A Guide to Moist-Soil Wetland Plants of the Mississippi Alluvial Valley

A Brief History of the Mississippi Alluvial Valley and Moist-Soil Wetlands

3 A Brief History of the Mississippi AlluvialValley and Moist-SoilWetlands The Mississippi River is the fifth largest river in the world, with its river basin encompassing 30 states in the United States and the province of Saskatchewan in Canada. In the northeast, the river drainage begins at the foothills of the Alleghany Mountains of western New York and Pennsylvania. Far to the west, glaciers of the Rocky Mountains of Montana melt into streams that slowly become the Missouri River, a major tributary of the Mississippi. Water from over 1.2 million square miles eventually drains through the 120-mile-wide flat land of the Mississippi Alluvial Valley. The Mississippi Alluvial Valley starts just south of Cape Girardeau, Missouri , where the steep bluffs that follow the river for hundreds of miles along its western edge quickly disappear into the flat lands of the alluvial valley. From southeastern Missouri to the Gulf of Mexico the ancient Mississippi River flooded regularly, spreading nutrient-rich sand, silt, and clay across the Mississippi Alluvial Valley. These periodic floods created and regularly rejuvenated a lush landscape of bottomland hardwoods,oxbows,and intermittent forest openings. Early records are scarce, but regular scouring of the Mississippi Alluvial Valley by rivers, periodic shifts in river channels, and floods that left permanent water for extended periods likely created openings in the bottomland hardwood forest, allowing the growth of shade-intolerant native shrubs, grasses, sedges, and aquatic plants. These forest openings provided a unique habitat in an otherwise vast expanse of towering hardwoods, tupelo breaks, and massive bald cypress trees. Beginning in the mid-nineteenth century, construction of levees along the Mississippi River and its major tributaries allowed for the expansion of agriculture throughout the Mississippi Alluvial Valley. The clearing of forests, A Brief History 4 draining of swamps, and building of levees were standard practices for the economic development of agricultural areas. The Army Corps of Engineers adopted a “levees-only” policy to reduce flooding, stabilize the Mississippi River channel, and increase downstream velocity. It was thought that earthen levees could deepen the river channel and allow self-dredging and maintenance , thereby providing perpetual flood control. Rich bottomland soils were farmed without fear of loss of crops to floods, and plantation life flourished. On March 12, 1927, however, a crevasse that would eventually produce a 100-foot-deep scour hole adjacent to the levee opened at Mounds Landing, Mississippi. The crevasse poured waters throughout the Mississippi side of the alluvial valley, eventually submerging houses 75 miles away from the river. Levees broke at 145 locations. The flood covered 27,000 square miles, nearly the entire Mississippi Alluvial Valley, including large portions of the Arkansas , Red, and White River Basins. The Mississippi River reached a maximum width of 60 miles,and an estimated 700,000 people were displaced from their homes.Waters did not recede until August 1927, and damage estimates topped $400 million. The Great Mississippi Flood of 1927 resulted in a new engineering approach to the Mississippi River,and for the first time the federal government assumed control of regional flood control efforts. The Flood Control Act of 1928 authorized the Army Corps of Engineers to implement a full-scale evaluation of flood control programs throughout the Mississippi Alluvial Valley. Ultimately , this legislation resulted in the Mississippi River and Tributaries Project and the end of the “levees-only” era. River engineering now included the creation of upstream reservoirs, floodways, outlet channels, channel stabilization , and other basin-wide engineering that facilitated river transportation, greatly reduced the potential effects of flooding, and secured the economic development of the Mississippi Alluvial Valley.Reservoirs were built throughout the Mississippi River Basin to help regulate the seasonal flow of the river. Levees were built larger and stronger, and floodways and outlet channels were developed using the latest engineering methodology. The ancient Mississippi River was gone.To date,3700 miles of levees have been built in the Mississippi Basin, breaking the critical link between the river’s nutrient-filled floods and the surrounding hardwood forests. The Mississippi Alluvial Valley is one of the most productive agricultural areas of the world, and aggressive engineering of the Mississippi River is the single largest factor facilitating the current agronomic infrastructure. Flood control changed the hydrology of the Mississippi Alluvial Valley, allowing A Brief History 5 for timber harvesting, land clearing, and development of agriculture on land previously too wet for farming. The...