2011 Abstract Volume - World Water Week

Changing Shoreline Due to Coastal Erosion,Accretion and Saline Water Intrusion Due to theConstruction of Madras HarbourAuthor:Keywords:Dr. Tiruvettipuram Venkatakrishnan Gopalakrishnan, Sri Venkateshwara College ofEngineering & Technology, Indiaharbour, erosion, accretion, mitigation, remediesIntroduction/Problem IdentificationIndia has 6000 km coastline with 11 major ports for the purpose of trade, passenger transport, military,shipbuilding, recreation and marine resources. The port of Madras planned and executed bythe British regime from the year 1876 became one of the major ports in South India. This man madeinterference with the nature has created ecological imbalance, altered sediment transport phenomenonand shoreline dynamics as well as environmental issues. Since the port is protruding 1.5 kms intothe sea from the shoreline resulted in blocking the movement of littoral drift playing a vital role inchanging the morphology of the beach and coastline with severe erosion in the north of the harbourendangering the urban community near the coastline.Analysis/Results and Implications for Policy and/or ResearchIn order to control and mitigate the natural and man-made problems of beach erosion and accretion,protective coastal structures are constructed. However, these measures against the forces of nature havesometimes proved not only to be futile but also expensive and destructive. In India, for example, theconstruction of Madras Harbour has resulted in severe erosion of the beach to nearly 8 kms stretchalong the coast and 1 km width on the North of the harbor and tremendous accretion leading toincrease of 1.5 kms beach width and 10 kms length and heavy siltation of the mouth of river Cooumin the South of the harbor blocking the natural drainage resulting in severe pollution of the riverdue to domestic and Industrial waste disposal requiring periodical dredging of river mouth. Coastalsediment movement is of particular importance because what may be beneficial to a harbor may provedetrimental for the preservation of a Coastal strip threatened by erosion.The frequent changes in the shorelines and beaches are due to the changes in the littoral transport.Littoral drift which mainly manifests itself parallel to the coast as long shore sediment transport playsa vital role in changing the morphology of beaches and coasts. The long shore transport is directlyrelated to the direction of wave approach or the angle of the wave attack to the shore. The long shoremovement of sand on beaches manifests either as accretion or erosion wherever this natural movementis obstructed by the construction of man-made structures like jetties, breakwaters, groins etc. Suchstructures act as barriers to the littoral drift, causing a build up of the beach on the up drift side andsimultaneous erosion on the down drift side.The process of urbanisation along the North and South Madras coastal belt caused considerablelowering of water table elevation as a result of decreased recharge and increased withdrawals. During1950’s there used to be a quantitative balance in the hydrologic system due to rainwater recharge, dueto less paved area and return of the domestic waste water to the ground water below in the absenceof domestic and storm water sewer systems.26 Workshop 1: Cities in a 3-D Landscape Perspective – Hidden Risks