Distribution of the “genetically pure” wild populations of the Japanese chary Salvelinus leucomaenis which might not be hybridized with stocked hatchery-reared charr in the Yunishi Stream, a headwater of the Tone River, in central Honshu Island was estimated by “inquiring survey” during January-March period in 1996. Years and locations which hatchery-reared charr were stocked and locations of the potential upstream movement barriers (waterfalls and dams) for stocked charr were obtained at the local fishery cooperatives. For the dams, years of the construction were also obtained at the branch office of Ministry of Construction, Department of Public Works and Department of Forestry of the prefectural government. In the present study, the chary inhabiting upper reaches of the waterfalls and dams which had been constructed before the chary stocking program commenced were regarded as the genetically pure populations. Genetically pure populations of the chary were estimated to inhabit the upper reaches of fish barriers in some tributaries. Most of the barriers were dams for erosion control and some were waterfalls. Lengths of each stream reach where the genetically pure populations inhabited was exceedingly short and most of the reaches were divided into shorter length by dams without fish way. In order to conserve these local and genetically pure chary populations, fish ways should not be installed with the dams which may prevent the stocked fish from upstream movements and they should be installed with the dams constructed within the reaches inhabiting the genetically pure populations.
This treatise is a report for the recorded original erosion-control dams, which are called the Sunadome in Mt. Kinugasa or Mt. kannonzi in Shiga Prefecture (Ohomi district). They are considerd as the most old ones in existing Sunadome in Japan. We state the present condition about them, then the point of view of government to the control to debris flow to the towns around the Kannonzi castle.
Heavy rain attacked Fukushima Prefecture during August 26-31, 1998. Consequently, very severe disasters generated. Then, the investigation was made to get the site status and by inquiring of the inhabitants about generation time of the disaster, their behavior, and investigating geologically. The following finding and the lesson were obtained by these investigations. 1) To get the proper standard rainfall for warning and evacuation, we have to set rainfall gauge more densely toward east-west direction. 2) It has been understood to be effective to use a single rainfall index of accumulated rainfall or working rainfall, decrease to half in 24 hours over. And many collapses occurred when working rainfall (decrease to half in 72 hours) is over 370mm. 3) There was differences of about two hours in the generation time of disasters between the collapse sites which are located only 200m distance. It was presumed that this would be caused by the difference of the catchment area, and depth of permeable layer.
There was a possibility that series of riverbed aggradation and degradation occurred at some breaking points of embankments of the Hime River in the 1995's disaster. But such kind of riverbed fluctuation during the flood we could not observe only with the field survey before and after the flood. Because of this, a new measurement method has been needed to measure the stream traverse for such kind of riverbed fluctuation. The degradation sensor was newly developed by Public Works Research Institute, Ministry of Construction, and installed Yamamoto observation point at the Hime river. The sensor succeed in the measuring the of riverbed degradation at the first half of flood on September 15, 1999. And surveyed riverbed level after the flood was as almost same level with that of before flood. So it become clear that series of riverbed aggradation and degradation occurred at this point. We simulated the measured riverbed degradation by using an one-dimensional riverbed fluctuate calculation. It shows that the sensor is useful to measure the riverbed degradation during flood.
Various phenomena such as inundation, slope failure and debris flow are occurred compositely by a localized torrential downpour. Since the situation differs in each area's factors and how disaster prevention facilities are maintained, each area needs individual warning and evacuation standard and system. Detail survey with the inhabitants soon after every disaster is useful for preparing the individual standard and system. The followings are proposals based on the survey data. Everyone watching System -E.W.S- : areas linked system against each local disaster. Disaster Integrated Watching Rainfall -D.I.W.R- : precipitation for judging the phenomena under the localized torrential downpour whether it is dangerous or not. Country Watching Map -C.W.M- : map to know the local disaster, which include D. I. W. R and necessary information for evacuation. I hope these proposals are well applied and work effectively.
Flush flood struck a party of boy's football team and killed one person. It occurred in the Yubiso River, Minakami town, Gunma Prefecture, at about 15:00, August 6, 2000. There was no rainfall around them. The authors made field surveys and analysis on rainfall data acquired by radar to clarify the reason for its occurrence. Conclusions are as follows. 1) The depth, the velocity and the peak flow rate of the flush flood are estimated to be 1-1.1m, 2.0-4.7m/s, and 18-51m3/s, respectively. 2) There was a rainfall of the maximum intensity of 20mm/hr at a part of the watersheds. 3) The result of the flood simulation shows that rainfall onto the partial watersheds can trigger the flush flood. 4) A deficiency of the calculated peak flow rate to the estimated one implies some contribution of snow melt to the flush flood.