreased as a result of human activities, primarily the construction of dams and irrigation (e.g., Dai et al 2009;Meade and Moody 2010;Milliman and Farnsworth 2011, and references therein), thereby influencing the rivers' deltas (e.g., Syvitski et al 2009;Yang et al 2011 and references therein). The response of SSC in estuarine and adjacent waters to human activities, however, has seldom been addressed (Schoellhamer 2011), probably due to a lack of adequate datasets.…”

Design and methods of the Midwest Stream Quality Assessment (MSQA), 2013

“…As a result, the Midwest contributes substantially to nutrient, suspended sediment, and contaminant loading to the Mississippi River and the Gulf of Mexico (not shown) (Aulenbach and others, 2007;Meade and Moody, 2010;Heimann and others, 2011). The MSQA region is estimated to contribute about 64 percent of the nitrogen load reaching the Gulf of Mexico in a typical year (Robertson and others, 2009) although the region covers only about 20 percent of the Mississippi River watershed area.…”