Origin of Step-Pool Systems in Mountain Streams

by Jeffrey G. Whittaker, Research Fellow; Dept. of Agric. Engrg., Univ. of Canterbury, Lincoln Coll., Canterbury, New Zealand,
Martin N. R. Jaeggi, Sr. Research Engr.; Lab. of Hydr., Hydrology, and Glaciology, Federal Inst. of Tech., Zurich, Switzerland,

Serial Information: Journal of the Hydraulics Division, 1982, Vol. 108, Issue 6, Pg. 758-773

Document Type: Journal Paper


Mountain streams very often present a step-pool aspect. Antidune formation alone; dispersion and sorting theory or velocity reversal as advocated for the origin of riffle-pool sequences do not explain how steps and pools form. Experiments have been conducted to clarify their origin. It was found that the step-pool aspect appears after high flows had deformed the bed. During the presented tests a self armoring process occurred which resulted in a stabilization of the bed. When coarsening of the top layer was little classic antidunes resulted. An important coarsening was accompanied by a structuring of the bed into roughness elements whose spacing did correspond to maximum flow resistance. The substantial increase in resistance was an essential factor in bed-stabilization.

Subject Headings: Flow resistance | Mountains | Rivers and streams | Dunes | Hydraulic roughness | Load and resistance factor design | Soil deformation | Armor units

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