Dynamics of 30 large channel bars in the Lower Mississippi River in response to river engineering from 1985 to 2015

Abstract Channel bars are a major depositional feature in alluvial rivers and their morphodynamics has been investigated intensively in the past several decades. However, relatively less is known about how channel bars in alluvial rivers respond to river engineering and regulations. In this study, we assessed 30-yr morphologic changes of 30 large emerged bars located in a 223 km reach of the highly regulated Lower Mississippi River from Vicksburg, Mississippi, to the Mississippi-Atchafalaya River diversion. Landsat imagery and river stage data between 1985 and 2015 were utilized to characterize bar morphologic features and quantify decadal changes. Based on bar surface areas estimated with the satellite images at different river stages, a rating curve was developed for each of the 30 bars to determine their volumes. Results from this study show that the highly regulated river reach favored the growth of mid-channel and attached bars, while more than half of the point bars showed degradation. Currently, the mid-channel and attached bars accounted for 38% and 34% of the total volume of the 30 bars. The average volume of a single mid-channel bar is over two times that of an attached bar and over four times that of a point bar. Overall, in the past three decades, the total volume of the studied 30 bars increased by 110,118,000 m 3 (41%). Total dike length in a dike field was found mostly contributing to the bar volume increase. Currently, the emerged volume of the 30 bars was estimated approximately 378,183,000 m 3 . The total bar volume is equivalent to ~ 530 million metric tons of coarse sand, based on an average measured bulk density of 1.4 t/m 3 for the bar sediment. The findings show that these bars are large sediment reservoirs.

[1]  C. Vörösmarty,et al.  Anthropogenic sediment retention: major global impact from registered river impoundments , 2003 .

[2]  D. Walling,et al.  Recent trends in the suspended sediment loads of the world's rivers , 2003 .

[3]  Harry H. Roberts,et al.  The Mississippi Delta Region: Past, Present, and Future , 2012 .

[4]  Hans Middelkoop,et al.  Flood management along the Lower Mississippi and Rhine Rivers (The Netherlands) and the continuum of geomorphic adjustment , 2008 .

[5]  Nicholas J. Clifford,et al.  Geomorphological explanation of the long profile of the Lower Mississippi River , 2007 .

[6]  Suzanne R. Hawes,et al.  Historical and projected coastal Louisiana land changes: 1978-2050 , 2003 .

[7]  P. Hudson,et al.  A new longitudinal approach to assess hydrologic connectivity: Embanked floodplain inundation along the lower Mississippi River , 2013 .

[8]  Joseph H. Wlosinski,et al.  Trends in flood stages: Contrasting results from the Mississippi and Rhine River systems , 2006 .

[9]  Julie C. Bernier,et al.  Rapid subsidence and historical wetland loss in the Mississippi Delta Plain: likely causes and future implications , 2005 .

[10]  P. Ashworth.  MID‐CHANNEL BAR GROWTH AND ITS RELATIONSHIP TO LOCAL FLOW STRENGTH AND DIRECTION , 1996 .

[11]  Colin R. Thorne,et al.  Morphological changes of the Lower Mississippi River: geomorphological response to engineering intervention , 2005 .

[12]  R. H. Meade,et al.  Causes for the decline of suspended‐sediment discharge in the Mississippi River system, 1940–2007 , 2009 .

[13]  J. Hooke,et al.  Channel bar dynamics on multi‐decadal timescales in an active meandering river , 2011 .

[14]  Harry H. Roberts,et al.  Drowning of the Mississippi Delta due to insufficient sediment supply and global sea-level rise , 2009 .

[15]  J. Milliman,et al.  50,000 dams later: Erosion of the Yangtze River and its delta , 2011 .

[16]  R. H. Kesel,et al.  Human modifications to the sediment regime of the Lower Mississippi River flood plain , 2003 .

[17]  Bo Wang,et al.  Long-term geomorphic response to flow regulation in a 10-km reach downstream of the Mississippi–Atchafalaya River diversion , 2016 .

[18]  J. Hooke.  The significance of mid‐channel bars in an active meandering river , 1986 .

[19]  N. Bi,et al.  Sedimentation in the Three Gorges Dam and the future trend of Changjiang (Yangtze River) sediment flux to the sea , 2009 .

[20]  C. C. Watson,et al.  Analysis of the Impacts of Dikes on Flood Stages in the Middle Mississippi River , 2013 .

[21]  Guido Zolezzi,et al.  Modelling mid‐channel bars in meandering channels , 2010 .

[22]  I. Overeem,et al.  Sinking deltas due to human activities , 2009 .

[23]  Bo Wang,et al.  Sediment Trapping by Emerged Channel Bars in the Lowermost Mississippi River during a Major Flood , 2015 .

[24]  R. H. Kesel,et al.  An approximation of the sediment budget of the lower mississippi river prior to major human modification , 1992 .

[25]  Y. Xu,et al.  Estimation of sedimentation rates in the distributary basin of the Mississippi River, the Atchafalaya River Basin, USA. , 2015 .

[26]  E. Viparelli,et al.  Sand as a stable and sustainable resource for nourishing the Mississippi River delta , 2014 .

[27]  D. Walling.  Human impact on land : ocean sediment transfer by the world's rivers , 2006 .

[28]  L. Smith,et al.  The response of the Lower Mississippi River to river engineering , 1996 .

[29]  N. Pinter,et al.  Flood trends and river engineering on the Mississippi River system , 2008 .

[30]  Yoshiki Saito,et al.  Dam impacts on the Changjiang (Yangtze) River sediment discharge to the sea: The past 55 years and after the Three Gorges Dam , 2006 .

[31]  Y. Xu,et al.  A Hydrograph-Based Sediment Availability Assessment: Implications for Mississippi River Sediment Diversion , 2014 .