Stress on Embankment as Negative Feedback in the System of Reclaimed Sundarban-A Case Study along the Raimangal

Abstract

In an environment of active delta building through the interaction of hydrologic, atmospheric and tidal processes, the intervention through erection of embankments closer to the tidal channels for reclamation of the inter-tidal areas sets a serious impact on system dynamics which are adjusted through embankment breaching. High tide becomes swifter and higher indicating the potentiality of overtopping and erosion. This reclamation makes the channels hydraulically ‘unfit’ and those are gradually narrowed down. It provokes in complete closure of the interior channels through construction of series of longitudinal and transverse embankments and completes occupying of the channel areas for fishing, cultivation and habitation. The increased hydraulic head of 0.43m allows an additional 167309 m³ more flood water to enter into the reclaimed area through a representative breach of 7.65m plan length of curved breach crest, 4.32m height of the tide level from the base of embankment and 4.86m hydraulic head on breach crest at breach channel centerline. Geotechnical analysis shows that the embankment materials may get stability at the repose angle of 2°, but in many cases, the slope on the embankment exceeds 50° that indicates absolute internal instability of the materials.