HR: 0800h
AN: H51C-0369    [Abstracts]
TI: Simulated Effect of a Forest Road on Near-Surface Hydrologic Response
AU: * Mirus, B B
EM: bmirus@pangea.stanford.edu
AF: Department of Geological and Environmental Sciences, Stanford University, Stanford, CA 94305-2115 United States
AU: Ebel, B A
EM: bebel32@pangea.stanford.edu
AF: Department of Geological and Environmental Sciences, Stanford University, Stanford, CA 94305-2115 United States
AU: Loague, K
EM: keith@pangea.stanford.edu
AF: Department of Geological and Environmental Sciences, Stanford University, Stanford, CA 94305-2115 United States
AB: Forest roads alter both surface and subsurface hydrologic-response processes by introducing near-surface permeability contrasts and changing the topography at the road-cut. Roads are known to increase the likelihood of overland flow, seepage, and slope instability. For example, on the road surface, lower permeability values caused by compaction can result in reduced infiltration and subsequently Horton overland flow; up-gradient of the road, modified subsurface flow paths can result in elevated pore pressures and the development of a seepage face with exfiltrating subsurface stormflow. This study examines the hydrologic impact of a forest road using a comprehensive physics-based model known as the Integrated Hydrology Model (InHM). InHM simulates fully coupled transient 3D variably-saturated water flow in the subsurface and 2D water flow over the land surface and in channels. The forest road site focused on in this study is the 1.7 ha C3 catchment within the H.J. Andrews Experimental Forest. The C3 data set includes enough information to parameterize and evaluate InHM for continuous hydrologic-response simulations for a 43 day period. InHM simulations were conducted in both 3D and 2D for the C3 catchment. The results from the 3D InHM simulations compare well with the C3 observations of runoff and total head. Concept development analyses include assessments of spatially and temporally variable soil-water contents, subsurface pore pressures, surface water depths, and groundwater-surface water interactions. The 3D simulations show that (i) discharge is dominated by subsurface stormflow exfiltrating from the roadcut, (ii) Horton overland flow occurs only on the road during high intensity rainfall, (iii) positive pore pressures develop within the hollow at the soil/bedrock interface, (iv) subsurface flow in the saturated zone converges to the axis of the hollow. Results from 2D (vertical-slice) InHM simulations, as compared to 3D simulations, under-predict pore pressures, confirming the importance of subsurface flow convergence in the development of high pore pressures that can lead to slope failure.
DE: 1803 Anthropogenic effects (4802, 4902)
DE: 1830 Groundwater/surface water interaction
DE: 1847 Modeling
SC: Hydrology [H]
MN: Fall Meeting 2005