Characterization of mixing and dilution in heterogeneous aquifers by means of local temporal moments
Characterization of mixing and dilution in heterogeneous aquifers by means of local temporal moments
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DOI：
10.1029/1999wr900354
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发表时间：
2000-05-01
影响因子：
5.4
通讯作者：
Kitanidis, PK
中科院分区：
文献类型：
--
作者：
Cirpka, OA;Kitanidis, PK
利用时间矩分析了保守示踪剂在非均质二维含水层中的穿透曲线。通过断面平均浓度得到的等效一维含水层的平均流速和纵向宏观弥散系数可以由在域的出流边界上积分的突破曲线的第一和第二中心矩来定义。的综合突破曲线的基础上，不能区分实际的溶质稀释，这涉及浓度降低，并在不同的横截面位置的羽流的部分之间的到达时间的可变性。分析在域内的“点”处的穿透曲线的时间矩给出关于示踪剂的稀释度的附加信息。从这些局部第一和第二中心矩可以导出表观渗流速度v（a）和混合的表观分散度α（a）。对于短的传播距离，alpha（a）等于局部尺度的纵向色散。它随移动距离的增加而增加，但比宏观分散度慢得多。在大距离极限下，α（a）最终可能达到宏观弥散度的水平。透镜的高电导率地下水流收敛被确定为优先增强混合的区域。这些区域的空间分布导致一个域内α（a）的高度变异性，表明早期阶段稀释定量的高度不确定性。在随附的文件[Cirpka和Kitanovich，这个问题]的结果保守示踪剂运输的研究混合控制的反应性运输。
Breakthrough curves of a conservative tracer in a heterogeneous two-dimensional aquifer are analyzed by means of their temporal moments. The average velocity and the longitudinal macrodispersion coefficient of the equivalent one-dimensional aquifer obtained through cross-sectional averaging of concentration can be defined from the first and second central moments of a breakthrough curve integrated over the outflow boundary of the domain. On the basis of an integrated breakthrough curve, one cannot distinguish between actual solute dilution, which involves concentration reduction, and variability of arrival times among parts of the plume at different cross-sectional positions. Analyzing the temporal moments of breakthrough curves at a "point" within the domain gives additional information about the dilution of the tracer. From these local first and second central moments an apparent seepage velocity v(a) and an apparent dispersivity of mixing alpha(a) can be derived. For short travel distances, alpha(a) equals the local-scale longitudinal dispersivity. It increases with the travel distance but much more slowly than the macrodispersivity. At the large-distance limit, alpha(a) may eventually reach the level of macrodispersivity. Lenses of high conductivity where groundwater flow converges are identified as regions of preferential enhanced mixing. The spatial distribution of these regions causes a high degree of variability of alpha(a) within a domain, indicating a high degree of uncertainty in the quantification of dilution at early stages. In an accompanying paper [Cirpka and Kitanidis, this issue] the results of conservative tracer transport are utilized for the study of mixing-controlled reactive transport.