To clarify factors governing the impulsive load of collapsed soil acting on structures, laboratory experiments were conducted. The experiments were conducted using a cascading sediment experimental flume. The head of flume was fitted with a vertical steel gate for suddenly release a static sediment mass and initiating an avalanche. All cascading sediment consisted of dry sand and gravel. The impulsive load measure device was installed on the flume. We used two kinds of impulsive load measurement devices : a compression load cell type (displacement under load 7.0 X 10-4 mm/ kN) and a spring type (displacement under load 1.0 X 102 mm/kN). Results of experiments showed that measured impulsive load of cascading sediment can be calculated based on changes in the momentum of the cascading sediment in the vertical direction on the acting surface of the device. We also found that measured load by the spring device is equal to that by the load cell device. This means that the displacement of structures give small impacts on the impulsive load of cascading sediment acting on structures.
We estimated the damaged area of riparian forest and the volume of timber lost from or trapped by the riparian forest in the Appetsu River basin, caused by Typhoon 0310 (Etau). This typhoon caused heavy damage in the Hidaka and Tokachi districts of Hokkaido, Japan. Using photo-retouching software, the damage was classified into three categories (lost, fallen, or intact) according to the color and tone of aerial photographs taken just after the flood. About 33 hectare of the riparian forest were lost, and 67 hectare were fallen. The area of lost forest was the greatest along the main stream (upper-middle reach), while less area was lost on each branch. The area of fallen forest was the greatest on the main stream (middle-lower reach). The estimated 11, 000 m3 of fallen timber were trapped by the riparian forest, which exceeded the 8, 000 m3 of wood lost from the riparian forest. Therefore, in this flood, the riparian forest served as a sink for woody debris rather than a source. Most of the lost forest was located around the center of the inundated area, where the power of the water was likely greatest during the flood.
Contrary to expectation, there has not been much progress to date as far as the construction of countermeasures against sediment-related disasters is concerned. In order to advance these construction projects efficiently, it is important to examine the risk-ranking of dangerous spots for sediment-related disasters in order to determine construction priorities. However, there is currently no unified analytical technique to address this issue and this poses a problem to each selfgoverning body. As a method to solve this problem, the risk-ranking determination method for public works using Data Envelopment Analysis (DEA) is proposed. However, since DEA is an analytical method that searches for the relative efficiency of data, one of its drawbacks is the long computational time. In order to perform an investigation involving a large number of data, such as in the analysis of dangerous spots for sediment-related disasters, it is therefore necessary to examine the new calculation model for the purpose of increasing its processing efficiency. In this study, a distributed computational model that enabled the processing of large amount of data by DEA was examined. Moreover, this computational model was applied to the determination of ranking of dangerous spots within Yamaguchi Prefecture regarding sediment-related disasters.
The processes of outbursts of a landslide dam, consisting of sand, and a mixture of sand and bentonite were observed through flume experiments. The discharge rate of the outflow overflowing the top of the dam was measured. As a result, it was observed that there were a number of peaks appearing in the flow discharge hydrograph during the outbursts. The maximum discharge rate was observed at its first peak when the vertical erosion rate was most intensive. The value was then in a range from a few to a few tens times the inflow rate. These peak flow discharge rates were evaluated through the equation of Tabata et al. The second and the following peaks were caused by horizontal erosion in the eroded channel. Further, we also found that the temporal variations of the outbursts on the landslide dam were affected greatly by the adhesive qualities of the landslide dam earth.
Debris flow had been called in the various ways in Japanese, such as “Yama-tsunami”, “Yama-shio”, “Oshidashi”, or “Teppou-mizu”. This paper shows how the debris flow has been called academically, administratively, linguistically, or in journalistic ways. There are differences in transitions in the expressions of debris flow between academic, administrative, linguistic or journalistic ways. For example, “Doseki-ryu” was firstly used in the textbook of the Sabo engineering in 1916, while newspapers generally began to use “Doseki-ryu” in mid-1970 s. Until mid-1970 s, they used “Yama-tsunami” or “Teppou-mizu”. These transitions were executed with regard to the historical and social backgrounds. Here I also examined the origin of “Doseki-ryu” using literatures of France and Austria, because these countries had already done many studies about debris flow in 19th century. Based on these investigations, it can be thought that “Doseki-ryu” was composed by combining “doseki (stones and soils)” and “ryu (flow)”. While, other terms, like “Yama -tsunami”, are metaphoric expressions, “Doseki-ryu” can be considered to be very reasonable technical term, in terms of situation of occurrence, flow materials, behaviors of flow and linguistics.