VIRTUAL VELOCITIES OF SAND- AND GRAVEL-SIZED MINE TAILINGS IN BIG RIVER, OZARK HIGHLANDS

Tailings materials produced by historical lead mining were used as tracers to estimate the virtual velocities of sand- and gravel-sized sediments in Big River (2,500 km²) which drains the Ozark Highlands of southeast Missouri. 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. Transport distances typically ranged from 30-80 km over a monitoring period of about 100 years. Maximum virtual velocities of sediment transport decreased with grain size in the following order: 1-2 mm, 559 m/yr; 2-4 mm, 450 m/yr; 4-8 mm, 380 m/yr; and 8-16 mm, 245 m/yr. Virtual velocities tend to be lower than estimated sediment wave migration rates. Therefore, disturbance zone activity in Ozark river channels may be controlled more by local variations in channel storage or excess channel stream power than by gravel delivery rates from upstream over historical timescales.