Shallow and local or deep and regional? Inferring source groundwater characteristics across mainstem riverbank discharge faces
Shallow and local or deep and regional? Inferring source groundwater characteristics across mainstem riverbank discharge faces
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DOI：
10.1002/hyp.14939
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发表时间：
2023-07
影响因子：
3.2
通讯作者：
A. Haynes;M. Briggs;E. Moore;Kevin Jackson;J. Knighton;D. Rey;A. Helton
中科院分区：
文献类型：
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作者：
A. Haynes;M. Briggs;E. Moore;Kevin Jackson;J. Knighton;D. Rey;A. Helton
河岸地下水排放面是空间上广泛的优先渗流区，在低河水流量时暴露于空气中。一些概念水文模型表明，流量面代表了高度可变的年龄和长度的地下水流道的空间收敛，而另一些模型则表明地下水源特征具有更大的一致性。我们通过以下方式完成了对主要河岸排放面上嵌套的优先排放点的详细实地调查：(1)利用新的基于温度的递归估计（扩展卡尔曼滤波）建模方法来评估季节、日和事件驱动的地下水通量模式；(2)开发一个基于易于测量的属性的多参数工具包，对一般水源地下水流道深度和流道长度尺度进行分类；(3)评估跨排放面的优先流点是否倾向于代表共同或收敛的地下水来源。利用热红外图像绘制了美国康涅狄格州法明顿河沿岸的五个主要地下水排放面。然后在39个优先排放点直接安装垂直温度廓线仪，历时4.5个月跟踪垂直排放通量模式。每月还收集了排放点的水化学以及水和溶解氡气的稳定同位素的空间天气图。我们发现，在上游沿宽谷段的深基岩排放面普遍存在浅层地下水来源，主要证据是明显的日流量模式。在大型河流流量事件期间，流量的季节性趋势和河岸蓄水量的变化进一步表明了浅层的局部来源。相比之下，与近地表横切基岩相关的下游排放面表现出深层和区域性的源流道特征，如更稳定的排放模式和温度。然而，跨放电面的许多相邻点具有相似的放电通量模式，但氯化物和氡浓度不同，这表明局部流道非均质叠加对更大规模流道特征的附加影响。
Riverbank groundwater discharge faces are spatially extensive areas of preferential seepage that are exposed to air at low river flow. Some conceptual hydrologic models indicate discharge faces represent the spatial convergence of highly variable age and length groundwater flowpaths, while others indicate greater consistency in source groundwater characteristics. Our detailed field investigation of preferential discharge points nested across mainstem riverbank discharge faces was accomplished by: (1) leveraging new temperature‐based recursive estimation (extended Kalman Filter) modelling methodology to evaluate seasonal, diurnal, and event‐driven groundwater flux patterns, (2) developing a multi‐parameter toolkit based on readily measured attributes to classify the general source groundwater flowpath depth and flowpath length scale, and, (3) assessing whether preferential flow points across discharge faces tend to represent common or convergent groundwater sources. Five major groundwater discharge faces were mapped along the Farmington River, CT, United States using thermal infrared imagery. We then installed vertical temperature profilers directly into 39 preferential discharge points for 4.5 months to track vertical discharge flux patterns. Monthly water chemistry was also collected at the discharge points along with one spatial synoptic of stable isotopes of water and dissolved radon gas. We found pervasive evidence of shallow groundwater sources at the upstream discharge faces along a wide valley section with deep bedrock, as primarily evidenced by pronounced diurnal discharge flux patterns. Discharge flux seasonal trends and bank storage transitions during large river flow events provided further indication of shallow, local sources. In contrast, downstream discharge faces associated with near surface cross cutting bedrock exhibited deep and regional source flowpath characteristics such as more stable discharge patterns and temperatures. However, many neighbouring points across discharge faces had similar discharge flux patterns that differed in chloride and radon concentrations, indicating the additional effects of localized flowpath heterogeneity overprinting on larger scale flowpath characteristics.