4:00 PM - 4:15 PM
[HDS08-08] Topographic rearch of flood characteristics using historical material in the area around Gyoda City, Saitama Prefecture
Keywords:flood, topography, historical material, Tone River, Gyoda City
The area around Gyoda City in Saitama Prefecture is close to the center of subsidence in the central Kanto Plain due to tectonic movement, and the topographical conditions make it prone to flooding because the flows of the Tone River and the Arakawa River are stagnant in the central part of the plain. As a result, the area has been prone to floods in the past, and the Cyujo embankment that functioned as a retarding basin from the Edo period to the Meiji period.
In this study, the 1910 Tone River Flood in the Meiji period (Meiji Flood) and the 1742 Flood in the Edo Period (Edo Kanpo Flood), which caused enormous damage due to the levee breaches of the Tone and Arakawa Rivers, were reconstructed. Geospatial information was obtained from place names and time information of damages collected from historical materials, and superimposed analysis was performed on the topography to examine the relationship between the inundation status and the topography. In addition, the authers aimed to clarify the characteristics of the flood inundation around the Gyoda City by comparing the damage and inundation conditions of the Meiji Flood and the Edo Kanpo Flood.
As a result, the following facts were clarified. In the Meiji Flood, the Tone River flooded and split into two large streams. One is the western route, which flows down the Hoshikawa River, Moto-Aarakawa River, and Ayasegawa Rivers, and the other is the eastern route, which flows down the Aainokawa River, Furu-Tonegawa River, and Shonai-Furukawa rivers. Comparing the floodwater arrival time in the southern part of the Nakagawa lowland, the route on the western side was faster, as the slope of the riverbed in western side is steeper. Natural levees and sand dunes obstruct the flow of flood water and reduce flood damage. Even if they were far away from the rupture point, houses were washed away in the narrow back marshes between the plateaus. The plateaus of the middle-stream lowlands of the Tone River were buried in the alluvium due to tectonic movements, so the height relative to the lowlands was small, and flood damage occurred even on the plateaus.
A comparison of the Edo Kanbo Flood and the Meiji Flood showed no difference in the behavior of the main floodwaters. The Cyujo Embankment, which protected the downstream area by flooding the Tone River, has now been abolished. Therefore, if a flood like the Meiji flood occurs in the future, there is a risk that the flood will spread downstream in a short period of time.
In this study, the 1910 Tone River Flood in the Meiji period (Meiji Flood) and the 1742 Flood in the Edo Period (Edo Kanpo Flood), which caused enormous damage due to the levee breaches of the Tone and Arakawa Rivers, were reconstructed. Geospatial information was obtained from place names and time information of damages collected from historical materials, and superimposed analysis was performed on the topography to examine the relationship between the inundation status and the topography. In addition, the authers aimed to clarify the characteristics of the flood inundation around the Gyoda City by comparing the damage and inundation conditions of the Meiji Flood and the Edo Kanpo Flood.
As a result, the following facts were clarified. In the Meiji Flood, the Tone River flooded and split into two large streams. One is the western route, which flows down the Hoshikawa River, Moto-Aarakawa River, and Ayasegawa Rivers, and the other is the eastern route, which flows down the Aainokawa River, Furu-Tonegawa River, and Shonai-Furukawa rivers. Comparing the floodwater arrival time in the southern part of the Nakagawa lowland, the route on the western side was faster, as the slope of the riverbed in western side is steeper. Natural levees and sand dunes obstruct the flow of flood water and reduce flood damage. Even if they were far away from the rupture point, houses were washed away in the narrow back marshes between the plateaus. The plateaus of the middle-stream lowlands of the Tone River were buried in the alluvium due to tectonic movements, so the height relative to the lowlands was small, and flood damage occurred even on the plateaus.
A comparison of the Edo Kanbo Flood and the Meiji Flood showed no difference in the behavior of the main floodwaters. The Cyujo Embankment, which protected the downstream area by flooding the Tone River, has now been abolished. Therefore, if a flood like the Meiji flood occurs in the future, there is a risk that the flood will spread downstream in a short period of time.