| Whereas the integrated geophysical investigation of levee systems has been widely adopted to assess seepage and seismic risks, it was rarely applied to levees in large urban cities, or the lowermost reaches due to highly developed and noisy circumstances. On the contrary, vulnerability assessment of levee systems in large urban areas is the top priority task above all else. To certify the applicability of the method and to figure out appropriate measuring parameters, we conducted a feasibility study of integrated geophysical investigation along an urban river levee, crown of which is used as a two-lane trunk highway, and river-side slope is widely protected with various kinds of revetments. Capacitively coupled resistivity survey using OhmMapper, hybrid surface wave surveys including walk-around surface wave method were adopted in this study.As a result, 2D Vs and resistivity structure was clearly delineated up to 30 m below the survey line, set along a sidewalk of the trunk highway. Regretfully, limited reference information was available to interpret the study result, however the geophysical structure was consistent with ancient river geomorphology and the levee system was inferred to be safe in the view point of seepage. In the next production survey stage, survey lines are recommended to be set along a traffic lane under restriction. |
