A field study on turbidity currents initiated from spring runoffs

Abstract

The hydrodynamics of turbidity currents from spring runoffs of an influent river is examined by measuring velocity, water temperature, and concentration of suspended sediment in a reservoir. Crosssectional measurement of turbidity currents, made from a bridge, shows the effect of centrifugal force on the downstream movement. This is due to considerable meandering of the old river channel. The turbidity currents, initiated at high sediment concentration of 1,700 mg/L, were bifurcated into an underflow and some interflows in the downstream reach, because of the relatively dense bottom water of the reservoir. The “lower layer” of turbidity currents exhibits a log linear relationship between dimensionless velocity and height under a hydraulically smooth condition. The velocity distribution in the upper and lower layers could be explained by overall Richardson number. Two drag coefficients, related with shear stresses at bottom bed and interface, generally decrease with increasing densimetric Froude number, but are independent of Reynolds number. The conditions of sediment deposition and erosion by turbidity currents can be explained by using the “extended Shields diagram.”