HR: 1340h
AN: H43G-1701    [Abstracts]
TI: Effect of Spatial Variation of Infiltration on Overland Flow Generation and Hydrological Processes in a Small Catchment covered by Japanese cypress plantation
AU: * Miyata, S
EM: smiyata@kais.kyoto-u.ac.jp
AF: Graduate School of Agriculture, Kyoto University, Kitashirakawa Oiwakecho, Sakyoku, Kyoto, 606-8502, Japan
AU: Kosugi, K
EM: kos@kais.kyoto-u.ac.jp
AF: Graduate School of Agriculture, Kyoto University, Kitashirakawa Oiwakecho, Sakyoku, Kyoto, 606-8502, Japan
AU: Nishi, Y
EM: nishi8@kais.kyoto-u.ac.jp
AF: Nippon Koei Co.,Ltd., Kojimachi 5-chome, Chiyoda-ku, Tokyo, 102-8539, Japan
AU: Gomi, T
EM: gomi@slope.dpri.kyoto-u.ac.jp
AF: Japan Science and Techonology Agency, 4-1-8, Honcho, Kawaguchi-shi, Saitama, 332- 0012, Japan
AU: Sidle, R C
EM: sidle@slope.dpri.kyoto-u.ac.jp
AF: Disaster Research Institute, Gokasho, Uji, 611-0011, Japan
AU: Onda, Y
EM: onda@geoenv.tsukuba.ac.jp
AF: Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, 1-1- 1, Tennoudai, Tsukuba, 305-8572, Japan
AU: Mizuyama, T
EM: mizuyama@kais.kyoto-u.ac.jp
AF: Graduate School of Agriculture, Kyoto University, Kitashirakawa Oiwakecho, Sakyoku, Kyoto, 606-8502, Japan
AB: We examined the effects of overland flow on storm runoff in a headwater catchment by investigating the spatial distribution of soil moisture and infiltration rate along a hillslope transect, Hortonian overland flow, stream discharge, and soil water potential. The study was conducted in a small catchment covered by 40-year-old Japanese cypress forest with a stand density of 3500 stem/ha. Overland flow observations were conducted on a hillslope plot (8 x 20 m) that extended from a ridge to the middle of a hillslope adjacent to the transect. Stream discharge was monitored at the outlet of the 0.43-ha catchment. We measured the infiltration rate 15 times over 20 months at each of three plots (0.3 x 0.3 m) installed in the upper, middle, and lower parts of the hillslope transect. The infiltration rate in the lower plot (average 1.37 mm/min) was significantly greater than that in the middle (average 0.90 mm/min) and upper (average 0.81 mm/min) plots. The relationship between the infiltration rate and soil moisture in each plot was negative, indicating the effect of soil water repellency on infiltration and overland flow generation. Likewise, the overland flow for storm events was greater during a dry period (May–July 2005: 332 mm of precipitation) than during a wet period (May–July 2006: 528 mm of precipitation). The storm runoff from the catchment showed the opposite tendency, i.e., it was greater during the wet than the dry period. During storm events in both dry and wet periods, stream discharge began to increase sharply when lateral subsurface flow formed groundwater at the bottom of the hillslope transect, whereas overland flow was responsive to rainfall intensity throughout the events. Thus, subsurface flow, rather than Hortonian overland flow, dominated storm runoff from the catchment, probably because overland flow on hillslopes infiltrated into the soil matrix lower on the slopes, where the infiltration rate was high. However, during short, intense storms under dry conditions, stream runoff increased, as did overland flow, without increases in soil water potential below 10 cm in depth, suggesting that Hortonian overland flow was the main contributor to storm runoff during these events.
DE: 1838 Infiltration
DE: 1850 Overland flow
DE: 1860 Streamflow
DE: 1866 Soil moisture
SC: Hydrology [H]
MN: 2007 Fall Meeting