Development of Drain Direction Model based onGTOPO30 and Global Data Sets 
Shiro Ochi and Ryosuke Shibasaki 
Institute of Industrial Science, Univ. of Tokyo 
Japan 
ochi@cc.iis.u-tokyo.ac.jp, shiba@skl.iis.u-tokyo.ac.jp 
Commission II, Working Group 1 
KEY WORDS: Drainage, DTM, GTOPO30, Water Resources. 
ABSTRACT 
In order to develop hydrological models for flood and water resource analysis of river watersheds continental scale 
watersheds such as Yangzhu River(China), Mekong River, Brahmaputra/Ganges River, “Drainage Model”, which 
has surface flow direction for each pixel in raster base, is very much required even in rough resolution of 1km. In 
this paper, procedure to produce the drainage model is reported. In the first step, method to generate the flow 
direction using only the GTOPO30 - 1km digital elevation data - is introduced. However the generated river stream 
is not match with the stream lines in DCW(Digital Chart of the World) and/or classified rivers in the land cover 
map using NOAA data. In the second step, a method to correct the primary drainage model is introduced, in which 
DCW and USGS 1km land cover map is used to make reasonable stream lines. After the drainage model is 
established, topographical characteristics of watersheds, such as terrain features, land cover distribution and NDVI 
seasonal changes are analyzed for main rivers in the world. The developed drainage model can be applied to 
hydrological modeling. 
1. INTRODUCTION 
Drainage Direction Matrix(DDM) is defined as mesh 
data where each pixel has flow direction showing 
where the rain and the water body on a mesh flows. By 
making DDM, boundary of watershed can be 
delineated, calculation of watersheds area and 
hydrological analysis based on watersheds will be 
possible in computer. In order to make DDM, Digital 
Elevation Model(DEM) is used. If DEM express the 
detail of the real topography of the land, the flow 
direction of each pixel can be easily set. However, 
DEM usually include some error, and it represents a 
specific heights( ex. Mean, Maximum or Minimum 
height) depending the mesh size, so it is difficult to 
obtain a consistent DDM from DEM. 
The problems are the existence of concave pixel which 
has lowest height among the surrounding 9 pixels and 
no flow direction, and the existence of flat area where 
the heights of the neighboring 9 pixels are same. Both 
of the problems are quite complex and are picked up as 
subjects for many study papers(Hayakawa, 1995, Lu, 
1995). And some solutions are also suggested(Nogami, 
1998). But even the problems are solved, the computer 
extracted river systems are not always similar as actual 
river systems or map extracted river systems. In this 
case, manual correction comparing the computer 
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