Abstract Predictions of river channel adjustment to changes in streamflow regime based on relations between mean channel characteristics and mean flood magnitude can be useful to evaluate average channel response. However, because these relations assume equilibrium sediment transport, their applicability to cases where streamflow and sediment transport are decoupled may be limited. These general relations also lack the specificity that is required to connect specific characteristics of the streamflow and sediment regime with the dynamics of channel morphological change that create channel complexity, which is often of ecological interest. We integrate historical records of channel change, observations of scour and fill during a snowmelt flood, measurements of sediment transport, and predictions from a two-dimensional streamflow model to describe how annual peak flow magnitude and peak-flow duration interact with the upstream sediment supply to control channel form for a 15-km study reach on the regulated Green River in Canyonlands National Park, Utah. Two major decadal-scale episodes of channel narrowing have occurred within the study area. For each of these episodes, the reduction in average channel width was consistent with the change predicted by hydraulic geometry relations as a function of average flood magnitude. However, channel narrowing occurred during periods of exceptionally low annual floods. The most recent episode of channel narrowing occurred between 1988 and 2009, during low-flow cycles when the 5-yr mean peak flow was less than 60% of the long-term (1959–2016) mean peak flow. These findings, together with findings from previous studies, demonstrate that decreases in peak-flow magnitude caused by streamflow regulation, climate change, or a combination of those factors have driven episodes of channel narrowing on the Green River. Observations of streamflow, sediment-transport, and morphologic change coupled with predictions from a two-dimensional streamflow model indicate that peak flow magnitudes of at least 75% of the long-term mean peak flow are required to transport bed-material sand in suspension in all regions of the multi-thread channel and that the ~2-month duration of the snowmelt flood played an important role in creating conditions necessary to maintain channel conveyance. These results indicate that detailed characterizations of channel response such as these are needed to predict how river channels will respond to changes in streamflow regime that affect annual peak flow magnitude and duration.

中文翻译：

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美国犹他州峡谷地绿河洪水规模和持续时间在控制河道宽度和复杂性方面的作用

摘要 基于平均河道特征与平均洪水量级之间关系的河道调整对水流情势变化的预测可用于评估平均河道响应。然而，由于这些关系假设泥沙输运平衡，因此它们在水流和泥沙输运分离的情况下的适用性可能会受到限制。这些一般关系也缺乏将河流和沉积物状况的特定特征与造成河道复杂性的河道形态变化动力学联系起来所需的特异性，这通常具有生态学意义。我们整合了河道变化的历史记录、融雪洪水期间冲刷和填埋的观察、沉积物迁移的测量、以及来自二维河流模型的预测，以描述年峰值流量大小和峰值流量持续时间如何与上游沉积物供应相互作用，以控制犹他州峡谷地国家公园受管制绿河上 15 公里研究范围的河道形式。研究区内发生了两次主要的十年级航道变窄事件。对于这些事件中的每一个，平均河道宽度的减少与水力几何关系预测的作为平均洪水大小的函数的变化一致。然而，渠道变窄发生在年度洪水异常低的时期。最近一次航道变窄发生在 1988 年至 2009 年之间，在低流量周期期间，5 年平均峰值流量小于长期（1959-2016 年）平均峰值流量的 60%。这些发现，结合先前研究的结果，表明由流量调节、气候变化或这些因素的组合引起的峰值流量大小的降低导致了绿河上的河道变窄。对水流、沉积物输送和形态变化的观察以及二维水流模型的预测表明，需要至少 75% 的长期平均峰值流量的峰值流量大小才能在多线程通道的所有区域以及大约 2 个月的融雪洪水持续时间在为维持通道输送创造必要条件方面发挥了重要作用。