Abstract:
The objective of this study was to determine Pran buri reservoir operation using information of forecasting inflow. The planning will also consider the effect of small irrigation project in Pran buri basin and the real water demand from field measurement.The forecasting monthly inflow have four steps: to evaluate the relation between rainfall and inflow data, to forecast the amount of rainfall in the basin by HEC-4 model, to transform monthly rainfall to monthly inflow, and to analyze the effect of small scale irrigation project in the upstream area to the inflow. To determine monthly inflow, optimization method was applied to identify runoff coefficient considering rainfall accumulation during rainy season. Finally, the results in implementation of HEC-3 model to evaluate the effect of small scale irrigation project indicated the reduction of annual inflow about 4/54 percent.The measurements of domestic water use indicated that the new pipeline to Hua Hin supplied water at the rate 0.277 cms by gravity and 0.451 cms by pumping. The average water use for the old pipeline to Hua Hin was 0.6286 cms. In addition, the irrigation efficiency of Pran buri project was 38.2 percent in the rainy season and 39.1 percent in the dry season. Results from simulation model indicated that it had enough water to irrigate the whole project area if the storage in the reservoir at the end of rainy season was higher than 221 MCM. But the irrigation area should be reduced accordingly if the storage was less than 221 MCM.