Independent Review of Simulation of Net Infiltration for Present-Day and Potential Future Climates Page: 36 of 45
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probably occurs at some locations of Yucca Mountain on a scale that exceeds a 30 x
30 m pixel.
Many field studies in arid environments have found a strong correlation between
vegetation, soil and terrain characteristics, and net infiltration (e.g., Guan, 2005;
Gutierrez Jurado et al., 2006; Sandvig and Phillips, 2006). Since only a very small
part of Yucca Mountain has been disturbed by human activities, there is a high
likelihood for detection of subsurface lateral flow settings using a "digital soil
mapping" approach (Lagacherie et al., 2007; Lamotte et al., 1994; McBratney et al.,
2003). Those experimental studies corroborate and emphasize the presence of a
significant subsurface lateral flow component in semi-arid hillslopes that needs
specific attention during vadose-zone flow modeling.
Recently, Kampf and Burges (2007) provided an exhaustive review of available
conceptual and computer models for surface and subsurface hydrologic modeling, at
hillslope and catchment scale. The review discusses the significance of various
coupled surface-subsurface hydrologic process models that are one-, two-, and three-
dimensional. They show that, depending on need and computational burden, complex
multi-dimensional hydrologic models may be adopted in part of the modeling domain
and important findings extrapolated to the entire region.
Another model is the new Integrated Landscape Hydrology Model (ILHM) used to
integrate widely available hydrologic and landscape data in a synergistic and
computationally efficient manner to assess temporal and spatial changes in important
hydrologic processes (Hyndman et al., 2007). The Soil Moisture Distribution and
Routing Model (SMDR) was developed for humid, well-vegetated areas with steep to
moderate slopes with shallow soils and high infiltration capacity soils (Soil and Water
Laboratory, 2003). Both models take subsurface lateral flow into account and are
evidence that the inclusion of subsurface lateral flow in infiltration models is a
standard practice in hydrology today.
Guan, 2005 (Chapter 5) compares-among other aspects of mountain block
recharge-estimates of net infiltration at a semi-arid soil-bedrock interface using
HYDRUS-1D and HYDRUS-2D. Simulations were carried out to compare net
infiltration on north- and south-facing 20-degree slopes with soil thickness of 30 cm
and 100 cm, hillslope conditions not uncommon at Yucca Mountain. For these
specific conditions, the net infiltration of the 1D simulations is between that from the
2D top-slope and mid-slope simulations. Since 1D simulations can only represent
vertical infiltration and not subsurface lateral flow, they underestimate along the
entire slope consisting of top slope and mid-slope. For the 20-degree slopes, the 1D
simulation underestimated the net infiltration for the entire slope by about 15%
compared to the geometric mean of 2D top-slope and mid-slope results. In general,
the 2D simulations on mountain hillslopes yield different net infiltration rates than 1D
simulations. Guan (2005) concludes that the magnitude of the difference between 1D
and 2D simulations depends on slope aspect, slope steepness, and soil thickness
(factors examined in the study), and probably also on soil type and bedrock
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Oak Ridge Institute for Science and Education. Independent Review of Simulation of Net Infiltration for Present-Day and Potential Future Climates, report, August 30, 2008; Oak Ridge, Tennessee. (https://digital.library.unt.edu/ark:/67531/metadc897028/m1/36/: accessed May 27, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.