Bed configurations in steady unidirectional water flows; Part 3, Effects of temperature and gravity

Abstract

ABSTRACT A change in bed configuration caused by a change in water temperature without any change in flow and sediment variables in a unidirectional flow is analyzed in the context of the dimensionless depth-velocity-size diagram discussed in Part 2. Bed states that differ only in water temperature are termed temperature-related states. These are attainable from any given state solely by a change in water temperature. Such a set of bed states forms a curve in the dimensionless depth-velocity-size diagram. This curve, a straight line in a log-log-log plot, is termed a temperature-change line. To predict the change in bed state consequent upon a change in water temperature alone, one finds the temperature-related state lying along the temperature-change line passing through the ori inal bed state in the dimensionless depth-velocity-size diagram. Three examples from the literature are analyzed in this way to show how such changes in bed configuration can be put into the context of existing stability relationships among the various bed phases, without however addressing the general dynamical problem of why those relationships are as they are. The effect of the acceleration of gravity on the bed configuration is also examined from the standpoint of the dimensionless depth-velocity-size diagram. The results show that in a hypothetical open-channel water flow on Mars a given transition between two adjacent bed phases with increasing flow velocity (e.g., ripples to dunes) would take place at a lower velocity on Mars than on earth, by a factor of 0.74.