HR: 08:30h
AN: H11H-03    [Abstracts]
TI: How do preferential flow features connect? Combining tracers and excavation to examine hillslope flow pathways on Vancouver Island, British Columbia, Canada.
AU: * Anderson, A E
EM: axela@interchange.ubc.ca
AF: Department of Forest Resources Management University of British Columbia, 2037-2424 Main Mall, Vancouver, BC V6T 1Z4 Canada
AU: Weiler, M
EM: markus.weiler@ubc.ca
AF: Department of Forest Resources Management University of British Columbia, 2037-2424 Main Mall, Vancouver, BC V6T 1Z4 Canada
AB: Preferential flow is a complex process that influences water flow and solute transport in soils at different scales. Many studies have advanced our understanding about the physical structures of preferential pathways and their effects on water flow and solute transport at the column and plot scale. However, we still know very little about how preferential flow features connect over large distances and how they influence water flow and solute transport at the hillslope and catchment scale. Working in a forested watershed on northeast Vancouver Island in British Columbia, Canada, we conducted several artificial tracer experiments under natural and steady state flow conditions to investigate how water and solutes move through a hillslope section above a road cutbank. After these ``black-box'' tracer experiments we applied a blue food dye and excavated the hillslope to visualize the stained flow pathways. Under natural conditions two of the largest preferential features transmitted water at rates up to 30 liters/min. When a NaCl tracer was applied 12 m upslope of the road cutbank one soil pipe transmitted 97% of the recovered tracer during two large storms. When tracer was applied 30 m upslope of the road a more diffused response was observed. For the steady-state conditions we pumped water into trenches excavated at 12 m and 30 m above the road and then applied NaCl during constant outflow. Pumping water into the 12 m trench produced flow from only two preferential features, but a response in all preferential features was observed when water was pumped into the 30 m trench. The detailed excavations showed that the largest preferential feature was connected to the lower trench by large soil pipes at the interface of the organic and mineral soil horizons that were connected by flow through the organic soil. Other cross sections between 12 and 30 m upslope revealed concentrated flow through coarse mineral soil, diffused flow through mineral and organic soil, flow along roots, flow diverted by large boulders, and flow through soil pipes located in the organic and mineral soil horizons. These experiments showed that the transport of water and solutes is not only governed by the presence of distinct preferential features like pipes or macropores but also by the material that connects them. In addition, water exploits the pathways with the lowest resistance to flow independent of the gradient of the surface or bedrock topography. The information gained about length, area, frequency and connectivity of individual preferential flow pathways will be used to develop a hillslope model incorporating a statistical representation of theses features.
DE: 1826 Geomorphology: hillslope (1625)
DE: 1832 Groundwater transport
DE: 1895 Instruments and techniques: monitoring
SC: Hydrology [H]
MN: Fall Meeting 2005