Prediction of Erosion Rate at Several Land Units in Upper Watershed of Batang Mangau, West Sumatera

Assessment of erosion in a watershed is very important for the purpose of determining whether a watershed has been degraded and damaged or not, so it is useful for the planning of the future for the watershed areas so as to achieve sustainable land use and environmentally friendly.Study of erosion prediction and mapping erosion hazard rate (TBE), and determine the rate of erosion that can be tolerated in a variety of land units, and determining alternative land use followed by the appropriate conservation measures in order to suppress erosion as small as possible or equal to Etol (tolerable erosion ) has conducted research on upstream Mangau Padang Pariaman and Agam districts. The study lasted in September 2011 until January 2012. The experiment was conducted using the survey method. Secondary data obtained from statistical data, maps and the results of previous researches. The results showed that the greatest erosion occurs in people's gardens land units with steep slopes (KrF), with a percentage of 62% slope and slope length of 45 m. While the smallest erosion occurs in wetland units with a gentle slope (SWB), the percentage of 7% slope and slope length of 28 m. Land units experiencing mild erosion rate is 37.80%, of the total study area. Then the land units suffered heavy erosion rate is as much as 20.81%, and further land experiencing very severe erosion hazard level is sebayak 37.86% of the total study area. Actual erosion rate greater than can be tolerated erosion found 4 unit of land is the garden of the people with a rather steep slope (KrD), mixed garden with a rather steep slope (KcD), and their fields with steep slopes (KrF). Furthermore, there are 8 land unit value erosion rate is less than the erosion rates that can be tolerated so that the use of the land does not need changing. Alternative use of land for every land units that have greater erosion speed of the tolerable erosion is the land units of protected forest with steep slopes (HlF), the secondary forest with steep slopes (HsF). Whereas, the land unit of rice paddy soil with relatively steep slopes (SwD), rice paddy soil with gentle slopes (SwB), scrub with relatively steep slopes (SmD), scrub with steep slopes (SmF) and farm people with mild slopes (KrB) fixed defended. Furthermore, the alternative use of the land for the unit of farm people with steep slopes (KrF) and farm people with relatively steep slopes (KrD) and a mixture of garden soil units with relatively steep slopes (KcD) is recommended for improved by adding high density mixed garden and make bench terrrace with good construction and land cover tightly coupled.