HR: 0800h
AN: H51B-0447    [Abstracts]
TI: Effects of Levee Construction on Groundwater Flow in the Kushiro Mire, Northern Japan
AU: * Kawaguchi, T
EM: teppei8@env.agr.hokudai.ac.jp
AF: Research Faculty of Agriculture, Hokkaido University, Kita 9 Nishi 9, Kita-ku, Sapporo, 060- 8589, Japan
AU: Yamada, H
EM: hiroyama@env.agr.hokudai.ac.jp
AF: Research Faculty of Agriculture, Hokkaido University, Kita 9 Nishi 9, Kita-ku, Sapporo, 060- 8589, Japan
AU: Nakamura, T
EM: t3nakamu@bioindustry.nodai.ac.jp
AF: Tokyo University of Agriculture, Yasaka 196, Abashiri, 099-2493, Japan
AU: Yabe, K
EM: k.yabe@scu.ac.jp
AF: Sapporo City University, Geijyutuno-mori, Minami-ku, Sapporo, 005-0864, Japan
AB: Degradation of mire ecosystems has resulted from changing hydrological conditions associated with watershed developments because the biota are related strongly to hydrological conditions. In Kushiro Mire, the largest in Japan, drastic changes in vegetation have been observed since the 1970s. Those changes have been manifested as a transition of a sedge/reed-dominated area into alder forests. Furthermore, large levees were constructed throughout the mire for flood management. After their construction, vegetation changes have occurred around the levee. It was presumed that the changes resulted from hydrological condition changes. This study is intended to clarify effects of the levee on hydrological conditions. This study was conducted in the mire, which has both the levees and vegetation changes. Each groundwater investigation and numerical analysis of ground-water flow was performed using MODFLOW software. A belt transect (1.5 km long) was set to intersect the levee; observation wells were set at 50 m intervals. Investigations of the groundwater table and vertical hydraulic gradient (VHG) were performed with a digital manometer during 2005–2006. Because of the investigation, the water table was lower than the ground surface in summer. The water table varied more in areas closer to the levee. The VHG distribution indicates that down-welling occurred near the levee, and upwelling occurred at the middle transect area in the protected area. Results suggest that groundwater was drained by a drainage ditch which was set to protect the levee. Two-dimensional cross-sectional analysis was conducted in each case before and after (present status) levee construction. Results indicate that flow directions differed between the former and the latter cases, and that the present water table is lower. The latter case showed that water in the levee is infiltrating into the mire area because the water table at the levee was higher than around the mire area. As shown by results of VHG investigation, upwelling at the middle transect area was shown for the latter case. In contrast, it was never shown for the former case. These results suggest that the upwelling was caused by the levee. The existence of the levee lowered the mire water table and influenced the direction of groundwater flow around the levee.
DE: 1829 Groundwater hydrology
DE: 1831 Groundwater quality
DE: 1834 Human impacts
DE: 1849 Numerical approximations and analysis
DE: 1890 Wetlands (0497)
SC: Hydrology [H]
MN: 2007 Fall Meeting