GIS as a Tool to Identify a Coastal Sediment Management Option using Remote Sensing - A Study of Songkla Bay in Southern Thailand
4 Discussion 1. The determination of long-shore direction is very important for the delineation of coastal cells. The one-line model is based on the long shore transport of sediments and the long-term cross-shore equilibrium. This necessitates the identification of long-shore direction and the long shore direction changes. Depending on the spatial resolution, the irregularities in the land and sea interface such as bays and projections makes it very difficult to identify uniformly spaced beach cells that would have the surf zone as one boundary of the cell. In this study the identification of general long shore direction using bathymetric information enabled the smooth delineation of shoreline cells. This is an important identification of a physical feature in the Songkla bay area to study long shore sediment transport. The general direction method also avoided errors that may arise from the beach segments not being equally spaced. The approach of the present study, using a general direction showed a clear rationale. 2. It is of extreme importance that the shoreline cell delineation uses the strengths of today’s GIS software to automatically draw perpendicular lines to the general direction of long-shore movement. Eye estimated lines using visual image of shore line projected on screen would raise serious concerns with respect to the sediment estimations done using such work. In the present work all computations and delineations were carried out with the use of in-built GIS functions and therefore is a good example for similar work. 3. The analysis of sediment movement relationships with beach profile change identified the possibility that the surf zone boundary may be beyond a 4 meter depth. Wave data, adjacent coastal structures and other features of the coastline need to be carefully studied to improve the identified relationships. 4. The water level for each year was assumed constant and the tidal influence was considered minimal. The digitizing from bathymetry maps, registration of bathymetric data, remote sensing data play an important part in the quality of results. The present study used the previously used data set for computations. The survey data and methods also significantly influence the quality of outputs. These need to be subject to careful investigation to improve results. 5. The present work identified the presence of a linear relationship between linear coastline shift to associated sediment volumes. The 1950 – 1977 dataset indicated a linear trend away from the origin. The 1977 – 1990 relationship was linear and through the origin, indicating a stable coastline sediment behaviour that could be used for future and coastal zone sediment management. |
