京 都 大 学 防 災 研 究 所 年 報 第 50 号 B 平 成 19 年 4 月
Annuals of Disas. Prev. Res. Inst., Kyoto Univ., No. 50 B, 2007

Extending a Distributed Hydrological Model to Use Globally Available
Topographic DataP.B. HUNUKUMBURA*, Yasuto TACHIKAWA* and Kaoru TAKARA*Department of Urban and Environmental Engineering, Kyoto University
Synopsis
The KsEdge2D model is a distributed hydrological model developed at Kyoto University andit has been well studied and successfully applied for many basins in Japan. As the model wasinitially developed to utilize the Japanese topographical and river network data, it is not possible toapply for international basins due to the discrepancy of input topographical and river network dataformats. This study presents the extension of the KsEdge2D model to use globally available
topographic data. User friendly software named, DEM-V0-Maker was developed to generate therequired topographical and channel network input data for the KsEdge2D model. Two basins, theKamishiba Basin, Japan and the Mae Chaem basin, Thailand were selected to apply the KsEdge2Dmodel using freely available topographic data. The results of both basins were compared with theobserved data and it showed a good agreement.
Keywords: KsEdge2D model, globally available topographic data, Rainfall Runoff modeling, Mae
Chaem Basin, Kamishiba Basin

1.

Introduction
2.

Understanding the hydrological response andquantification of available water in a basin is essential for
proper management to cope with the possible water
related disasters and to limited water resources. With
regard to this, distributed hydrological models play animportant role as it is capable of incorporating the basin
heterogeneity. The KsEdge2D model (Tachikawa et al.,
2004; Ichikawa et al., 2001) is a distributed hydrologicalmodel developed at Kyoto University and it has been
well studied and successfully applied for many basins inJapan. As the model was initially developed to utilize theJapanese topographical and river network data, it is notpossible to apply for international basins due to thediscrepancy of input topographical and river network
data formats. This study presents the extension of theKsEdge2D model to use globally available topographic
data.

The KsEdge2D model

The model is based on the one dimensional kinematicwave theory and developed by Ichikawa et al., (2001).
The basin's topography is represented in the modelaccording to the methodology described in Shiba et al.,(1999). In the model, it is considered that the basin
consists of number of rectangular slope elements which
drains to the deepest gradient of its surrounding (Fig.1).

Fig.1 Representation of the Topography
The area of each element depends on the number－ 63 －of connections it has (Eq.1). Slope flow produced due torainfall is routed one dimensionally. Then it flows to thechannel network and routed to the basin outlet.
Areaofthe CellA,

Areaofthe NodeB ab

Areaofthe NodeC ac

Areaofthe SlopeEdgeBCA4A
3½°°¾°°
ab ac ¿(1 )It is assumed that the each slope segments of thebasin covered with a permeable soil layer composed ofcapillary soil layer and non capillary soil layer. The flow
processes of both soil layers and the overland flows arerepresented with kinematic wave model using adischarge–stage relationship introduced by Tachikawa etal., (2004). Figure 2 shows the flow process and the stage
discharge relationship used in the KsEdge2D model.

the NodeV0 files, using the globally available Digital
Elevation Model (DEM).
3.1 Required data for the DEM-V0-Maker
Starting from DEM, the X, Y and Z Coordinates of
the center point of all cells are obtained. After filling thesink and removing the pits using the sink and pit
removing functions available in ArcInfo, the flow
direction is derived according to D8 method (Jenson andDomingue, 1988). This method considers 8 surrounding
cells to find the maximum slope direction of each celland assign an identical number for the cellcorresponding to the maximum slope. Figure 3 shows
the numbering system used for the flow direction grid in
the DEM-V0-Maker software.

32

64168128
142Fig.3 Eight flow directions numbering system used in
DEM-V0-Maker
Fig.2 Flow process and Stage-discharge relationshipThe relationship is described as follows;qE½­§ h ·°Vc d c ¨¨ ¸¸
0 d h d dc °°°°°© dc ¹dc  h d ds ¾®Vc d c  Va h  d c°°Vc d c  Va h  d c  D h  d s m d s  h°°
¯°
¿°(2)

Where, q is the discharge per unit width; h is thestage; Va and Vc are flow rates from the capillary poreand non capillary pore respectively
3.

