Geographical Review of Japan Vol. 68 (Ser. B), No. 2, 218-242, 1995

Geomorphological Maps of Alluvial Plains and their Utilization for Mitigation of Natural Hazards: Flooding and Soil Liquefaction

Masahiko OYA Nihon Kensetsu Consultant Inc., Higashi Gotannda, Shinagawa, Tokyo 141, Japan (Emeritus professor, Waseda University)

Abstract: After World War II Japan faced the simultaneous problems of food shortages and flood hazards. To resolve these problems, agricultural and civil engineers were requested to obtain information on alluvial plains which provide land for major food production in the Japanese Islands. Fortunately, Japanese geographers had already begun to study the alluvial plains as deposi tional geomorphology, greatly aided by the availability of aerial photographs. These circum stances gave birth to the Geomorphological Survey Map Showing Classification of Flood Stricken Areas. The maps enable us to estimate the features of flooding not only of the past but also of the future. The reason why such a survey map serves the purpose of defining the type of flood is that the irregular surface of the plain, however slight, as well as the sandy and gravelly deposits, were formed by repeated floods. Consequently, the micro-topography of the plain, i.e., fans, natural levees, deltas, etc. tell the history of past floods. From this point of view, the author compiled the first "Topographical Survey Map of the Kiso River Basin (Nobi Plain) Showing Classification of Flood Stricken Areas" in 1956. The accuracy of the map was actually confirmed by the high tide caused by the Typhoon Ise-Bay in 1959, i.e., three years after the preparation of the map. The results of the flood were almost the same as those predicted by the map. It is especially noteworthy that the area of invasion of flooding, caused by the high tide, coincides exactly with the delta area. This close relationship between high tide and geomorphology is manifested in many other cases, for example, in the routes of high tides and features of flooding in each geomorphological unit. Utilizing the combination of geomorphological units, the flood type is classified into the following three types: overflow type, concentration type, and a combination type. An example of the overflow type is seen in the lower reaches of the Kiso River and Han River, the concentration type in the Chikugo River, and the combination type in the Vientiane Plain along the Mekong River. The map is useful for estimating not only flooding but also soil liquefaction sites caused by earthquakes, and for the selection of bridge sites.

Key words: Geomorphological survey map, Flood, Alluvial plain, Soil liquefaction

Geomorphological Survey Maps Showing tated by frequent floods caused by typhoons and other heavy rains. In order to increase rice Classification of Flood Stricken Areas in production, the Japanese needed to improve the the Alluvial Plain rice fields in the alluvial plains. The Archipela

History of geomorphological survey maps go was devastated by large scale typhoons in 1945 (Typhoon Makurazaki), 1947 (Typhoon showing classification of flood stricken areas Catherine), 1948 (Typhoon Ion), 1950, 1951, After the Second World War, Japan faced 1953 and 1954. The devastation was especially simultaneous problems of food shortages and extensive from Typhoon Catherine, when the flood hazards. The staple food was rice, grown embankment of the Tone River collapsed, and mainly in the alluvial plains which were devas the main part of the Kanto Plain and the city of Geomorphological Maps of Alluvial Plains 219

