Land forest development and flash flood phenomenon: a case of Sungai Lembing, Pahang

A flash flood which is caused by excessive rainstorm in a short period of time (less than 6 hours), could lead to river water rising rapidly. Most of the flash flood studies in Malaysia focusses on the lowlands. However, in this study Sungai Lembing catchment which is located approximately 45 km from the coastal line of Pahang has been selected as a case study. This study examines the changing pattern of land cover and hydrological behaviour from 1980 to 2002 in Kuantan River Basin. This study showed that the deforestation of the uplands catchment area (especially within the year 1990-2000) has altered the catchment's hydrological cycle and significantly affected the river's baseflow or low flow. The most obvious form of channel modification in the catchment include straightening and culverting has increased flood peaks downstream especially area near Jalan Panching and Sg Isap, Kuantan. The reduction of vegetation cover in the uplands also has caused the hydrograph's time-to-peak to be reduced. The result based on the interviews with people has also revealed the uncontrolled logging activity (including illega logging) was the main factor triggering flash flood at the area.