Constant-shear-drained triaxial tests, tests that mimnic the field stress path, and anisotropically consolidated undrained triaxial tests performed at the in-situ stress level indicite that undrained loading is a prerequisite for flow failure. To establish appropriate stability analysis procedures, the behavior of soil from a debris flow source area is investigated. Rainfall-induced debris flows are flow failures in residual and colluvial soils initiated by a reduction of confining stress as a result of pore-water pressure rise during or following periods of intense rainfall. Flows with higher concentrations appear to be hyperconcentrated and to have sediment transport rates higher than those predicted by the model. Testing reveals that the model gives good unbiased predictions of phi in flows with sediment concentrations less than 0.20. The equation indicates that the dimensionless sediment transport rate phi is a function of, and therefore can be predicted by, the dimensionless shear stress theta, its critical value theta sub(c), the resistance coefficient u/u*, the inertial settling velocity of the sediment w sub(i), the roughness concentration C sub(r), and the roughness diameter D sub(r). Using dimensional analysis, a total-load transport equation is developed for open-channel flows, and this equation is shown to apply to interrill flows both with and without rainfall. Given the diverse shapes, sizes and concentrations of these elements, the transport model is likely to apply to a wide range of ground surface morphologies.

Stones, cylinders and miniature ornamental trees are used as roughness elements. A model for predicting the sediment transport capacity of turbulent interrill flow on rough surfaces is developed from 1295 flume experiments with flow depths ranging from 3.4 to 43.4 mm, flow velocities from 0.09 to 0.65 m s super(-1), Reynolds numbers from 5000 to 26949, Froude numbers from 0.23 to 2.93, bed slopes from 2.7 degree to 10 degree, sediment diameters from 0.098 to 1.16 mm, volumetric sediment concentrations from 0.002 to 0.304, roughness concentrations from 0 to 0.57, roughness diameters from 1.0 to 91.3 mm, rainfall intensities from 0 to 159 mm h super(-1), flow densities from 1002 to 1501 kg m super(-3), and flow kinematic viscosities from 0.913 to 2.556 x 10 super(-6) m super(2) s super(-1).

Floyd netmap