Estimation of dimensionless time-area diagram of catchments

Time-area hydrograph and Clark’s methods are commonly used for prediction of runoff in catchments. In the both methods, the Time-Area Diagram (TAD) of the catchment is needed. In this study, two methods for estimation of Dimensionless Time-Area Diagram (DTAD) are introduced. In the first method, called geometric method, a hyperbolic function for the geometry of the catchment is assumed. Furthermore, travel time is assumed to be proportional to an exponent ( ) of flow distance to outlet. It was shown that the resultant DTAD equation is equal to USACE (1990) equation when is one. In another method, called Nash-TA, DTAD equation was derived as a function of Nash model parameters. The two developed methods were applied to Ajay catchment, in India, and Kasilian, Jafarabad, Shourandika catchments, located in Iran, and the results were compared to those obtained from the kinematic wave method. The efficiency coefficients for geometric method with being 0.6 and for the Nash-TA method were 0.971 and 0.955, respectively. The efficiency coefficient for geometric method in cases of =1, 1.5, 1.67 were 0.824, 0.484 and 0.161, respectively. The efficiency of the geometric method ( =0.6) and the Nash-TA method was satisfactory.