Reach‐scale at‐a‐station hydraulic geometry (AHG) relationships are power laws that describe variations of reach‐averaged water depth, wetted width, and current velocity in stream reaches when discharge varies. Modeling AHG exponents is important, because the variations of hydraulics with discharge in stream networks influence physical habitats of aquatic species, biodiversity, water temperature, nutrient fluxes, and sediment transport. Theoretical approaches indicated that AHG exponents should depend on topographic descriptors of cross sections and roughness elements. Empirical approaches suggested that AHG exponents partly depend on hydraulic characteristics measured at a single discharge. We used a unique data set of AHG observed in 812 stream reaches (obtained from measurements at several discharge rates or from hydrodynamic models) to (1) test the consistency of theoretical and empirical predictions of AHG exponents and (2) test the generality of AHG predictions across rivers of different countries with variable landscape settings. We found that observed AHG depended on topographic predictors (describing cross‐section shape and substrate size) as expected from theory. However, AHG exponents were better predicted by empirical hydraulic characteristics of reaches: the ratio of wetted width to bankfull width and the reach Froude number. The effects of hydraulic variables were consistent with those of topographic predictors. In addition, relations between AHG and hydraulic predictors were significant and with similar direction in different data sets. Despite limited explanatory power, our results help identifying general drivers of AHG exponents. Their application still requires measurements at a single discharge rate but open perspectives of generalized AHG prediction by remote sensing.

中文翻译：

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流域中站台水力几何指数的理论和经验预测一致

到达站静态水力几何关系（AHG）关系是功率定律，描述了当排放量变化时，河段平均水深，湿润宽度和溪流中当前流速的变化。对AHG指数进行建模很重要，因为水流中水力随排水的变化会影响水生生物的物理生境，生物多样性，水温，养分通量和沉积物迁移。理论方法表明，AHG指数应取决于横截面和粗糙度元素的形貌描述。经验方法表明，AHG指数部分取决于单次排放时测得的水力特性。我们使用了在812条河段观测到的独特的AHG数据集（从几个排放速率的测量值或从流体动力学模型获得）来（1）测试AHG指数的理论和经验预测的一致性，以及（2）测试AHG的一般性不同国家/地区河流景观变化的预测。我们发现观察到的AHG取决于理论所期望的地形预测因子（描述横截面形状和基质尺寸）。但是，通过河段的经验水力特性可以更好地预测AHG指数：湿宽度与河岸宽度之比以及河段Froude数。水力变量的影响与地形预测因子一致。此外，AHG和水力预报器之间的关系很明显，并且在不同的数据集中具有相似的方向。尽管解释力有限，但我们的结果有助于确定AHG指数的一般驱动因素。它们的应用仍然需要以单个放电速率进行测量，但是对通过遥感进行的广义AHG预测的开阔视野。