Accurate and reliable estimates of water levels are essential to assess flood risk in river systems. In current practice, uncertainties involved and the sensitivity of water levels to these uncertainties are studied in single-branch rivers, while many rivers in deltas consist of multiple distributaries. In a bifurcating river, a feedback mechanism exists between the downstream water levels and the discharge distribution at the bifurcation. This paper aims to quantify the sensitivity of water levels to main channel roughness in a bifurcating river system. Water levels are modelled for various roughness scenarios under a wide range of discharge conditions using a one-dimensional hydraulic model. The results show that the feedback mechanism reduces the sensitivity of water levels to local changes of roughness in comparison to the single-branch river. However, in the smaller branches of the system, water-level variations induced by the changes in discharge distribution can exceed the water-level variations of the single-branch river. Therefore, water levels throughout the entire system are dominated by the conditions in the largest branch. As the feedback mechanism is important, the river system should be considered as one interconnected system in river maintenance of rivers, flood-risk analyses, and future planning of river engineering works.

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分叉河流系统的反馈机制：对水位敏感性的影响

准确可靠的水位估算对于评估河流系统的洪水风险至关重要。在目前的实践中，所涉及的不确定性以及水位对这些不确定性的敏感性在单支河流中进行了研究，而三角洲中的许多河流由多个支流组成。在分叉河流中，下游水位与分叉处的流量分布之间存在反馈机制。本文旨在量化分叉河流系统中水位对主河道粗糙度的敏感性。使用一维水力模型对各种排放条件下的各种粗糙度情况下的水位进行建模。结果表明，与单支河流相比，反馈机制降低了水位对局部粗糙度变化的敏感性。然而，在系统的较小支流中，由流量分布变化引起的水位变化可能超过单支河流的水位变化。因此，整个系统的水位由最大分支的条件决定。由于反馈机制很重要，因此在河流的河流维护、洪水风险分析和河流工程的未来规划中，河流系统应被视为一个相互关联的系统。