NUMERICAL-SIMULATION OF TURBIDITY-CURRENT FLOW AND SEDIMENTATION .1. THEORY

A computer-based numerical model of turbidity current flow and sedimen tation is presented that integrates geological observations with basic equations for fluid and sediment motion. The model quantifies those a spects of turbidity currents that make them different from better-unde rstood fluvial processes, including water mixing across the upper flow boundary and the interactions between the suspended-sediment concentr ation and the flow dynamics and sedimentation. The model includes thre e numerical components: (1) a layer-averaged three-equation flow model for tracing downslope flow evolution using continuity and momentum eq uations, (2) a sedimentation/fluidization model for tracing sediment-s ize fractionation in sedimenting multicomponent suspensions and (3) a concentration-viscosity model for quantifying the changes in resistanc e of such suspensions toward fluid and sediment motion. The model trac es the evolution of a model turbidity current in terms the layer-avera ged flow velocity, flow thickness, sediment concentration distribution . and the rate of sedimentation and sediment size fractionation. It ge nerates synthetic turbidites with downslope variations in thickness an d grain-size structuring at each point along the flow path. This study represents an effort to evaluate quantitatively the effects of basin geometry, sediment supply and sediment properties on the mechanics of turbidity current flow and sedimentation and on the geometry and grain size characteristics of the resulting deposits.