HR: 11:50h
AN: H31G-06    [PDF]
TI: Modeling Investigation of Water Partitioning at a Semi-arid Hillslope and its Implication
AU: * Guan, H
EM: hdguan@nmt.edu
AF: Earth and Environmental Science, New Mexico Institute of Mining and Technology, Leroy Place 801,, Socorro, NM 87801 United States
AU: Wilson, J L
EM: jwilson@nmt.edu
AF: Earth and Environmental Science, New Mexico Institute of Mining and Technology, Leroy Place 801,, Socorro, NM 87801 United States
AU: Newman, B D
EM: bnewman@lanl.gov
AF: Environmental Dynamics and Spatial Analysis Group, Los Alamos National Laboratory, MS J495, Los Alamos National Laboratory, Los Alamos, NM 87545 United States
AU: Simunek, J
EM: jiri.simunek@ucr.edu
AF: Department of Environmental Sciences, University of California, 900 University Avenue, Riverside, CA 92521 United States
AB: Recent generic modeling studies (Guan and Wilson, 2002, 2003) confirm conventional opinion that climate and bedrock (matrix and fracture) permeability are primary controls on the amount of water partitioning from the land surface into the underlying bedrock of semi-arid mountain blocks. Both steady and quasi-steady simulations show that the annual percolation rate across the soil-bedrock interface approaches saturated bedrock hydraulic conductivity when the mean net infiltration rate into the soil exceeds rock conductivity. When the mean infiltration rate is lower, the percolation rate approaches the mean infiltration rate. However, field observations of bedrock water content at a semi-arid hillslope (precipitation 450~700 mm/yr) with a highly permeable tuff (saturated hydraulic conductivity, Ks = 3*105~106 mm/yr) suggest only negligible percolation to the rock (Wilcox et al. 1997), while the sum of surface runoff and interflow through the soil was estimated to be 10~60 mm/year. The inconsistency of actual percolation and modeling prediction may have been due to the simplified generic modeling setting (no ET, macropore free soil cover, homogenous soil and bedrock), and the high permeability of the modeled soils in contrast to soils in the field situation. For example, low permeability soil layers (minimum Ks = 3 mm/year) in a multi-layer soil cover impede downward water movement; root dominated subhorizontal macropores enhance the downslope interflow through the soil; and roots extract the water from the soil which otherwise could percolate into the bedrock. We examine these mechanisms via rigorous 2D numerical modeling. The macropore is represented with a dual-permeability model. Evapotranspiration is simulated based on the atmospheric demand and the hydraulic conditions in the modeling domain. This work is aimed at improved understanding of water partitioning on hillslopes and distributed mountain block recharge in semi-arid areas.
DE: 1818 Evapotranspiration
DE: 1860 Runoff and streamflow
DE: 1875 Unsaturated zone
DE: 1884 Water supply
SC: Hydrology [H]
MN: 2003 Fall Meeting