Low‐Temperature Effects on Flow in Sand‐Bed Streams

Laboratory experiments were performed in a 40‐ft long, 2‐ft wide, 1‐ft deep $(12‐m\times 0.6‐m\times 0.3‐m)$ tilting flume to elucidate the effects of temperature variations on the flow and sediment‐transport characteristics of streams with beds of fine sand ($D_{50}=0.11\mathrm{mm}$ in these experiments). Nearly constant depth was maintained with three different constant discharges, and temperatures were varied from approximately 30° C to near 0° C. In the two series of experiments at higher velocities and Froude numbers, temperature reductions produced major increases in sediment discharge and uniformity of concentration distributions and smaller, but still significant, increases in friction factor and bed‐form height. An analysis of the experimental results within the framework of a theoretical sediment‐transport model revealed that the increased sediment discharge with decreasing water temperature in flows carrying significant amounts of suspended sediment are caused by increases in both bed‐layer sediment concentration and the uniformity of the concentration profiles. The sediment discharges of low‐velocity $(F=\simeq 0.30)$ flows, which were just above the threshold of sediment motion, were not significantly affected by water temperature. It was concluded that temperature affects the near‐bed concentration only if the bed‐layer Reynolds number (based on bed‐layer thickness) is greater than about 20.