Sixty six years ago, Miyata River in Hitachi City was flooded by Kathleen typhoon in September, 1947, and the serious harm was caused by centering on the Hitachi mine company houses. In this paper, the relation between runoff characteristics in small mountainous basin and the occurrence of sediment disaster is discussed dynamically, referring the previous study. The runoff analysis results show the soil layer of mountain slope mostly attained to saturation by the rain which got down intermittently about one week, and the danger of debris flow occurrence was high enough. But the presumed maximum flow discharge by rainfall and debris-flow can't cause the river flood. Then it thinks about the obstruction of the river cross section area due to sediment and washing things such as driftwood and slag at the actual flooding point. There is a possibility to generate the flood in the above mentioned maximum flow discharge, and it is assumed enough from victim's testimony and documentary photography.

In general, the effect of forest conservation projects does not appear in the short term. Koyama and Okumura analyzed the changes in flow regime with the progress of conservation works in a small mountainous basin in Tottori Prefecture by three tank models: the 1981, 1983 and 2000 models, which reproduced the runoff for the year before the conservation projects were started, the year they were completed, and eighteen years after completion, respectively. In the present study, the long-term trends of the change of runoff characteristics due to forest conservation projects are discussed by focusing on the unit hydrograph method with a multiple regression model in the same basin as in Koyama and Okumura's study. Three unit hydrographs are made that match Koyama and Okumura's study and used to analyze the same rainfall data observed in 2001. Base on the analytical results, both the flood and scarce water control functions were temporarily lowered during the conservation project. But eighteen years after their completion, both have improved. These results greatly agree with Koyama and Okumura's results.

In 1992, a new program was introduced to the profit-sharing forest system of the national forest of Japan. Based on an investigation of the current operations of one national forest, we described three aspects of the new program: ways in which private enterprises can take the initiative in using the contract forest; ways in which numerous organizations and individuals participate in, and obtain various benefits from, forest management activities; and why participants, including private enterprises, do not consider money an important result of the agreement. In addition, we identified three problems of the new program. First, public relations have not yet been sufficiently developed, although almost all prefectural governments have begun to promote the participation of private enterprises in private forest management. Second, the new program involves natural forests, which differs markedly from previous programs with planted coniferous forests; however, the actual agreement procedure remains unchanged, which has led to problems associated with applying the same procedure to natural forests. Third, under the new program, organizations or people other than the contracted enterprises can use the contracted forest at any time. Thus, the national forest must be managed in a way to accommodate this type of utilization.

To clarify the current situation and identify the problems in cooperation between national and private forest organizations, including the introduction of intensive forest practices, and the future direction of the cooperative system, questionnaires were administered at 66 District Forest Offices that govern the designated area of cooperation between national and private forest management systems. The collection rate of the questionnaire was 97.0%. Intensive forest practices have not progressed almost at all. Problems in the current system for cooperation in forest practices can be divided into the following four areas: communication, forest road networks, cooperative marketing, and ordering policies. Cooperation between national and private forest holders in the construction of forest road networks can clearly provide benefits to both parties. Cooperative marketing would also be beneficial, but new initiatives to develop markets for logs from thinning have just started. Communication is obviously important for the development of forest road networks and cooperative marketing. Differences in ordering policies between national and private forest holders represent a severe and intractable problem. Even if communication among members is perfect, it is difficult to operate intensive forest practices under the present ordering policies, which differ completely between national and private forest managers. There are very high expectations that a joint ordering system for national and private forests will be introduced, but the immediate introduction of a new system appears to be difficult. To institute a new joint ordering system, local problems also need to be reported to the central office of the Forestry Agency.