| Abstract: | Management of river systems can create a reduction in flow with associated potential impacts on channel morphology. A total of 30 flume runs were conducted with two different sediment sizes to determine the effect of a reduction in flow on pool size and depth in confined channels. The experiments were conducted in a 6 m long, 0.5 m wide recirculating flume. Pools were scoured adjacent to a triangular‐shaped obstruction to flow from an initially flat bed. After 3 h of high flow, bed topography was measured and the flow was changed to a level of 50, 67, 80, 85 or 100% of the original flow. Changes in bed topography were then measured after 3 h under the modified flow regime. Results indicate that a reduction in flow creates smaller volume pools. With well sorted, fine‐sand substrate, changes in pool volume, volume of deep habitat and depth were significant for both 50 and 80% reductions in flow level. However, development of an armor level in experiments with poorly sorted, very coarse sand limited sedimentation at lower flows. Consequently, no changes in pool size were statistically significant with this sediment. The results suggest that data on the dimensions of pools are needed prior to any flow modifications in order to detect degradation of the physical pool habitat. Monitoring programs initiated after flow regulation may only identify changes in a limited number of cases where sediments are mobile at low flows and the reduction in flow level is severe. Copyright © 2005 John Wiley & Sons, Ltd. |
