Flood damages are brought frequently on the land of Japan by heavy rainfall in typhnon season (from middle August to late September) and the rainy season (from early June to middle July), and her communities suffer a large amount of loss by those damages.
In 1958, from Sept. 26 to 27, a large scale typhoon (So called the Kanogawa Typhoon) attacked the eastern Japan (Fig, 1), and the followed heavy rainfall caused violent flood damages on several parts in these regions. The distribution of rainfall at that time was very complicateb (Fig. 2), and an extremely heavy rainfall were concentrated on the middle part of Izu Peninsula, Tokyo metropolitan area and another several regions. The characteristics of disasters, however, much differed in each regions, in accordance with their physio-and socio-characters.
In Tokyo metropolitan area, the extensive alluvial plain develops to the east, and flood damages happened often there by overflowing from large rivers (the Arakawa, the Edogawa and Tamagawa etc.). But rainfall distribution brought by that typhoon was somewhat un usual and the rain did not concentrate on the upper part of these large river area but on the place near Tokyo Bay. So, by overflowing rlom small rivers, flood damages were more severe in and around the low upland and the hill to the west of city than on the extensive alluvial lowland along to these large rivers. The total amount of flooded houses reached to about 460 thousands at that time.
Kanogawa is a small stream which runs in the nouthern part of Izu Paninsula. The disaster occured in the Kanogawa river basin was characterized by the violent inundation, covered almost whole lowland in this river basin, and the severe damage, caused by this inundation: for example, 1, 273 of people were killed and injured, the amount of flowed and destroyed houses exceeded the number of flooded houses and the amount of flowed and buried arable lands are much more than the quantity of flooded (Table 1).
Chiefly from the physical points of view, we tried to make clear the causes which brought the disasters in this river basin. These causes may be briefly summarized as follows;
1) The extremely heavy rainfall concentrated on the upper part of this river basin, and theextremely volumenous runoff took place very rapidly, because of the full saturation of the land surface by foregoing much rainfall and the steep gradient of the river and its branches.
2) Moreover, bridges obstructed the flowing of runoff and temporarily reserved more volumenous water behind them. So, when these bridges were destroyed, the extremely volumenous runoff flowed suddenly downwards.
3) Consequently, the volume of maximum discharge far exceeded the estimated hiqh waten dis charge flood and the bank was broken at everywhere. The bank on undercut slopes of meander course were especially destroyed than others.
4) At the mountain region, many landslides and debris flows occurred, and the debris flows caused some damages on roads and horseradish (Wasabi) fields which are the important fields for the cash products in this region.

