Aquarius Engineering has developed new computer modeling concepts for water flow above the water table, called unsaturated flow. The findings point out some serious, common and basic modeling errors that can predict unsaturated flow that is in error by orders of magnitude and even in the wrong direction. Although these errors can possibly be made in models ranging from poultry litter to nuclear waste contaminant transport and infiltration, it should be pointed out that no one has yet determined that any models which are critical to public health and safety make these mistakes.
This work gives all such modelers a new modeling and mathematical
framework with which to judge the appropriateness of some basic
flow calculations and their approximations. It develops a new
scaling parameter which shows how such flow calculations change
with both the model and soil or rock characteristics. It develops
the difficult calculations of true flow consistent with modeling
assumptions, and then offers new approximations more suitable
for running models.
The public should understand that all such models are several
approximations removed from reality. A numerical computer method
approximates an equation which approximates an ideal soil which
approximates a real soil, simply because there is no better way
to do it. In addition, there are very real difficulties in determining
just what the real soil or rock is, buried under hundreds or thousands
of feet of itself.
As this work demonstrates, the understanding of such processes
is still changing, and will continue to change. Star Trek computers
are still just fiction. A policy decision which asserts that a
problem such as nuclear waste disposal will be completely solved
in a given number of years is just that, a policy decision. Such
things change neither the mathematics of a problem, nor the human
understanding of it. They can only channel resources in either
aid or obstruction of it.
The definitive report on this work, Developing Darcian Means in
Application to Topopah Spring Welded Volcanic Tuff, DOE/ER/82329-2,
a graduate-level tutorial on the concepts and their applications,
can be obtained shortly in printed version from:
U.S. Department of Energy
Office of Scientific and Technical Information (AD-21)