The initial moisture conditions of a watershed immediately before a rainfall event begins affect the characteristics of the subsequent storm runoff. The authors found a drainage basin in the Soya Hills, northern Japan, where two different types of flood hydrograph are clearly distinguished for each flood event, and investigated the effect of the initial moisture conditions of the watershed and rainfall on the shape of the hydrograph. The watershed studied (Fig. 1) is underlain by Neogene shale (Wakkanai formation, Wk). With joint planes about 10cm apart and fissure zones approximately 10m apart, Wk is permeable and does not constitute a hydrological basement. As a result of water level observation on an experimental watershed (drainage area A=0.69km2) in a Wk-hill, two types of flood event are recognized. Type-1 floods (Fig. 2-a) have only one runoff peak corresponding to each rainfall event. This peak appears within 2 hours after the termination of rainfall. Type-2 floods (Fig. 2-b) have two runoff peaks for one rainfall event. The time lag between the primary runoff peak and the termination of rainfall is similar to that of Type-1 flood events, while the secondary runoff peak occurs 7 to 26 hours after the primary one. This time lag varies for each event (Table 2). The runoff ratio of Type-2 flood events are more than 10times greater than Type-1 flood events (Fig. 4). For Type-2 flood events, 90% of the total storm runoff is produced by the secondary peak runoff. Type-1 floods and the primary peak runoff of Type-2 floods have similar runoff ratios (Fig. 5). These runoffs are explained as the direct rainfall runoff and shallow groundwater discharge from moist areas near the channel. The conditions under which the secondary peak runoff occurs are expressed by the combination of initial discharge (q0) and rainfall (P1) before the termination of primary peak runoff (Fig. 6); the secondary peak runoff appears when either q0 or P1 is sufficiently large, while it is not detected when both qo and P1 are small. The authors defined the flood-controlling storage (S) as the amount of water storage in a basin directly contributing to storm runoff and attempted to express this value as a function of discharge (q). First, a two-component recession formula for one recession period is established as q(t)=e-0.0250t-1.78+1/(0.0103t+3.67)2 where t is the time (h) after the beginning of recession and q (t) is discharge (mm/h) at t. Then, using the theoretical relationship between q and S for each runoff component, we obtain S(t)=e-0.0250t-1.78+1/(0.0103t+3.67)2 where S(t) is the flood-controlling storage (mm) at t. These two formulae implicitly represent the relationship between q and S (Fig. 7). Using this relationship, conditions under which Type-2 flood events occur are expressed as S0+P1>32mm where S0 is the initial water storage and P1 is rainfall before the termination of primary peak runoff (Fig. 8). There exists, however, an example when the secondary peak is not clearly detected when S0<20mm. The value of S0+P1 is also related to the time lag between two peaks of Type-2 flood events; the time lag TL (h) is expressed as TL=39.5-0.512 (S0+P1) R2=0.610 (Fig. 9). This means that the response of secondary peak runoff is faster when the watershed is relatively wet.
Coral terraces at Huon peninsula, Papua New Guinea, are well-known key areas for the study of late Quaternary sea level fluctuations and tectonic movement. Our new international research group, composed of 14 members from five countries who have different specialties, has succeeded in establishing new sea level curves, tectonic process for uplift, and erosional process for terrace denudation, based on data newly obtained by field work in 1992 and 1993. These results have contributed considerably to the understanding of Quaternary history and environmental changes. This paper describes the purpose, study method, organization, new results and presentation of the results for fundamental information on the planning of future, successful international and interdisciplinary joint research.
The great Hanshin-Awaji earthquake disaster prompted the reconsideration of natural hazard prevention programs in Japan. This paper discusses the role of geography in natural hazard prevention programs for the twenty-first century. Natural hazard prevention programs have been decided upon by the government without sufficient social discussion. However, as there is a variety of natural hazards and they are very complicated, it is impossible to effectively control all of them. As we enter the twenty-first century, the decline in the Japanese population brings with it a reduction of financial resources readily available for such programs. It is therefore important to elicit social consensus on an appropriate safety level for disaster prevention. Points of discussion for the reconstruction of hazard prevention programs are as follows: (1) establishing the principle of self-decision for hazard reduction; (2) importance of prevention programs appropriate to the regional characteristics of natural hazards; (3) balance between prevention and reduction of hazards; (4) discussion of priorities to be included in hazard prevention programs based on the analyses for the probability of each hazard; (5) sustainability of the hazard prevention program itself; and (6) required natural hazard education based on current advances in science. Geographical studies that should be promoted for the advancement of natural hazard prevention are as follows: (1) mechanism of natural hazards; (2) hazard mapping and its application for a geographic information system; (3) review of hazard prevention and development programs in the twentieth century; (4) comparative and cognitive study on the views of natural hazards in various countries; (5) regional policy for hazard reduction; (6) education for natural hazard prevention; and (7) review of concrete planning for natural hazard reduction.
Space and Society, a commission of the Association of Japanese Geographers, published in 1996 a reader containing the following seven seminal papers which had been published in the period from the late 1960s to early 1980s and had provided human geography with a new perspective on the conceptualization of space in society: A. Buttimer (1969), “Social space in an interdisciplinary perspective”; D. Harvey (1976), “Labor, capital and class struggle around the built environment in advanced capitalist societies”; D. Ley (1977), “Social geography and the taken-for-granted world”; E. Soja, “Sociospatial dialectic”; D. Gregory (1981), “Human agency and human geography”; D. Cosgrove (1984), “Towards a radical cultural geography”; and N. Thrift (1983), “On the determination of social action in space and time”. In order to facilitate the understanding of the spatial conceptions contained in these seminal papers, which are significant for the future development of alternative (or critical) geography in Japan, this paper extracts some quotes from the above papers and lists them under the following basic tenets of spatial conceptions: 1. Space is the objective, material existence which supports society and human subjects. 2. Society and Humans are not passive in space. They positively subsume it to create new (humanized) space and to reproduce themselves. 3. Socioeconomic relations or values produce space, and the spatial entity thus produced supports the stabilization and reproduction of the relations and values for a longer period. 4. Space once produced ossifies itself into structure (the built environment), which reacts to control, differentiate, and transform social relations. 5. Every subject must deploy an expanse of bounded space and a relative position for its action. The form of their deployment is specific to the social relations. 6. A social structure on an upper tier of space produces territories on a lower tier, each of which forms a separate entity in the structure. This stratified configuration of space displaces social relations spatially, and alters the original relations in return. 7. Spatial relations displacing conflict on a particular spatial scale can reify or modify the social relations on different scales. 8. Space and subject fuse together spontaneously to constitute a unique “place, ” the focal point where subjects converge into a social structure, mediated with all of its embeddedness. 9. The subject attempts to strengthen the embeddedness and resists its disruption. This place consciousness may obscure the consciousness of social relations. 10. The distanciation and isolation arising from relative space make the subjects in proximity interact more intensely, giving rise to a localized social group. 11. The spatial coexistence of heterogeneous elements of a society and their mutual sharing of the same built environment create social conflict. 12. The built environment exerts a common coercive power over people to stabilize the modes of production and living over the long term. 13. A social group is fragmented and its fractions formed according to the spatially uneven and fixed components of a spatial configuration and natural landscape. 14. The range of subjective space is smaller than that of the objective thus rational behavior is not guaranteed since one obtains information imperfectly from subjective space. 15. The modes of production and experience create collective absolute spaces, the most pivotal of which is the separation between the places for living and for work. 16. It is essential for a social revolution to involve a revolution in spatial configuration.