AN ALTERNATIVE APPROACH TO THE IDENTIFICATION OF NET SEDIMENT TRANSPORT PATHS BASED ON GRAIN-SIZE TRENDS

Progressive changes in grain-size parameters have long been linked to net sediment transport paths. However, the methods employed to date suffer from limitations potentially leading to serious interpretational errors, which necessitate the formulation of an integrated, quantitative technique. The approach advocated here is a step in this direction, as it eliminates some of the problems inherent in the older methods. Previously, trend vectors were obtained by comparing the grain-size parameters of only two sampling stations at a time, which gives a low probability of identifying the actual transport direction. In the proposed method, groups of five stations (comprising a central station and four satellite stations) are used for each trend vector. Grain-size parameters are first combined in such a way that bias towards any one of them is eliminated. The resultant dimensionless numbers are then substituted for the proportional frequencies of recorded directions in conventional vector analysis. The satellite stations must be located equally far from the central station on radials 90-degrees from each other, which is seldom the case. An iterative trigonometric technique is therefore employed to determine the combined grain-size parameters at these localities. Conventional vector analysis, adapted to the situation of using four radials instead of 10-degrees sectors, allows the calculation of a vector mean azimuth and vector magnitude.