This paper presents a prediction method on the slope failure probability at mountainous area near the source of river by using both the neural network and the similarity analysis. The causative factor, i.e., geological data and remote sensing data are categorized by using similarity analysis to loosen the nonlinearity of prediction function around the boundary between different categories. The slope failure potential is computed as the probability of failure occurrence among the data which have a certain similarity each other. Finally, the relationship between the failure probability and those data in a category is fitted by the neural network system which is associated with geological basic data, remote sensing data and precipitation data. Applicability of the proposed method is discussed by using real data obtained at Shigenobu river basin.

View full abstract

In this study, a distributed runoff model based on the surface runoff prediction model using the numerical solution of Richard's equation, the surface runoff model and saturated flow using the kinematic-wave method, and the unsteady flow model using the dynamic-wave method was proposed. This model allows calculations to be made for different infiltration characteristics in the study basin.
The digital elevation model consisted of nonstructural grids, and the hydrographic basin was divided into slope divisions and channels in this runoff model.
The calculation to obtain the runoff hydrograph was verified by actual hydrographs obtained by hydraulic monitoring at the newly tephra-mantled basin in Miyakejima volcano, which erupted in July 2000 and deposited thick fine-grained tephra. All the parameters of the soil properties of the deposited volcanic ash were obtained by laboratory and field tests.
The verification shows that the calculation results by this distributed runoff model show good accordance with the actual hydrograph.

View full abstract

In Japan, a lot of hillslope collapses triggered by heavy rainstorm almost every year. In spite of continuous effort to elucidate the mechanism of landslide occurrence, sufficient answer explaining why the particular position of the hillslope collapses have not been obtained. It has been pointed out that there is a close relationship between the landslide and underground water paths according to observations around the collapse site ; i.e. outlet of soil pipes on the scarp, clouding, stopping or spouting of spring water just before or after the landslides. However, detail of these relationships has not been clearly understood yet, partly due to lack of an effective method to detect the water path within the slope. Recently, a new method to detect the underground water path positions measuring sound of ground water flow by a sound sensor “hydrostat” was developed.
In this study, water path position is detected by this new method. And estimated water position is compared with the collapse position in natural slopes and road cut slope. As the result, the hydrosonic in collapse position is higher than non collapse position. This result indicates that collapses is triggered at the position where the ground water gathers. In this investigation, there were the slopes that have the high hydrosonic position. Change of these slopes after heavy rainstorm ware monitored. As the result, the high hydrosonic position in slopes was collapsed, because of heavy rainstorms by the typhoon. These results clarified bellow. In the slope, there is the position which ground water concentrates on a daily basis, and this position was supplied bags of water by the heavy rainstorms. Therefor, the ground water concentrating position was collapsed. It is clear that supply condition of ground water is different in collapse position and another position.

View full abstract

The combined penetrometer-moisture probe (CPMP) developed in our previous study is a useful tool for measuring vertical profiles of soil penetration resistance and water content simultaneously, providing essential information for detecting vulnerable points for shallow landslide on steep landscapes. However, we found that the moisture probe of CPMP is occasionally broken when it hits against hard pebbles in soil profile. Moreover, soil water content measured with CPMP tends to be lower than actual water content probably because of inadequate contact between soil and the moisture probe. In this study, the structure of the moisture probe was improved so that it is hard enough to measure water content in a soil profile containing many pebbles. The improved probe consists of two parallel stainless wires, each 0.55mm in diameter, coiled around acrylic column along grooves on the surface of the column. In order to confirm the cause for the underestimation of water content, we conducted detailed observations of soil surface in contact with the moisture probe during laboratory penetration experiments. As a result, many cracks were found on the soil surface affected by penetrations of the sensor rod, which was detected to be a main reason for the measurement error. Then, we evaluated most appropriate structure of the moisture probe for minimizing the error. Nine probes, which have diameters between 19 and 21mm and coiling widths between 2 and 5mm, were tested by field penetration experiments. Results showed that the moisture probe 20mm in diameter and 3 or 4mm in coiling width was the best for reducing the water content underestimation.

View full abstract

The history of erosion control dams started with a series of dams constructed with stones by dry masonry method, as part of the erosion control dam program under the direct control of the Ministry of Home Affairs during the Meiji Era. Many of those old dams have been destroyed as a result of frequent sediment discharges. However, some of the existing old dams have blended in with local landscaper and have been registered at tangible cultural properties due to their historical significance. Most of those valuable old dams, however, are decayed from repeated outflow of earth and sand, and repairs and/or reinforcement measures must be taken for them immediately. This paper focuses on the Kamatsusawa Erosion Control Dam, which is one of the historic erosion control dams registered as tangible cultural properties, forming a group along the Inari River, Nikko City, Tochigi Prefecture, as an example of efforts to effectively preserve historic erosion control facilities. Appropriate stability collation constants are set on the basis of in-situ tests and laboratory experiments, and it is indicated that aging facilities can be maintained effectively by taking minimum reinforcement and/or repair measures involving stability collations with a multilayered structure weight calculation method for the dam body and multilayered ground banking-sand calculation method applied.

View full abstract

To clarify role of hillslope scale on extension of dangerous area of snow avalanches, we examined relationship between relative height(H)and horizontal ravel distance(L)from initiation area to deposited area of snow avalanches. We analyzed 741 snow avalanches data in literature. We found that angles of elevation from deposited area to top of initiation area were varied from 18 to 40 degrees. When the H is less than 100 m, the angle of elevation of most of snow avalanches is more than 28 degrees. While, the angle of elevation of relatively large snow avalanches(H>500m) is larger than that of small H avalanches. This means that the relative height controls the angle of elevation, suggesting that the hillslope scale is an important factor for estimating dangerous area of snow avalanches.

View full abstract

Grid type dam to catch debris flow consists of vertical bars and horizontal bars. But it is often that it is installed at a slope that debris flow flows and stops. Sediment in such an area may take form of sediment flow. Therefore it is important to check the ability of sediment trap on a gentle slope. And so we prepared vertical members and horizontal members and aimed for estimating their ability by flume experiments and considering about influence by the difference of running sand form and the following flow. As a result of experiments, we ascertained that vertical bars were principal part and horizontal bars were subsidiary part about sediment trap. Because a rate of sediment which were carried by the following flow decrease. On the other hand, we ascertained running sand may take form sediment flow on a gentle slope and coarse sediment may not flow in the front, too. Therefore when installing steel pipe sabo-dam on a gentle slope, it is important to understand position of steel pipes and measures against debris flow in an area more downward than dam.

View full abstract

Arid land is defined by dry-index and precipitation depth (UNEP), and arid land amounts to the 40% of terrestrial parts of the world. Nowadays sediment-related disasters by sediment movement such as debris flow, sediment flow and so-on, occur in and land. For example, intense rainfall events results in sediment flow that causes miserable damages to human lives, houses, agricultural land and infrastructure facilities in Jordan.
From now, intense rainfall will occur more frequently by climate change, and development area will be sprawling by increase of population on the dangerous alluvial fan in arid land of Jordan. Therefore sediment-related disasters will increase in arid land in future. So it needs the development of the and land sabo works that means not only to prevent the sediment-related disasters but also to use the water of surface flow or flowing water. To make the safety in the arid land of the world, I propose the arid land sabo works with due regard to the characteristics of arid land.

View full abstract