河口低平農地における高潮氾濫モデルに関する研究

The development of geographic information analysis has increased user's needs for flood simulation. However, flood simulation requiresa detailed representation of the flooding area or adaptation to the design of facilities. It is necessary to evaluate the influence of a rise in sea level and stronger typhoons, which are thought to be caused by climate change, because these will cause more storm surge disasters in coastal farmland. However, the present flood analysis models cannot properly evaluate the functions of irrigation and drainage facilities in case of a flood disaster, because these models cannot easily include simulations of agricultural fields and facilities. This report proposesa numerical simulation model by the finite element method for estimating the areas inundated by storm surges in coastal farmland. This report shows, by analyzing three storm surge disasters, that disasters affect many coastal farmlands in various areas. An increase in abnormal storm surges due to increasingly strong typhoons caused by climate change in the Ariake Sea was verified by simulations using two model typhoons. The simulation results showed that this increase is correlated to the rise in sea level reported by the IPCC in AR4. A finite element model for flood analysis of coastal farmland is proposed. This model combines two different models: one simulates flood flow in two dimensions, and the other treats channel flow in one dimension. This combined model includes small rivers and channels for the flood analysis of coastal farmland. The flood process of the storm surge caused by typhoon 9918 was taken as an example for the simulation. In simulating the storm surge disaster in the Yatsushiro Sea caused by typhoon 18 in 1999, the process by which flooding from the river dike increased the flood damage was qualitatively represented. On the other hand, a comparison of the simulated inundation area and the damaged area estimated by analyzing satellite images showed that the simulation over-estimated the inundated area. A moving element algorithm that moved nodes on the shoreline was proposed to develop amoving boundary technique, which can maintain the continuousness of flood flow. The operation of the moving element algorithm was confirmed by the slope of the same angle divided into arbitrary triangle element meshes. In a verification that used the slope of compound angle, a change of bottom was caused only when the shoreline passed the points where the angle of slope changed by the proposed algorithm, whereas the bottoms always change by the Lagrange method. A finite element model using the MINI element was developed and the reproducibility of the model was verified by simulating tidal currents in the Ariake Sea. It was confirmed that the model could represent the tide level at the three observation stations and the harmonic constant of tidal current of the four main components of tide at 12 observation points in the Ariake Sea. A model of flooding caused by storm surges in coastal farmland was proposed and verified by simulation of a hydraulic model test of flooding from channels. To simulate the hydraulic jump that occurred in the channel in the hydraulic model test, a one-dimensional analysis model that applied the CIP method to the finite element model using a quasi-bubble function element was developed. The verification results for the dam break flow showed that the adaptation of the CIP method made the simulation stable without inducing artificial viscosity. On the other hand, it was confirmed that the proposed flood model was able to represent the speed of flood front and the shape of flooding areas. The proposed flood analysis model attains high spatial resolution and high reproducibility not only for estimating flood areas, but also for evaluating the scale of facilities that are required for reducing damage.