WORKING GROUP 8 
NAKANO-OHYA-KANAKUBO 
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also makes the results of the survey more uniform in accuracy and amount of 
detail shown. The preliminary map is then put into its final form by field 
checking. 
The quality of the photos was good, the images being clear and distinct. 
Viewed stereoscopically, they allowed a detailed landform classification of 
Japan to be made, especially of the plains. 
The land surface is divided into three main types, the mountains and hilly 
areas, upland and terrace areas, and plains. The plains are then further 
subdivided by criteria such as form, altitude, slope, moisture, structure, 
vegetation and land use, into valley plains, fans, natural levees, deltas, tidal 
flats etc. Fig. 1 is an example of a landform classification map for flood preven 
tion. From this map we can easily forecast the nature and duration of floods, 
should the dykes be destroyed. 
Relief Map 
The smallest contour interval on the 1 : 25,000 topographic map, even in 
the plains, is normally 2,5 m. If we wish to depict microrelief, however, a 
contour interval of between 0,5 and 1 m is required. 
Relief maps of the plains were compiled from the aerial photographs, ground 
levelling, and the detailed landform classification map. Thus the contour lines 
show the micro-relief of the plains. Fig. 2 is part of the relief map of the Nobi 
Plain, at the mouth of the River Kiso. 
Mapping flooded areas from aerial photographs 
Maps have also been made of these areas, showing the actual flooding 
caused by typhoons and cloudbursts. A provisional map is compiled from 
aerial photographs taken immediately after the flood. These are analysed for 
the extent of the inundation, the direction of the flood current, erosion and 
deposition, and damage to dykes, lines of communication, houses, bridges etc. 
After the high tide caused by the Ise-wan Typhoon, over 6,000 aerial 
photos, taken over a period of time, were analysed. Using infrared photo 
graphy, not only was it possible to delimit the maximum extent of the inun 
dation, but also a distinction could be made between areas flooded by salt, 
and those flooded by fresh water. 
Completion work consisted of field measurements of the period and depth 
of stagnation, the duration of the inundation, the depth of deposition, and the 
limits of the tidal waves. 
The relationship between inundation and landform 
The flooding of the lower reaches of the River Kiso resulting from the Ise- 
wan Typhoon (Typhoon “Vera”) in 1959, was an invaluable test of the use 
fulness of the flood prevention maps. On 28th September, 1959, the city of