SEDIMENT MOVEMENT AT INDIAN PORTS

Abstract

India has a large coastline being bounded on three sides by water* On the vest side, the coastline faces the Arabian Sea. Similarly the coastline on the east side is bounded by the Bay of Bengal* The Indian ocean separates the Arabian Sea and the Bay of Bengal at the southern-most end of the coastline (Fig* 1] Since the last IS years, there have been proposals from time to time to establish new harbours or Improve existing harbours or save vast lengths of coastal strips from erosion by wave action In evaluating the merits and de-merits of the sites, a study of the coastal sediment movement is Important since what may be beneficial to a harbour may be harmful for preservation of a coastal strip* Defective planning may cause the loss of the entire shoreline and or the complete blocking of the harbour areas* Improper use of protective structures such as seawalls. breakwatersf groins, jetties etc* will not only be unscientific and uneconomical but accelerate the changes along the shoreline rather than stop them. The frequent or long-term changes In shoreline, beach, offshore zone, inshore zone, under ground bars, spits, lagoons, tombolas and similar characteristics of the coastline have significant meanings regarding the sediment motion at the coastline* Hith respect to sediment available for motion, the shor< may be a source, a drain, ovemourlshed, undernourished, sufficiently nourished (Per Bruun, 1955), or a physiographic unit (Mason, 1950). With each type, coastal works will be dlfferent for shoreline improvement and for harbour maintenance. Erosion and accretion by natural processes extend upto offshore zones while with man-made structures, erosion will always start in th< inshore and foreshore zones of the shallow water area. This distinguishing feature in the changes of a shoreline will be a good and reliable preliminary check to determine the type of erosion* Having classified a shoreline according to its sediment nourishment and as a source or a drain, the type of coastal rotection may be selected tentatively. The selected works may then he studied by model techniques. If the premilinary analysis was complete and accurate, the tentatively selected type of coastal work will be found to be most satisfactory thereby saving unnecessary waste of time and money from testing various types of works by model analysis* This method of analysis will be found to be extremely useful in many countries where investigations of the coastlines are far from adequate* Analysis of the changes at existing coastal structures along the coastline and the interpretations of the results as outlined above will be the most satisfactory method* The coastline of India may also be Interpreted similarly in relation to erosion, accretion, and transportation of sediment from the data available from existing structures, harbours and coastal strips, and divided into arbitrary overnourished, sufficiently nourished and undernourished strips and classified as sources or drains as far as possible so that various suitable types of coastal protective structures may be suggested* Indian coastline as a preliminary step may be divided into the West coast facing the Arabian Sea and the East coast facing the Bay of Bengal since the characteristic features of both the coastlines are entirely of different nature with respect to the wind forces, erosion, accretion, and littoral drift along them.