Author(s): D. G. Wren; E. J. Langendoen; R. A. Kuhnle
Linked Author(s): Roger A. Kuhnle
Keywords: No Keywords
Abstract: Many dams in the USA and elsewhere have exceeded their design life and are being considered for remediation or removal, which will result in the reintroduction of fine sediments, often into coarse grained armored substrates, downstream of dams. The deposition of sand in the interstices of the gravel substrate complicates the prediction of sand transport due to difficulties in predicting the effective shear stress, the exposed area of the sand, and the resulting changes in water depth. An adjustable-slope, recirculating laboratory flume was used to evaluate the effects of a stepwise addition of sand to an immobile gravel bed on the properties of flow and sediment transport. Detailed measurements of fluid velocity, sand transport rate, bed texture, and bed topography were collected for four different discharges (Fr=0.1, 0.3, 0.5, and 0.6). A Laser Doppler Anemometer and an Acoustic Doppler Velocimeter were used to measure mean and turbulent flow quantities while a flow-through density cell and physical samples were used to monitor sand transport. Additions of sand had no measurable effect on flow structure until the depth of sand was approximately 5 cm below the top of the gravel layer. It was found that elevation of the sand bed relative to the top of the gravel and grain shear stress were the major factors controlling the rate of sand transport.
Year: 2009