Net sediment transport in Pampanga Bay, Northwestern Manila Bay [Philippines] derived from grain size trends, bathymetric change and landsat data

Pampanga Bay recieves 50% of the total annual freshwater budget of Manila Bay and has the largest river sediment input. The supply of high loads of sediments has significant implications on the aquatic productivity, coastal evolution and contaminant dispersal in the bay. Sediment dispersal patterns were determined using Landsat Thematic Mapper (TM) imageries, trends of grain size parameters, and water depth changes. Satellite data showed a west-southwest and southward alongshore transport of suspended sediments. Transport of bottom sediments is defined by the analysis of grain size trends, showing seaward trending vectors in shallow waters (approx 5 m depths) and landwater trending vectors in deeper waters, which indicate that sediments deposited in the offshore region are further reworked predominantly northward toward the middle part of the bay. This transport pattern is further supported by bathymetric changes over a period of 13 yr. The central region of the bay shows net shoaling while deepening is dominant nearshore. Results of this study generally agree with reported numerical circulation models of the bay except near the mouth of Pampanga River. The differences can be attributed to high rates of subsidence, which yields a better understanding of coastal sediment transport since net and seasonal variations in transport pathways can be established as well as the potential of deposited sediments for networking. Satellite images provide a significant advantage in that they reveal instantaneous lateral distribution and transport of surface sediments, while analyses of grain size trends and bathymetric changes present information on the long-term fate of the sediments after they have are deposited over a longer time scale. This multiple approach is particularly useful in the prediction of areas vulnerable to contamination within the bay.