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On 26 September 1958, a severe typhoon advanced into eastern Japan and heavy rainfall occurred on the Izu Peninsula and in the southern Kanto District. Especially an extremely large amount of precipitation was concentrated to the upper part of the Kanogawa River Area, resulting in a violent and disastrous inundation of the middle part of the Izu Peninsula.
The purpose of this paper is to reveal the details of rainfall distribution over the Izu Peninsula and its adjacent area at that time. To this end, the pattern of time change in the precipitation was analized.
The locations and the numbers of the various kinds of observation stations are shown in Fig. 1. As for small scale analysis, available data are extremely sparse, so it was hardly possible to construct maps of small-scale wind field and hourly rainfall distribution.
Therefore, first of all, a detailed map of the total rainfall distribution of that area was drawn, using coaxial method, since the rainfall distribution in a mountainous region is greatly affected by the complexity of the topography. The topographical factors were thus represented as follows:
1. Heights.……The mean value of the elevations of eight points on the circumference of a circle, drawn around the observation station using a 5km radius.
2. Valley-direction, ……Equivalent to the direction from the center of the point of minimum elevation of the circumference of the same circle.
3. Mountain-derection (Maximum inclination).……The direction of maximum inclination is equivalent to the direction from the center of maximum elevation of the circumference of a similar circle with a radius of 2.5km).
4. Exposure.……Unshadowed parts by more than 400 meter heigher mountains than the elevation of the obsevation station. (expressed by the center-angle of a circle, drawn around the observation station with radius 20km)
5. Distance from the path of the typhoon center.……expressed in terms of the minimum distance from the track of the center of the typhoon.
6. Distance along the path of the typhoon center.……The initial point being mesuared from Nagatsuro Local Meteorological Observatory.
7. Region.……Determined by the results of the construction of coaxisual nomogramms, which describe two regions; 1. Most of Izu Peninsula 2. The northern patr of the Izu area.
The coaxial graph shows that the factors 1, 2, 3 and 7 were significant. The topographical factors were measured, and the rainfall amount were culculated graphically and plotted on the maps with each 4 km-meshed grid points. Thus the density of the places where the rainfall amount was estimated is three times greater than the actual rain-gage stations, and the isohyeth were drawn with ease and exact (Fig. 3).
As is seen in Figs. 2 and 3, a larger amount of rain was precipitated on the northern slope of Amagi Mountains than on the southern slopes and the belt of heavy rainfall crossed from southwest to north-east. In the central part of the Izu Peninsula as much as 700mm rainfall was recorded.
In order to get time chages of precipitation patterns which evolved with the approach of the typoon, hourly rainfall amounts were converted into percentages (assuming the total rainfall was 100 percent) at each hourly observation station. These percentage values were then plotted on the maps (scale 1/500, 000) and isohyeths were drawn. (An example was represented in Fig. 4) Next, using the Figs. 3 and 4, hourly precipitation pattern were drawn (Fig. 4) The results show that the heavy rainfall zone was located unwavingly in the middle of the Izu Peninsula on the afternoon of 26th September 1958. Particuarly unchanged the location of the maximum rainfall where 80mm of hourly rainfall between 8 and 9 p.m, and 120mm of rainfall between 9 and 10 p.m. were recorded. That was at Yugashima Village in the Middle Izu Peninsula.

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The writer conducted an investigation of the relationship between the rainfall accompanying the Kanogawa typhoon and its resultant landslides, including landslides and the transportation of materials produced by landslides, and the scouring and deposition produced by the flood of Sept. 26, 1958 in the upper drainage basin of the Kano River (Fig. 1).
Many investigations have been made of the various forms of damage caused by heavy rainfall, such as landslides, scouring, transportation and deposition produced by flood water, but little work has been done on the relationships between these phenomona from the upper to the lower course in a drainage basin.
The main purpose of this paper, therefore, is to make clear these relationships.
The conclusions of this paper are summarized as follows:
1) In the upper drainage basin of the Kano, many landslides have occurred as a result of heavy rainfall accompanying typhoon No. 5822. The severity of these landslides is especially high in an area from the southwestern to the northeastern part of the town of Yugashima (Fig. 2). These landslides have also coincided strongly with the area of heaviest rainfall even occurring in the area of the same rock type. From these observations, it might be said that there is little relationship between the distri-bution of landslides and of rock types, but that there is positive relationship between the distribution of landslides and of rainfall amount. The area where landslides are most frequent coincides with that the amout of rainfall is from 550 to 700mm. during this period of the typhoon (Fig. 2, Kawamura's Figs. 3 and 4).
2) Many boulder-size terrace gravels were also removed from riversides to stream beds by the scouring of flood water in the upper course from Yokose which is a town of Shuzenji (Fig. 1). Materials produced by landslides are mostly deposited on the mountain-sides and in small mountain stream beds except for landslides extending to the river beds.
3) It has been found by many researchers that the materials produced by landslides were transported only a very short distance, while the writer found that the bulk of the materials—derived from the great landslide in Ikadaba which is situated in the upper reach of the Omi River (Fig. 4, Tab. 3 and Photo 1) and composed of pumiceous sand and gravel was transported very long distance by the water of only one flood.
4) The locality of scouring and deposition by flood water could be determined by geomorphological characteristics such as the relationship between the ratio of river-width to valley-width and the stream gradient (Fig. 6, abscisa: the ratio of river-width to valley-width, ordinate: stream gradient). Geomor-phological factors determining the locality of scouring and deposition by flood water seem to be very important for flood control.

