Author(s): Qianru Lin; Weiming Wu
Linked Author(s): Weiming Wu
Keywords: Sediment transport; Near-bed concentration; Waves; Current; Multiple-sized
Abstract: Most of the existing near-bed suspended-load concentration formulas are developed for single-sized or uniform sediments, and very few studies have concerned non-uniform sediments in coastal environments. However, non-uniform sediments have significant influence on bed roughness, sediment transport, morphological change, wave dissipation, etc. Therefore, a multiple-sized formula for near-bed suspended-load concentration under current and waves has been developed in this study. The formula relates the near-bed suspended-load concentration to the grain shear stress and takes into account the hiding and exposure effect among different size classes in the nonuniform bed material through a correction factor for the critical shear stress. Methods have been selected to determine the grain bed shear stress due to current only, waves only, and current-wave coexisted. The reference level or the bed-load layer thickness is related to the bed material size and bed ripple height. Due to lack of the near-bed suspended-load concentration data, the developed formula has been tested by comparing the measured single- and multiple-sized suspended-load transport rates against those calculated by integrating the product of the suspended sediment concentration and current velocity along the depth from the reference level to the water surface. The formula provides reliable predictions in both fractional and total suspended-load transport rates. More than half of the test cases are predicted within a factor of 2 of the measured values, i. e., half or twice as the measurement, and more than 90% of the cases are within a factor of 5.
Year: 2013