We present an experimental analysis of hydraulic roughness variations due to changes in alluvial cover in a mixed bedrock-alluvial meandering channel with larger bedrock roughness than alluvial roughness. Three sets of experiments were conducted in a highly sinuous flume: one with bare bedrock, and two with enough sediment to cover 21% and 78% of the bedrock respectively. We compare our results with data from experiments previously conducted in the same flume with flat- and smooth-bed, and data from experiments with fully alluvial conditions. Our results show that: (1) hydraulic resistance in a mixed bedrock-alluvial channel changes with the degree of alluviation; (2) hydraulic resistance is greater for bare-bedrock conditions, and decreases as sediment supply increases; (3) if bedforms appear, hydraulic resistance may be larger than for bare bedrock conditions due to form drag; (4) fluctuations in alluvial cover due to freely-migrating bars lead to instantaneous changes in hydraulic resistance.

我们目前进行的水力粗糙度变化的实验分析是由于混合基岩-冲积曲折河道中冲积层的变化所致，基岩粗糙度大于冲积粗糙度。在高度弯曲的水槽中进行了三组实验：一组具有裸露的基岩，另外两组具有足够的沉积物，分别覆盖了21％和78％的基岩。我们将我们的结果与之前在同一槽中使用平床和光滑床进行的实验数据以及在完全冲积条件下的实验数据进行比较。我们的结果表明：（1）混合基岩冲积河道的水力阻力随冲积程度而变化；（2）在裸基岩条件下，水力阻力较大，并随着沉积物供应的增加而减小；（3）如果出现床形，由于形成阻力，水力阻力可能比裸露的基岩条件大；（4）由于杆的自由移动，冲积层的波动导致水力阻力的瞬时变化。