A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering, School of Engineering and Technology

Thesis (M.Eng.) - Asian Institute of Technology, 1984

The absence of adequate streamflow records and pertinent observational data in this region necessitates this investigation on the performance of four relatively simple hydrologic models on monthly streamflow estimation. These are: the Monthly Runoff Calculation Technique, the Regional Monthly Rainfall-Runoff Model, the Modified R-Index Method and the tank Model. Several aspects of streamflow estimation are studied. These include: the applicability of the models in the region; an intercom parson on the relative merits of the models in the region; an intercomparson on the relative merits of the Model/ and, the use of regionalized model parameters in streamflow estimation. The models are modified to suit the conditions and data availability in this region. Except for the Regional Monthly Rainfall-Runoff Model, the others are found flexible enough o warrant the study. These models are tested on ten (10) small basins in Northeast Thailand. The results obtained indicate several important points. First, the prospect of the models' applicability to monthly streamflow estimation in this region is promising. Second, the models' performance are satisfactory provided the data used are representative of the basin and that adequate information on the watershed characteristics are available. Third, an intercomparison of the models indicates that the Tank Model is more consistent with regard to the applicability of its model parameters to different time periods. Last, the reliability of the regionalized model parameters for ungagged basins diminishes as the extent of the area to which they are applied increases. An in-depth study on each model is suggested to fully understand the model's performance relative to the actual behavior of the system.