CS(AR)-4/99-2000 : Comparison of single and multiple flow direction algorithm for computing topographic parameters in topmodel

Abstract

The topography is one of the factors that most influence the physical phenomenon of rainfall-runoff dynamics. Indeed, it plays a primary role in the effects produced by the gravity drainage within a basin. In the last decade, ever-developing computer techniques associated with the greater availability of terrain data in digital form has favoured the production of physically based models, which have spatial variability of topography built into their structure. The TOPMODEL developed by Beven, in 1979 is one of the many models which uses the topographic feature in simulating the flows. The topographic features are represented in the model as topographic index, In (a/tanB), in which 'a' represents the cumulative upslope area that drains through a point, and tanB is the local slope at the same point. The index reflects the spatial distribution of soil moisture and saturated surface within the basin. The topographic index, In (a/tanB) distribution can be computed using the two different approaches, namely, Single Direction Flow Algorithm (SDF) and Multiple Direction Flow Algorithm (MDF).

In the present study, the TOPMODEL has been applied to Malaprabha catchment. The topographic index was computed using the SDF and MDF. An attempt has been made to analyse the effect of these approaches on the simulation of flows and on the model parameters.

The results show that, the SDF and MDF have slight effect on the efficiency of the model and also on the model parameters. However, choice of these approaches does not have any effect on the simulation of flows.