Tokyo were inundated. Maximum flood dis ing of rice plants, but it was impractical because charge at that time was 15,000m3/sec. at Yatta the time needed to carry out the plan would jima, 14,500m3/sec. at Kawamata and 13,000 have been too long. Therefore, only the improve m3/sec. at Kurihashi along the Tone River ment of land remained as a feasible measure. which has largest catchment area in Japan. Ac As a result, agricultural civil engineers required cording to the records of flood discharge at the geomorphological knowledge of alluvial plains. lower part of the Tone River kept since the Meiji Fortunately, the time had already come for Restoration, the maximum flood discharge the study of alluvial plains among Japanese amount has been increasing gradually even geographers. Before the war, topographic study though there has been little change in the was strongly influenced by studies in Europe amount of precipitation in the upper reaches of and in the United States. Almost all the studies the river. Aki (1952) and some civil engineers had been done in mountainous regions formed believe that this phenomenon is due in part to by erosion, as in Europe and the United States. river conservation works, for example a short Furthermore, considerable parts of the plains in cut in a meandering course, and in part to the Europe and North America were formed by change of land use. Therefore, many civil engi glacial processes. In contrast, the alluvial plains neers require integrated knowledge of the river in Japan were formed by deposition by fluvial basin for flood control (Oya 1972). action. Tada and his study group, including the Directly after the typhoon, the Geographical author, wanted to begin research on the topo Survey Institute, Ministry of Home Affairs graphy of depositional areas. (1947), researched the flooding and made a map Directly after the Second World War, the Re showing the area of inundation, periods of sub sources Council was established by the govern mergence, depth of submergence, flood iso ment of Japan following the recommendation chronal lines, and direction of flood current. of Dr. Ackerman who was a geographer in the Widespread breaches of embankment oc General Headquarters (GHQ). The Resources curred at the right bank of the Tone River Council was a good place for discussions among which is located in the upper 4km of Kurihashi; civil engineers, agricultural engineers and ge the water then flowed into the extinct river ographers. "A Topographical Sur course which used to be the main Tone River in vey Map of the Kiso the Edo Period, and stagnated each back-marsh. River Basin Showing Classification of Flood Flooding was controlled by each natural levee Stricken Areas", which was the first geomor along the extinct river courses, and the flow phological survey map showing classification down the Old Tone River Basin devastated pad of flood stricken areas, was born under these dies in the back-marsh and upland crop fields in circumstances. the natural levee (Oya and Haruyama 1987). What is "a geomorphological survey map of a According to the research, the relationship river basin showing classification of flood between the micro-topography of the plain and stricken areas"? features of inundation becomes clear. The re search had an influence on the birth of Geo A geomorphological survey map of a river morphological Survey Maps Showing Classi basin enables us to estimate the nature and fication of Flood Stricken Areas. extent of an area submerged, the length of time On the other hand, the problem of food short an area would be under water, the depth of the age was very severe. The Ministry of Agricul standing water, the direction of flood currents, ture wanted to increase the production of chem changes in the river course, the possibility of ical fertilizer. Unfortunately, almost all the fac erosion and deposition, and numerous other tories of chemical fertilizer were destroyed by details. bombing during the war because they were The reason why such a survey map helps to being used temporarily to manufacture gun indicate flood types is that the relief features of powder. a plain and its sandy and gravelly deposits have There was also an idea to improve the breed been formed by repeated floods. Consequently, 220 M. Oya the micro-topography of the plain and its sand phological survey maps showing classification and gravel accumulation preserve traces of past of flood stricken areas of the main rivers in floods very well. Japan and S. E. Asia. Geomorphological features, such as terraces, These maps include those of the Kiso River valley plains, fans, natural levees, back-marshes, and the Chikugo River in Japan, and those of deltas, etc., influence the extent and the nature the Mekong River on the Indo-China Peninsula, of the flood. For example, on the alluvial fan, the Brahmaputra-Jamuna River in Bangladesh, erosion and deposition of sand and gravel are Padang City in West Sumatra, and the Central common. Changes in the river channel are fre Plain of Thailand. These maps were requested quent; flood water drains off quickly and depos by the Resources Bureau of the Science and its consisting mostly of sand and gravel are left Technology Agency, the Ministry of Construc on the fan. The depth of the stagnant water is tion, the Economic Commission of Asia and the shallow, and sand deposited on the levees by Far East (ECAFE), the Economic Commission of flood water drains off well. In back-marshes, Asia and the Pacific (ESCAP), the Japan Interna however, the water is generally deep and re tional Cooperation Agency (JICA) and the Na mains stationary for a long time, leaving a tional Research Center for Disaster Prevention mantle of silt and clay. In a delta, the depth of (Table 1). water is shallower than that of a back-marsh Method of preparing a geomorphological area, but delta areas are sometimes subjected to survey map of a river basin showing classific high tides caused by typhoons and "tsunamis" ation of flood stricken areas in the alluvial (tidal waves) resulting from earthquakes (Tada plain and Oya 1959). This shows clearly that by classifying the In the preparation of a map, the target area is geomorphological configuration of an area first classified by major geomorphological units subjected to frequent flooding, one can deter such as mountains, terraces and lowlands. Sec mine the nature of previous floods as well as the ondly, the mountains are classified by altitude, probable nature of future floods. From this structure, form and so forth. We classify the point of view, the author has prepared geomor terraces into lava plateaus, upper, middle, and

Table 1 Geomorphological survey maps showing classification of flood stricken areas Geomorphological Maps of Alluvial Plains 221 222 M. Oya

lower terraces; the lowlands into dissected fans, of man-made topography, such as reclaimed alluvial fans, natural levees, back-marshes and land, and artificially filled fields, utilizing aerial deltas. In addition, we include the classification photographs. The map, thus prepared, is then Geomorphological Maps of Alluvial Plains 223

Table 2 Relationships between geomorphological units and state of flooding (including man made topography)

checked using information related not only to (Japan), G. B. Castiglioni (Italy), and J. Suzupri geomorphology but also to flooding. The rela yczynski (Poland). tionships between geomorphology and features The purposes of the Working Group were a) of flooding are shown in Table 2. the compilation of geomorphological maps of the flood areas in some important plains in the Comparison between Japan and continental world, and b) making a country report on the regions (Europe and North America) in terms of the geomorphology utilizing the geomor geomorphology of plains related to natural and man made hazards (Oya 1990). phological land classification map Through the result of the studies by the The I. G. U. Commission on Geomorphological above mentioned Commission and Working Survey and Mapping, which was formerly called Group, the author has recognized the following the I.G. U. Commission on Applied Geomorphol difference on geomorphology and mapping be ogy from 1956 to 1968, completed the Interna tween the Continental Region especially in tional Geomorphological Map of Europe (1/ Europe and North America, and Japan. 250,000) in 1976. The commission was guided (a) In Europe, the geomorphological classi by J. Demek (C.S. S. R.), H. Th. Verstappen (The fication has been done based on the agent; slope, Netherlands), F. Joly and J. Tricart (France), J. F. composition, age of formation, formal coastal Gellert (Germany), G. B. Castiglioni (Italy), C. line were added to this classification. In Japan, Embleton (U. K.), M. Klimazewski (Poland), N. V. the classification has been done based on the Bashenina (U.S. S.R.), and St. Onge (Canada). morphology, especially utilizing the break The legend of the map was compiled by J. points of geomorphological units. Demek as the "Manual of Detailed Geomorpho (b) In Europe, the classification laid stress logical Mapping" (1972). on climatic geomorphology and erosional geo In 1980, the I.G. U. Working Group on Geo morphology but in Japan, on depositional geo morphology of River and Coastal Plains was morphology. established. The Working Group was guided by (c) In Europe and North America the classi J. A. M, ten Cate (The Netherlands), M. Oya fication is based on glacier and glacial geomor 224 M. Oya

Figure 1. Topographical survey map of the Kiso River Basin (Nobi Plain) showing classification flood stricken areas (Oya 1956).

