Investigation of shoreline dynamics is one of the most important aspects of coastal management and planning programs. Long-term coastal analysis uses historical data to identify sectors along the coast where the shoreline position has changed, either advancing or retreating. The erosion or accretion rates at each location can be used to forecast future shoreline positions and to define development setbacks. Conventional techniques used to study shoreline evolution are generally based on transects perpendicular to a baseline at selected points. Orthogonal air photography started in late 1930’s and satellite imagery has been available since 1960’s. With the invent of Geographical Information Systems (GIS), airphotos and satellite images have been increasingly used in shoreline change analysis in recent years. Comparison of historical airphotos and satellite images in GIS has made shoreline change analysis over large areas possible.
Shorelines and Top of Bluff (TOB) lines from the 1967 and 1993 air photos and the 2005 QuickBird (QB) satellite image were traced and compared in GIS. The tidal range in Chabahar area exceeds 2 m and the beach slope in many areas is very mild; except about the entrance headlands and outer regions. The location of waterline is therefore very sensitive to the tidal elevation at the time of imagery. In addition, the beach sediment in many parts of Chabahar Bay is greenish and dark, making the waterline almost invisible in the imagery. On the other hand, the highest level that water can reach under the combined action of tides and waves is clearly visible in the images. The location of HighWater Mark (HWM) was therefore traced as representative of the shoreline in each area.
Figure below shows comparison results at Tiss and Water Desalination Plant areas.