TOPMODEL CAPABILITY FOR RAINFALL-RUNOFF MODELING OF THE AMMAMEH WATERSHED AT DIFFERENT TIME SCALES USING DIFFERENT TERRAIN ALGORITHMS <a href="http://dx.doi.org/10.4090/juee.2011.v5n1.001014">(doi: 10.4090/juee.2011.v5n1.001014)</a>

Abstract

In this study the rainfall- runoff response of the Ammameh watershed located in Tehran, Iran was studied using TOPMODEL, a semi-distributed and geomorphologic model that simulates runoff at the watershed outlet based on the concepts of the saturation excess runoff and subsurface flow. Topographic index as an indicator of the spatial distribution of excess runoff generation in the catchment was calculated using Dinf and D8 methods which compute the flow direction from each cell using two different algorithms. The analysis was done at three time scales: event, daily, and monthly. The modeling performance of TOPMODEL in simulating runoff process for each of three types of time series was analyzed and compared visually and statistically. Also, the effects of D8 and Dinf methods on rainfall- runoff modeling were validated and compared and it was realized that modeling result of Dinf algorithm, especially in event- based rainfall- runoff modeling was more accurate than the D8 algorithm; whereas, the difference between the results were not notable in the daily modeling. Although the obtained results demonstrate the capability of the TOPMODEL in both event-based and daily simulations, the model could lead to the more reliable results in daily modeling because of considering the watershed soil moisture conditions, perfectly.