In this study, we explore the use of unsteady transit time distribution (TTD) theory to model solute transport in biofilters, a popular form of nature‐based or “green” storm water infrastructure (GSI). TTD theory has the potential to address many unresolved challenges associated with predicting pollutant fate and transport through these systems, including unsteadiness in the water balance (time‐varying inflows, outflows, and storage), unsteadiness in pollutant loading, time‐dependent reactions, and scale‐up to GSI networks and urban catchments. From a solution to the unsteady age conservation equation under uniform sampling, we derive an explicit expression for solute breakthrough during and after one or more storm events. The solution is calibrated and validated with breakthrough data from 17 simulated storms at a field‐scale biofilter test facility in Southern California, using bromide as a conservative tracer. TTD theory closely reproduces bromide breakthrough concentrations, provided that lateral exchange with the surrounding soil is accounted for. At any given time, according to theory, more than half of the water in storage is from the most recent storm, while the rest is a mixture of penultimate and earlier storms. Thus, key management endpoints, such as the pollutant treatment credit attributable to GSI, are likely to depend on the evolving age distribution of water stored and released by these systems.

中文翻译：

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非平稳过渡时间分布理论预测绿色雨水基础设施中的溶质运移

在这项研究中，我们探索了使用非稳态迁移时间分布（TTD）理论来模拟生物滤池中的溶质运移，该滤池是一种基于自然或“绿色”雨水基础设施（GSI）的流行形式。TTD理论有可能解决与预测污染物命运和通过这些系统的运输相关的许多未解决的挑战，包括水平衡的不稳定（时变的流入量，流出量和存储量），污染物负载的不稳定量，时间依赖性的反应以及扩大到GSI网络和城市集水区。从统一采样下的非稳态年龄守恒方程的解中，我们得出一个或多个风暴事件期间和之后溶质突破的明确表达。使用溴化物作为保守示踪剂，在加利福尼亚州南部的一个现场规模的生物滤池测试设施中，使用来自17次模拟风暴的突破性数据对解决方案进行了校准和验证。如果考虑到与周围土壤的横向交换，TTD理论紧密地再现了溴化物的突破浓度。根据理论，在任何给定时间，超过一半的存储水来自最近的风暴，而其余部分则是倒数第二和更早的风暴的混合物。因此，关键的管理终点，例如可归因于GSI的污染物处理信用，可能取决于这些系统存储和释放的水的年龄变化。只要考虑到与周围土壤的横向交换。根据理论，在任何给定时间，超过一半的存储水来自最近的风暴，而其余部分则是倒数第二和更早的风暴的混合物。因此，关键的管理终点，例如可归因于GSI的污染物处理信用，可能取决于这些系统存储和释放的水的年龄变化。只要考虑到与周围土壤的横向交换。根据理论，在任何给定时间，超过一半的存储水来自最近的风暴，而其余部分则是倒数第二和更早的风暴的混合物。因此，关键的管理终点，例如可归因于GSI的污染物处理信用，可能取决于这些系统存储和释放的水的年龄变化。