Independent Review of Simulation of Net Infiltration for Present-Day and Potential Future Climates Page: 18 of 45
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2. Subsurface lateral flow excluded by the modeling approach. The potential for
capturing the impact of subsurface lateral flow is excluded by the one-dimensional
mass-balance modeling approach used. Extension of the MASSIF model to include
subsurface lateral flow, or at a minimum, comparison to models that account for
subsurface lateral flow, is needed to better understand the predicted lack of net
infiltration in the wash environments during wetter climates and the lack of variability
of infiltration in upland areas. Such an analysis is necessary to quantify the spatial
distribution of net infiltration into Yucca Mountain.
3. Incompletely defined bounds of uncertainty. The bounds of uncertainty have not been
fully defined due to the lack of site-specific data for determining uncertainty in
parameters due to spatial variability, as well as comparison of the model results with
site-specific data and with alternative modeling predictions. Comparison with a more
realistic, coupled surface-subsurface model would be helpful. Such a comparison
could focus on a small-scale representative watershed, or just a hillslope, comparing
the net infiltration predicted by MASSIF with the net infiltration from a more
conceptually realistic model capable of capturing interactions between adjacent
columns. Such a comparison would test the impact of the assumption that the effect
of subsurface lateral flow is negligible.
4. Limited validation examples. The validation cases are not sufficient to show that the
range of uncertainty has been captured. Additional validation can come from two
sources: (1) validation experiments (i.e., actual infiltration testing) and (2) existing
site-specific data that has apparently not been used for parameterization in this
modeling effort. If quality assurance issues prevent the use of existing data in the
model simulations, those measurements still represent a valuable dataset that could be
used for validation of the infiltration model.
5. Parameters estimated in a lumped manner. A number of parameters were estimated in
a lumped manner, such as assumed constant rooting depth and constant soil depth,
whose variability likely affects the spatial distribution of net infiltration. Additional
site-specific data will lead to better resolution of these parameters. Accounting for the
variability in soil depth and rooting depth will likely result in more precise
predictions of the spatial distribution of net infiltration. Resolution of Soil Group
5/7/9 back to its constituent soils is warranted to provide a more precise spatial
distribution of net infiltration. The effect of surface soil thickness in the MASSIF
model needs to be better evaluated, especially in bare soils and in vegetated soils
during non-growing periods.
6. Cubic convolution possibly truncating the range of evapotranspiration values. It is not
clear why cubic convolution was used during the geocorrection process to resample
data from the Landsat TM images in the evapotranspiration submodel. Using cubic
convolution results in the original pixel values being replaced by weighted means of
sixteen pixels, which results in considerable smoothing of the data and may average
out the smallest and largest evapotranspiration values. While cubic convolution
resampling is often used to make images more attractive, it compromises subsequent
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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/m1/18/: accessed May 23, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.