As for the estimation of sediment transport accompanied with tsunami, a numerical model considering the exchange sediment volume of the bed-load layer and suspended-sediment layer has been proposed. As for the Takahashi et al. (1999) model, properly setting of the saturation concentration as a parameter is considered one of the key issue, since this parameter may affect the calculation result. In this study, we compared the submarine topography changes calculated by two different models in extensive calculation domain under the condition that the saturation concentration was given as constant value, and showed that the aspect of topographic change greatly differs between both models. And also, we applied relational formula related to the saturation concentration proposed by Sugawara et al., 2014 and considered the spatial and temporal transition of this parameter. As a result, it is considered that the volume of suspended- sediment is estimated to be excessively large overall in this extensive calculation domain with the setting that the saturation concentration is given as constant value of 1%. In addition, it is also shown that it is difficult to determine the appropriate constant value applicable to the extensive calculation domain.
This paper presents a stochastic rainfall event model, which generates a long-term synthetic rainfall series (or distributions), as a component of a flood risk model for the whole Japan. Annual frequency of rainfall event, accumulated volume of rainfall, and spatiotemporal distribution of rainfall are statistically modelled, and then synthetic rainfall events are generated by a Monte Carlo simulation. The model was verified with the observed rain data in terms of frequency of heavy rain and return period of annual maximum 72-hour/24-hour rainfall. The annual maximum rainfalls at 100 year return period that was estimated from the synthetic rainfall events were in good agreement with those estimated from the observed rainfall data. Thus, the synthetic rainfall events were thought to be valid for a flood risk model.
This paper describes a framework to evaluate flood risk in terms of probabilistic distribution of flood damage. The main characteristics of our model are the followings: (1) flood risk in Japan is evaluated as an exceedance probability curve of flood loss and an annual average loss, (2) an integrated rainfall-runoff/flood-inundation model is used to estimate the inundation depth in whole Japan, (3) uncertainties in flood hazard followed by rainfall distribution and levee break and those in flood vulnerability of properties are considered. The model was verified with an application to the plant assets of manufacturing industry. The results showed that the modeled annual average loss of manufacturing industry is in good agreement with the actual 10-year-averaged loss. This model enables quantitative assessment of flood risk and thus it is helpful for flood risk management in government and other industries as well as insurance companies.
Detailed analyses of liquefaction in historical documents help evaluations of possible future occurrences of this hazard. The 1854 Iga-Ueno earthquake caused damage in Yamashiro, which is the old name for what is now the southern part of Kyoto prefecture. Occurrence of localized liquefaction at Fushimi, which is characterized by eruption of mud and sand, and damage to a storehouse, is documented in a journal of the Bizen-Okayama domain. The site where the liquefaction occurred is located in detail by examination of historical documents and maps. The old maps and excavational investigations show that the site had been a buried pond and consists of loose sand layers. The liquefaction possibly occurred under local conditions of high groundwater level and the existence of loose sand layer.
An index calculated by weighted linear summation of normalized data requires rational sets of the weighting factors. We proposed a method to calculate the weighting factors by applying Analytic Hierarchy Process (AHP) to the results of questionnaire to experts, and applied it to a risk index called Gross National Safety for natural disasters (GNS). The questionnaire regarding the alternatives (natural disasters and disaster prevention measures) considered in GNS was addressed to three groups in charge of disaster prevention. Sets of the weighting factors determined by AHP for each group showed slightly different trend, reflecting the regional characteristics of the disasters. The sets of weighting factors for disaster prevention measures were characterized by the criteria regardless of the groups, meaning reasonable selection of the alternatives.