A Mountain‐Front Recharge Component Characterization Approach Combining Groundwater Age Distributions, Noble Gas Thermometry, and Fluid and Energy Transport Modeling
A Mountain‐Front Recharge Component Characterization Approach Combining Groundwater Age Distributions, Noble Gas Thermometry, and Fluid and Energy Transport Modeling
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DOI：
10.1029/2020wr027743
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发表时间：
2020-12
影响因子：
5.4
通讯作者：
K. Markovich;L. Condon;K. Carroll;R. Purtschert;J. McIntosh
中科院分区：
文献类型：
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作者：
K. Markovich;L. Condon;K. Carroll;R. Purtschert;J. McIntosh
山前补给（MFR），或来源于山体的盆地填充含水层的所有入流，是盆地填充含水层系统补给的重要组成部分。区分和量化MFR的表面和地下成分对于水资源规划和管理是必要的，特别是因为气候变化可能以不同的方式影响这些成分。本研究检验了一个假设，即可以通过（1）地下水年龄和（2）补给的中位高程来区分长滤网、盆地填充生产威尔斯井中的MFR组分。我们开发了一种MFR表征方法，将使用氚、氪-85、氩-39和放射性碳的六口威尔斯井的年龄分布与惰性气体温度测量的中值补给高程结合起来，并结合数值实验，使用流量和能量来确定补给温度递减率传输建模。我们发现，地下水年龄分布提供了有价值的信息，用于表征盆地填充生产威尔斯井捕获的主要流动系统行为。示踪剂表明存在旧的（即，没有检测到氚）的水在一口井完成风化基岩位于靠近山前。两个生产威尔斯井表现出年龄分布的二元混合之间的现代和一小部分的老水，而其余的威尔斯井捕获主要是现代的流动路径。稀有气体测温提供了重要的补充信息的年龄分布，但是，假设恒定的补给温度递减率产生不可能的补给海拔。数值实验表明，表面MFR，如果来自融雪，可以局部抑制在盆地填充含水层的地下水位温度，与惰性气体测温估计的补给海拔的影响。
Mountain‐front recharge (MFR), or all inflow to a basin‐fill aquifer with its source in the mountain block, is an important component of recharge to basin‐fill aquifer systems. Distinguishing and quantifying the surface from subsurface components of MFR is necessary for water resource planning and management, particularly as climate change may impact these components in distinct ways. This study tests the hypothesis that MFR components can be distinguished in long‐screened, basin‐fill production wells by (1) groundwater age and (2) the median elevation of recharge. We developed an MFR characterization approach by combining age distributions in six wells using tritium, krypton‐85, argon‐39, and radiocarbon, and median recharge elevations from noble gas thermometry combined with numerical experiments to determine recharge temperature lapse rates using flow and energy transport modeling. We found that groundwater age distributions provided valuable information for characterizing the dominant flow system behavior captured by the basin‐fill production wells. Tracers indicated the presence of old (i.e., no detectable tritium) water in a well completed in weathered bedrock located close to the mountain front. Two production wells exhibited age distributions of binary mixing between modern and a small fraction of old water, whereas the remaining wells captured predominantly modern flow paths. Noble gas thermometry provided important complementary information to the age distributions; however, assuming constant recharge temperature lapse rates produced improbable recharge elevations. Numerical experiments suggest that surface MFR, if derived from snowmelt, can locally suppress water table temperatures in the basin‐fill aquifer, with implications for recharge elevations estimated from noble gas thermometry.