HR: 12:05h
AN: H31G-07    [PDF]
TI: The Role of Dry Soil Connectivity Barriers on Hillslope-Stream Connections
AU: * McNamara, J P
EM: jmcnamar@boisestate.edu
AF: Department of Geosciences Boise State University, 1910 University Dr., Boise, ID 83725
AU: Chandler, D
EM: dchandle@mendel.usu.edu
AF: Department of Plants, Soils, and Biometeorology Utah State University, 4820 Old Main Hill, Logan, UT 84319-4820
AU: Seyfried, M
EM: mseyfrie@nwrc.ars.usda.gov
AF: Northwest Watershed Research Center USDA ARS, 800 Park Blvd, Plaza IV, Suite 105, Boise, ID 83712-7716
AB: Hydraulic connectivity on hillslopes can be an important control on runoff generation. In this study we investigate the relationships between annual soil moisture patterns, lateral hillslope flow, and streamflow in a semi-arid, snowmelt driven catchment. We identify five periods of soil moisture conditions:, 1) a summer dry period, 2) a transitional fall wetting period, 3) a winter wet, low flux period, 4) a spring wet, high flux period, 5) and a transitional late spring drying period. We then present a conceptual model of how streamflow is generated with respect to the moisture conditions, based on field studies and computer simulations. Transitions between the periods are driven by changes in the water balance between rain, snow, snowmelt and evapotranspiration. However, the transition from a dry moisture state to a wet moisture state is not necessarily synchronous with a switch from vertically dominated to laterally dominated flow. The climatic shift primes the catchment for lateral flow generation, but hydraulic connectivity within the hillslope is then dependent on the organization of that lateral flow, in this case along the soil/bedrock interface. The time lag between the dry-to-wet switch and the vertical-to-lateral switch occurs because the snowpack delays the delivery of water to the soil and the subsequent advance of the wetting to the base of deep soil zones. The resulting hydraulic disconnection at the soil-bedrock interface in the deep-soil regions of the catchment must be breached for significant lateral translation of water, pressure, and solutes occur.
DE: 1800 HYDROLOGY
SC: Hydrology [H]
MN: 2003 Fall Meeting