International Journal of Computational Engineering Research||Vol, 03||Issue, 9|| ||Issn 2250-3005 || ||September||2013|| Page 68 Arima Application as an Alternative Method of Rainfall Forecasts In Watershed Of Hydro Power Plant Sri Mawar Said 1 , Salama Manjang 2 , M.Wihardi Tjaronge 3 , Muh. Arsyad Thaha 3 S3 students Civil Engineering 1 , Electrical Engineering Lecture 2 , Civil Engineering Lecturer 3 Hasanuddin University, Makassar-Indonesia I. INTRODUCTION Hydro power plans is a plant that uses water as the potential energy of a turbine to drive a generator. Hydro power plant in Indonesia generally uses the reservoir to accommodate the flow of water from a river. The amount of water that can be accommodated in the reservoir depends on the intensity of rainfall in the watershed at the catchment area of a hydroelectric plant.The problems that occurred in Indonesia is a lots of the hydro power plant do not operate optimally after operated more than 15 years [1,2,3,4] . It is because water resources in the power plant is degraded by time, therefore we need to conduct a study research about the sustainability of water resources by making predictions of the rainfall will occurrence in the watershed hydropower. The study was conducted in the watershed Mamasa. This watershed supplies the resource of Bakaru hydro power plans (hydropower Bakaru). Location of the plant's reservoir is geograp-hically located between 3 0 30'00"- 2 0 51'00"LS and119 0 15'00"-119 0 45'00" BT. II. REVIEW OF LITERATURE 1.1 Rainfall The amount of rainfall affects the flow of water in hydro power plans reservoirs in Bakaru.Rainfall data obtained from the Meteorological Agency, Climatology and Geophysics Maros. Data used is collected from theMamasa station, Sumororang station, and the Lembang Station. The amount of the average monthly rainfall can be seen in Table 1, the annual rainfall in the reservoir in 2012 Mamasa of 1465 mm, 4087 mm of Sumarorang station, and 3331 mm at Lembang Station. Assuming all three recording station can represent the flow of water into the reservoir hydropower before it is deducted by the sediment carried by the flow of surface water is equal to 8883 mm. ABSTRACT Water resources of a hydro power plant generally is influenced by rainfall in the watershed. Rainfall prediction is done by using monthly rainfall data at each station. Water resources are usually derived from some streams that flow into the hydropower reservoirs. The research was conducted by predicting rainfall at three locations. These locations are considered to have a very large impact on water resources of the plant. The method used is the time series. KEYWORDS: water resources, hydropower, time series.