phology, with karstic regions being very de Japan utilizing methods of the above mentioned "Manual of Detailed Geomorphological Map tailed, but being very simple in Japan. The Author estimate that the above men ping". She concluded that she couldn't use the tioned differences on geomorphology resulted legends of the International Land Classification from the background, i.e., the main parts of directly and that she would be forced to add Europe and North America belong to the epeir legends suitable for the Japanese situation in ogenic zone with small precipitation, but Japan order to apply the standard of the International is located in the orogenic zone with typhoons. Land Classification made in epeirogenic move Uchida (1976) applied the international geo ment areas to Japan's orogenic movement morphological land classification of Europe to areas. Geomorphological Maps of Alluvial Plains 225

can be easily recognized. The line connecting Experiments Using Natural Flooding and the northern part of Nagoya City and Tsushima Validation of a Geomorphological Survey City to the south is a delta which was formed Map of a River Basin Showing Classific by fluvial action of rivers and by marine action. ation of Flood Stricken Areas The southern-most part of the delta is land reclaimed after the 17th century. Around High tides caused by the Typhoon Ise-Bay and Nagoya Port is an artificially filled field, which a geomorphological survey map of the Nobi was built after the Meiji Restoration in 1867. Plain located at the lower reaches of the Kiso On September 26, 1959, the southern part of River the plain where the city of Nagoya is located The author prepared the map of A Topo was attacked by a super scale typhoon, the graphical Survey Map of the Kiso River Basin Typhoon Ise-Bay. The high tide caused by the Showing Classification of Flood Stricken Areas typhoon was reported to be as high as 3.89m in 1956 (Fig. 1). The Nobi Plain in the lower (12.8 feet) in Nagoya Port. As a result of the reaches of the Kiso River consists of fans, natu disaster, some 5,200 persons died and about 530 ral levees with back-marshes, deltas, etc. There billion yen (about $1,472,000,000 at that time) is a large fan, the apex of which is at the City of in properties were lost. Inuyama. In addition, three or four distinct The map's utility was demonstrated by the natural levees are also seen south of the fan. typhoon in 1959. The results of the flood were When a river bed is greatly raised, it causes the almost the same as those predicted by the map. river channel to shift (Oya 1988). The close relationship between high tides and In the Nobi Plain, several divergent natural geomorphology was highly visible in many levees, which were formed by repeated flooding, cases. It is especially noteworthy that the area

Figure 2.1. Location of the profile of high tide (Nakano and Oya 1960; modified). 226 M. Oya

Figure 2.2. Features of the profile of high tide (Nakano and Oya 1960; modified).

of invasion of flooding, caused by the high tide, at spring tide the next day was 1meter above coincides exactly with the delta area. sea level. The extremity of the influx was seen (1) Features of the flooding at the boundary of the delta, that is, the coastal The flood type-the extremity of the high line from the latter prehistoric age to early tide and that of the sea water, the depth of the historic age (Fig. 2). stagnant water, its period of stagnation, the (3) Invasion Routes of High Tide velocity of the current, the erosion, and deposits The main routes of the high tide invasion are -vary remarkably according to the landforms . provided by landforms like rivers, channels, an Here, factors such as fans, natural levees, back cient waterways, etc. marshes and the deltas have a decisive in Rivers: The three large rivers, the Kiso River, fluence upon deciding the types of floods the Nagara River, the Ibi River, and other small (Nakano et al. 1960). rivers flow into Ise-Bay. These rivers made (2) Limit of intrusion of high tide convenient routes for the high tide to proceed. The coast of Nagoya Port was hit by a high The high tide proceeded as far as about 24km tide of 3.89meters above sea level. The high from the mouth of the Kiso River. The velocity tide intruded on the inland area with high ve of the transmission of the highest water level locity. But did not proceed very far, disappear of the tidal waves was very fast: from 5m/sec. ing at about sea level. The line where the high to 8m/sec. tide disappeared was found at the boundary of Channels: There are many channels in the reclaimed land, that is, the coastal line of the 16 city of Nagoya: Nakagawa Channel, Horikawa th century. Beyond this line, the sea water seen Channel, etc. These channels provided easy Geomorphological Maps of Alluvial Plains 227

