Field observations and assessment of riverine geomorphologicalenvironments in view of integrated floodplain management

• Project/Area Number: 22681026
• Research Category: Grant-in-Aid for Young Scientists (A)
• Allocation Type: Single-year Grants
• Research Field: Natural disaster science
• Research Institution: Kyoto University
• Principal Investigator: AZUMA Ryoukei 京都大学, 防災研究所, 助教 (50464201)
• Project Period (FY): 2011 – 2012
• Project Status: Completed (Fiscal Year 2012)
• Budget Amount: ¥9,100,000 (Direct Cost: ¥7,000,000、Indirect Cost: ¥2,100,000); Fiscal Year 2012: ¥910,000 (Direct Cost: ¥700,000、Indirect Cost: ¥210,000); Fiscal Year 2011: ¥2,600,000 (Direct Cost: ¥2,000,000、Indirect Cost: ¥600,000); Fiscal Year 2010: ¥5,590,000 (Direct Cost: ¥4,300,000、Indirect Cost: ¥1,290,000)
• Keywords: 河岸侵食 / 河川地形環境 / 氾濫原マネジメント / 堆積環境 / 宇治川 / 河道地形変化 / 水害地形環境 / 侵食崖

Research Abstract

This study focuses on the unconfined groundwater table fluctuations in a floodplain of river channel that occur in response to water level changes of the low channel. The array of observation wells normal to the low channel bank was set up at the floodplain near the 43.0km station of Uji River. The observed performance of a rapid rise and slow fall in the groundwater table clearly captured the response to a flood stage associated with a typhoon and heavy rainfall. Careful time-series analyses identified lateral infiltration during the rising period and vertical infiltration during the falling period. The apparent coefficients of permeability in floodplain soil during the rising and falling period were calculated as equal to 1.6×10-2~1.32 cm/s and 1.9~3.4×10-4 cm/s, respectively. The residual groundwater table during the falling period closely related to a process of bank erosion. A discussion is made to identifying practical implications for future river management.