Evaluation and Detection of Filled up Inland Water Area by Comparison Between Old and Current Topographic Maps in Osaka, Central Japan

要旨

Many Japanese big cities are developed in the delta areas along big rivers. For the anti-flood measure, meandering river channels have been filled up and changed to straight line around those cities. Around the Seto Inland Sea areas, southwest Japan, many irrigation ponds had been constructed to make up for shortage of agricultural water in summer. But, many ponds have been filled up and shifted to other land use by the process of urbanization. Those filled up inland water area is pointed out that those are weak for liquefaction from the earthquake damages of the past. Thus, the detection of the filled up inland water area is very important to grasp the weak area for the liquefaction damages on earthquake. In this paper, the filled up inland water area in the Osaka Plain is detected with GRASS GIS by comparison between old and current topographic maps. Those detected filled up areas are compared with land use data. As the result of the study, 24 % of the filled up areas is used for public use which will be use as evacuation area at earthquake disaster. Those maps are available for the inspection of earthquake disaster fragility.