HR: 1330h
AN: H12B-1000    [PDF]
TI: Two-Component Hydrograph Separation and Mean Residence Time at Small Forested Catchments in Japan
AU: * Kubota, T
EM: ktayoko@ffpri.affrc.gp.jp
AF: Forestry and Forest Products Research Institute, Matsunosato 1, Tsukuba, Ibaraki, 305-8687 Japan
AU: Tsuboyama, Y
EM: tsubo@affrc.go.jp
AF: Forestry and Forest Products Research Institute, Matsunosato 1, Tsukuba, Ibaraki, 305-8687 Japan
AB: Two-component hydrograph separation was conducted, and mean residence time (MRT) was calculated for small forested catchments in Japan to understand runoff processes. The study site is located on the east coast of Japan . Annual precipitation averages 1426.9 mm over the past 20 yrs (1981-2001). Soils are derived from volcanic ash (Inceptisols). Surficial geology is primarily schist and amphibolite. Streamflow was continuously monitored using a V-notch weir at the outlets of the entire basin (HX, 75.28 ha) as well as subbasins including HO (15.68 ha), HB (2.48 ha), HA (0.84 ha), and HV (0.82 ha). HA is nested in the upper portion of HB, which is covered with a mature (80 yr old) forest of Japanese cedar and cypress. HB is nested in the lower portion of HO, which is covered with a young (12 yr old) stand of the same species except for HB. Streamwater was collected at these gauging stations approximately every 10 days from 1998 through 2001. Bulk samples of rainwater were collected at an opening of the meteorological station at the same intervals, together with bulk samples of throughfall under the canopy in HA. Streamwater during runoff were also sampled at HA and HB. Sequential throughfall was sampled in HA. Water samples were analyzed for oxygen-18 and deuterium. The variation of d value (d=ݎD-8ݎ18O) in throughfall ranged from approximately 5 to 25 permils, while that in streamwater was approximately 11.5 to13.5 permils. The seasonal variations of throughfall and streamwater were approximated by sinusoidal functions. The MRT was calculated using the damping of the amplitude, and its relationship with basin size was examined. In addition, two-component hydrograph separation was conducted at HA and HB based on variable source areas. It was found that generally more than half of pre-event water discharged into the stream. In this study, MRT was calculated for HA and HB considering the large amount of pre-event water discharging into the stream during the storm runoff period.
DE: 1800 HYDROLOGY
DE: 1860 Runoff and streamflow
SC: Hydrology [H]
MN: 2003 Fall Meeting