A comparison of particle-tracking and solute transport methods for simulation of tritium concentrations and groundwater transit times in river water
A comparison of particle-tracking and solute transport methods for simulation of tritium concentrations and groundwater transit times in river water
复制标题
模拟河水中氚浓度和地下水渡越时间的粒子追踪和溶质输运方法的比较
DOI：
10.5194/hess-18-3109-2014
复制
发表时间：
2014
影响因子：
6.3
通讯作者：
M. Stewart
中科院分区：
文献类型：
--
作者：
M. Gusyev;D. Abrams;M. W. Toews;U. Morgenstern;M. Stewart
本研究的目的是模拟氚浓度和地下水过境时间在河水中的粒子跟踪（MODPATH），并比较它们的溶质运移（MT3 DMS）模拟。河水中氚的测量对于颗粒跟踪和溶质运移模型的校准以及对流域存储动态的理解是有价值的。在先前的研究中，我们使用MODFLOW-MT3 DMS模型（Gusyev等人，2013年）。该模型进行了校准，以测量河水中的氚在基流的Waihaha，Whanganui，Whareroa，Kuratau，和大森河流域的WLTC。在这项工作之后，我们现在使用WLTC的相同MODFLOW模型，使用稳态粒子跟踪MODPATH模型计算地下水粒子的路径（及其相应的氚浓度）。为了模拟基流氚浓度与MODPATH，过境时间分布（TTD）是必要的，以了解示踪剂的入口和排放点之间的滞后时间，并生成的河流网络的五个WLTC流出。TTD是用在卷积积分与输入氚浓度的时间序列从沉淀测量。由此产生的MODPATH氚浓度产生一个非常好的匹配测量的氚浓度，并与MT3 DMS模拟的氚浓度相似，最大的变化发生在炸弹峰值附近。MODPATH和MT3 DMS也产生类似的平均过境时间（MTTs）的地下水对河流基流的贡献，但实际形状的TTD是惊人的不同。虽然这两种分布都提供了有价值的信息，但用于得出技术指标的方法有根本的不同，因此必须作出不同的解释。使用当前的MT3 DMS模型设置，只有MODPATH使用的方法才能提供用于卷积积分的真实TTD。
The purpose of this study is to simulate tritium concentrations and groundwater transit times in river water with particle-tracking (MODPATH) and compare them to solute transport (MT3DMS) simulations. Tritium measurements in river water are valuable for the calibration of particle-tracking and solute transport models as well as for understanding of watershed storage dynamics. In a previous study, we simulated tritium concentrations in river water of the western Lake Taupo catchment (WLTC) using a MODFLOW-MT3DMS model (Gusyev et al., 2013). The model was calibrated to measured tritium in river water at baseflows of the Waihaha, Whanganui, Whareroa, Kuratau, and Omori river catchments of the WLTC. Following from that work we now utilized the same MODFLOW model for the WLTC to calculate the pathways of groundwater particles (and their corresponding tritium concentrations) using steady-state particle tracking MODPATH model. In order to simulate baseflow tritium concentrations with MODPATH, transit time distributions (TTDs) are necessary to understand the lag time between the entry and discharge points of a tracer and are generated for the river networks of the five WLTC outflows. TTDs are used in the convolution integral with an input tritium concentration time series obtained from the precipitation measurements. The resulting MODPATH tritium concentrations yield a very good match to measured tritium concentrations and are similar to the MT3DMS-simulated tritium concentrations, with the greatest variation occurring around the bomb peak. MODPATH and MT3DMS also yield similar mean transit times (MTTs) of groundwater contribution to river baseflows, but the actual shape of the TTDs is strikingly different. While both distributions provide valuable information, the methodologies used to derive the TTDs are fundamentally different and hence must be interpreted differently. With the current MT3DMS model settings, only the methodology used with MODPATH provides the true TTD for use with the convolution integral.