David S. Biedenharn

Recent morphological evolution of the Lower Mississippi River

Abstract This study documents slope and stream power changes in the Lower Mississippi River during the pre-cutoff (1880s–1930s), and post-cutoff (1943–1992) periods. The study reach extends from New Madrid, MO, to Natchez, MS, a distance of about 900 km. Analyses for six major reaches and 13 sub-reaches for the pre- and post-cutoff periods indicate that the river presently has a much larger slope and stream power than prior to the cutoffs. The largest increases have occurred between Fulton, TN, and Lake Providence, LA, where slope and stream power increases range from about 27% to 36% and 20% to 38%, respectively. Increases in slope and stream power in reaches upstream and downstream have also occurred, but to a lesser degree. Previous investigations have shown that no coarsening of the bed material has occurred since 1932, and that the bed material may actually be somewhat finer overall. As the Lower Mississippi River is not a sediment-starved system, an increase in stream power with no change in D50 would be expected to be offset by an increase in the bed material load as the river adjusts towards equilibrium. Previous investigators have inferred a reduction in the sediment loads on the Mississippi River this century based on analyses of total measured suspended loads. However, these results should be viewed as primarily representing the changes in wash load and should not be taken to imply that bed material loads have also decreased. Therefore, the bed material loads in the study reach should be greater than in the pre-cutoff period. Excess stream power in the sub-reaches directly affected by cutoffs resulted in scour that increased downstream bed material load. These elevated sediment loads play a key role in driving morphological adjustments towards equilibrium in the post-cutoff channel. The stability status of the channel in the study reach currently ranges from dynamic equilibrium in the farthest upstream reaches through severe degradation to dynamic equilibrium in the middle reaches, and aggradation in the lowest reaches. These evolutionary trends cannot be explained by consideration of changes in slope and stream power alone. Changes in the incoming bed material load to each reach generated by upstream channel evolution must also be considered.

Stage adjustment in the lower Mississippi River, USA

This study documents the stage adjustments in the Lower Mississippi River during the pre-cut-off (1880s–1930s), and post-cut-off (1943–1994) periods. The study reach extends from Columbus, Kentucky, just downstream of Cairo, Illinois, to Natchez, Mississippi, a distance of about 970 km. The analysis shows that the majority of the pre-cut-off study reach was not undergoing any significant system instability such as channel aggradation or degradation, and, therefore can be considered to have been in a state of dynamic equilibrium during this period. However, the analysis did show that the upper portion of the study reach in the vicinity of Columbus was undergoing a significant aggradational trend during this period. Specific gauge records and peak stage–peak discharge plots for the time period 1950–1994 were analysed to document stage adjustments and to divide the river into the following seven reaches based on observed stability: Columbus to New Madrid (dynamic equilibrium); New Madrid to Fulton (transitional/dynamic equilibrium); Fulton to Sunflower (degradational); Sunflower to Rosedale (transitional); Rosedale to Lake Providence (dynamic equilibrium); Lake Providence to Vicksburg (transitional); and Vicksburg to Natchez (aggradational). Thus, the entire Mississippi River, between Natchez and Columbus is responding in a manner similar to the response of a stream to a single cut-off as described by Lane (1947). Recognition of this evolutionary trend is a first step in developing a comprehensive understanding of this complex system, and will help the engineers and scientists of the US Army Corps of Engineers to develop management strategies for the Mississippi River in the long and short term.

Mississippi River Streamflow Measurement Techniques at St. Louis, Missouri

AbstractStreamflow measurement techniques of the Mississippi River at St. Louis have changed through time (1866–present). In addition to different methods used for discrete streamflow measurements, the density and range of discrete measurements used to define the rating curve (stage versus streamflow) have also changed. Several authors have utilized published water surface elevation (stage) and streamflow data to assess changes in the rating curve, which may be attributed to be caused by flood control and/or navigation structures. The purpose of this paper is to provide a thorough review of the available flow measurement data and techniques and to assess how a strict awareness of the limitations of the data may affect previous analyses. It is concluded that the pre-1930s discrete streamflow measurement data are not of sufficient accuracy to be compared with modern streamflow values in establishing long-term trends of river behavior.

System Level Analysis of Watershed Instability in the Yalobusha Basin, Mississippi

Channel modifications during the 1960s have resulted in watershed instability in the Yalobusha River Basin, Mississippi. A comprehensive analysis of the watershed was conducted to provide a basis for design of diverse watershed rehabilitation practices. Proposed actions range from instream grade control to upland best management practices. Results of the analyses demonstrate a coupled geomorphic-hydraulic engineering approach can be utilized.