access for the high tides to proceed. However , Relationships Between a Combination of there were gates in the mouth of the Nakagawa the Geomorphological Units and Flood Channel, which prevented the high tides from intruding. Types of the River Basin: Overflowing Ancient waterways: Ancient waterways are Type, Concentration Type and Combina seen in the delta here and there. The ancient tion Type waterways were changed to paddy fields sever Overflowing type: the Kiso River, Nobi Plain al hundred years before the high tide, but , nev ertheless, the routes were very convenient for and Han River, Korea the intrusion of the high tide. The Kiso River: The Kiso River flowing Application to the Ariake-Sea Lowland: Esti across the Nobi Plain has formed big alluvial mation of the potential state of flooding fans, natural levees and deltas in its lower caused by high tides reaches. This triple combination of geomorpho logical units, The Ariake-Sea Lowland consists of fans , Fan+Natural Levee+Delta, lower fans, upper deltas, deltas and reclaimed (Back-marsh) land. The Sagaego River, located east of Saga indicates that the deposition by the main City, runs from west to east, i.e., parallel with stream is remarkable. the coastline. This is unlike most of the rivers in A cross section of the Kiso River and its this area which flow from north to south. Many surrounding plain shows that the land becomes shell mounds are seen in the northern part but higher as one moves nearer to the river. That is none in the southern part (Fig. 3). why when a flood occurs the water spreads The author has presumed that the line con from the natural levee to the back-marsh or necting Saga City and Sagaego River is a delta. There has been no severe flooding during former coastline, around 3m, correlates with the last 300years, but due to the Typhoon Ise the line connecting the cities of Nagoya and Bay, the high tide went upstream through the Tsushima in the Nobi Plain. Kiso River, the Nagara River and the Ibi River We have experienced high tides several times breaking the embankment and overflowing in the Ariake Sea, Kyushu. For example , on from the main stream to the adjacent lowland September 14, 1959, a typhoon attacked the (Oya 1973a, 1988). Ariake Sea which resulted in a high tide. Utiliz There is a close relationship between the top ing the record of high tide caused by the ty ographic features of the alluvial plain and the phoon, the Ministry of Construction calculates mountain. About 53.3% of the drainage area of the potential height of the high tide to be 7.5m . the Kiso River is above 700m. Similarly more Using the theory which was established in than 52.2% of that drainage area is steeper than the Typhoon Ise-Bay in the Nobi Plain, the 30 degrees. The relief energy of the area is big , author estimated the inner limit of a high tide showing a maximum of 1,300m. The moun or the sea water and state of flooding in the tains were uplifted about 2,000m i.e. 60-70% of area. the present height during the Quaternary Age . If we have a high tide with a height of 7.5m , Uplift of the ground is continuing at a rate of 5 the high tide and sea water which intrudes the 11cm in the last 50-60years. The principal inland area will be stopped at the 3m line. rocks include granite, andesite, etc. which are From this point of view, the Ariake-Sea Low weathered easily. These geomorphological fea land can be divided as follows: (1) those areas tures of the Kiso River Basin clearly demon which will be devastated by the high tide; strate a large and continuous supply of sand (2) those areas which will be partly devastated and gravel in the region. Even the reservoirs by the high tide and sea water; and (3) those for hydroelectric power stations at Yaotsu and areas which will be slightly submerged by sea Oi are facing a great problem of silting owing water. to the heavy influx of sand and gravel in the river. 228 M. Oya Figure 3. Geomorphological survey map of the g Basin showing classification of flood-stricken areas (Oya 1977a; modified). Geomorphological Maps of Alluvial Plains 229

Figure 4. Topographical cross-section of the lower reaches of the Kiso River Basin (Oya 1973a).

Owing to these geomorphological and geolog three or four natural levees are also seen from ical features of the basin, landslides occur the fan margin to the south. When a river bed during severe rainfalls and a large quantity of is greatly raised shifting of the river channel debris is deposited on the river bottom. The brings big floods forming a new natural levee river runs along a continuous canyon and there along the channel. In the Nobi Plain, several is no intermontane depression along its course. divergent natural levees which were formed by Therefore, the sand and gravel which is depos this process can be easily recognized (Fig. 1). ited by landslides does not stop on the way but Although the topography of the Nobi Plain is flows directly down to the plain. susceptible to flooding, it is beneficial in the A large alluvial fan, the apex of which is at utilization of the river for irrigation and as a the city of Inuyama, was formed. In addition, water supply throughout the Nobi Plain (Fig. 4). 230 M. Oya

Figure 5. Topographical cross-section of the plain of the lower reaches of the Chikugo River Basin (Oya 1973a).

This kind of overflowing type is also seen in the Kiso. The maximum relief energy is a mere 800 Han River, Korea. m in the former, while it is 1,300m in the latter. Hence, the Chikugo River Basin is less suscep Concentration (retarding) type: Chikugo River tible to landslides. Plain There are several intermontane depressions, The Chikugo River: The Chikugo river has such as, the Oguni and Hida depressions along large fans formed by the tributaries coming the main stream and the Handa Plateau and from north and south of the main stream, but Kusu Depression along the Kusu River which is has a tiny fan formed by the main river. Even a tributary of the Chikugo River. When a river the natural levees, which are seen in general has a depression, a considerable part of the along the lower course from the fan, are rarely larger gravel transported from the upper rea seen here. The width of the middle and lower ches is stopped in the depression preventing delta which is developed along the main course sand and small-size gravel from moving down is narrow, about 7km. The combination of ward. Leveling from 1893 to 1963 shows that the geomorphological units is as follows most of the upper part of the Kusu depression

(Fig. 3). sunk 9.19cm during the 70years, while the Fan •« canyon located in the lower reaches of the de pression rose 9.2cm. This crustal movement is Tiny Fan+Delta+Tidal Delta+Subaquatic Delta •ª one of the causes of the stopping of the flow of sand and gravel to the lower reaches. A study Fan of the silting of the reservoir of the Yoake Dam If we compare these geomorphological fea shows that the deposition rate is only 1/42 of tures with that of the Kiso River Basin, we can the Kiso River (Tada et al. 1957). see distinct regional differences between the In the middle reaches of the Chikugo River, two basins. For example, the mountains in the the closer to the river the land is, the lower it Kiso Basin are higher than the Chikugo Basin. becomes (Fig. 5). This is mainly due to erosion Similarly the slope of the Chikugo Basin, as and the ground dipping along the main stream, might be expected, is smaller than that of the and maximum deposition by the tributaries Geomorphological Maps of Alluvial Plains 231

Figure 6. A Geomorphological survey map of the Mekong River Basin indicating area subject to flooding (Oya 1967).