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Japan forming a part of the circum-pacific orogenic zone is rich in various kinds of volcanoes in their shapes and structures. This study has been done with the view of clarifying some characters of lanslides occurred in such volcanic areas, in relation to the topographical and geological feartures.
Landslides and debris flows in the Kano valley caused by the Kanogawa typhoon are characteristics of landslide arising from the volcanic area.
The characters of these landslides and outflow of the debris are summarized as follows:
(A) Landslides occurred on and around the contact zone of the two different rocks. This is due to the fact that the Izu Peninsula is composed of weak formation and covered with various kinds of volcanic ejecta. Therefore, the distribution and structure of geological formation, by which Izu Peninsula is composed of, are considerably complicated. Consequently these landslides occurred by the divergence of physical properties to water between the upper formation and the under one, by which the mountain slope is composed of.
(B) Landslides caused by the exfoliation of the weathering materials. The outbreak of these landslides is due to the fact that fair part of the geological formation, by which Izu Peninsula is composed of, had been mollified by severe metamorphism or by weathering.
(C) Landslides and debris flows occurred in ancient times.
The outbreak of these landslides is closely related not only to the condition of (C) but also to the conditions of (A) and (B). In this region, large scale of volcanic activities and earthquakes have occurred so frequently that the destruction of volcanic mass, the formation of earthquake fault and landslides or landcreep caused by them have repeatedly occurred. It is due mainly to that reason that the Izu Peninsula is apt to cause the outbreak of landslide. Therefore, a portion of the deposit of landslides and debris flows occurred in ancient times (perhaps in the prehistorical and historial ages) gave rise to landslides much like to the landcreep and landslip recurred on the deposit of the old ones. And owing to the outbreak of these collapses, great quantities of debris and gravels were carried to the river floor.
(D) Lateral erosion by the flood-streams, and the outflow of debris and gravels. As a result of lateral erosion by the flood-stream and the outbreak of debris flows, the river floor was supplied with great quantities of debris and gravels. And also in the lower part of the Kanovalley, the fine grained materials ejected by volcanoes originating in various landslides as mentioned above were deposited in rich amount.
Judging from the characters of landslides and the outflow of debris and gravels as mentioned above, it can be said that these natures are characteristics of landslides arising from volcanic area, especially in the green tuff region where severe volcanic activities have continued on and after the Miocene epoch.

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To make clear the character of the flood by the Kanogawa Typhoon, the writer studied the transformation of the river beds and the flood in the lower stream area of Kano gawa.
The results of the survey are summarized as follows:
1. Kano gawa runs northward in its middle and lower stream, deepening in alluvial plains.
2. In comparison with the cross sections of the river beds three times during measured 1941 to 1958, a lowering of the river bed is found in many parts.
3. Meanwhile, according the cross sections before and after the Kanogawa Typhoon at each point of 200m interval along the river, the quantity of the accumulated silt, sand and gravels in the river bed in the lower stream area below Ohhito (26km S. from the mouth of the river) is calculated as the amount of 5_??_6×10⁵m³. The great part of the these matters accumulated in the limited part, and its quantity corresponds comparatively well to that of the silt, sand and gravels brought out from the up-side of depositional one.
4. The erosion of the river bed is particularly marked in the part where gradient changes suddenly and in the up-side of the broken bank. Namely the erosion took place even in the area of the lower stream. Accordingly it is not right that the area of the lower stream of the Kano gawa is a depositional one.
5. The movement of the river bed gravels are not altogether remarkable even in such a great flood by the Kanogawa Typhoon.
6. Though the quantity of silt accumulated by the flood in thd protected lowland cannot be calculated exactly, it is estimated to be between 2_??_10×10⁵m³. It is understood that this quantity includes mud from the broken banks (3×10⁵m³), silt of the river beds away at the breaking of embankments and silt produced by erosion in the protected lowland.
7. It is impossible to consider that, during the great flood of the Kanogawa, all of the debris from mountainous areas of the drainage of the Kanogawa have been transported and accumulated directly into the lower drainage area.

