The mechanistic basis for storage‐dependent age distributions of water discharged from an experimental hillslope
The mechanistic basis for storage‐dependent age distributions of water discharged from an experimental hillslope
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实验山坡排水的存储依赖年龄分布的机制基础
DOI：
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发表时间：
2017
期刊：
影响因子：
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通讯作者：
C. Harman
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文献类型：
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作者：
L. Pangle;Minseok Kim;C. Cardoso;M. Lora;A. A. M. Neto;T. Volkmann;Yadi Wang;P. Troch;C. Harman
水运时间分布(TTD)和相关的存储-选择(SAS)分布是景观内水文运输的空间综合度量。最近的研究证实，TTDS和SAS的分布形式应该被认为是时变的--可能以可预测的方式取决于景观内水的动态储存。我们报道了一项为期28天的周期性稳态示踪实验，该示踪实验在一台1m~3的倾斜蒸渗仪内的模型山坡上进行。利用实验数据，我们校准了基于物理的、空间分布的流动和传输模型，并使用校准后的模型来生成随时间变化的SAS分布，随后将其与从实际实验中直接观察到的分布进行比较。其目的是利用模型中存储和通量的空间分布估计来表征水存储的时间变化如何影响流道配置的时间变化，以及由此产生的SAS分布。模拟的SAS分布很好地模拟了观测分布的形状，一旦模型域反映了渗漏仪土壤的空间异质性。空间分布的通量向量说明了水通量的大小和方向是如何随着地下水位的上升和下降而变化的，当地下水位上升到更接近土壤表面时，产生更大的年轻水的贡献。所说明的机制符合最近其他研究得出的结论，并支持反向储存效应的概念，即较年轻的水离开系统的可能性随着储存的增加而增加。这一机制可能普遍存在于山坡和水源集水区，在这些地区，流量动态受无承压含水层地下水位的垂直波动控制。
Distributions of water transit times (TTDs), and related storage‐selection (SAS) distributions, are spatially integrated metrics of hydrological transport within landscapes. Recent works confirm that the form of TTDs and SAS distributions should be considered time variant—possibly depending, in predictable ways, on the dynamic storage of water within the landscape. We report on a 28 day periodic‐steady‐state‐tracer experiment performed on a model hillslope contained within a 1 m3 sloping lysimeter. Using experimental data, we calibrate physically based, spatially distributed flow and transport models, and use the calibrated models to generate time‐variable SAS distributions, which are subsequently compared to those directly observed from the actual experiment. The objective is to use the spatially distributed estimates of storage and flux from the model to characterize how temporal variation in water storage influences temporal variation in flow path configurations, and resulting SAS distributions. The simulated SAS distributions mimicked well the shape of observed distributions, once the model domain reflected the spatial heterogeneity of the lysimeter soil. The spatially distributed flux vectors illustrate how the magnitude and directionality of water flux changes as the water table surface rises and falls, yielding greater contributions of younger water when the water table surface rises nearer to the soil surface. The illustrated mechanism is compliant with conclusions drawn from other recent studies and supports the notion of an inverse‐storage effect, whereby the probability of younger water exiting the system increases with storage. This mechanism may be prevalent in hillslopes and headwater catchments where discharge dynamics are controlled by vertical fluctuations in the water table surface of an unconfined aquifer.