Particle-driven gravity currents down planar slopes

Particle-driven gravity currents, as exemplified by either turbidity curren ts in the ocean or ignimbrite flows in the atmosphere, are buoyancy-driven flows due to a suspension of dense particles in an ambient fluid. We presen t a theoretical study on the dynamics of and deposition from a turbulent cu rrent flowing down a uniform planar slope from a constant-flux point source of particle-laden fluid. The flow is modelled using the shallow-water equa tions, including the effects of bottom friction and entrainment of ambient fluid, coupled to an equation for the transport and settling of the particl es. Two flow regimes are identified. Near the source and for mild slopes, t he flow is dominated by a balance between buoyancy and bottom friction. Fur ther downstream and for steeper slopes, entrainment also affects the behavi our of the current. Similarity solutions are also developed for the simple cases of homogeneous gravity currents with no settling of particles in the friction-dominated and entrainment-dominated regimes. Estimates of the widt h and length of the deposit from a monodisperse particle-driven gravity cur rent with settling are derived from scaling analysis for each regime, and t he contours of the depositional patterns are determined from numerical solu tion of the governing equations.