Groundwater dynamics in continental rift zone settings remain poorly understood because of the spatial heterogeneity in flow, storage, and recharge dynamics. The Central Kenya Rift is an excellent example where, though groundwater is important for domestic, irrigation, and geothermal energy exploitation, its hydrogeological properties remain largely unknown. Existing conceptual groundwater models assume flow from the high-elevation, humid rift flanks to the low-elevation, semiarid rift floor, but the role of the faults that fracture the aquifers is commonly unaccounted for. We applied geochemical, isotopic (δ¹⁸O, δD, ⁸⁷Sr/⁸⁶Sr, ³H-³He), multivariate statistical methods, and knowledge of geological structures to determine recharge sources, flow, and residence times to revise the conceptual flow model. Results show that groundwater is primarily recharged by meteoric waters, river input, and Lake recharge. The faults impart a control on the groundwater flow within four sub-compartments. Major differences in flow patterns exist between the eastern and western rift flanks: surface and groundwater transfer from the eastern flanks to the rift floor occurs via relay ramp structures, and flow on the west side takes place laterally from the high escarpment. Although ³H-³He dating shows that the age of groundwater ranges from a few to >>50 years, most of the groundwater in the rift-floor area is free of ³H and was recharged before the 1960s. Hence, we propose that these areas receive episodic recharge and represent the most sensitive groundwater resources in the rift. To inform sustainable groundwater development, a robust monitoring network is required to capture the heterogeneous groundwater dynamics.

中文翻译：

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断层火山含水层地下水补给和流动的构造控制

由于流动、储存和补给动力学的空间异质性，大陆裂谷带环境中的地下水动力学仍然知之甚少。肯尼亚中部裂谷是一个很好的例子，尽管地下水对于生活、灌溉和地热能源开发很重要，但其水文地质特性在很大程度上仍然未知。现有的地下水概念模型假设从高海拔、潮湿的裂谷侧翼流向低海拔、半干旱的裂谷底，但断裂含水层断裂的作用通常无法解释。我们应用地球化学、同位素 (δ ¹⁸ O, δD, ⁸⁷ Sr/ ⁸⁶ Sr, ³ H- ³He)，多元统计方法和地质结构知识，以确定补给源、流量和停留时间，以修正概念流量模型。结果表明，地下水主要由大气水、河流输入和湖泊补给补给。这些断层控制了四个子隔间内的地下水流。裂谷东侧和西侧的流动模式存在主要差异：地表水和地下水从东侧向裂谷底部的转移是通过中继坡道结构进行的，而西侧的流动则从高悬崖横向发生。虽然³ H- ³ He 测年表明地下水年龄从几年到 >>50 年不等，但裂谷底区的地下水大部分不含³H 并在 1960 年代之前充电。因此，我们建议这些区域接受间歇性补给并代表裂谷中最敏感的地下水资源。为了告知可持续的地下水开发，需要一个强大的监测网络来捕捉异质地下水动态。