n 
of 
1S 
al 
JC 
ta 
  
  
Fig.8 Wtershed areas which was made from 
elevation data and virtual river by using GIS 
tion of the algorithm for generation of rivers and 
watershed. Then we extract watershed areas from 
the virtual rivers. Many analysis were performed 
by us. For example, relationship between land- 
slide areas and inclination angle, geology, tem- 
perature of ground surface ,NVI were analyzed 
based on the each watershed areas. 
4.2 EXTRACTION OF VIRTUAL 
RIVER AND LARGE WATERSHED 
Figure 6 shows the virtual river extracted by el- 
evation data. Figure 7 shows the digitized rivers 
made from 1/25000 scale maps by map digitize. 
We confirmed that the rivers on two figures cor- 
responded. The result proved that the rivers made 
by elevation data and GIS were computed cor- 
rectly. Then we extracted watershed areas from 
^v lr 
"4 = 
Fig.7 Real river on the map 
figure 6. On the GIS software we point out the 
cross section of mail river and tributary on 
manual operation. Figure 8 shows the watershed 
areas of Monzen district. 
5. RESULTS AND DISCUSSIONS 
5.1 ANALYSIS OF INCLINATION ANGLE 
Figure 9 shows the relationship between propor- 
tion of landslide area to total area in each water- 
shed and inclination angle on the Minazuki dis- 
trict. This figure shows that as the proportion of 
landslide area increase inclination angle de- 
creases. We realized that landslide has been oc- 
curred on areas of gentle slope. 
5.2 ANALYSIS OF GEOLOGY 
Figure 10 shows the relationship between pro- 
portion of landslide area to total area in each 
watershed and geology. Symbols on the horizon- 
tal axis shows the geological types. Frequency 
diagram on the figure 10 shows the total areas of 
the geologies which is correspond to right side 
axis. On the other hand , the solid line which cor- 
respond to the left side axis shows proportion of 
landslide area to each geology. This value repre- 
sent the proportion of landslide area to total area 
in each watershed. The geology which has high 
values on the left side axis shows geology of the 
tertiary era. It is well known that the geology for 
the period of tertiary era easily occurs landslide. 
Figure 11 shows the relationship between pro- 
portion of landslide area to total area in each 
watershed and geology on Yanagida district. The 
values of left side axis shows the sequence of 
dangerous geology . In this district, we realized 
landslide depend on geology. 
789 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B4. Vienna 1996