GEOGRAFIA Online TM Malaysian Journal of Society and Space 12 issue 13 (145-156) © 2016, ISSN 2180-2491 145 Hakisan tanih dan masalah sedimen di Alur Ilmu, UKM Mokhtar Jaafar, Hafizi Mat Salleh Pusat Penyelidikan Kelestarian Sosial, Persekitaran dan Pembangunan, Fakulti Sains Sosial dan Kemanusiaan, Universiti Kebangsaan Malaysia, 43600 Bangi, Malaysia Correspondence: Mokhtar Jaafar (e-mail: m_jaafar@ukm.edu.my) Abstrak Masalah bahan mendak terutama sedimen terampai adalah salah satu daripada punca pencemaran yang berlaku dalam aliran Alur Ilmu, UKM. Salah satu penyumbang kepada muatan sedimen terampai dalam Alur Ilmu adalah proses hakisan tanih. Sehubungan itu kajian dilakukan bagi menganggar hasilan sedimen dalam aliran Alur Ilmu melalui proses hakisan tanih jangka pendek di bahagian hulu lembangan Alur Ilmu. Teknik radionuklid berilium-7 digunakan bagi menganggar kadar hakisan tanih melalui model profil taburan tanih. Manakala penjanaan sedimen terampai ditentukan berdasarkan data muatan sedimen terampai dan hakisan tanih berdasarkan peristiwa hujan semasa. Hasil kajian mendapati kadar anggaran bersih hakisan tanih adalah 42.1 t ha -1 dan nisbah hasilan sedimen adalah 0.683 peratus. Ini menghasilkan sekurang-kurangnya 36.23 t km -2 sedimen terampai daripada sesuatu peristiwa hujan semasa dan proses hakisan tanih. Jumlah hasilan sedimen terampai ini adalah tinggi bagi lembangan Alur Ilmu yang hanya bersaiz kecil. Sehubungan itu, usaha mitigasi harus pertimbangan sewajarnya pada kejadian proses hakisan tanih yang berlaku di bahagian hulu lembangan Alur Ilmu. Ini termasuk memulihara cerun musnah akibat daripada hakisan galur, dan menambah kepadatan tumbuhan di permukaan landskap sedia ada. Katakunci: Alur Ilmu, berilium-7, Geografi, hakisan tanih, radionuklid, sedimen Soil erosion and sediment problems in the Alur Ilmu, UKM Abstract Suspended sediment problem is one of the pollution sources that occurs in the Alur Ilmu, UKM. Among the contributors to the suspended sediment load in the Alur Ilmu is the soil erosion process. Therefore the study was conducted to estimate the sediment yield in the Alur Ilmu flows through the short-term soil erosion process at the upperstream of Alur Ilmu basin. Radionuclide technique of beryllium-7 was used in estimating the rate of soil erosion through the model of soil distribution profile. Meanwhile the generation of suspended sediment was determined based on the suspended sediment load and soil erosion through the initial rainfall event. The findings show that the estimate rate of net soil erosion is 42.1 t ha -1 and the ratio of sediment yield is 0.683. This produces at least 36.23 t km -2 of suspended sediment from the initial rainfall event and soil erosion process. The total of this sediment yield is considered high for the small area of the Alur Ilmu basin. Therefore mitigation efforts should be consider the occurence of soil erosion process at the upperstream of Alur Ilmu basin. This includes conserving damaged slopes from gully erosion, and increased the density of vegetation on the existing landscape surface. Keywords: Alur Ilmu, beryllium-7, Geography, soil erosion, , radionuclide, sediment.