Hyporheic exchange flow (HEF) can generally be quantified through two different approaches. The first approach, which is deductive, entails physically based models, supported with relevant observations. The second approach includes inductive assessments of stream tracer tests using solute transport models, which provide a useful mathematical framework that allows for upscaling of results, but included parameters often have a vague physical base, which limits the possibilities of generalizing results using independent hydromorphological observations. To better understand how the physical basis of HEF-quantifying parameters relates to stream hydromorphology at different spatial scales, we cross-validated the results from (a) tracer test assessments using a 1D solute transport model that accounts for HEF and (b) an independent hydromechanical model that represents HEF driven by multiscale pressure gradients along the streambed interface. To parameterize the models, topographical surveys, tracer tests, and streambed hydraulic conductivity measurements were performed in 10 stream reaches, differing in terms of geomorphology, slope, and discharge. The results show that the models were cross-validated in terms of the average exchange velocity, providing a plausible physical explanation for this parameter in small alluvial streams with low discharges, shallow depth, and moderate slopes. However, the hydromechanical model generally resulted in wider residence time distributions and occasionally higher average residence times compared to the tracer test assessments. From the cross-validated multiscale hydromechanical model, we learned that water surface profile variations were the main drivers of HEF in all investigated streams and that spatial scales between 20 cm and 5 m dominated the estimated HEF velocity.

中文翻译：

---

具有不同水文形态特征的河流中低流交换流的交叉验证流体力学模型和示踪剂测试评估

Hyporheic 交换流 (HEF) 通常可以通过两种不同的方法进行量化。第一种方法是演绎方法，需要基于物理的模型，并得到相关观察的支持。第二种方法包括使用溶质传输模型对河流示踪剂测试进行归纳评估，该模型提供了一个有用的数学框架，允许放大结果，但包含的参数通常具有模糊的物理基础，这限制了使用独立水文形态观察概括结果的可能性。为了更好地理解 HEF 量化参数的物理基础如何与不同空间尺度的河流水形态学相关，我们交叉验证了来自（a）示踪剂测试评估的结果，该评估使用一维溶质运移模型来解释 HEF，以及（b）一个独立的流体力学模型，代表由沿河床界面的多尺度压力梯度驱动的 HEF。为了对模型进行参数化，在地貌、坡度和流量不同的 10 个河段进行了地形调查、示踪剂测试和河床水力传导率测量。结果表明，这些模型在平均交换速度方面进行了交叉验证，为具有低流量、浅深度和中等坡度的小型冲积流中的该参数提供了合理的物理解释。然而，与示踪剂测试评估相比，流体力学模型通常导致更宽的停留时间分布和偶尔更高的平均停留时间。从交叉验证的多尺度流体力学模型中，我们了解到水面剖面变化是所有研究河流中 HEF 的主要驱动因素，并且 20 cm 和 5 m 之间的空间尺度主导了估计的 HEF 速度。