Abstract:
Watershed (DAS) is rainwater catchment area that need to be managed properly so the interactions between components in the watershed system are positively synergized. If mismanagement happens, there will be negative interaction that will impact to the flood disaster, erosion and silting of the river. The purpose of this research is to find optimal the land use direction to reduce volume of surface run off, erosion and sediment in sub-Watershed of Masang Besar in Masang Watershed in Agam Regency, West Sumatera. The method that has been used is land survey to take the soil sample and ground check to the field and followed by analysis of soil samples in Andalas University soil laboratory, Faculty of Agriculture. Soil samples were taken in purposive random sampling from the land unit, for representative sample. Whereas the rainfall and river discharge data was taken from related institution, which from the Water Resources Management Office.The Surface run off data was analyzed by soil conservation service (SCS) model, soil erosion analyzed by USLE model and sediment by using sediment delivey ratio (SDR) model. Monthly surface run off data, erosion and sediments are the coefficeient index in linear programming (LGP) model to determine the land use optimization. The results showed that the volume of surface run off in the Masang Besar sub-Watershed is highest found in mixed garden land use, which is 0.001239 m3 / ha / s. The lowest erosion rate occurs in forest land. The amount of erosion is 1.78-11.92 t / ha / yr and this erosion is lower than the tolerated erosion which is 29.33 t / ha / yr. The optimal land use pattern scenario refers to the Agricultural Minister's regulation No.837 / Kpts / Um / 1980, about 30 percent of forest land availability in the Watershed area, can suppress surface run off 66.59 m3 / s. Whereas the erosion and sediment can be pressed accordingg to the target or the limit of tolerance.
