UM-14 : Application of Tank model for daily Runoff Analysis

Abstract

Tank model is a simple conceptual rainfall-runoff model developed in Japan by Sugawara (1967) This model is used for daily runoff analysis for both humid and non humid basins with continuous dail data generally for a period of three to four years. Tank model for daily runoff analysis can also be used with snowmelt component. The structure of tank model applicable to humid basin consists of four tanks laid vertically in series. However, 4 x 4 tank model is used for non humid basins by dividing them into four zones depending soil moisture content. First initial set of parameter values of the model is finalised based on the procedure stated in this user manual for computer programme of the model. The parameters along with the daily storm data are supplied as input. The programme simulates outflow hydrographs. Six hydrographs are plotted simultaneously viz., observed discharge, output from the fourth tank, sum of outputs from third and fourth tanks, sum of output from second, third and fourth tanks, sum of output from all the four tanks and final simulated discharge in log scale against time in natural scale. These hydrographs are compared with observed discharge hydro-graph to find which runoff component plays main role in the particular period. Calibration of parameters may be performed by trial and error procedure. Values of each of the parameters are successively changed and from comparison of fit of simulated hydrograph with observed one, best fit parameter values are ascertained. The parameters calibrated in this way lead to final model structure.,

The programme has been implemented and tested on VAX-11/780 system at National Institute of Hydrology, Roorkee. The input and output specifications for the programme have been described with an illustrative example. The programme can be run on computers other than VA(-11/780 system having FORTRAN compiler after making suitable software modifications.

This programme can be used for daily analysis of runoff for humid basin. However, some modifications in the programme are required in order to use it for non-humid basin.