The flow accumulation grid is obtained from theflow direction grid and all these grid files are converted
in to ASCII text file format as the DEM-V0-Maker
designed to read the information directly from the ASCII
text files. Gird functions, FLOWDIRECTION,FLOWACCUMULATION and GRIDASCII available
in ArcInfo was used in this regard. In addition to thesedata, it is necessary to give the basin boundary
information. Therefore, basin boundary grid is preparedin such a way that the cells which are inside the basin
defined by the basin outlet are assigned an integer value
and for out side cells are assigned the number –9999.

Methodology

The KsEdge2D model requires basically two files,
one with coordinates and the elevation of grid cells
center points (NodeV0) and the other having theconnection details and the properties of each edges of thebasin (EdgeV0), to represent the topography and thestream network of the basin. A computer model,
referred as DEM-V0-Maker is developed to generate twofiles having the same data structure as the EdgeV0 and

3.2 Representation of the channel network inDEM-V0-Maker
The original KsEdge2D models utilize the channel
network detail available in Japan. But in general it isdifficult to find such detail channel network informationin other places specially in the developing countries.
Therefore, channel network information also derived
using flow accumulation information of the basin. In thisregard, the cells having flow accumulation value grater－ 64 －than a threshold are treated as streams. Figure 4
described the Edge and Node arrangements at different
places in the basin when representing the channel
network for the KsEdge2D model.

Fig.4 Edge and Node arrangements at different placesin the basin

4.

Model application and Results

Two basins, the Kamishiba in Japan and the Mae
Chaem in Thailand were selected to apply theKsEdge2D model using globally available topographic
data.
4.1 The Kamishiba Basin JapanThe Kamishiba basin is situated in the Miyasaki
Prefecture in Japan and having basin area of 211 km2.
Average annual rainfall of the area is about 3000 mm.
The KsEdge2D model has been applied successfully tothe Kamishiba basin by using Japanese topographic andriver network data and the model parameters werecalibrated. Several modelling studies are been carried out
for this basin during past few years. Therefore it is agood basin to take as a test basin for DEM-V0-Maker
software. Figure 6 shows the location of the Kamishibabasin and the 90m Shuttle Radar Topography Mission(SRTM) DEM of the basin (http: //seamless. usgs.gov/).

The model calculates the flow through slope edgesdue to the rainfall and stored at each river node (VirtualNode). In the KsEdge2D model, there are two ways ofcalculating the stream flow at the basin outlet.
[1] Without considering the river routing; here the storedvalues at each virtual node are added together.
[2] Include river routing model; virtual nodes connect tothe River model and routed to the basin outlet.
3.3 Graphical User Interface (GUI) of theDEM-V0-Maker software
The DEM-V0-Maker was coded using Visual Basic
2005 programming language and it was design to have auser friendly graphical environment to locate the input
data, arrange the output files and etc.
Fig.6 The Kamishiba Basin, JapanFig.5 GUI of the DEM-V0-Maker software

After removing the sinks and pits of the DEM, theflow direction, flow accumulation grids were obtained.
Then the basin boundary was delineated and converted
all these raster grid data in to ASCII text file format
using ArcInfo software. These files were then used as
the input files for the DEM-V0-Maker and the required
data files for the KsEdge2D model were generated.
Observed rainfall and discharge data for one flood event(Sep.1997) was obtained. The same calibrated model
parameters for Japanese topographic data were used to－ 65 －run the model for SRTM data and compare the resultswith observed and predicted discharges. The calibrated
model parameters using Japanese topographic data areshown in Table 1and the Fig.7 shows the observed andmodel predicted hydrograph for the flood event.

parameters shown in Table 1 are used.

Table 1 – Calibrated KsEdge2D model parameters
Parameter

Value-1/3

Manning coefficient (m s)Kinematic parameter (-)
Hydraulic conductivity (m/s)
Depth of A-layer (m)Depth of field capacity (m)Beta (-)

0.3
1.667
0.55
0.45
40.65
Fig.8 Effect of threshold on the predicted hydrographFig.7 Observed and KsEdge2D model
predictedhydrograph for Kamishiba Basin – 1997/September
flood event
It is observed that the KsEdge2D model predictions
using SRTM topographic data shows good agreementwith the observed discharge. Therefore, it is goodevidence to prove that the converted globally available
topographic data in to the input data format of theKsEdge2D model using
the DEM-V0-Maker
software is correct.
Channel network represents in the DEM-V0-Maker
by using a flow accumulation threshold value. Therefore
it is important to study on the effect of threshold value on
the model prediction. Study was carried out Using 90m
DEM for the Kamishiba basin for different thresholdvalues and the results are shown in Fig.8. Same model