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We made a field survey immediately after the disastrous flood in the Kano river basin on Sep. 26, 1958 and investigated the actual conditions of the flood flows and the flood deposits brought by this flood water. The results are epitomized as follows:
1) The Kano river basin may be divided into two main areas; that is, the area upstream of Shuzenji bridge where scour exceeded deposition and the area below this bridge where deposition predominated scour. (Fig. 1).
2) The condition of inundation by the flood water is shown in Fig. VI-2 which gives the direction and the force of the flood flows at various spots. For the most part, the flood flows ran down straight regardless of river channel. Such a tendency is remarkably recognized in the upper part of the river basin. Also there is an indication that some 5 miles downstream of Shuzenji bridge, one of the flood flows ran along the older channel.
3) Bank collapses mostly happened in the river impinging undercut slope of meander. Especially, rips on the right bank are pronouncing and as damage by inundation was serious in the eastern half of the river basin, it seems that at the time of flood the river Kano had a tendency to shift its channel eastwards.
4) Fig. 3 represents the depth of the flood deposits in the protected lowland measured immediately after the flood. As shown in the figure, a large quantity of sediments deposited in the area downstream of Shuzenji bridge attaining at some places a depth of some 2 meters. Fig. 4 is the distribution map of the largest gravels that were found both in the river bed and in flooded arable land in the foreland. As can be seen from the figure, grain size of the gravels become abruptly smaller below Shuzenji bridge or thereabouts. Accordingly, we can make distinction of river regimen by setting up this point as the boundary. It may be said in this connection that the amount of sediment deposited by this flood reached nearly 4, 000, 000m³ in the area downstream of Shuzenji bridge.
5) The Kano river flood can be broadly divided into 4 types (3 types of bank-collapse and 1 type of overflowing) from the condition of inundation and deposition. Details are given below.
Type (A); Flood flows of this type ran violently down spreading lingulately below the rupture. Also, voluminous sediments were transported to a great distance. This type was the most extensive among the bank-collapse types and the depth of the flood deposits attained its maximum. Type (B); In the narrow valley area where the force of the flood flows was violent, the flood flows completely destroyed embankment along the channel and became a main factor of the disaster. Type (C); Like former two types, the cause of flood of this type was bank-collapse, only the water invaded the upstream lowland in conrtaverse direction to the flow of the river by the influence of geomorphological settings. The flood flows fanned out and the force of the flows was weaker than the former two types. Sediments were transported only in a short distance and deposited not too deeply. Type (D); This type was caused by overflowing of flood water. The direction of the flows was not so clearly indicated. This type was marked two variations; namely, in one type the flood flows invaded low ground below the level of the banks. The water of low ground remained long after the river level returned to its normalcy. Sediments were deep for its scale of flooding. In the other type the flood flows retarded rapidly with the recession of water as the altitude of flooded area was equal to the height of banks. The flood deposits were comparatively coarse and their depth was not so deep.
6) Seeing from the physical character, flood deposits were generally well sorted, although in the upper part of the basin soil class of the flood deposits was coarse sand and their external area per unit weight was extremely small.

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The author has made the damage state map including inundation area, direction of flow, distribution and thickness of deposits, strongly damaged villages, paddy fields, etc. in the mid-stream area of the River Kanogawa (Fig. 1), and some profiles showing changes of surface feature (Fig. 2). From his observations he has learned some important results for flood damage problems. Especially artificial relief, for example, road and canal, has an important effect upon the change of surface features and degree of damage.

