Modeling framework for sediment deposition, storage, and evacuation in the floodplain of a meandering river: Application to the Clark Fork River, Montana

A theory for the evolution of a river floodplain and the associated movement of tracer sediment is applied to the case of the upper Clark Fork River, Montana, whose floodplain is contaminated with tailings derived from historical mining activities. Deposition of mine tailings raised the elevation of the floodplain, which now contributes contaminated sediment to the channel. The theory is capable of reproducing the basic aspects of the system's evolution, including aggradation of the floodplain during the mining era and subsequent net supply of sediment from floodplain to channel after the cessation of mine input. Results indicate that the natural removal of tailings from the floodplain could take thousands of years, a period longer than is required for the channel to simply rework the tailings. The self-stabilizing nature of the model results in an evolution toward a new postmine steady state, with tailings eventually almost entirely removed from the system.