DISTURBANCE ZONES AND MINING SEDIMENT REMOBILIZATION IN THE LOWER BIG RIVER, SOUTHEAST MISSOURI

The Old Lead Belt mining district of east-central Missouri was a global leader in lead production from 1864-1972. Historical mining activities created six major tailings disposal areas in St. Francois County, which are currently stabilized by federal Superfund. However, channel and floodplain deposits along 170 km of the Big River from Leadwood to its confluence with the Meramec River are contaminated with mining sediments as lead is released to the river by erosion and weathering. These contaminated sediments pose a long-term environmental risk to the river system. Although in-channel and floodplain contamination has been documented, bank erosion as a source of lead contamination along the Big River is poorly understood. The purpose of this study is to quantify historical changes in stream channel planform and determine the spatial distribution of bank erosion along the lower Big River to evaluate the present-day pollution risk of remobilized mining sediment. The objectives are: (i) use aerial photography to quantify historical river channel planform change, (ii) calculate bank erosion rates, and (iii) identify spatio-temporal trends of bank erosion inputs to the channel. The study area includes 17 km of the lower Big River from Rockford Beach Dam to the confluence of Big and Meramec Rivers near Eureka, MO. Using georeferenced aerial photographs from 1937 to present as basemaps, active channel and bars are digitized to reconstruct historical planimetric change. In addition, field surveys will be used to construct a detailed landform map of the lower reach of the Big River, which will be used to determine the locations of contaminated floodplain deposits and reaches with the highest bank erosion rates. Preliminary results suggest that the channel of the Big River has been relatively stable throughout the study period. However, bank erosion occurs in discrete disturbance zones along the Big River. Thus, bank erosion presently represents an important source of lead contamination to some segments of the river. Understanding the role that floodplain bank erosion plays in the present-day contamination of the river system will help officials prioritize the best remediation practices needed for the Big River.