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It has been well known that the flood-type varies greatly accordiag to the topographical elements the moutains, the basin and so forth. Accordingly, if we subclassify the topography of those flood visited areas, we can tell their flood-types. For example, in the case of the plain, the greater part of the plains in Japan is alluvial and they are formed by sand and gravels transported by the frequent flood-waters. So the microrelief of the plain and the state of the accumulated sand and gravels show the history of flood. If we have floods in future, it is possible for us to foretell the flood-type by the studying the micro-topography of the plain.
From this point of view, the writer surveyed the topography of the middle and lower courses of the Kanogawa river basin, Izu peninsula in the central part of Japan, by means of aerial photograph and by field survey. And he has drawn up the “topographical survey map of the middle and lower courses of the Kanogawa river basin showing classification of flood stricken areas.” Furthermore, he surveyed the great flood which visited the Kanogawa river basin on Septermber 26th, 1958 and has drawn up the “Map of the Kanogawa river basin showing the state of flood which visited the place on September 26th, 1958.” And he found the depth of the stagnant water, its period of the stagnation, the direction of the current, the velocity of the current, the erosion and deposit vary remarkably according to its area. In such a case, the following factors, for example the valley plain, the fan and the the delta, have a decisive influence upon deciding the types of flood. And then, he divided the flood-type in this district into the following five types.
(1) The flood-type seen in the valley plain. (2) The flood-type seen in the natural levee and back-marsh. (3) The flood-type seen in the dum up basin. (4) The flood-type seen in the narrow (canyon). (5) The flood-type seen in the delta.

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The writer has discussed the social and economic characteristics of the flood damage by the Kanogawa Typhoon in the Kanogawa basin.
There is much difference in this basin between the upper course and the lower one. The upper course with several tributaries runs through the steep slope mountainous area. The mountain land yields forest products and the land on the narrow botton of the valley is cultivated as farm land, especially a kind of horseradish (Eutrema wasabi) cultivated in the moutain stream is of the best quality in Japan, . Most people in the upper course occupied partly in farming and partly in forest production. There were many landslides in the forest mountain, and the farm land was carried away by the flood.
The lower course of the Kano river flows on alluvial plain, and the upper part of the lower course suffered most from the flood. In this area the degree of agricultural land use is very high. The postwar land reform program not only brought about social and economic stability to rural area, but also contributed to the raising of agricultural productivity in the area. There are many settlements, some people living there are being engaged in some occupation other than agriculture. In this area, many houses, bridges and banks were carried away by the flood and a portion of the farm land was covered by flooded materials.
An early planned repair of damage is necessary; however, through this damage, what we must keep in mind is that, although the principle of reconsteuction has already been adopted, it is necessary not only to repair the damage, but also to take permanent measures to prevent disasters in order that such damage will not be repeated by peoples organized co-operation.

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The writer investigated the actual conditions of the houses that were damaged by the flood caused by the heavy rainfall accompanying the Kanogawa Typhoon in the Kano River Basin. From the research, he tried to set up types of flood damage as follows:
Type a) Some private houses were buried and destroyed, others washed away by the debris flow owing fo landslides. Most settlements locating at dale side in the uppermost part of the river basin suffered from this type of damage. Type b) In the upper part of the basin, some settlements locating on the lower terraces were washed away by the overflowing flood. The primary cause of overflow is thought to be deposition of materials on the river bed at meander part of the river. Type c) In some cases, piers temporarily dammed up flood water until they were carried away by high water pressure accompanied with extraradinary flood wave. As the results of it, houses lying in the vicinity of bridges were swept away with this extraordinary flood wave. Type d) A number of hohses were away collectively due to the rip on the embankment in the alluvial lowland downstream of Shuzenji Bridge (Fig. 1). This type of damage caused a great loss of lives. As to the immediate cause of bank collaption, it is confectured to be the effect of extraordinary flood wave which rose after the washing away of Shuzenji Bridge. Type e) In the lowland area downstream of Chitose Bridge (Fig. 1) where water drains ill, a large number of houses were flooded above floor level by the inundated flow. However, few houses. were swept away and few lives were lost. Type f) In the lowermost part of the basin, the flood water of the main stream did not overflow its banks, but that of somet ributaries which were prevented from joining the main stream inundated in the urban area and numerous houses were flooded above floor board.
Among these types of flood damage, type c) expanded the scale of this disaster one. The residential shelter belt proved to be remarkably effective as a flood control (Fig. 5) and as to the structure of houses, such houses as built of stone and of anchor-bolt were effective in preventing them from disaster.

