Logjams with a gap at the bed form naturally in small channels and are used in engineering practice to maintain river connectivity at base flow. Limited understanding of a jam's effect on backwater rise and flow velocity limits assessment of geomorphic and ecological impacts of natural logjams, design of river restoration interventions, and representation in flood models. The distribution of flow through and beneath the jam satisfies a two-box, momentum-based model constrained by drag generated in the jam, momentum loss in flow through the lower gap, and net pressure force. The model was validated with 68 flume experiments. Backwater rise is predicted from discharge beneath the jam following established models for solid sluice gates. As a result, backwater rise increases with jam resistance, which forces a greater discharge beneath the jam. Below-jam velocity and Shields parameter increased with ratio of friction coefficient to slope and decreasing gap height.

中文翻译：

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具有较低间隙的堵塞：通过两箱动量平衡预测的回水上升和流量分布在堵塞下面和通过堵塞

河床有间隙的木塞自然形成在小渠道中，并在工程实践中用于保持河流在基流处的连通性。对堵塞对回水上升和流速影响的有限理解限制了自然堵塞对地貌和生态影响的评估、河流恢复干预措施的设计以及洪水模型中的表示。通过堵塞和下方的流量分布满足基于动量的双箱模型，该模型受堵塞中产生的阻力、通过下部间隙的流动的动量损失和净压力约束。该模型通过 68 个水槽实验进行了验证。根据已建立的固体闸门模型，从堵塞下方的排放预测回水上升。结果，回水上升随着堵塞阻力而增加，这迫使堵塞下方有更大的排放。