Time-variable transit time distributions and transport: Theory and application to storage-dependent transport of chloride in a watershed
Time-variable transit time distributions and transport: Theory and application to storage-dependent transport of chloride in a watershed
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DOI：
10.1002/2014wr015707
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发表时间：
2015-01-01
影响因子：
5.4
通讯作者：
Harman, Ciaran J.
中科院分区：
文献类型：
--
作者：
Harman, Ciaran J.
通过许多水动力系统的迁移过程和路径随时间而变化，通常是由总储水量的变化所驱动的。本文开发了一种非常通用的方法来模拟非稳态运输通过一个任意的控制体积（如分水岭），占时间变化的基础运输动力学。从存储的水排放的选择的控制封装在概率分布Q（ST，t）的年龄分级存储S-T（存储中的水的体积从最年轻的到最老的排序）。这个框架适用于一个长期的降雨量和径流氯化物在一个小的，潮湿的流域Plynlimon，英国的记录。虽然（Q）的时不变伽马分布与数据拟合良好，但当允许分布随集水区蓄水量变化时，拟合效果显著改善。然而，这种变化与储存具有纯稀释效应的良好混合系统的变化相反。在高存储量的排放预计包含一个更大的比例比在低存储量的最近事件的水。运输涉及的有效存储量为3411毫米，在平均集水区湿度，但下降了71毫米，每1毫米的额外集水区存储，而事件水排放的分数增加了1.4%。这种逆存储效应足以再现所观察到的流氯化物的长记忆1/f分形光谱结构。量化存储效果的强度和方向的建议作为有用的签名，并指向一个统一的框架，观察和模拟耦合流域水流和运输。
Transport processes and pathways through many hydrodynamic systems vary over time, often driven by variations in total water storage. This paper develops a very general approach to modeling unsteady transport through an arbitrary control volume (such as a watershed) that accounts for temporal variability in the underlying transport dynamics. Controls on the selection of discharge from stored water are encapsulated in probability distributions Q(ST,t) of age-ranked storage S-T (the volume of water in storage ranked from youngest to oldest). This framework is applied to a long-term record of rainfall and streamflow chloride in a small, humid watershed at Plynlimon, UK. While a time-invariant gamma distribution for (Q) produced a good fit to data, the fit was significantly improved when the distribution was allowed to vary with catchment storage. However, the variation was inverse to that of a well-mixed system where storage has a pure dilution effect. Discharge at high storage was predicted to contain a larger fraction of recent event water than at low storage. The effective volume of storage involved in transport was 3411 mm at mean catchment wetness, but declined by 71 mm per 1 mm of additional catchment storage, while the fraction of event water in discharge increased by 1.4%. This inverse storage effect is sufficient to reproduce the observed long-memory 1/f fractal spectral structure of stream chloride. Metrics quantifying the strength and direction of storage effects are proposed as useful signatures, and point toward a unified framework for observing and modeling coupled watershed flow and transport.