Monday, November 5, 2007 - 12:55 PM
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Hydrologic Flowpaths in an Oak Woodland Catchment.

Alexandre Swarowsky1, Anthony Toby O'Geen2, and Randy Dahlgren1. (1) One Shields Ave., University of California-Davis, University of California-Davis, Dept. Land Air & Water Resources, Davis, CA 95616, (2) Dept. Land, Air & Water Resources, University of California-Davis, One Shields Avenue, Davis, CA 95616

Temporal and spatial patterns of hydrologic flowpaths are important factors in understanding stream flow dynamics. We hypothesize that hydrologic flowpaths in soils change from vertical percolation during fall wet-up to lateral flow when saturated in winter and early spring. An oak woodland watershed in northern California was instrumented to monitor watershed hydrology. Stream flow was measured at 15-minute intervals during the 2006-2007 water year. Water content was monitored in 60 soil profiles within four horizons (A, AB, Bt, and C/Cr). A perched water monitoring trench located at the base of the watershed was retrofitted with tipping buckets to measure lateral flow from three soil profiles within the same four horizons. A total of 50 cm of rain was recorded for the year resulting in two stream flow events. The first event, from 2/09/07 to 2/12/07, occurred after 32 cm of cumulative rain. Before the event (2/8/07), water content in the top 10 cm of soil ranged from 0.19 to 0.39 m3 m-3 in the watershed. During the storm, water content in the top 10 cm ranged from 0.25 to 0.45 m3 m-3.  Lateral flow was missed due to equipment failure. The second event (2/24/07-3/01/07) occurred after 5 cm of additional rain, and corresponded in time with lateral flow from AB horizons. The total amount of lateral flow over the 16-hr storm event was 0.3 m3 in A, 1.5 m3 in AB, 0.4 m3 in Bt, and 0.2 m3 in C horizons.  Before the event (2/24/07), water content in the top 10 cm ranged from 0.14 to 0.40 m3 m-3 in the watershed. During the storm, water content in the top 10 cm ranged from 0.21 to 0.47m3 m-3. Preliminary information indicates that stream discharge responds immediately to lateral flow once watershed storage capacity is reached and AB horizons are saturated.