Assuming that the equilibrium geometry of river channels does not depend on their initial state but solely on boundary conditions, several formulas have been derived that relate the channel depth and width to the river bankfull discharge and bed material. However, due to the existence of a threshold for sediment motion and the strong non-linearity between sediment transport and flow rate, this assumption might not be generally valid for gravel-bed rivers. This research clarifies the role of the initial conditions, more specifically the initial channel width, on the geometry of gravel-bed rivers considering a variety of boundary conditions. The approach includes laboratory experiments and two-dimensional modeling, reproducing the evolution of alluvial channels with different starting widths, discharge regimes and sediment input rates. The experiments represent the Arc River (France). Thus, the characteristics of this river were used in the numerical model to obtain a realistic virtual case complementing the experiments. Different boundary and starting conditions resulted in either braided or single-thread channels. We found that the initial width strongly influences the evolution process and leaves a footprint on the river braid-belt extension. The active width of braided systems and the width of single-thread channels do not depend on the starting condition. They depend on sediment input rather than on discharge variability. Different initial widths result in different final bed levels. This indicates that the initial channel width may affect the degree of channel incision or aggradation. The results of this study justify the use of equilibrium formulas for single-thread rivers.

假设河道的平衡几何不取决于它们的初始状态，而仅取决于边界条件，推导出了几个公式，将河道深度和宽度与河岸流量和河床材料联系起来。然而，由于泥沙运动阈值的存在以及泥沙输送和流速之间存在很强的非线性，这种假设可能不适用于砾石河床。本研究阐明了初始条件（更具体地说是初始河道宽度）对考虑各种边界条件的砾石河床几何形状的作用。该方法包括实验室实验和二维建模，再现具有不同起始宽度、排放方式和沉积物输入速率的冲积通道的演变。实验代表 Arc River（法国）。因此，在数值模型中使用了这条河流的特征，以获得补充实验的现实虚拟案例。不同的边界和起始条件导致编织或单线程通道。我们发现初始宽度强烈影响演化过程，并在河流辫状带延伸处留下足迹。编织系统的有效宽度和单线通道的宽度不取决于起始条件。它们取决于沉积物输入而不是排放变化。不同的初始宽度导致不同的最终床层高度。这表明初始通道宽度可能会影响通道切口或积聚的程度。