Temperature Effects in Flows over Nonplanar Beds

Laboratory results show that in flows over ripple and dune beds a 15-20°C increase in water temperature can affect significant changes in bed-load discharge, bed form and roughness. These results are correlated with data from natural streams. The analysis indicates that temperature related changes in a stream at constant discharge are primarily a function of grain-roughness boundary Reynolds number R߱∗_b. In flows in which R߱∗_b is less than a value near 10, an increase in water temperature effects an increase in bed-load discharge and an early (lower-velocity) transition from ripples to dunes. Whereas 10 〈 R߱∗_b 〉 20 which is obtained in several American rivers, the temperature effect on bed-load discharge depends on the distribution of bed sediment sizes due to a qualitative change in temperature effect on bed-load discharge that takes place in this range of R߱∗_b and bed form transitions, e.g., dunes to flat bed, occur at lower velocities with cold water.