Author(s): Norbert L. Ackermann; Hung Tao Shen; Roger W. Ruggles
Linked Author(s): Hung Tao Shen
Keywords: No Keywords
Abstract: When the number density or concentration of ice fragments on the surface of a river is sufficiently low, the ice is transported with the same velocity as the surrounding water. Under such conditions, the ice discharge for a given river flow is directly proportional to the concentration of ice on the river surface. At larger concentrations, the ice fragments forming the surface layer can be considered as a granular continuum that develops interparticle or intergranular stresses between adjacent ice fragments. These stresses can become sufficiently large to prevent movement of the surface ice layer. Prior to reaching this "no flow" condition, the ice fragments collide with one another causing interparticle stresses that affect the velocity of the surface layer and hence influence the ice-carrying capacity of the river. For a given river water discharge, the maximum ice discharge was found to depend upon the channel cross-section geometry, bed slope, dimensions of the individual ice fragments and the surface roughness of the ice and channel bed. The ice conveyance capacity was determined from a theoretical analysis that considered the river water and surface ice layer as two components of a system that interacted with each other as well as the boundaries of the river channel. When the upstream ice supply is in excess of the river's maximum ice discharge capacity, conditions forming an ice jam are considered to occur. The results of this analysis are presented in dimensionless form enabling the maximum ice conveying capacity to be determined for a channel having a specified trapezoidal cross-section, water discharge, channel slope, and ice fragment thickness and diameter.
Year: 1981