| The Great Flood of 1993 damaged the floodplain of the Lower Missouri River when over 500 levees failed. These levee failures created large scours and deposited massive amounts of sediment on the agricultural floodplain. The U.S. Fish and Wildlife Service acquired areas heavily damaged by the 1993 floods and incorporated them into the Big Muddy Fish and Wildlife Refuge. One purpose of this refuge system is to restore the Missouri River system within the refuge from its highly engineered state to a more natural form.; Analysis of a combination of remote sensing data, fieldwork, and finite element flow models was used to investigate the biogeomorphic evolution of one of these new wetlands refuges, the Lisbon Bottoms/Jameson Island Refuge. Four landcover mapping techniques were used to track changes with time: (1) geomorphic mapping, (2) maximum likelihood classification of Landsat TM data, (3) a linear spectral unmixing model using Landsat TM data, and (4) polarimetric and minimum distance classification of AIRSAR radar scattering data.; Research showed that a biogeomorphic feedback loop in which the flow field, geomorphology, sediment, and vegetation interactions controlled the rapid evolution of the refuge after 1993. The 1993 flood first entered the area through levee breaks, forming scour zones, sweeping away most non-woody vegetation, and leaving behind a largely uniform, sand-covered floodplain. Field and remote sensing data showed that xeric sparse vegetation species encroached on high, dry sands, whereas mesic species populated lower, wetter scours. Smaller floods after 1993 entered the levee breaks, extended the scours into chutes, and draped silt and clay over the sand, allowing vegetation to spread rapidly. Remnant levees protected most of the area from fast flows, allowing cottonwood and willow saplings to spread across the study area and dominate the landscape, except in floodplain chutes. Expansion of saplings and the absence of flooding in 1999–2000 limited the influence of the feedback loop. Without the feedback loop operating to insure landcover diversity, the study area moved toward a uniform, static forest of dense cottonwood and willow saplings. Overall, the refuge's return to a natural state is limited by anthropogenic control structures required to meet the needs of other river users. |
