Geospatial Analysis of Long-Term Morphological Changes in Cochin Estuary, SW Coast of India

The Cochin estuary along the SW coast of India has undergone tremendous environmental changes due to continuous alterations. Geospatial information available since 1967 has been compiled to evaluate the long-term morphological changes. Quantification of geomorphological changes that occurred over the decades was made to have an integrated profile to ascertain the changes in the extent. Toposheet maps (1967) and satellite imageries for 2004 and 2011 have been interpreted. Quantitative comparison of inner island segments showed significant changes in island widths through time. It was found that the areas covered by the islands within the estuary during 1967, 2004, and 2011 were 81.62, 89.26, and 89.52 km(2), respectively, and those covered by the water body were 130.68, 121.3, and 118.01 km(2), respectively. The shrinking rate of the estuarine system was estimated to be 0.288 km(2)/y. About 11 km(2) of island area was found to be prograded, and 3 km(2) was eroded. In effect, the reduction in the aerial extent of the estuarine system was estimated to be 12.67 km(2). The evolution of the western estuary margin has been characterized by a strong progradation during the past 4 decades. The results obtained conclusively show that the estuary is being inflicted with major geomorphic changes at several segments, resulting in reduction in the extent. Geomorphic differences may lead to factors in modifying estuarine flows, which ultimately affect the dynamic processes within the estuary. Observed trends of morphological changes generate concern in the background that the region may continue to remain vulnerable in the coming decades due to development pressures in the adjoining hinterlands.