ACCURATE DETERMINATION OF OVERLAND-FLOW TRAJECTORIES IN SIMULATED WATERSHEDS OF COMPLEX TOPOGRAPHY

When developing a physically based mathematical description of hydrolo gical processes over natural watersheds, the modeller faces the requir ement of complete spatial specification of the saturated and unsaturat ed hydrogeological parameters as well as the ground surface characteri stics. The usual approach, i.e. the use of representative average valu es in simplified configurations of the actual conditions, often leads to discrepancies. A detailed description of the topography is therefor e needed but, on such a topography, the accurate determination of over land flow trajectories often poses difficult problems. The hydrologica l component of the DELTA code aims to provide more insight into the ab ove mentioned problems. To simulate overland trajectories of run-off w ater, the DELTA/HYDRO module uses the topography representation by adj acent triangular surfaces of known properties (i.e. slope, orientation , soil texture, land use, area), produced by the DELTA/GAIA module. Th e simulated surface flow may feed channels, terminate at a local minim um of altitude or reach the boundaries of the domain under considerati on.