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The coastline of Hai Hau District, located on the northeast coast of Vietnam with about 30 km of shoreline, is chronically eroding. Previous studies have tried to highlight the main causes of the erosion along this coastline, and several hypotheses exist. To examine the hypothesis that gradients in the longshore sediment transport rate and cross-shore fine sediment lost offshore are the main causes generating the serius erosion at Hai Hau Beach, a newly developed numerical model of shoreline change based on the one-line theory was applied and compared with data. Sea dike segments, reinforced by stones and mortar, were modeled using a seawall boundary condition, and the sediment continuity equation was modified to take into account the offshore transport of fine-grained sediment. The simulated shorelines agreed well with the measured shorelines, both for the calibration and validation periods. The calculated sediment budget shows that the net sediment transport is in the southward direction and that a large amount of finegrained sediment is lost into deep water. These two sinks of sediment are believed to be the main causes of the serious erosion at Hai Hau Beach. [ABSTRACT FROM AUTHOR]

The geomorphology and processes of land loss in the Pontchartrain Basin for the period 1990-2001 are mapped and the results of the classification presented. This data set is compared to an earlier classification, which covered the period 1932-1990 to determine the status and trends of wetland loss in the Pontchartrain Basin between 1932 and 2001. Results of the land loss classification indicate land loss rates have remained steady between the two periods (13 km2/y between 1932 and 1990 and 12 km2/y between 1990 and 2001). The geomorphology and processes of loss have shifted from primarily interior loss as a result of direct removal and submergence in the first period to primarily shoreline loss as a result of erosion in the second period. Three areas of concentrated land loss between 1990 and 2001 represent portions of the upper, middle, and lower basin. Land loss at all three locations shifts from interior to shoreline loss between the two periods. In the second period, interior loss through the process of submergence is still occurring but at much reduced rates at locations 1 and 2. Interior loss through the process of direct removal is only occurring at location 1 during the second period and accounts for less that 2% of the loss. At location 3, land loss is completely in the form of shoreline erosion during the second period. [ABSTRACT FROM AUTHOR]