Longitudinal Changes in Suspended Sediment Loading and Sediment Budget of Merbok River Catchment, Kedah, Malaysia

Merbok river catchment situated in the Kedah State receives its input from Bongkok River and Puntar River flowing down and joining Lalang River to flow down to the Merbok Estuary. The Merbok catchment (440 km(2)) is experiencing several degrees of complex land uses activities that poses some impact on the suspended sediment production of the Merbok river. A study was conducted to investigate the suspended sediment loading of rivers draining the Merbok catchment from January to December 2013. Suspended sediment budget of the Merbok catchment were estimated. The river suspended sediment concentrations (SSC) and suspended sediment (SS) load increased during wet season compared to dry season. The SS loads increases from upper catchment to river mouth. The sediment loadings were divided into three segments-the upstream, middle segment and lower segment. The SS loads increased from 10 t yr(-1) in the upper part of Bongkok river to 3336 t yr(-1) in upper segment. The sediment loading then increase to 4299 t yr(-1) in the middle segment of the catchment (at Bongkok 4), and then exiting the Merbok Estuary, as the lower segment, with a total amount of sediment output estimated at 7156 t yr(-1). From this total sediment output, most of the sediment source came from the tributaries; the Bongkok River at B3 (3337 t yr(-1)), Puntar River (2924 t yr(-1)) and Lalang River (1370 t yr(-1)), which were much higher than its proportion in terms of its length and drainage area. As a conclusion, the inconsistence in SSC in the river were influenced by the various anthropogenic activities (especially agriculture and urbanization activities) the catchment area which necessitate future land use and sediment control to avoid sediment and possible nutrient loading into the estuary.