Analysis of Hydrograph Shape Affected by Flow-Direction Assumptions in Rainfall-Runoff Models

Abstract

Different approaches for flow-direction determination have been continuously proposed to perform a more realistic simulation of surface runoff, yet the diversity of the existing methods causes significant differences in the extractions of geomorphic parameters as well as the results of rainfall-runoff simulations. In this study, the three most widely used flow-direction methods were separately applied in hydrological models to thoroughly investigate their effects on the simulation output. The results show that the drainage area is a significant factor that affects not only the flow-collecting ability but also the time to peak discharge; however, the definition and calculation of the drainage area become different when the consideration of multiple flow directions is involved in a terrain analysis. This study adopted two area indexes, flow concentration area and flow dispersion area, to understand their consequences in the aspects of the flow volume of simulated hydrograph and the delay of time to peak discharge. The multiple-flow-direction methods show the later time to flow peak and less amount of outflow volume in comparison with the single flow-direction method. By merely extracting two area indexes, a transformation approach is suggested to predict hydrograph shape and to quantify the extent of hydrograph deviations induced by using different flow-direction methods.