SOURCE-TRANSPORT INVERSION - AN APPLICATION OF GEOPHYSICAL INVERSE-THEORY TO SEDIMENT TRANSPORT IN MONTEREY BAY, CALIFORNIA

Application of forward coastal sediment transport models in situations involving large temporal and spatial scales or topographically comple x environments can be highly problematic since the distribution of hyd rodynamic parameters is rarely adequately known. Where rocky topograph y is present, flow patterns may be altered and sediments trapped by to pographic barriers. A frequently employed approach to these problems i s the application of the statistical technique known as empirical orth ogonal function (EOF) analysis. One limitation of EOF analysis of grai n size and mineralogical data is that EOF is a purely geometric techni que which does not allow incorporation of a priori knowledge we may ha ve regarding the physical environment. In fact, there is no guarantee that a meaningful physical interpretation of the results of an EOF ana lysis actually exists. This is not true of geophysical inverse theory, which is capable of incorporating diverse forms of information and is not limited to purely geometric manipulations of data. We have formul ated an inverse theoretical approach to study sediment transport which we call STI, short for source-transport inversion. STI relaxes the no nphysical assumption of orthogonal end-members and can handle many for ms of a priori information. STI has been developed initially in the co ntext of modeling the sediment supply and dispersal system of Monterey Bay, California. Using the geographical distribution of heavy mineral ogy data, significant sources are identified and sediments traced from those sources along transport pathways. Model results are encouraging both in terms of goodness of fit between model and data and in terms of the agreement of model results with the sediment sourcing and dispe rsal patterns inferred in previous studies. Model results indicate tha t beach sediments are primarily derived from the open coast north of t he bay, that a littoral cell boundary exists in the center of the bay at Moss Landing, and that beach deposits produced by paleolittoral dri ft during a sea level low stand lie along the 100-m isobath.