Sediment Modeling: Issues and Future Directions

Abstract

This special issue on sediment modeling comprises recent articles that attempt to quantify this complicated dynamic process, each article focusing on a different aspect and using a different mathematical approach. The genesis for the special issue came out of the Sediment Modeling Task Committee under the Computational Hydraulics Technical Committee of ASCE. Research into the interaction between sediment and flow has been studied by such great minds as Vito Vanoni, Hans Albert Einstein, John Kennedy, Hunter Rouse, and Daryl Simons, as well as many contemporaries, many of whose are among the authors included in this special issue of the Journal of Hydraulic Engineering. The Forum article in this special issue highlights the life and achievements of Daryl Simons, a longtime professor and researcher at Colorado State University. This tribute is fitting in that he recently passed away. In addition, many institutions have aided in our understanding of sediment behavior. The list is too long to enumerate here. A summary of the most recent meetings of one of the prime organizations in the sediment community, the Federal Interagency Sediment Committee, is presented in the Editorial, providing many details and information as to how to access the proceedings, an important document. The modeling of sediment has been a challenging endeavor for many years and has presented challenges to many great minds. The complicated feedback between the watershed variables such as precipitation, infiltration, evaporation, and the groundwater table interacts with the hydraulic variables such as riverbed slope, flow depth, velocity, turbulence, and bed forms to result in an intricate sculptor/sculpture relationship. The question can therefore be asked whether the water forms the bed or vice versa. Part of this puzzle is the interaction between the bed material and the flow boundary layer, since bed sediment particles can move in a variety of ways. The particles can slide, roll, saltate, or flow in suspension just above the bed in a sheet-flow mode, thereby having an effect on the bed roughness and inner layer of the flow-sediment boundary. This mechanism is explored in the article entitled “Transition between Two Bed-Load Transport Regimes: Saltation and Sheetflow.” The behavior of bed material particles can be thought of as either a deterministic or a stochastic process in which particles have only a certain probability of moving or perhaps hiding behind other particles. This is especially relevant when the bed has a nonuniform distribution of particle sizes, as most natural channels do. The use of stochastic analysis to examine the portion of the bed that moves in a nonhomogeneous bed mixture is demonstrated in the article entitled “Surface-Based Fractional