Felipe Rios

Over the years, human activity and environmental problems have impacted the Chacahua Lagoon in the State of Oaxaca, Mexico. In an attempt to gain more insight into the current environmental conditions of this lagoon, twenty-eight bottom sediment samples were collected in August 2003. Using depth, physical properties (grain-size and texture) and biological characteristics (organic matter and CaCO3 contents) of sediments as environmental indicators, three depositional facies were identified implementing cluster analysis, each facies seems to be under the influence of different processes. In terms of environmental concern, it was determined that the central part of the lagoon presents a high potential of pollutant sorption, thus this sector should be closely monitored.

During June 1997, bottom sediment samples were collected at 76 stations on a rectangular grid in a small port (Lirquén Harbor, south-central Chile) facing siltation problems. The spatial changes in grain-size parameters, analyzed by using three different methodologies to infer net sediment transport paths, are compared with the measured water circulation of the study area and sediment dispersal patterns on aerial photographs. A Geographical Information System (GIS) is used to determine the degree of similarity between the results of the three grain-size trend methodologies. The results of this study confirm that because of its formulation and underlying assumptions, the McLaren-Bowles methodology tends to confuse the space-scale of sediment transport processes. In this way, the obtained transport patterns are in poor correlation with the observed hydrodynamics and aerial photographs and they seem to represent a combination of the spatial macroscale and mesoscale sediment transport p...