along the foot hill with decreasing tendency 1953 when the left bank dikes were broken at towards the main stream. Owing to this pecul Eri and flood water invaded the protected area iar topography, the flood water flows down breaking the left dike from the back side and from the higher surrounding area into the main rejoining the main river. stream. In fact, when overflow occurs, the flood Due to the floods of 1921, 1935 and 1941, water does not disperse but flows into the main shortcuts were made at the meandering section stream at the lower reaches. This type of flood of the Chikugo River which resulted in the ing contrast was observed during the flood of shortening and straightening of the river 232 M. Oya course. Because of these shortcuts and the build courses, and back-marshes generally occupy ing of continuous embankments the velocity the area between two natural levees or between became faster. Whereas in 1925-32 it took 9.2 a natural levee and a terrace. hours from Hida to Kurume, in 1942-52 the The geomorphological survey map of the time was reduced to only 4.8hours. Owing to Mekong River Basin helped the author to esti this increased velocity of flood current, the mate the maximum area under water in periods river bed between the river mouth and Ryochi of exceptional flooding such as that of 684.7 ku Bridge, which is situated 45km upstream km2. The total area under water during the from the river mouth, was lowered by 43cm 1966 flood was 499.5km2 which proved that (from 1923 to 1953 and 1961). This lowering the 1966 flooding was of the largest magnitude was caused not only by the man-made construc during the Holocene Age. The overflow type tion which affected the velocity of the river, but was seen in the upper part of the Vientiane also by the excavation of sand and gravel in the Plain, while the lower part of the plain was river bed. Thus, in the middle reaches of the dominated by the concentration type. Hence, Chikugo River, erosion is more important than protective dikes are more useful in the upper deposition; this is due to the nature of the phys part of the plain rather than in its lower part. ical features and changes brought in by human The map also helped in the construction of a skill. railway line between Nongkhai and Vientiane In this area inundation is small and deposi and in the selection of sites for stations on the tion is limited. But the topography is inconve terraces which avoided flood-prone areas (Oya nient for water use. Moats which are well devel 1967, 1980). oped in the lower reaches of the Chikugo River are counter measures to this condition of water Utilization of a Map of a Plain Where shortage. Flood types similar to the Chikugo Flood Control Work Has Been Done Well River occur in the Shonai and Yamagata Inter montane Depression (the Mogami River) and in Inundation by local rainfall without bank col the Niigata Plain (the Agano River), (Tada et al. lapse in the urban region 1956, Oya 1973b, 1977). The inundation caused by local rainfall has Overflowing type and concentration type: become remarkable in the urban area in Japan Vientiane Plain in the Mekong River in the last few several decades. The nature and A third type, which is rather rare, can be extent of such inundation can also be estimated designed by combining the two main types. by using geomorphological survey maps of the For example, the Kano River Plain is divided region which exhibit the relationship between into two parts: the Takata Plain in the upper the topography of the Neyagawa River Basin course is characterized by the overflow type, near Osaka and inundation caused by the local and the lower part by the concentration type. rainfall in July 1967. The region is bordered by The Mekong River: the Vientiane Plain in the the Ikoma Mountains in the east, Uemachi Ter Mekong River of Indo-China presents the com race in the west, the Yamato River in the south, bination of overflow and concentration types of and the Yodo River in the north. The former flooding. Under the Pa Mong Dam Project, the river has a big natural levee and the latter has a author was asked to determine the present state small one. The nearer to the rivers the land is, of flooding in the Vientiane Plain, for which a the higher it becomes. The drainage-basin of geomorphological survey map of the Mekong the Neyagawa River is surrounded by these River Basin was prepared (Fig. 6). It was ob hilly areas, so drainage is difficult. served that the alluvial fan has very limited The southern part of the drainage-basin of area in this region owing to the flatness of the the Neyagawa River has been formed by the topography and weathering of the rocks to lat deposition of the Yamato River. Due to great erite by chemical processes. On the other hand, quantities of gravel, sand, and other deposits there are big natural levees along the river from the Yamato River, the southern part of the Geomorphological Maps of Alluvial Plains 233 region is slightly higher with steeper slopes tion it is necessary to introduce the concept of than its northern counterpart. The entire area comprehensive flood control. The concept was is divided by many natural levees indicating first initiated in the U. S. A. In the U. S. A. and the former courses of the Yamato River, and its Canada, the study of flood-plain management tributaries. Also, there are numerous back by G. F. White, and his dedicated group of marshes surrounded by natural levees which researchers gained national attention as they accelerate local inundation. The northern part pursued the problems of increased urban occu of the drainage-basin of the Neyagawa River pancy of the flood plain (Dougal 1969). has been formed by the small volume of deposi The concept puts emphasis on non-structural tion transported by the Yodo River. The height methods such as building codes, flood insur of the area is lower, and the slope is more gentle, ance, etc. In this case the zoning on flood pro so inundation happens easily. Urbanization is tection has been done by utilizing not the geo very fast while the preparation of sewerage is morphological map but a map showing the insufficient, causing obstruction to natural dra state of flooding, especialy the maximum flood inage. Fortunately, the natural levees are still in the area. The above mentioned method is quite safe in times of flooding (Oya and Naka used when the flood plain has been formed by mura 1969). erosion and its relief is very small. The first example of non-structural flood con Estimation of a map of an area affected by trol was implemented by the city of Nagoya. integrated flood control After the Typhoon Ise-Bay in 1959, the city In Japan urbanization has advanced ex authorities of Nagoya and the Ministry of Con tremely rapid during recent years. Urbaniza struction took measures for comprehensive tion not only causes obstruction to natural dra flood prevention. On the basis of the flood inage but augments the rate of run off and features and damages, the southern part of the velocity. As a counter measure to such a situa city was divided into five zones and building

Figure 7.1. Construction zoning to meet flood danger (Oya 1970). 234 M. Oya

Figure 7.2. Regulation of architecture (Oya 1970).