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In the Kanogawa river basin, various sorts of commercial agriculture are highly developed, such as strawberry, eutrema wasabi, tobacco, dairy milk, sericulture, etc. other than rice production. The flood by the Kanogawa Typhoon brought about severe damage on the agricultural production in this basin. The author interviewed 71 farmers at four rural settlements (J, O, S, N) located at the upper, middle, and lower parts of the flooded area, and asked them about real status of the dmage and their way of living since the accident.
The influences of the damage on the individual farms are different by the size of the farms and their social classes.
1. Landlord class (class A): Many of them avoided damages, because of their monopolistic ownership of safty land.
2. Upper class farmers (class B) and part-time farmers (class D): They overcomed their damages through their own economic potentialities.
3. Lower class farmers (class BC) and part-time farmers (wage earners)(class C): The degree of their damages was rather high and the effects were very severe. Consequently, many of BC class farmers are going to fall down to the unstable worker-peasant class.
As for the regional difference of the restoration from the damage, settlement of higher standard's agricultural production (settlement N) is rather active. In the settlement S severely damaged by the collapse of dykes, joint cooking and reconstruction for the damage were successfully carried out.

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Owing to the Kanogawa Typhoon, more than 460, 000 houses were damaged by the flood in Tokyo. This is a record-breaking damage by the flood in Tokyo. The flooded district by the Kanogawa Typhoon in Tokyo may be divided into two main classes from the topographical point of view, namely A) the delta region in the eastern and the south-eastern parts of Tokyo, and B) the western suburbs of Tokyo on the Musashino upland (in the south of the Kanto plain).
The vast flood in the delta region had been caused by the broken banks of the Arakawa, the Tama, the Edo, etc. In case of the Kanogawa Typhoon, however, the water gathered into the great part of the delta region and remained for a long time without no broken banks. Few parts of the districts along the small streams and the hollow places in the western suburbs of Tokyo on the Musashino upland had been flooded. However, the great part of the western suburbs on the plateau was flooded by the Kanogawa Typhoon. This fact is one of characteristics of the flood damage in the western suburbs of Tokyo in case of the Kanogawa Typhoon. Because the heavy rain was centred around the Musashino upland by the Kanogawa Typhoon, and many hollow places and the small river basins on the plateau were flooded.
The flooded districts caused by the Kanogawa Typhoon in the western suburbs of Tokyo on the Musashino plateau were the districts along the small streams, which have headsprings on the plateau and many hollow places. The great part of the damaged houses in the western suburbs of Tokyo were mostly newly built ones, by the streams or on the hollow places after World War II. As there has been a sudden rise in prices of the land in the western suburbs of Tokyo, many houses have been built in low-price lands. This fact is the other characteristic of the flood damege in the western suburbs of Tokyo.
In conclusion, it may be said as follow:
1) The flood damage caused by the Kanogawa Typhoon is “the flood damage on the upland” in the western suburbs of Tokyo,
2) the natural causes of the flood damage increased because of the rapid expansion of residential districts in the western suburbs of Tokyo.
Note: The shaded portions of Fig. 1 and 3 show damaged districts.

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