Abstract:
Tank model technique has been widely employed for estimating the runoff from rainfall data. The model comprises of a number of parameters. To serve as a rough guide, concerned data obtained from 7 stream ganging stations in the Pasak River Basin were investigated. The main objectives of the study are: 1. To establish the relationship between rainfall and runoff within the watershed area of less than 1,000 sq.km. 2. To derive on appropriate approach for generating each parameter for estimating the flow of an unganged stream whose catchment area of not more than 1,000 sg.km. 3. To determine the possibility that parameters generated from the sub-basin could lead to be used with the entire basin. With the records from 6 stations having watershed area less than 1,000 sq.km.each ant the other one with larger than 1,000 sq.km. catchment area, results of the investigation can be summarized as follows. 1. For small watershed areas, the relations between rainfall and runoff established with the help of tank model technique gave satisfactory results. However variation in value of parameters from each station seemend rather large and these parameters were presented in table 5-1 2. The estimations of parameters for the tank model in case of ungauged streams ware studied in connection with 14 parameters generated from 6 stations with small catchments. Comparisons were made with five basin characteristics, namely size of watershed, length of stream, slope of stream, soil type and shape of watershed. The relations between parameters and basin characteristics can be used to estimate acceptable initial value of parameters for the model. The study indicates that only 7 parameters out of 14 ones had correlations with any basin characteristics at the 80% level of confident. These parameters can be estimated from basin characteristics, by the relationships given in table 7-3. The relations between another 7 parameters and the basin characteristics are of questionable value. 3. In applying of using sub-basin parameters to estimate entire basin parameter for the computation of the rainfall-runoff relationship it can be concluded that the parameters of each station showed considerable variation and should not be used for entire basin parameter estimations