Sorting characteristics of beach materials along Cox's Bazar - Teknaf coast

Abstract

The beach between Cox's bazar and Teknaf lies between the latitude 20044.7'N and 21 °24.30'N and longitude 92°20. 12'E and 91 °57.88'E. The beach extends between the Bagkhali river at the north upto the Naf river at the south at Teknaf through Ukhia and Nhila and is oriented in 333 ° north-west in clock wise direction at Teknaf. This study is concerned with sand characteristics of the beach. A reconnaissance survey was made and six main stations were selected for collecting beach materials samples from the surface, at 0.3m and 0.6m depth. The locations of the stations were fixed by a Nav 1000 Pro Global Position Survey (GPS) receiver. There are seven tidal khals crossing this 60.0 km. long beach between Cox's bazar and Teknaf. Bed materials were collected from these khals also except at Katabunia khal. A secondary station was also selected for collection of beach materials samples. Total sixty one samples, each 1 kg. in weight were collected by standard method and preserved in the plastic bags and carried to Hydraulics and River Engineering Laboratory in BUET for necessary analysis. A team consisting of 5 members equipped with GPS receiver, levelling instrument and transport worked to do the necessary levelling works across the beach at different stations during winter 1995. The study reveals that the sea beach is more flatter at the north towards Cox's bazar compared to the south at Teknaf, the elevation of the sea beach with respect to mean sea level is increasing towards south. The grain size distribution curve were plotted and the sorting characteristics of the sand were studied both along and across the beach. The beach sands are dominated by fine sand with a trace of medium sand and fine grained materials (silt and clay), the coarse sand is absent from the whole beach and snails are present in some cases. The beach soil sample tends to become progressively coarser in sizes from north to south within the foreshore zone and progressively finer within the backshore zone. Twelve water samples were also collected, six from the main stations, five from the bed of the khals and one from the secondary station where the beach is with boulders. Since its analysis was beyond the scope of the study, these have been kept in the Hydraulics and River Engineering Laboratory for future study. A comparison of the result has been made with the earlier studies and with the Coast of U.S.A. It has been found from the comparison that the mean diameter of the beach materials of the South-eastern Coast of Bangladesh has the similarity with those of the Texas Coast of U.S.A. Finally, recommendations have been made for further studies .