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Quantification of Bed-Load Transport on the Upper Mississippi River Using Multibeam Survey Data and Traditional Methods

PURPOSE: This Coastal and Hydraulics Engineering Technical Note (CHETN) describes the progress made in using multibeam bathymetric data to determine bed-load transport in large sand bed rivers. Work was conducted as part of the Monitoring of Completed Navigation Projects (MCNP) Program in coordination with the Coastal Inlets Research Program (CIRP). INTRODUCTION: The need for quantifying bed-load transport is universal in riverine and coastal processes. In the past many analytic and mechanical methods have been devised to try and quantify bed-load transport on large sand bed rivers. To date, most methods are only marginally successful. In this MCNP work unit, being able to quantify the bed load accurately would be extremely helpful in determining whether or not river training structures in combination with a drawdown of the navigation pool would have an effect on net sediment movement through a given reach of river. In other words, accurate measurements would help resolve whether or not the altering of the pool stage and flow schedules might also be used as a sediment management tool. With these considerations in mind, a new methodology for the computation of bed-load transport was developed using multibeam bathymetric data. This methodology could also be applicable in evaluating transport in and around coastal structures throughout a tidal cycle. MEASUREMENT METHOD: Two methods were initially conceived. One would be based on the celerity of the traveling sand waves, the other on the difference of surfaces. At this writing, the surface difference method was pursued and implemented. It is called the Integrated Surface Difference Over Time (ISDOT) technique. The method processes multibeam data and quantifies a bed-load transport rate for a given river cross section. This is accomplished by taking at least two sets of bathymetric data, at different times, for the same spatial location. The two data sets are interpolated to a spatial grid and a difference plot is produced. Incremental volumes are calculated and summed over the entire cross section. The total volume change with time, when multiplied by the density of the water sediment mixture, yields a mass transport rate. As of this date the method is still in the developmental stage, but has shown surprisingly close results with some of the other standard estimation methods. The method of wave celerity, previously mentioned, might prove more reliable if worked out, but presents more computational obstacles than the ISDOT method. In this technical note, only the ISDOT method is considered.