The influence of geology on the morphologic response of the Lower Mississippi River

The Mississippi River is heavily influenced by structural and geologic controls involving regional uplifts, faults, clay plugs, outcrops of Tertiary clay, and Pleistocene gravel in its bed and tributaries. Degradation is continuing to migrate upstream on the Lower Mississippi River (LMR) and has presently moved as far upstream as the Hickman, KY, area. Left unchecked, this degradation could continue to advance on the LMR and ultimately migrate upstream into the Ohio and Middle Mississippi River systems. This degradation would not only adversely affect the stability and environmental features in the main stem of the river but also introduce headcutting into the many tributaries that enter the river in this degradational zone. Detailed studies of the exact role of these features, particularly with respect to retarding or halting long-term degradational processes along the river, have not received much attention. In this study, potential areas where geologic outcrops may influence river morphology are identified, and examples are provided that support the concept that geologic outcrops may be extremely important features that serve as temporary or permanent grade control along the river. DISCLAIMER: The contents of this report are not to be used for advertising, publication, or promotional purposes. Citation of trade names does not constitute an official endorsement or approval of the use of such commercial products. All product names and trademarks cited are the property of their respective owners. The findings of this report are not to be construed as an official Department of the Army position unless so designated by other authorized documents. DESTROY THIS REPORT WHEN NO LONGER NEEDED. DO NOT RETURN IT TO THE ORIGINATOR. MRG&P Report No. 17 iii

Large-scale geomorphic change in the Mississippi River from St. Louis, MO, to Donaldsonville, LA, as revealed by specific gage records

Specific gage records were developed for 25 stations on the Mississippi River between St. Louis, MO, and Donaldsonville, LA. Generation and initial inspection of these records for the Mississippi River establish that complex morphologic adjustments have occurred throughout the river system for at least a century and indicate that these adjustments continue to the present day. Further, although no attempt was made in this study to conduct a detailed analysis of the effects of the numerous natural and anthropogenic factors on the morphologic trends in the river in the initial assessment reported herein, preliminary evaluation of the specific gage records demonstrates that they provide a powerful framework that, when combined with other geomorphic assessment tools, will aid in understanding and explaining the complex morphological processes that drive the Mississippi River. These and other comprehensive analyses are planned for future Mississippi River Geomorphology & Potamology Program efforts. DISCLAIMER: The contents of this report are not to be used for advertising, publication, or promotional purposes. Citation of trade names does not constitute an official endorsement or approval of the use of such commercial products. All product names and trademarks cited are the property of their respective owners. The findings of this report are not to be construed as an official Department of the Army position unless so designated by other authorized documents. DESTROY THIS REPORT WHEN NO LONGER NEEDED. DO NOT RETURN IT TO THE ORIGINATOR. MRG&P Report No. 10 iii

Channel geometry trends of the Mississippi River, Old River Control Complex to St. Louis, Missouri

A geometric data analysis was conducted for the Mississippi River from the Old River Control Complex to St. Louis, MO, or approximately River Mile 325 Above Head of Passes to RM 180 Above Mouth of Ohio River. The purpose of the study was to document long-term trends in the dimension, pattern, and profile of the Mississippi River channel within the study reach. Hydrographic survey data from 1956 to 2013 were used to determine spatial and temporal variations in channel geometry and volume. Trends of geometric change in the channel were identified along defined geomorphic reaches of the river. Observed trends indicate the lower portion of the study reach from Old River to Vicksburg, MS, has experienced a general decrease in channel area and volume. Conversely, the reach from Helena, AR, to Hickman, KY, has undergone a general increase in area and volume. The reach of the middle Mississippi River above Cairo, IL, has seen a slight lowering of the channel. The results of this study will be part of a detailed geomorphic assessment of the Mississippi River to be conducted as part of the on-going Mississippi River Geomorphology and Potamology Program sponsored by the U.S. Army Corps of Engineers, Mississippi Valley Division Science and Technology Office. DISCLAIMER: The contents of this report are not to be used for advertising, publication, or promotional purposes. Citation of trade names does not constitute an official endorsement or approval of the use of such commercial products. All product names and trademarks cited are the property of their respective owners. The findings of this report are not to be construed as an official Department of the Army position unless so designated by other authorized documents. DESTROY THIS REPORT WHEN NO LONGER NEEDED. DO NOT RETURN IT TO THE ORIGINATOR. MRG&P Report No. 11 iii

Watershed Approach to Stream Stability and Benefits Related to the Reduction of Nutrients

A number of streams in the hill area of north central Mississippi have been experiencing varying degrees of instability for the last several decades. This instability, bed degradation and bank failure, has resulted in numerous problems including damage to local infrastructure, the loss of productive agricultural land, deposition in flood control channels, and environmental degradation. The Mississippi Delta Headwaters Project (formerly the Demonstration Erosion Control Project) administered by the Vicksburg District of the Corps of Engineers has been successful in stabilizing some of these streams. The Mississippi Delta Headwaters Project (MDHP) restores stream stability at a reasonable cost by addressing problems in the entire drainage basin, i.e. the systems approach.