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
Pl-7-1