regulations were issued for each zone (Fig. 7). prepared the following comprehensive flood The first area, covering artificially filled land control plan on the rivers in the cities. The around the Port of Nagoya, was asked to con drainage river basin is divided into three parts: struct all future buildings in concrete. The a water holding area, a water retarding area, second area, where the reclaimed land is surro and a lowland. unded by artificially filled land on the sea-side A water holding area: a mountainous or hilly and by rivers in the west and east, was allowed area in the upper reaches. In this area, rainwa to have included refuge room of at least 3.5m ter infiltrates through the ground and is held as above ground level in the buildings. The third soil-and ground-water temporarily. area consisting of reclaimed land for urban pur A water retarding area: a valley plain or inter poses was given similar instructions as the mountane depression in the upper reaches. In second area. The fourth area of the older recla this area, water flow is retarded. imed land and the fifth area of reclaimed land In the above mentioned two areas, construc utilized for agriculture were asked to construct tion of a regulation pond or pillottes architec buildings with water resistant structures up to ture would be highly recommended. 3.5m high. A lowland area: a flood plain in the lower reaches. The area becomes inundated with over Utilization of the map in the integrated flood flowing water from the river. The inundation control system prepared by the Ministry of of the area is protected by the embankments. Construction The above mentioned classification has been At present, the Ministry of Construction has done utilizing the geomorphological survey Geomorphological Maps of Alluvial Plains 235 map which shows classification of flood strick tions of the area. For example, in the case of a en areas first, and the land use map second. relatively large plain composed of various geo morphological units such as the Nobi Plain or Utilization of a Geomorphological Survey the Kanto Plain, the site of liquefaction varies Map of a River Basin Showing Classific according to the location of the epicenter of the ation of Flood Stricken Areas for Estima earthquake; that is whether the epicenter lies tion of the Area affected by Soil Lique inland or in the sea, or in the lowland or the faction in an Earthquake mountain district. (2) In each alluvial plain, a close relationship may be seen between various geomorphological Soil liquefaction units and the occurrence of soil liquefaction. Earthquakes cause large scale damage Thus the prediction of soil liquefaction be through faulting, cracks, upheaval, subsidence, comes possible in every geomorphological unit dislocation, landslide, soil liquefaction ac (Table 3). companied with spouting water, sand or mud. (3) The probability of liquefaction in every Particularly the effect of soil liquefaction is dra unit mentioned above varies according to the matic and drastic when it occurs in the central geomorphological type of the plain: (a) the area of a city, and can result in large scale valley bottom plain has a low probability of collapse of buildings. This type of damage liquefaction except of the area close to the epi occurred to various buildings in the city of center of the earthquake; (b) the alluvial fan has Niigata at the time of the Niigata Earthquake in a probability of liquefaction at the apex and on 1964. Akagiri and Wakamatsu (1991) con the skirts of the fan lying near the epicenter; (c) ducted research on site conditions of liquefac the natural levee has a high probability of liq tion in four typical plains of Japan, i.e., the Nobi uefaction; (d) the back-marsh shows low proba Plain, the Kanto Plain, the Shonai Plain and the bility of liquefaction except the marginal part Fukui Plain. Figure 8 shows the distribution of of a natural levee and the former river courses; liquefied sites in the Shonai Plain (Oya et al. and (e) the delta, reclaimed land and artificially 1982). filled fields have a high probability of liquefac You can find close relationships between geo tion. morphology and liquefied sites in the plain. The above mentioned relationships were seen (1) The characteristics of soil liquefaction frequently, for example, in the Nihonkai Chubu are influenced by geomorphological condi Earthquake (1983, M=7.7), the Chibaken Toho

Table 3 Relationships between geomorphological element and possibility of Liquefaction subject to seismic ground motion of the J. M. A. initensity 5 236 M. Oya

Figure 8. Geomorphological land classification map and liquefied sites in Shonai Plain (Oya et al 1982).

Oki Earthquake (1987, M=6.7), and the Hyogo magnitude 7.2, the Hyogo Prefecture Nanbu Prefecture Nanbu Earthquake (1995, M=7.2). Earthquake, occurred in Kobe City and its vi cinity. As a result of the earthquake about 6,300 The Hyogo Prefecture Nanbu Earthquake, people died. The heavy damage that occurred 1995: the Great Hanshin Earthquake was due to the location of the epicenter-direct On January 17, 1995, a strong earthquake of ly under the ground of Kobe City and its vicin Geomorphological Maps of Alluvial Plains 237

