164 
Figure 12. Comparison between computed flow 
accumulation: 
a) Flow accumulation computed by the aspect 
based algorithm; 
b) Flow accumulation computed by the form 
based algorithm, 
c) Flow accumulation computed by 
ARC/INFO. 
5.0 CONCLUSION 
The proposed algorithms have demonstrated their ability to produce a better simulation for flow- 
accumulation compared with the ‘eight direction’ algorithm which is commonly used in today’s GIS. 
However, the results have to be statistically tested, by applying the different algorithms to 
mathematically generated surfaces. Another challenge in future research will be focused on appropriate 
algorithms for generating drainage network and introduction of more environmental variables into the 
hydrological modelling processes. 
6.0 REFERENCES 
Eklundh, L. and Pilesjo, P. (1990). Regionalization and spatial estimation of Ethiopian mean annual 
rainfall, International Journal of Climatology , Vol. 10, pp 473-494. 
ESRI (1991). Cell-based Modelling with GRID , Environmental System Research Institute, Redlands, CA.