102 Sediment balance of the lowland tropical reservoir of Timah Tasoh... Sediment balance of the lowland tropical reservoir of Timah Tasoh, Perlis, Malaysia Imbangan endapan di tanah pamah tropika empangan Timah Tasoh, Perlis, Malaysia Zullyadini A. Rahaman & Wan Ruslan Ismail Hydro Geomorphology Research Group, Geography Section, School of Humanities, Universiti Sains Malaysia, 11800 Minden, Penang e-mail: zully@usm.edu.my Abstract A study was carried of out to assess the sediment balance of a shallow Timah Tasoh Reservoir (Area: 191 km 2 ). Streamflow gauging and water sampling was carried out at three river inputs to the reservoir, and at the reservoir outlets. River water samplings were carried out every two weeks but frequent and intensive sampling during storm events. The land use in the catchment area ranging from urban area to agriculture, sugar cane, rubber, paddy, rural villages, small towns, quarrying and mining activities. Suspended sediment load data was used to derive the sediment balance. Jarum River (S1), Upper Pelarit River (S2) and Chuchuh River (S3) produced 10,032.3 t; 6,439.2 t; 1,061.4 t of sediment respectively while suspended sediment yield in S1, S2 and S3 were 155.8 tkm -2 yr -1 , 150.7 tkm -2 yr -1 , and 71.7 tkm -2 yr -1 respectively. Storms play a major role in transporting sediment from the catchment areas. Almost 88.7% of the total suspended sediment yield is transported from S1, 56.7% from S2 and 80.1% from S3. The annual sediment output load at the reservoir outlet was 1 653.0 t. From the total of 17 532.9 t of suspended sediment input to the reservoir, 15 879.9 t was stored in the reservoir. The estimated trapping efficiency of the reservoir is 90.6%. Designing sediment control and management strategies as well as increasing storage elsewhere in the watershed will help reduce the efficiency of sediment delivery from the individual catchment to the river. Alternatively, reductions could also be achieved by reducing sediment output through the construction of wetlands and the use of buffer strips. Keywords sediment balance, sediment yield, lowland reservoir, tropical, Timah Tasoh Abstrak Satu kajian telah dilakukan pada tahun 2002 dengan tujuan untuk menilai imbangan endapan sebuah kawasan takungan yang cetek iaitu Empangan Timah Tasoh (berkeluasan: 191 km 2 ). Pencerapan luahan sungai dan sampel air telah dijalankan di tiga input sungai yang mengalir masuk ke empangan, dan juga di saluran keluar empangan. Pencerapan di lapangan dilakukan setiap dua minggu dan digabungkan dengan pencerapan intensif secara berkala semasa kejadian hujan ribut. Guna tanah di kawasan lembangan terdiri daripada kawasan perbandaran serta pertanian, iaitu penanaman tebu, getah, padi sawah, perkampungan, bandar kecil serta aktiviti Geograi Vol 1, No 1 (April 2013), 102-119 © Penerbit Universiti Pendidikan Sultan Idris 2013