This paper mainly concerns the following matters since 1980, with reference to the Journal and the documents of the JSECE, etc. 1) The main amendment and changes of articles and regulations, before transferring to the incorporated association and thereafter 2) Sections and committees to execute society affairs and their contents 3) Size and composition of membership, during its transition 4) The number and themes of papers and technical reports in the Journal of the JSECE, and the themes of research presentations. The number of presentations and presenters organizational belongings, their transition. Trends in symposium, workshop, investigation and research activities. 5) Publishing, urgent disaster investigations domestically or overseas, contract research activities, international academic exchange, etc.
Distributed hydrological models, which calculate topographically-driven rainwater movement within a catchment, have been combined with mechanical analyses of slope stability, producing spatial and temporal variations in safety factors against slope failures. These methods have been used as practical tools in real-time warning systems for shallow landslide and debris flow hazards. This study examined accuracies and limitations of one of these methods by conducting intensive hydrological observations within a head-water catchment（Nishi'otafuku-Yama catchment）located in the Rokko mountain range of southern Hyogo Prefecture. Observations of a discharge hydrograph, soil mantle groundwater levels, and bedrock groundwater levels indicated that a large amount of rainwater infiltrates into the bedrock and recharges bedrock aquifers. In downstream regions along a main hollow of the catchment, the bedrock groundwater exfiltrates into the soil mantle forming perennial and semi-perennial soil mantle groundwater and a large amount of base flow discharge. Thus, the recharging and discharging processes of the bedrock groundwater dominantly controlled hydrological phenomena of the catchment. The distributed model, which does not consider the recharging and discharging processes of the bedrock groundwater, produced inaccurate estimations of the observed discharge hydrograph and soil mantle groundwater levels. Nevertheless, the model produced reasonable decreases in the safety factor at some past landside locations where topographically-driven rainwater convergences were computed. However, the result did not necessarily guarantee accurate predictions of these landslides, since the model produced unsatisfying predictions of the soil mantle groundwater levels and timings and locations of landslide initiation were greatly controlled by soil internal frictions and cohesions. Thus, unless the hydrological model is validated by observed groundwater levels, computed safety factors should be treated as indices representing relative landslide vulnerabilities. For some past landslides located in downstream regions along the main hollow of the catchment, the model failed to detect decreases in the safety factor. Rainwater convergences by the bedrock groundwater exfiltration were suggested to be a controlling factor for the occurrences of these landslides, which clearly suggested limitations of the distributed hydrological model that calculates topographically-driven rainwater movement.
In Akita Prefecture, to promote the demand expansion of the Japanese cedar produced in Akita Prefecture and to activate the local areas by centering timber industry, various civil engineering structures used timber have been proposed and developed, and have been actually constructed. Wooden check dam is one of these, there are two kinds of wooden check dams called “Akita standard”. One of which is “all wood type” dam composed only wood members and lag screws, and usage rate of timber is up to 90%. Another is “hybrid dam” packed the thinned wood and gravels in the steel flexible frame, and usage rate of timber is about 80%. In this study, we presented the details of all wood type wooden check dam and hybrid type. In all wood type wooden check dam, we reported results of the strength test of joint used lag screw and failure test of real-size dam specimen, which were conducted before construction, and monitoring study at construction site. In addition, we accessed the strength property, usage rate and cost performance of each Akita standard dam by comparing the crib dam which ever have spread in the whole country. In the failure test, it was shown that the specimen have safety rate 10 for the design load. With regard to monitoring study, from actual water level inside dams, it found that phreatic line was lower than design position. In comparison with the crib dam, although for used amount of timber Akita standard dam was very effective, for cost there was no difference.
Snowmelt-type mudflow is often observed when a pyroclastic flow, surge, blast or a hot-debris avalanche moves over a snow-covered slope. We constructed the experimental equipment to simulate snowmelt due to high-temperature rock fragments moving over a snow-covered channel. The experiments were carried out for nine different cases, changing the parameters of temperature, rock particle diameter, and snow density. On comparing the hydrographs of these nine cases, we found that the following conditions lead to rapid snowmelt and large peak flow : (1) the temperature of the pyroclastic material is sufficiently high ; (2) the snow density is remarkably high, as in the case of solid ice ; and (3) snow is saturated with liquid water, as in the case of slush. The results indicate that the volume of the snowmelt-type mudflow particularly depends on the snow density and the temperature of the pyroclastic materials.
This paper presents an experimental approach on the load of debris flow with woody debris for open type steel frame check dam structure. The hydraulic model experiments are carried out with various parameters, i.e., driftwoods containment ratio of debris and slit interval of the structure. When the debris contains woody debris, the driftwoods are gathered the front of debris, and slit interval of the structure is blocked by the stuffed woods. And the impact load acting on the column caused by debris flow with woody debris is smaller than the one caused by debris of gravels. The accumulation of driftwoods acts like a shock absorber for the columns. The accumulation of driftwoods induces the lopsidedness of static load for the columns, because the accumulation is formed unevenly.
Improved flood prediction in mountainous catchments requires knowledge of the hydraulic characteristics of mountain streams. The flow and flow resistance of steep mountain stream channels are not well understood because of a lack of measured data. Therefore, we simultaneously measured discharge, using a v-notch weir and the water depth 50 m downstream of the weir in a small natural channel, in the Aono Research Forest of the Arboricultural Research Institute of the University of Tokyo Forests on the Izu Peninsula, Japan. The Manning's roughness coefficient decreased almost one order of magnitude from 1.88 to 0.14 as the water depth increased. Moreover, the coefficient was large and decreased dramatically with increasing water depth as the water surface was below the top of most of the gravel in the stream bed(maximum water depth<0.2 m). Once the water surface was above most of the gravel (>0.2 m), the coefficient then changed little with increasing water depth. The minimum Manning's roughness coefficient observed was similar to previously reported values of 0.09 to 0.23 in steep step-pool channels under high flow conditions. These findings indicate that the roughness characteristics of steep mountain streams can exceed a Manning's roughness coefficient of 0.1.