A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering

Thesis (M.Eng.) - Asian Institute of Technology, 1989

The WATBAL model is a semi-distributed rainfall-runoff model and represent an intermediate approach as compared with the two-alternative rainfall-runoff model, i.e. lumped and fully distributed model. The main purpose of the WATBAL model is to predict the continuous stream flow for an ungauged watershed. The WATBAL model was applied in two catchments in Central Java, Indonesia. One as a "reference" gauged watershed and the other as "ungauged" test watershed. For the purpose of predicting the continuous runoff at ungauged watershed, initially the model was applied at the gauged watershed. After that, the model was tested to ungauged watershed without calibration by transferring calibrated parameters value of a gauged watershed after being adjusted according to the characteristics of ungauged watershed. The calibration process was also done in the ungauged catchment in order to know the uncertainty of the model parameters. Sensitivity analysis of some parameters were carried out to investigate the effect of these parameters on the model simulation and to increase the efficiency of the calibration process. Comparing between simulated and observed runoff show that the model can predict a continuous runoff for gauged and ungauged watershed with satisfactory result, especially monthly and annual flow.