DEVELOPMENT OF A BASIN GEOMORPHIC INFORMATION-SYSTEM USING A TIN-DEM DATA STRUCTURE

To make a distributed rainfall-runoff model, it is very important to b uild a model of topographic surface of a basin which takes account of the direction of water flow. In this paper, a geographic information s ystem in hydrologic modeling, the BGIS (Basin Geomorphic Information S ystems) are presented for modeling a river basin using a TIN-DEM (Tria ngulated Irregular Network - Digital Elevation Model) data structure. The BGIS have two core systems, which are the TIN-DEM generating syste m and the topographic analysis system. In the TIN-DEM generating syste m, landscapes are modeled as a set of contiguous non-overlapping trian gular facets whose vertices are made up of points on a regular grid DE M and on river segments. These triangular facets are subdivided, if ne eded, so that each of them has only one side through which water flows out. The TIN-DEM generating system is made up of four modules, (1) a module for generating triangles from a grid DEM, (2) a module for gett ing rid of pits, (3) a module for joining discontinuous valley segment s to a channel network, (4) a module for subdividing triangular facets . In the topographic analysis system, using datasets processed with th e TIN-DEM generating system, a watershed source area for any segments in a stream network are delineated automatically, and topographic attr ibutes of slopes, aspects, flow path lengths and upslope contributing areas are computed.