Recent demand of water other than that for agricultural use has been increased because of Japan's industrialization and urbanization. Water dispute has often occurred between agricultural and urban water users, because both have obtained fresh water supply from streams. Thus the increasing demand for urban water has led to the development of new water resources mainly by the construction of multi-purpose dams. Moreover, urban water users have acquired their new water rights not only by controlling the stream discharge but also by the transfer of water rights from agricultural users. In this paper, the author followed the recent changes of water uses in the lower reaches of the Takahashi River.
The agricultural water users in the lower reaches of the Takahashi River have solved the deficiency of water supply during the dry period through the organization of the Tozai Irrigation Association which had integrated small-size users after the river improvements carried out around the 1910's, and through the constructions of Osakabe dam, Godo barrage and Lake Kojima which had expanded the area included within the same water management system after 1950.
It is since the 1960's that large plants have started their operation at the Mizushima district in Kurashiki city and that the new demand of industrial water has occurred in the area of the lower reaches of the Takahashi River. This demand has been also satisfied with the public water-supply system for industry using the new water resources from Komoto dam constructed by the authority of Okayama Prefecture, and from Shinariwagaw a dam by Chugoku electric power company. There is no conflict concerning the position of intakes between those for industrial water-supply and those for irrigation and waterworks in the lower reaches, because the former are located lower than the latter along the river course.
The demand for residential water began to increase somewhat later than that for industrial water. In this case, water rights for residential water have been obtained b Y the partial transfer of water rights for irrigation, since there was no surplus of water for new water rights in the Takahashi River at that time. The volume of water rights transferred from the Tozai Irrigation Association to the residential water-supply was about 20, 000 m3/day.
The following factors may be considered as the general conditions of water right transfers from irrigation to urban use; (1) the deficiency of water supply for irrigation has been solved by the improvement or establishment of irrigation facilities which have changed the form of water management system in the region, (2) the considerable area of agricultural land has been transferred into the urban uses, (3) the water use system for irrigation sustained by farmers in the region has deteriorated due to the outflow of the labor force from farming. In addition to the factors mentioned above, the manager of the Tozai Irrigation Association is the Mayer of Kurashiki city who is also the manager of the residential water-supply system in the district belonging to the Tozai Irrigation Association. Thus the transfers of water rights had been carried out quite easily. However, drastic change of water use system will occurr at the time when there will be no rests of water rights during non-irrigation season in the Takahashi River, provided that the transfers of water rights will be carried out in this manner.

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The Takahara River and its tributaries dissect rugged mountains in central Honshu Island, forming steep mountain slopes along the rivers. Small precipitious streams deeply dissecting the mountain slopes usually attain gradients more than twenty degree. Debrisflows have occasionaly occurred from these streams, bringing heavy damages to inhabitants.
The authors selected 271 streams from those in the study area and investigated the number of debris-flows occurred from each stream by the method of interviews to the inhabitants. It is revealed that the debris-flows occurred sixty times from the selectedd streams during the period from 1913 to 1979. The estimated average probability value of debris-flow occurrence from a stream, is accordingly calculated to be 3.3 × 10^-3/year. The estimated return period of debris-flow occurrence is, therefore, determined to be 3.0 × 10² year. The distribution of stream numbers classified by the number of debris-flow occur rence are conformed to the poisson distribution with the same probability, except four large streams (Table 2) . Accordingly, it is considered that the occurrence of debrisflow has a character of a randam phenomena as a whole.
The authors also measured the volumes of fifteen debris-flow deposits accumulated during the last seventy years, and found that the volume of each debris-flow deposit is explained as a function of the catchment area of each stream (eq. 2; Fig. 6). Six steps of fluvial terraces are distributed along the Takahara River and its tributaries; namely, Hongo, Miyahara, Nakagoe, Tono, Sakamaki and Miza terraces, from higher to lower.
Hongo terrace was formed by the deposition of volcanic mudflows mainly transported by the fluvial process. The volcanic mudflow deposit covers the underlying Sukusaka terrace deposit with slight unconformity (Koike, 1978) . Sukusaka terrace is a dissected alluvial fan formed along the Jinzu River, the main river of the Takahara, and correlated with fluvial terraces distributed scatteredly around the margin of Northern Japan Alps (Fukai, 1957; Machida, 1979). As the age of these terraces is considered to be ca. 50, 000_??_60, 000y. B. P., the age of Hongo terrace is estimated to be slightly younger than 50, 000years.
Miyahara terrace was mainly formed by the erosion of Hongo terrace deposit. An alluvial cone deposit intercalating the volcanic ash bed(DKP, 45, 000_??_47, 000y. B. P.) covers the terrace surface. Therefore, the age of Miyahara terrace is estimated to be ca. 47, 000y. B. P. Etchu Akatsuchi covers both Hongo and Miyahara terraces (Fig. 4).
Nakagoe terrace was formed by fluvio-volcanic mudflow deposit, derived from Kachigane mudflow. The age of the terrace was estimated to be 11, 000y. B. P., from the ¹⁴C age of wood intercalated in Kachigane mudflow (Koike, 1978). This terrace is not covered by Etchu Akatsuchi, but by brown forest soil with clear B-horizon.
Tono terrace was formed slightly eroding Nakagoe terrace deposit. This terrace is formed immediately after the formation of Nakagoe terrace. Sakamaki terrace is a strath terrace formed by usual fluvial process. This terrace is correlated with the buried terrace developed along the Ashiaraidani. The age of terrace deposit was measured to be ca. 5, 000y. B. P. with 14C-dating method by Fujii et al. (1974).
Miza terrace is another strath terrace. The terrace deposit unconformably covers Nakao pyroclastic flow deposit, the age of which is reported to be 2, 500y. B. P. by Fujii et al. (1974). The age of this terrace is, therefore, estimated to be 2, 300y. B. P. (Table 1).

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Alluvial fans in Tohoku District are classified into four types by cluster analysis based on 15 variables indicating their features and structures; namely, A-type (undissected largescale fans with thick deposits), B-type (dissected middle to small-scale fans with thick deposits), C-type (dissected fans with thin deposits), and D-type (undissected small-scale fans). In general, alluvial fans in Tohoku District are primarily classified by the thickness of alluvial fan deposits, and secondarily by the areal expansion of alluvial fan and the degree of dissection. Dissected alluvial fans with thick deposits are less distributed in the district. A lot of dissected alluvial fans with thin deposits are developed along the eastern foot of the Ou Range, while there are plenty of alluvial fans with thick deposits and undissected small-scale alluvial fans on the western foot of the range. These phenomena are expected to be explained based on the difference of the thickness of alluvial fan deposits.

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