Possible location of Gaspar Dias fort in relation to the present river bank, Mandovi estuary, Goa, India

Historical records reveal the existence of a military fort within the Mandovi estuary. The structure was built in 1598 opposite the Reis Magos fort, extended in the adjoining area of the present traffic circle of Miramar, was located close to the water line and was backed by sand dunes. At present, no structural remains of the fort can be identified and, as such, the exact location of the fort remains conjectural. The question about the position of the ancient shoreline thus arises. Therefore, it would be worthwhile to delineate the past river bank with respect to the present one, and to check whether any morphological changes occurred since then. Although the fort is marked by the river side in historical maps, the exact position of the shore is difficult to demarcate as the maps lack dimensions. The earliest map drawn on scientific lines is dated 1964, followed by naval charts of 1970, 1986, 2003 and 2007, in addition to a series of satellite images. Mapping of shoreline shifts was attempted by using multidated satellite imageries (1976-2011, 10 scenes) and Google Earth images (20022012, 8 scenes) on a GIS. Also, available maps, charts and satellite images were compared, and distances to the shoreline were measured from a fixed point on land. It is concluded that (1) the fort was away from the water line, and (2) the overall width of Miramar beach has neither increased nor decreased, but has oscillated between 220 m and 345 m over the past 50 years.