Figure 9. Geomorphological survey map of the Yodo River Basin showing classification of flood stricken areas and hazard by earthquake in 1995 (Oya and Kubo 1993; modified). ity. A remarkable movement of the fault line earthquake. The damage was especially great was seen in the northern part of Awajishima at the crossing point between the present river Island. But a clear fault was not seen in the city courses and the former river courses (Fig. 9), of Kobe. The embankments in the lower (Oya and Kubo 1993; modified in 1995). reaches of the Yodo River and the Ina River There was a close relationship between the were collapsed in many places because of this damage and geomorphology, with the greatest 238 M. Oya damage found along the former river courses, of river width and braiding of river channels in artificially filled fields, and at the foot of the are continuing (Fig. 10). fluvial fan. Nagarbari (Aricha) is located at the confl uence between the Ganges and Brahmaputra Utilization of a Geomorphological Survey Jamuna Rivers. The peak of the flood discharge Map Showing Classification of Flood of the Ganges generally occurs about one Stricken Areas for the Selection of a Pro month later than that of the Brahmaputra posed Bridge Site: Brahmaputra-Jamuna Jamuna River. Due to the back-water of the River in Bangladesh Ganges, bank erosion, change of river course, and shifting of the thalweg at Nagarbari Directly after the independence of Bangla (Aricha) are the greatest among the four pro desh, the government of Japan was requested posed bridge sites. The change is smaller at the to research the possibility of constructing a Gabargaon and Sirajganj sites. bridge across the Brahamaputra-Jamuna River. (2) The geomorphological map of the Bra In the construction of a bridge across a river, the hmaputra-Jamuna River has been prepared by most important thing to be considered is the utilizing the mosaic of aerial photographs shifting of the river course and changes of the which were taken in 1974 by the Japanese Re banklines of the river. The shift from the Old connaissance Team as a base map. The author Brahmaputra River to the present Brahmarut has prepared the map by the use of the photo ra-Jamuna River occurred in the latter half of graphs and conducted field observation by boat the 18th century. It is the fear of technical and jeep. officials who are in charge of the management The rivers, bordering with India to Sirajganj of the river in Bangladesh that the river may and having a braided flow, are similar to rivers shift after the construction of the bridge. The in an alluvial fan. There are natural levees, government of Japan was requested to fix the back-marshes, and abandoned river courses in whole river course of the Brahmarutra-Jamuna the alluvial fan around the Bahadrabad and River. This is, however, impossible for financial Gabargaon. The author estimated that the nat reasons because the river is both too long and ural levees and back-marshes were originally too wide. Bahadrabad, Gabargaon, Sirajganj formed by the Tista, Jamuna, and Jhinai Rivers, and Nagarbari (Aricha) were selected as pro and that the alluvial fan, formed by the Brahm posed bridge sites. The author was requested to aputra-Jamuna River, had partly covered the select the most stable and suitable site among natural levees, back-marshes, and former river the four for the bridge based on applied geomor courses after the shifting of the Brahmaputra phological research. Jamuna River. In the future, the area of the The main causes of the shifting of the river natural levees, back-marshes, and abandoned are remarkable crustal movements, deposition river courses in the fan will be buried by the of sand, variation in discharge, and a bank com shifting of the course. pletely consisting of sand. To make sure of the Sirajganj and Balktia, which are located stability of the river at the four proposed bridge across the river from Sirajganj, are situated on sites, the author (1) investigated the change of the old alluvial plain which was formed by the banklines and the location of thalweges and (2) Tista, Jamuna, and Jhinai River, more than 180 prepared a geomorphological map of the Bra years ago. The old alluvial plain is separated hmaputra-Jamuna River Basin (1:50,000) and a from the present alluvial plain by a cliff, whose geomorphological map of the Brahmaputra relative height is about 3m. The width of the Jamuna River and Ganges River Plain (1: new plain between the old plain is 7km at its 1,000,000). narrowest point. The author believes that (1) The author researched the change of firstly, the narrows have been formed by up banklines and the location of the thalweg from heaval, partly because the cliff is the highest at 1830 to the present. At the Bahadrabad site, Balktia and gradually decreases in height to the due to the rising of the river bed, the expanding north and south; secondly, the abandoned river Geomorphological Maps of Alluvial Plains 239

Figure 10. Geomorphologic map of the R. Brahmaputra-Jamuna and R. Ganges Plain (Oya 1977b).

courses were concentrated in the upper part of The above mentioned facts show that the nar the narrows and bifurcated in the lower part of rows will remain for a minimum of 100years the narrows; and thirdly, the small terraced which are the durable years of the bridge, and surface, its relative height being 1.5m at Bal the river will keep its stability in the direct ktia, was formed by the Brahmaputra-Jamuna lower reach of the narrows (Fig. 11). River. Moreover, the area has experienced up (3) The geomorphological map of the Bra heaval of about 1.5m during the last 180years. hmaputra-Jamuna Plain has been prepared 240 M. Oya

Figure 11. Geomorphological land classification map of the Brahmaputra-Jamuna River (Sirajganj and its vicinity) (Oya 1977b). by the author by the use of the mosaic of the Surface were formed by upheaval, and the infra-red images of ERTS-I taken in 1972 as a Sylhet Basin, Brahmaputra-Jamuna Valley and base map, interpretation of the images and field Ganges Plain were formed by tectonic sub observation by helicopter. sidence. The alluvial plains consist of an alluvial The Maduhupur Jungle Terrace, and Tippera fan formed by the Brahmaputra-Jamuna and Geomorphological Maps of Alluvial Plains 241 the old Brahmaputra River. The distribution of the geomorphological Postscript and Acknowledgment units is determined by the two directions of the echelon fault lines or by the lineament which I started to make the Geomorphological Survey originated from the fault. One fault line is from Map Showing Classification of Flood Stricken Areas around 1955 under the guidance of the late Dr. the Garo-Rajmahal Gap to the Burma Trench Fumio Tada who was a professor at the University of via the Meghna River Mouth, i.e., from NW to Tokyo. SE. The other is from the Sylhet Basin to the I express my heartfelt thanks to the late Dr. Fumio Swatch of No Ground via the river mouth of the Tada. Haringhata. If displacement is to occur with an Since the first Geomorphological Land Classific ation Map Showing Flood Stricken Areas in the Nobi earthquake, the guide bank would be lowered Plain, I prepared about 40 sheets of the map in the unequally and the bridge would consequently areas along lower reaches of main rivers, not only in be destroyed. According to the research, the Japan but also in S. E. Asia. In the research and color author found that the Bahadrabad and Gabar printing, a lot of funding was required. I have been supported by the Resources Bureau of the Science gaon are located near the fault line or linea and Technology Agency, the Ministry of Construc ment, but he could not recognize any remarka tion in Japan, ECAFE (ESCAP) of the United Nations, ble fault line or lineament at Sirajganj. and JICA in S. E. Asia. I want to express my profound Based on the above mentioned facts, the thanks to these organizations. author concluded that the Sirajganj site is the I have been able to compile these maps into one most suitable place of the four proposed sites atlas titled "Geomorphological Survey Maps Showing Classification of Flood Stricken Areas" which was for construction of the bridge. published by Waseda University Press in 1993. On this occasion I have been requested by Dr. Gil Conclusion bert F. White, a former professor at Chicago Universi ty and Colorado State University, to compile this The Geomorphological Survey Map Showing paper based on the atlas. I express my thanks to him for giving me the chance to write this paper. Lastly, Flood Stricken Areas is an essential tool in the I'd like to give my thanks to Ms. Y. Koizumi who hands of geographers and geomorphologists to typed the paper. identify flood stricken areas and landform (Received Aug. 25, 1995) types in plains. Its use is becoming popular in (Accepted Dec. 16, 1995) not only estimating the magnitude of past floods but also in predicting future trends as References well in order to take preventive measures for Akagiri, T., and Wakamatsu, K. 1991. Damage of soil minimizing the flood's severity and resulting liquefaction caused by earthquakes and use of geo damage. morphological maps. Bulletin of the Geographical We can estimate not only the features of flood Survey Institute 36: 53-65. ing in each geomorphological unit in the plain, Aki, K. 1952. Suigai no Nippon (Flood damage in i.e., fan, natural levee, delta, etc., but also the Japan). Tokyo: Iwanami-Shinsho. flood types, i.e., overflowing, concentration and Demek, J. 1972. Manual of detailed geomorphological combination type based on the features of the mapping Academia, Publishing House of the Czecho slovak Academy of Sciences, C.S. S. R. combination of the geomorphological units. Dougal, M. 1969. Flood plain management, Iowa's expe It may give us a new outlook in city planning rience. Iowa State University Press. as we can now avoid chances of inundation by Geographical Survey Institute 1947. Flooding in Sep local rainfall or it may even help in the estima tember, 1947, Flooding report for the Tone and Ara tion of liquefaction sites caused by the earth River. Geographical Survey Institute. quakes and in the selection of stable sites for Nakano, T., and Oya, M. 1960. Relationship between the construction of bridges, etc. geomorphology and flooding caused by the Ty In developing countries its use should be pop phoon Ise-Bay. Sokuryo (Measurement) 10(6): 1-13. (J) ularized and expertise should be developed to Oya, M. 1956. A topographical survey map of the Kiso take full advantage of this new technique in River Basin showing classification of flood stricken planning programs. areas. Appendant Map of the Resources Council 242 M. Oya

