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)