The key features of the equilibrium scour depth $d_{\mathit{se}}$, width $W_{\mathit{se}}$, length $L_{\mathit{se}}$ and the volume $V_{\mathit{se}}$ with large abutment aspect ratios (i.e., abutment width $L_c$ divided by its length $L$) in floodplain are different compared to narrow abutments. Seven models with $L_c/L$ ranging from 0.125 (narrow abutment) to 4 (very wide abutment) were tested. The results show that the combined effect in terms of the abutment aspect ratio $L_c/L$ is a key parameter with wide abutments. Furthermore, the average equilibrium scour width observed was much larger than previous studies and extends up to 3.5 times the floodplain water depth. This implies the current guideline by FHWA (Federal Highway Administration), (2009) to provide a riprap countermeasure apron width for 2 times the floodplain water depth may be insufficient. The much wider scour formation is caused by the migration of the maximum scour location around wide abutments. The results show generally the scour hole dimensions for setback abutments in compound channel are less than that abutments in rectangular channel under the same flow conditions. To this end, empirical equations, which agree well with the data from the present and previous studies are proposed to predict these characteristics at the equilibrium state.

平衡冲刷深度的主要特征$d_{\mathit{瑟}}$， 宽度$W_{\mathit{瑟}}$， 长度${\mathrm{大号}}_{\mathit{瑟}}$和音量${五}_{\mathit{瑟}}$具有大的基台纵横比（即基台宽度${\mathrm{大号}}_C$除以其长度$\mathrm{大号}$) 在洪泛区与狭窄的桥台相比是不同的。七款车型${\mathrm{大号}}_C/\mathrm{大号}$测试范围从 0.125（窄基台）到 4（非常宽基台）。结果表明，在基台纵横比方面的综合效果${\mathrm{大号}}_C/\mathrm{大号}$是宽基台的关键参数。此外，观察到的平均平衡冲刷宽度比以前的研究大得多，并延伸到洪泛区水深的 3.5 倍。这意味着 FHWA（联邦公路管理局）（2009 年）的当前指南提供 2 倍洪泛区水深的抛石对策围裙宽度可能是不够的。较宽的冲刷地层是由最大冲刷位置在宽基台周围的迁移引起的。结果表明，在相同水流条件下，复合渠道退台桥台冲刷孔尺寸普遍小于矩形渠道桥台。为此，提出了与当前和先前研究的数据非常吻合的经验方程，以预测平衡状态下的这些特征。