THE GEOLOGY OF THE LOWER MISSOURI RIVER AT LISBON BOTTOM--STRATIGRAPHY, GEOMORPHOLOGY, AND THE REHABILITATION OF FLOOD-PLAIN HABITATS

Before 1800, the Missouri River was one of North America’s most diverse and dynamic ecosystems. Since 1800, it has been transformed into a navigation system regulated by reservoirs and flood control structures. These modifications have reduced seasonal flow variability and sediment load and have disconnected the river from off-channel and flood-plain habitats. Flooding in 1993 and 1996 had a profound effect on the physical and political landscape of the lower Missouri River, and it increased public awareness of the management of the river’s natural resources. Knowledge of surficial geologic characteristics and processes in an alluvial setting like Lisbon Bottom provides a scientific basis for floodplain management. The Missouri River Valley at Lisbon Bottom has been characterized as a bedrock trench filled with 60 feet of highly permeable basal glacial outwash (sand, gravel, and boulders) overlain by postglacial sand and gravel, which in turn are overlain by postglacial interbedded sand, silt, and clay. Recent field study and interpretation of historic aerial photographs indicate that the uppermost part of the alluvium possesses an architecture that may be modeled to predict the spatial distribution of flood-plain wetland habitats at Lisbon Bottom and other sites along the lower Missouri River.