In 1982, the Mississippi Valley Division initiated the Lower Mississippi River Environmental Program (LMREP). The program provides environmental data to support sustainable development through the design, construction and operation of the Mississippi River levees and channel improvement features of the Mississippi River and Tributaries project.
The goals of the LMREP are as follows: to develop general environmental inventory data for the lower Mississippi River and its floodplain, to better understand the environmental effects of project features and to develop environmental engineering design considerations for levees, borrow pits, channel training dikes and revetments. To achieve these goals, the LMREP has conducted field investigations for vegetation, fish, invertebrate and wildlife within in the system, complete with extensive system-wide habitat mapping.
The 2.3-million-acre project area has been mapped for aquatic and terrestrial habitat. A geographic information system has been developed to store the maps and to conduct habitat spatial analyses. Aquatic habitat maps of the river channel for 1880, 1915 and for ten-year intervals from the 1930s to the 1990s, have been completed and are being used to assess historic habitat trends and to evaluate project effects on endangered species. Terrestrial habitat and land cover maps have been prepared for 1982 and 1992, and have been used to delineate jurisdictional wetlands and to plan levee construction to avoid and minimize adverse environmental impacts and maximize beneficial effects.
Studies were conducted of levee borrow pits to determine habitat value for fish and wildlife. These field investigations found that riverside levee borrow pits are valuable habitat for fish, birds and mammals, and support extensive sport and commercial fisheries. Levee borrow pits are second in abundance to oxbow lakes among floodplain aquatic habitats. Results of these studies, and data on the hydrologic and physical characteristics of borrow pits, were used to develop an environmental design manual for borrow pit construction. These techniques are now routinely used to design borrow pits that are productive fish and wildlife habitat even though they are used extensively for recreation.
LMREP investigations of stone dikes evaluate the effects of these structures on river habitat and are used to develop environmental design improvements. Diked secondary channels are found to consist of a diversity of habitat types and to support large fish populations. They function as fish feeding and nursery areas and provide important water bird habitat. These habitats are especially important during moderate to low flow river conditions. Secondary channel habitat is being degraded in some instances as a result of sedimentation. Weir sections are now routinely incorporated into stone dikes to reduce sedimentation and improve habitat conditions during low discharge periods. Physical models and field studies are being conducted to improve weir designs. This has lead to a program to systematically restore degraded secondary channels.
Articulated concrete mattress revetment (ACM) is used to stabilize the banks of the lower Mississippi River. Environmental studies of these revetments have been conducted. Results of these investigations have shown that revetments support abundant benthic invertebrate and fish populations and re-vegetate over time with early successional tree species such as willow and cottonwood. Extensive field tests have shown that the surface of the ACM could be grooved during the casting process, at no extra cost, to increase surface area and provide a favorable substrate for growth of aquatic insect larvae that are important fish food. Grooved ACM can increase larval insect production 2-3 fold. All lower Mississippi River revetments constructed since 1992 are grooved.