UC Santa Barbara

Synthesis of landscape evolution based upon the actual processes of transfer of energy and material is difficult, because the hydraulics of erodible channels are not fully understood. Previous workers have utilized variance minimization postulates to derive certain hydraulic relations, but these have been unsatisfactory because of the lack of a mechanism for variance minimization. This study examines the validity of the variance-minimization principle through an investigation of the changes in the longitudinal distribution of the bed-shear-stress components over a two-month period in two reaches, one meandering and one straight, of a rapidly eroding supraglacial stream. During this time the coefficients of variation of bed shear stress, skin resistance, and form resistance decreased in both reaches. Except for skin resistance, the values were lower for the curved reach than for the straight. Spectral analysis of the paths of the reaches and of the stress distributions indicates that the scale of the regularities decreases with decreasing discharge. Cross-spectral analysis of the shear-stress components on different dates indicates that in the curved reach, the locations of the minimum shear stresses at the end of the summer coincide with the locations of the maximum skin resistances at the beginning of the summer. © 1976.