U.S. Geological Survey, Reston, VA 20192, USA.
Ground Water. 2011 Mar-Apr;49(2):144-59. doi: 10.1111/j.1745-6584.2010.00764.x. Epub 2010 Oct 29.
Modeling subsurface solute transport is difficult-more so than modeling heads and flows. The classical governing equation does not always adequately represent what we see at the field scale. In such cases, commonly used numerical models are solving the wrong equation. Also, the transport equation is hyperbolic where advection is dominant, and parabolic where hydrodynamic dispersion is dominant. No single numerical method works well for all conditions, and for any given complex field problem, where seepage velocity is highly variable, no one method will be optimal everywhere. Although we normally expect a numerically accurate solution to the governing groundwater-flow equation, errors in concentrations from numerical dispersion and/or oscillations may be large in some cases. The accuracy and efficiency of the numerical solution to the solute-transport equation are more sensitive to the numerical method chosen than for typical groundwater-flow problems. However, numerical errors can be kept within acceptable limits if sufficient computational effort is expended. But impractically long simulation times may promote a tendency to ignore or accept numerical errors. One approach to effective solute-transport modeling is to keep the model relatively simple and use it to test and improve conceptual understanding of the system and the problem at hand. It should not be expected that all concentrations observed in the field can be reproduced. Given a knowledgeable analyst, a reasonable description of a hydrogeologic framework, and the availability of solute-concentration data, the secret to successful solute-transport modeling may simply be to lower expectations.
地下溶质运移模型比水头和水流模型更难。经典控制方程并不总是能充分代表我们在现场看到的情况。在这种情况下，常用的数值模型所求解的方程可能是错误的。此外，在对流占主导地位的情况下，输运方程是双曲线的，而在水动力弥散占主导地位的情况下，输运方程是抛物线的。没有一种单一的数值方法适用于所有条件，对于任何给定的复杂现场问题，由于渗流速度变化很大，没有一种方法在所有地方都是最优的。虽然我们通常期望对地下水流动控制方程进行数值准确的求解，但在某些情况下，数值弥散和/或振荡引起的浓度误差可能很大。与典型的地下水流动问题相比，溶质输运方程数值解的准确性和效率对所选数值方法更为敏感。然而，如果投入足够的计算工作量，就可以将数值误差控制在可接受的范围内。但是，不切实际的长模拟时间可能会助长忽略或接受数值误差的倾向。有效溶质运移建模的一种方法是使模型相对简单，并使用它来测试和改进对系统和手头问题的概念理解。不应期望能够重现现场观测到的所有浓度。只要有知识渊博的分析师、对水文地质框架的合理描述以及溶质浓度数据的可用性，成功的溶质运移建模的秘诀可能就是降低期望。
