Spatial variation in fine sediment transport in small upland streams: the effects of flow regulation and catchment geology

Abstract

AbstractIn cobble‐ and gravel‐bed streams, fine sediments (<4 mm diameter) are an important component of the bed material that can move at a full range of flows, not just during floods and spates. It has been hypothesized that the constant movement of this fine material, as it passes over the coarse bed, is an important ecological disturbance to plants and animals. In this study, I measured baseflow sediment transport rates across a number of regulated and unregulated sites in an upland catchment comprising isolated regions of granite/sandstone and acid volcanics in southern Victoria, southeastern Australia, as a precursor to a study examining the effects of sediment on aquatic biota. Examined on three separate occasions, transport rates for fine sediments were up to 100 times greater in the granite/sandstone streams, but diversion weirs, which greatly reduced downstream sediment loads in the granite/sandstone areas, moderated these differences. Measured transport rates within unregulated sections of the granite/sandstone streams were roughly equivalent to sediment loads found to disturb benthic communities in other experimental studies. On this basis, abrasion by sediment transport in these streams may be sufficient to influence the structure of benthic communities even at baseflow. This hypothesis forms the basis of other research examining the biota at these sites. Copyright © 2004 John Wiley & Sons, Ltd.