According to the figure, the time to peak of thepredicted hydrograph increases with the increasing of thethreshold value. When the threshold is 250 km2, thewhole basin treated as slope elements because in thatcase the basin size is less than the threshold. Therefore,
the threshold value 250km2 corresponds to themaximum deviation of the peak time for Kamishibabasin. According to the above results, it can berecommended to use a threshold value less than 30 km2.
In addition to the effect of the threshold, the effectof the grid cell resolution on the predicted hydrograph isalso studied. 1000m, 500m and 250m DEMs wereprepared by re-sampling the 90m SRTM DEM.
Required topographical input files for the KsEdge2Dmodel were obtained for each case by using
DEM-V0-Maker programme and applied the model withsame model parameters shown in Table 1. Results areshown in Fig.9.
It is observed that the peak discharge increases andshows a quick resection with the increase of the grid cellsize. To find out the reason for this model behaviour isneeded and at present it is been studying.

－ 66 －model predicted hydrographhydrograph are shown in Fig.11.

andtheobserved

Fig.9 Effect of grid cell resolution on the predictedhydrograph
4.2 The Mae Chaem basin, Thailand
The basin is 3853 km2 in size and 90% of the area
is covered with forest. Average annual rainfall and thedischarge of the basin are 1426mm and 1020 MCM
respectively. DEM (GeoTOPO 30) and daily hydrometeorological data are obtained from the research
project, “PUB-JP Blind Test in Mae Chaem Basin”(ICHARM, 2007). Figure 10 shows the location and theDEM of the basin.

Fig.11 The model predicted and observed hydrographs
The channel routing of the basin is neglected at thisstage and the model parameters are also not the optimum
parameters for the basin. This study was carried out as an
initial step to check the applicability of the KsEdge2Dmodel for large basin using global topographical data.
Therefore incorporating the channel network information
in to the model is in progress.
5.

Fig.10 Mae Chaem Basin, Thailand
The EdgeV0 and NodeV0 data files for the basin are
obtained using the DEM-V0-Maker programme
developed under this study. Then the KsEdge2D model
is successfully applied to the basin using the above data
derived from the DEM-V0-Maker programme. TheConclusions and future studies

5.1 Conclusions
The Kyoto University Distributed hydrologicalmodel, KsEdge2D was extended to applicable for any
basin in the world using globally available topographicaldata. Additional software named DEM-V0-Maker wasdeveloped to generate the input topographical datarequired for the model. It was tested by applying themodel to Kamishiba basin, Japan with SRTM 90m
DEM. The results revealed that the DEM-V0-Maker
successfully generates the topographical and channel
network data required for the KsEdge2D model fromglobal topographical data. The effect of the thresholdvalue on model predictions were also studied andconcluded that the threshold value less than 30 km2 issuitable. Furthermore, the model was successfully－ 67 －2007.
Ichikawa, Y., Murakami, M., Tachikawa, T., and Shiiba,M. (2001) Development of a basin runoff simulation
system based on a new digital topographic model. J.
Hydraulic, Coastal and Environ. Engng. JSCE 691(II-57)43-52.
Jenson, S. K., and J. O. Domingue, (1988). Extracting
Topographic Structure from Digital Elevation Data for
Geographic
Information
SystemAnalysis.
Photogrammetric Engineering and Remote Sensing,Vol. 54, No. 11: pp.1593-600
Shiiba, M., Ichikawa, Y., Sakakibara, T. and Tachikawa,Y. (1999) A new numerical representation form ofbasin topography. J. Hydraulic, Coastal and Environ.
Engng. JSCE 621 (II-47) 1-9.
Tachikawa, Y., Nagatani, G. and Takara, K. (2004)
Development of stage-discharge relationship equation
incorporating saturated–unsaturated flow mechanism.
Ann. J. Hydraulic Engng. JSCE 48, 7-12.

applied to a large river basin, the Mae Chaem basin inThailand.
5.2 Future studies
It is found that the model responds differently withthe input DEM resolution and further study will be
carried out to find out the governing factors for thesedifferences. It is planned to apply the model for different
basins in different hydrological regions in the world andstudy on the optimum model parameters for each region
will be carried out. Study on the accuracy of the spatial
stream flow prediction using distributed hydrologicalmodel will also be studied.
References
ICHARM, (2007) The International Center for Water
Hazardandriskmanagement
http://www.icharm.pwri.go.jp/html/network/index.html, Feb.

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