Monitoring changing position of coastlines using Thematic Mapper imagery, an example from the Nile Delta

Coastline movement due to erosion and deposition is a major concern for coastal zone management. Very dynamic coastlines, such as sections of the Nile Delta coast, pose considerable hazards to human use and development, and rapid, replicable techniques are required to update coastline maps of these areas and monitor rates of movement. The synoptic capability of Landsat Thematic Mapper imagery enables monitoring of large sections of coastline at relatively coarse (30 m) spatial resolution. By comparing positions of the Nile Delta coast in 1984, 1987 and 1990/1991, mapped using a region-growing image segmentation technique, areas of rapid change can be identified and targeted for more detailed monitoring in the field, or using higher resolution images. Rates of erosion and deposition can be estimated crudely, and areas where change appears to be accelerating can also be identified. Areas of severe erosion along the Nile Delta coast are found to be confined to the promontories of the present day mouths of the Nile at Rosetta and Damietta. Eroding shorelines are mostly flanked by accreting shorelines, showing that some of the eroded material is redistributed along the coast. The technique outlined here has potential to augment conventional field-based surveying for monitoring shoreline changes over short timescales.