Mixed bedrock–alluvial channel beds are common in mountain rivers. It is well-known that in such system the balance between sediment supply and transport capacity defines either the level of the exposure of bedrock (in the riverbed) or its coverage by alluvial material. We investigate whether applying the representation of the energy losses (caused by macro-roughness) developed for alluvial channels improve the capacity of bedload transport equations to predict the bedload transport in a mixed bedrock–alluvial stream. Therefore, the purpose of this study was to evaluate the performances of five bedload equations against field measurements, while considering the effects of macro-roughness on the equations and the limited availability of mobile sediment. We analyzed the data collected in a stream located in southern Brazil, which has a 2.3% gradient and mixed bed conditions. Optimal results in estimating the bedload transport rate were obtained when using the reduced shear stress $\left(\tau \text{'}\right)$ and reduction factor of the available bed material (Frm) together in the five tested equations. Analyzing the two approaches separately, the implementation of ${\tau }^{\text{'}}$ proved to be more critical for improving the performance of the equations than using Frm alone. Among all the equations, Recking (2013) presented the best result for the case in which 85.2% of the estimates fell within one order of magnitude of the measured transport rates (0.1 < r > 10.0); this was followed by the Recking (2010) (70.4% of estimates within one order of magnitude) and Meyer-Peter and Müller (1948) (37% of estimates within one order of magnitude) equations. In conclusion, we observed that even by implementing flow resistance and with the limited availability of mobile sediment, the equations overestimated the bedload transport rate in the studied river reach, indicating an underestimation of energy loss in the flow resistance equations of mixed bedrock–alluvial channels.

基岩-冲积河床混合床在山区河流中很常见。众所周知，在这样的系统中，沉积物供应和运输能力之间的平衡决定了基岩（在河床中）的暴露水平或被冲积物质覆盖的程度。我们调查是否应用冲积河道能量损失（由宏观粗糙度引起）的表示方法是否提高了基岩输运方程式的能力，以预测混合基岩-冲积流中的基岩输运。因此，本研究的目的是针对现场测量评估五个床荷方程的性能，同时考虑宏观粗糙度对方程的影响以及流动性泥沙的有限利用。我们分析了巴西南部一条溪流中收集到的数据，该溪流为2。3％梯度和混合床条件。当使用降低的剪应力时，获得了估算床载运输速率的最佳结果$\left(\tau \text{'}\right)$五个测试方程式中可用床料的折减系数（Frm）和折算系数。分别分析两种方法，实现${\tau }^{\text{'}}$事实证明，与仅使用Frm相比，改善方程组的性能更为关键。在所有方程中，Recking（2013）提出了最佳结果，其中85.2％的估计值落在所测得的运输速率的一个数量级之内（0.1 <r> 10.0）；其次是Recking（2010）（估计值在一个数量级内的70.4％）和Meyer-Peter andMüller（1948）（估计值在一个数量级内的37％）方程。总之，我们观察到，即使通过实施流阻和有限的流动性泥沙，这些方程也高估了所研究河段的基床输运速度，这表明混合基岩冲积河道的流阻方程中的能量损失被低估了。 。