By Alisha Renfro, Coastal Scientist, National Wildlife Federation
The Mississippi River is one of the most managed river systems in the world. However, that management has focused on navigation and flood control needs to the detriment of the economically and ecologically important coastal Louisiana landscape. This week, the U.S. Army Corps of Engineers and Louisiana’s Coastal Protection and Restoration Authority (CPRA) hosted a public meeting in New Orleans to present information and preliminary results of their joint effort on the Mississippi River Hydrodynamic and Delta Management Study. This large-scale, long-term study is developing tools to evaluate different combinations of restoration projects in an effort to address the long-term sustainability of the Mississippi River and its delta while balancing the needs of navigation, flood protection and restoration.
The scope of the study extends from Vicksburg, Miss. south to the Bird’s Foot delta. The study is actually comprised of two coupled, but somewhat distinct, efforts. The hydrodynamic portion of the study will focus on characterizing the dynamics in the river and developing models that can be used to evaluate river-side changes due to proposed freshwater and sediment diversion projects. It will also inform location and design of these projects to maximize their effectiveness and minimize the potential for shoaling in the river’s navigation channel. The delta management part of the study will focus on the basin-side benefits and changes caused by these restoration projects. The delta management portion of the study has not yet begun. Currently, the state of Louisiana and the Army Corps are working to define the depth and breadth of that part of the study.
The afternoon session of the meeting focused on detailed technical presentations on the study. The different tasks of the Mississippi River Hydrodynamic and Delta Management Study include a geomorphic assessment, data collection and an extensive modeling effort. The geomorphic assessment focuses on compiling historical river data, dredging records and satellite imagery to document the historical trends in the river. The data collection effort will compile existing data and conduct field work to fill in gaps in understanding of the water and sediment dynamics that currently exist in the river. The historical data and present data will be integrated into the modeling work to inform the models and to ensure that the models capture the dynamics of the river system. The modeling effort includes a suite of models that each has different strengths and weaknesses. These models will be used to forecast the large-scale, long-term and shorter-term regional changes expected in the river in both a future without river diversions and a future that includes different combinations of diversion projects.
The presentations from the technical meeting indicate that this collaborative state of Louisiana and Army Corps effort has moved forward significantly since it began. The geomorphic assessment has been completed and a final report on its results is expected by the end of this year. The data collection effort is ongoing, having captured the low discharge of the river last year and the higher flow discharge from this past spring. Many of the preliminary model simulations have begun, and the preliminary results presented at this meeting emphasized the dynamic nature of the Mississippi River system, where water discharge, sediment transport and deposition can not only vary greatly from year to year, but also from week to week. The preliminary results also point to the importance of appropriate size, location and operation of sediment diversions in order to maximize sediment conveyance into adjacent wetlands and to reduce potential riverside impacts.
The Mississippi River has been a key feature in the growth and development of the U.S. However, for more than 80 years, the management of the river has focused on balancing the needs of navigation and flood control. A shift away from that management scheme towards one that balances navigation, flood control and restoration is absolutely critical for the survival of the delta ecosystem and, ultimately, the communities and navigation industry that depend on the Mississippi River Delta. The Hydrodynamic and Delta Management study is poised to be the effort that changes the way we think about management of the river and how we build a more sustainable, holistic system for our future.