Sand and Gravel Dispersal Rates Using Mine Tailings Tracers In Big River, Ozark Highlands

Tailings materials produced by historical lead mining were used for this study as tracers to assess bed sediment dispersal in the Big River (2,500 km2) which drains the Ozark Highlands of southeast Missouri. Concentration mills released large quantities of dolomitic sand and fine gravel to the main channel at known source points from 1900 to 1935. Intensive channel bed and bar sampling was used to quantify downstream patterns of sediment storage, grain size distributions, tailings abundance by grain counting, and geochemical signatures of finer particles. As expected, tailings particles are sorted longitudinally according to particle size with finer sediments being dispersed farther downstream. Maximum virtual velocities of sediment transport decreased with grain size in the following order: 494 m/yr, 1-2 mm; 396 m/yr, 2-4 mm; 330 m/yr, 4-8 mm; and 227 m/yr, 8-16 mm. Average velocities are at least half of maximum values. These results suggest there is a low risk for degradation of downstream aquatic habitats by tailings wave sedimentation. Further, gravel disturbance zones in rivers draining the Missouri Ozarks may be controlled more by local changes in bed sediment storage and excess channel stream power than by sediment delivery rates from upstream segments over timescales from 10-100 years.