During rest periods, bedload tracers can be buried, while transport can move them to locations with different bed shear stresses or a different riverbed composition. This affects the mobility of the tracers compared to that of the bedload at the location where the tracers were seeded and has so far limited the explanatory power of field tracer studies on the virtual bedload velocity. This paper proposes a method to assess both the unsteady virtual tracer velocity and the unsteady virtual bedload velocity from field tracer studies. First, the virtual bedload velocity was conceptualized as the velocity of a relay run and contrasted with the velocity of the decelerating runs of bedload tracers. Then, a regression method for deriving the unsteady virtual velocity of bedload tracers was extended to account for tracer slowdown by including a corresponding function of the distance traveled. Finally, data from 65 bedload tracers in the Upper Drava River with very-high-frequency (VHF) transmitters were used for method testing. By linking the measured tracer mobility to the hydraulics and bed surface grain size near the seeding location, it was possible to determine the unsteady bedload velocity function as the unsteady tracer velocity function at a travel distance of zero. The tracer travels exhibited increasing slowdown effects with increasing tracer grain size, probably due to the dominant role of advection effects at the study site. The derivation of the bedload velocity ensures comparability to laboratory results and between tracer studies.

中文翻译：

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示踪剂速度与床载速度：从减速示踪剂推导出不稳定虚拟床载速度


在休息期间，床载示踪剂可以被掩埋，而运输可以将它们移动到具有不同床剪应力或不同河床成分的位置。与示踪剂播种位置的床载相比，这会影响示踪剂的移动性，并且迄今为止限制了现场示踪剂研究对虚拟床载速度的解释能力。本文提出了一种从现场示踪剂研究中评估非稳态虚拟示踪剂速度和非稳态虚拟床载速度的方法。首先，虚拟床载速度被概念化为接力运行的速度，并与床载示踪剂的减速运行的速度进行对比。然后，扩展了推导床载示踪剂非稳态虚拟速度的回归方法，通过包含相应的行进距离函数来解释示踪剂减慢。最后，使用来自德拉瓦河上游 65 个床载示踪剂和甚高频 (VHF) 发射机的数据进行方法测试。通过将测得的示踪剂迁移率与播种位置附近的水力和床表面颗粒尺寸联系起来，可以将不稳定的床载速度函数确定为行进距离为零时的不稳定示踪剂速度函数。随着示踪剂颗粒尺寸的增加，示踪剂旅行表现出越来越大的减速效应，这可能是由于研究地点平流效应的主导作用。床载速度的推导确保了与实验室结果以及示踪剂研究之间的可比性。