There has been a tendency for seismic failures to occur frequently on concave or flat slopes or slope having abrupt local unevenness. This tendency has been considered to be affected greatly by the topographic effects that amplify the acceleration of seismic waves. In order to clarify the quantitative evaluation of the amplitude of seismic acceleration and how the amplitude affects the slope displacements, a three-dimensional non-linear dynamic response analysis based upon the elasto-plastic theory was applied to three model slopes having different topographic features, that is, a convex slope, convex and flat slope, and uneven slope. The results of the analysis are summarized as follows. Amplitude of seismic wave acceleration is affected by slope having abrupt local unevenness. Especially, changes slope curvatures in the surface slope affect on amplification or attenuation of seismic wave acceleration. Residual displacements were not so clear, but it is to be greater by local unevenness.

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This study proposes an analytical approach to evaluate the absorption energy capacity of a damaged concrete filled tubular after being hit by rocks contained in a debris flow. The relationship between bending moment and curvature of the concrete filled tubular is estimated by using the sectional element partition method. In order to account for the damaged effect, the constitutive laws of virgin steel material is modified to include the residual plastic strain effect. This method can estimate relatively well the behaviors of damaged concrete filled tubular, especially maximum load and ultimate deformation related with the sectional breaking.

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The surface runoff prediction model specified for the Hortonian overland flow at the fine-tephra mantled slope is proposed in this study. Based on the numerical solution of the Richard's equation, this model proposes the new surface boundary condition that can describe the temporal change in an infiltration capacity. The calculation to obtain the infiltration excess and the runoff hydrograph, which is routined by the kinematic-wave method, is verified by the actual hydrographs obtained by the hydraulic monitoring at the newly tephra-mantled slope in the Miyakejima volcano, which erupted in July 2000 and deposited thick fine-grained tephra on its slope. All the parameters of the unsaturated soil properties of the deposited volcanic ash are obtained by the laboratory tests of the undisturbed soil sample of the deposited volcanic ash. The verification shows that the result of the calculation by the proposed prediction model shows good accordance with the actual hydrographs though the proposed method has no controlling factor to adjust to the actual hydrograph.

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This paper examines the circumstance of evacuating residents during water induced disaster in the Miyagawa Village, Taki County in Mie Prefecture on September 29 th, 2004, based on field research, interviews and questionnaires conducted among them. Most hamlets in this village are located on terrace or shelving planes developed along the Miyagawa river. Thus, roads along the river provide refuge passages. Unfortunately, these passages had become impossible to be used on the evacuation due to debris and sediment on the road, collapse of the road side, inundation caused by the swelling of the river, inundation affected by both bridge and driftwood, and aggradation in the tributary caused by a lowering in tractive force due to the water level raising. The interviews conducted with residents proved that knowledge about the warning signals of such disasters is important. However, early evacuation is still more important because “high risk” is subject to interpretation based on warning signals considering, that residents who do not know the warning signals, and know these but cannot cope with such emergent situations. Thus, the authors suppose that assistance with evacuation becomes integral. The questionnaire clarified that most residents had evacuated after the occurrence of the disasters and about 40 percent of the residents had evacuated during heavy rainfall. Therefore, many residents evacuated before the critical situation to be vulnerable to human body, and arranged accommodation and refuge prior to the occurrence of such a disaster. In addition, there are residents who want to evacuate, but cannot for a variety of reasons. This particular disaster has provided several lessons regarding what important measures need to be addressed in response to water induced disasters. Some critical components elucidated upon included safe passages and transportation arteries, safe refuge for citizens, a functional information network, and the indispensability of collectivity within a community located in an isolated mountainous area. The role of public office, which provides disaster-information to local areas, is crucially important particularly in rural mountainous villages where many old inhabitants live.

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