Morel-Seytoux Hubert J, Mehl Steffen, Morgado Kyle
Department of Civil Engineering, California State University, Chico, Chico, CA 95929-0930.
Ground Water. 2014 Sep-Oct;52(5):775-81. doi: 10.1111/gwat.12112. Epub 2013 Sep 6.
Knowledge of river gain from or loss to a hydraulically connected water table aquifer is crucial in issues of water rights and also when attempting to optimize conjunctive use of surface and ground waters. Typically in groundwater models this exchange flow is related to a difference in head between the river and some point in the aquifer, through a "coefficient." This coefficient has been defined differently as well as the location for the head in the aquifer. This paper proposes a new coefficient, analytically derived, and a specific location for the point where the aquifer head is used in the difference. The dimensionless part of the coefficient is referred to as the SAFE (stream-aquifer flow exchange) dimensionless conductance. The paper investigates the factors that influence the value of this new conductance. Among these factors are (1) the wetted perimeter of the cross-section, (2) the degree of penetration of the cross-section, and (3) the shape of the cross-section. The study shows that these factors just listed are indeed ordered in their respective level of importance. In addition the study verifies that the analytical correct value of the coefficient is matched by finite difference simulation only if the grid system is sufficiently fine. Thus the use of the analytical value of the coefficient is an accurate and efficient alternative to ad hoc estimates for the coefficient typically used in finite difference and finite element methods.
了解河流与水力连通的潜水位含水层之间的水量增减，对于水权问题以及试图优化地表水与地下水的联合利用而言至关重要。在地下水模型中，这种交换流量通常通过一个“系数”与河流和含水层中某一点之间的水头差相关联。该系数的定义以及含水层中水头的位置各不相同。本文提出了一个通过解析推导得出的新系数，以及在计算差值时使用含水层水头的特定位置。该系数的无量纲部分被称为SAFE（河流 - 含水层流量交换）无量纲传导率。本文研究了影响这个新传导率值的因素。这些因素包括：（1）横截面的湿周；（2）横截面的渗透程度；（3）横截面的形状。研究表明，刚刚列出的这些因素在各自的重要性水平上确实是有顺序的。此外，研究还证实，只有当网格系统足够精细时，有限差分模拟才能与该系数的解析正确值相匹配。因此，使用该系数的解析值是一种准确且高效的替代方法，可替代有限差分法和有限元法中通常使用的系数的临时估计值。
