The complexities of measuring fine sediment accumulation within gravel-bed rivers

Fine sediment storage within gravel beds is a key component of catchment sediment budgets and affects the health of benthic and hyporheic habitats. Here, we assess the performance of two substrate infiltration traps for the characterization of fine sediment ( < 2 mm) accumulation. One design, the vertically extending sediment trap, permits both lateral and vertical exchange in the sediment column, whereas the second type, a more traditional fixed-area sediment trap with impermeable side walls, permits only vertical exchange. Traps were deployed at three sites on the River Tame, Birmingham (UK), over varying installation periods (14-401 days). Results indicate that the facilitation of multiple pathways of exchange within the vertically extending sediment traps (vertical and lateral) resulted in a significantly greater amount of fine sediment being accumulated than in adjacent fixed-area sediment traps. This suggests that lateral transport is an important component contributing to fine sediment accumulation. However, there are notable and inherent problems associated with the use of different types of sediment trap and in the way the data should be presented and interpreted. This paper discusses the practical implications of the study findings and reflects on the complexities of undertaking accurate sediment deposition measurements in the field.