Mississippi River Mainline Levee (MRL)
Supplemental Environmental Impact Statement (SEIS II)

The U.S. Army Corps of Engineers (USACE) prepared a supplemental environmental impact statement to address the impacts associated with the construction of remaining authorized work on the Mississippi River mainline levees (MRL) feature of the Mississippi River and Tributaries (MR&T).  The MRL is one of the major features of the MR&T Project used to provide comprehensive flood damage control, protection, and risk reduction from the “Project Design Flood” (PDF) in the alluvial valley beginning at Cape Girardeau, Missouri to the Head of Passes, Louisiana. 


The National Environmental Policy Act (NEPA) requires federal agencies to analyze the impacts of their actions on the environment and disclose the impacts in Environmental Assessments (EAs) or Environmental Impact Statements (EISs).  This will be the second supplemental EIS (SEIS II) for MRL work since publication of the 1976 Final EIS.  A supplemental EIS (SEIS I) was prepared in 1998 to supplement the 1976 EIS to evaluate the effects of continued construction of the MRL levee enlargements, stability berms, seepage control, and erosion protection measures focusing on the levees of the MRL that were the most deficient in height and on seepage control measures for levee reaches with observable signs of seepage.  Since publication of the 1976 Final EIS and the 1998 (SEIS I), USACE has determined that various sections (reaches) of the mainline levee system are deficient in varying amounts, and that certain remedial measures need to be undertaken to control seepage and to raise and stabilize the deficient sections of the levee to protect the lower Mississippi River Valley against the PDF and maintain the structural integrity of the MRL system.  SEIS II was prepared to supplement and, as necessary, augment the 1976 EIS and SEIS I for construction of necessary authorized MRL Project features.  These features, may include but are not limited to, implementing seepage control measures and the construction of various remediation measures for deficient levee reaches to bring these reaches to the Project design grade.  SEIS II evaluated the potential direct, indirect, and cumulative impacts for an array of alternatives, including a No Action alternative. 



A Notice of Availability (NOA) for the Final SEIS II was published in the Federal Register on November 13, 2020.  This NOA commences the 30-day review period which shall continue through December 14, 2020. The Final SEIS II Main Report and all Appendices are available on this webpage.  For further information, please e-mail MRL-SEIS-2@usace.army.mil .



The Mississippi River has always been a threat to the security of the inhabitants of the valley through which it flows. The first European explorer in the region, Hernando de Soto, viewed the Mississippi River in 1541, and in 1543 the first record of a flood on the river was made. The necessity of flood control was recognized immediately by early settlers in the lower Mississippi River valley. When Bienville founded the city of New Orleans in 1717, his engineer, de la Tour, opposed the location of the city on the site selected because he knew that the settlement would be periodically overflowed by the river. Bienville overruled this objection, so de la Tour undertook the construction of the first levee system to be erected on the Mississippi River. The work was not completed until 1727.  As settlements developed along the river, the levee system was extended. By 1735, the levees on both sides of the river extended from approximately 30 miles above New Orleans to approximately 12 miles below the city. Although the system represented extraordinary effort, the works were of insufficient strength and were crevassed at many points by the unusually high water of that year. By 1812, when Louisiana was admitted to the Union, the levee system extended up the river to Baton Rouge on the east bank and to the vicinity of Morganza, 40 miles upriver from Baton . Rouge, on the west bank. , By 1844, in spite of several damaging floods, the levee system was continuous, except for a gap at Old River, from 20 miles below New Orleans to the mouth of the Arkansas River on the west bank and to Baton Rouge on the east bank. Efforts thus far to control Mississippi River floods had been almost entirely local in nature, with individual landowners bearing all costs.

The need for more substantial Federal participation in improvements to the river for navigation and flood control was generally recognized by 1879. The necessity for coordination of engineering operations through a centralized organization was apparent. That year, Congress established the Mississippi River Commission, which had as its assigned duties " ... to take into consideration and mature such plan or plans and estimates as will correct, permanently locate, and deepen the channel and protect the banks of the Mississippi River; improve and give safety and ease to the navigation thereof; prevent destructive floods; promote and facilitate commerce, trade, and the postal service .... " The flood of 1916 resulted in passage of the first Flood Control Act, approved 1 March 1917. This Act authorized the construction of levees for the control of floods and affirmed the policy of local cooperation. A major flood occurred in 1926 followed by the 1927 flood, the most disastrous in the history of the lower Mississippi River valley. This disaster awakened the national conscience to the dire need for flood control in the lower valley. Out of it grew the Flood Control Act of 1928, which committed the Federal Government to a definite program of flood control.

NEPA Process Flowchart