Reference Data 46, Prime Minister's Office. (J) Ministry of Construction. (JE) Oya, M. 1967. Geomorphological study of flooding im Oya, M and Haruyama, S. 1987. Flooding and urban mediately down-stream from Pa Mong in the Mekong ization in the lowland of Tokyo and vicinity. Natu River Basin. The Committee for Co-ordination of ral Disaster Science 9(2): 1-21. Investigations of the Lower Mekong Basin, ECAFE Oya, M. et al. 1988. Studies on the geomorphological (UN). features of the fluvial plains in Japan focusing the Oya, M., and Nakamura, S. 1969. Geographical study distribution, geomorphological land classification on the inundation caused by the local rainfall in the and its application. Geographical Review of Japan 61 Neyagawa River near Osaka. Miscellaneous Reports B: 35-49. of the Research Institute for Natural Resources 72: Oya, M. 1990. Report on the activities of the Working 13-32. (JE) Group on the Geomorphology of the River and Oya, M. 1970. Land use control and settlement plans Coastal Plains, International Geographical Union. in the flooded area of the city of Nagoya and its Gakujutsu Kenkyuu (Academic Studies), The school vicinity, Japan. Geoforum (Germany), 1970(4): 27-35. of Education, Waseda University, 39: 1-18. Oya, M. 1972. Recent trends of landform classific Oya, M. 1993. Atlas: Geomorphological survey maps ation studies in Japan. Geographical Sciences 17: 1 showing classification of flood stricken areas. Waseda - 6. University Press. (JE) Oya, M. 1973a. Relationship between geomorphology Oya, M. and Kubo, S. 1993. Geomorphological survey of the alluvial plain and inundation. Asian Profile map of the Yodo River showing classification of flood (Hong Kong) 1 (3): 479-538. stricken area. Yodo River Work Office, Ministry of Oya, M. 1973b. Basic-form of the combination of the Construction. (JE) geomorphologic elements in the alluvial plain. Gak Tada, F. et al. 1956. Reconnaissance topographical ujutsu Kenkyuu (Academic Studies), The school of survey on areas subject to flood part 1. Resources Education, Waseda University, 22: 23-43. (JE) Council Reference Data 46, Resources Council, Oya, M. 1977a. Comparative study of the fluvial plain Prime Minister's Office. (J) based on the geomorphological land classification. Tada, F. et al. 1957. Reconnaissance topographical Geographical Review of Japan 50A: 1-31. survey on areas subject to flood part 2: The relation Oya, M. 1977b. Applied geomorphological study on ship between topography and flood type in the Chikugo the selection of the proposed bridge-Site along the River. Material of the Resources Bureau Science Jamuna River in Bangladesh. National Geographer and Technology Agency, 13, Resources Bureau, Sci (India) 12(2): 101-113. ence & Technology Agency. (J) Oya, M. 1980. Multifunctional uses of geomorpholog Tada, F. and Oya, M. 1959. The flood-type and the ical survey maps in identifying flood-stricken areas classification of the topography. In Proceedings of and land types. National Geographer (India) 15(2): I. G. U. Regional Conference in Japan 1957, 192-196. 173-195. Uchida, K. 1976. Applying the standard of the inter Oya, M. et al. 1982. Geomorphologic land classification national land classification of I. G.U. to Japan. Map map of the Shonai Plain illustrating features of flood 14(3): 28-32. (JE) ing and soil liquefaction. Sakata Construction Office,