Wave and Seepage-Flow Effects on Sand Streambanks and Their Protective Cover Layers; Demonstration Hydraulic Models

摘要

Two-dimensional models at a scale of 1:1 (model:prototype) were used to demonstrate the effects of wave action, drawdown, and seepage flow on an unprotected streambank and to demonstrate and compare the effectiveness of some of the state-of-the-art streambank protection techniques. All of the protective cover layers that proved successful in stabilizing the sand streambank, during wave attack and/or seepage flow out of the streambank, failed when the filters were removed from the designs. The test series shows that protective cover layers that are adequately designed to be stable in a highly turbulent wave environment will not provide the needed streambank protection if adequate filters are not provided to reduce the wave energy reaching the sand streambank and prevent leaching of the sand when seepage flow out of the streambank is occurring due to a hydraulic gradient produced by either a drawdown or a static differential head condition. when filter fabric is being used in lieu of granular filters, care must be taken to ensure that the fabric is not punctured and that the sides and toe of the filter fabric are sealed, or trenched, so that leaching of the streambank sand does not occur. Care must also be taken to ensure that adjacent sections of filter fabric are attached together in such a manner that leaching cannot occur at the lap joints.