An analysis on the relationship between land subsidence and floods at the Kujukuri Plain in Chiba Prefecture, Japan

Y Ito,T Tokunaga,T Su,M Sawamukai,H Chen

doi:10.5194/piahs-372-163-2015

Abstract

Abstract. Surface environments at the Kujukuri Plain in Chiba Prefecture, Japan, in 1970, 2004, and 2013, were analyzed and compared to discuss the possible impact of land subsidence on the occurrence of floods. The study area has been suffered from land subsidence due to ground deformation from paleo-earthquakes, tectonic activities, and human-induced subsidence by groundwater exploitation. Meteorological data, geomorphological data including DEM obtained from the airborne laser scanning (1-m spatial resolution), leveling data, and the result of our assessment map (Chen et al., 2015) were used in this study. Clear relationship between floods and land subsidence was not recognized, while geomorphological setting, urbanization, and change of precipitation pattern were found to contribute to the floods. The flood prone-area is distributed on the characteristic geomorphological setting such as floodplain and back swamp. It was revealed that the urban area has been expanded on these geomorphological setting in recent years. The frequency of hourly precipitation was also shown to be increased in the past ca. 40 years, and this could induce rapid freshet and overflow of small- and medium-sized rivers and sewerage lines. The distribution of depression areas was increased from 2004 to 2013. This change could be associated with the ground deformation after the Tohoku earthquake (Mw = 9.0) in 2011.

Highlights

Land subsidence causes several problems which include changes in elevation, groundwater salinization in coastal area, structural damage, and increase in the potential for flooding (Galloway et al, 1999; Ng et al, 2015)
Spatial distribution of the Radar/raingauge-Analyzed precipitation data obtained from Japan Meteorological Agency in 2004 and 2013, indicate that the spatial rainfall pattern could affect the flooding area
In the central part of the Mobara City which is flood-prone area (Fig. 2), the floods occur on the flood plains surrounded by slightly highland such as natural levee and Holocene terraces

Summary

Introduction

Land subsidence causes several problems which include changes in elevation, groundwater salinization in coastal area, structural damage, and increase in the potential for flooding (Galloway et al, 1999; Ng et al, 2015). The Kujukuri Plain, Chiba Prefecture, Japan (Fig. 1), is one of the areas experiencing land subsidence which is caused by ground deformation from paleo-earthquakes, tectonic activities, and human-induced subsidence by groundwater abstraction. 1 m at the Mobara City during the period from 1969 to 2014 (Chiba Prefecture, 2014). This coastal area is relatively flat with its elevation lower than 10 m.

Climatic factor

Geomorphological factor

Human factor

Summary