ASSESSMENT EROSION 3D HAZARD WITH USLE AND SURFER TOOL IN PASAMAN WATERSHED, SUMATRA ISLAND-INDONESIA
Aflizar, Roni Afrizal and Edi Syafri Muzakkir
State Polytechnic Payakumbuh for Agriculture,Payakumbuh 26271, Indonesia. Fax :62-752-7750220,
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ABSTRACT
Quantification of soil erosion rate is an important basic to investigate and improve land use system in Indonesia which has not been sufficiently conducted. In this study, we have tried to clarify spatial distribution of 3D soil erosion and dominant erosion factor controlling loss or redistribution of soil sediment in order to efficiently discuss the sustainable management of Pasaman watershed where is a main palm oil plantation producing area in Sumatra Island. The Universal Soil Loss Equation (USLE) and Erosion Three Dimension (E3D) in Surfer tool were used to identify characteristic of dominant factor in Pasaman Watershed using data soil survey and watershed characteristic. Soil erosion in Pasaman watershed is affected by topography (LS) factor and soil erodibility (K) factor in long-term period. At present, erosion is accelerated by change in cover crop (C) factor, soil conservation practices (P) factor and high rainfall erosivity (R). Estimated soil erosion rate was generally higher in upper than in lower topographical positions. It possibly enhanced the redistribution of soil, especially fine soil particles, and might contribute to degraded water quality at river and sea water as outlet of Pasaman watershed. Annual average soil erosion for Pasaman watershed was 427.23 ton/ha/y in 2014 where exceed tolerable erosion 35,47 ton/ha/y. Average concentrations of PO4-P and NO3-N in sea water in the outlet of Pasaman Watershed ranged from 0.05-1.88 mg/L and 0-2.90 mg/L from 2014, respectively. PO4-P exceeded level standard by Indonesia. Natural factor, including heavy rainfall, local soil properties and land use change in a landscape susceptible to soil erosion were the fundamental factor responsible for the high soil erosion in the watershed. The USLE model in Surfer tool was used to identify specific region susceptible to soil erosion by water and was also applied to identify suitable sites to conduct soil conservation and agroecological land use planning in Pasaman watershed.
Keywords: Erosion 3D, Pasaman watershed, Palm Oil Plantation, USLE