Hyperconcentrations of Suspended Sediment

Extremely high suspended sediment concentrations in streamflow, those exceeding 40% by weight, are shown to consist largely of sands with an apparent minimum fine material concentration of approximately 15% by weight. X-ray diffraction analyses of the clay fractions show mostly montmorillonite and illite with some kaolinite. The volume occupied by the suspended sediment becomes appreciable at these higher concentrations, averaging 5.8% of the total runoff volume for the period 1948-1962 for the Rio Puerco in New Mexico and the Paira River in Arizona. No relation was found between streamflow discharge and the magnitude of hyperconcentration. Particle-size distributions of Paria River suspended-sediment samples appear to consist of two log-normal subdistributions: One of material finer and one of material coarser than 0.062 mm.