| Sedimentation processes can seriously limit the performance of a river-fed reservoir and cause significant morphological changes in the river channel. Loss of available storage, increased risk of flooding, silting up of the channel in the reach upstream of the reservoir, and problems with navigation are just some of the repercussions imposed by deltaic sedimentation in reservoirs and lakes.; A variety of numerical models for the deposition of bed-material load in reservoirs have been proposed to date. In addition, various models of turbidity currents in both lakes and reservoirs can be found in the literature. Nevertheless, none of these dynamically links the fluid mechanics of bottom turbid flows with fluvial dynamics to quantify the response of a lake or reservoir to deltaic sedimentation.; The numerical model presented here is the first interactive, physically-based, moving-boundary model that captures the co-evolution of river delta morphology and associated deposits. The novel one dimensional simulation algorithm consists of two coupled submodels: (1) a fluvial delta model that describes the deposition of sand on the river bed and its avalanching down the delta face into deeper water; (2) a turbidity current model that predicts the evolution of the bed of a lake or reservoir as a result of the mud deposition out of plunging turbidity currents. Consequently, the model captures three moving boundaries. Since the spatial and temporal scales of the fluvial and turbidity current processes are significantly different, the model can predict the deposits resulting from single flood events, as well as the succession of hundreds of individual floods.; The numerical model is verified against the results of three experiments on progradational sand-mud deltas carried out at the St. Anthony Falls Laboratory. All of them reproduced the typical structure of deltaic deposits observed in lakes and reservoirs, with a distinct migrating interface between sand and mud. Numerical predictions were found to be in excellent agreement with the measured data.; Finally, the model is applied at field scale. All simulations presented here are loosely based on the Nemadji River flowing into Lake Superior Harbor, Wisconsin. |
