Interpretation of coastal morphodynamics of Subarnarekha estuary using integrated cartographic and field techniques

Cartographic techniques are frequently applied for coastal mapping, but their application for the study of coastal morphodynamics is unpopular, as they only give limited parameters like plan-view, geometry, area-length measurement and lithology. On the other hand, detailed study of morphodynamics requires extra information like depthwise variation in lithology and absolute dating. Since both these techniques are expensive, cartographic techniques can be cost-effective supplementary. In the present study, morphodynamic history of Subarnarekha estuary from 7000 years BP has been interpreted applying data from cartographic techniques along with shallow wells, C-14-dating and literature survey. Geomorphologic features of the coastal plain were identified in the order of hierarchy, viz. chenier plain (first order); beach ridge complex, spit complex, chenier complexes (second order); cheniers (third order); and simplest ridge, spit, washover beach (fourth order). Following this field-investigated geological history of river dynamics (both Ganges and Subarnarekha) and sea-level changes identified by earlier researchers were merged with cartographically observed features. The studied ridge chronology provides six sequences of chenier complex development agewise, whereas geometry of spit complexes suggests chronological conversion of Subarnarekha estuary from initial wave-dominated to tide-dominated flow.