Planting pattern in an irrigation system is affected by water availability in river which may fluctuate from time to time. The objective of this paper is to assess the discharge fluctuation characteristic of Bedog and Gajahwong Rivers measured respectively in Cokrobedog and Mrican Weirs. The historical discharge data of the two rivers was assessed to predict river discharges of subsequent year as a basis of planting pattern determination. The ARIMA model was employed to predict water avalability. Model test showed that ARIMA (1,1,0) and ARIMA (2,1,0) could accurately predict river discharge of the two rivers. Considering parsimony principle, the ARIMA (1,1,0) model was chosen as the most suitable model. Based on predicted discharge, the previous planting pattern can still be applied in the future.