Multifrequency Acoustic Doppler Profilers

河道是水和沉积物通过景观的通道。它们的形态和动力学是由湍流与沉积物和边界的相互作用造成的，在冲积河流的情况下，边界可能是不稳定的，或者相对抗侵蚀，如基岩河流。在过去的几十年里，河道行为的预测有了很大的改善，这在很大程度上是因为我们有能力测试理论和数值模型的河流行为对高分辨率的观测泥沙动力学，河床形态，湍流。然而，我们对地球上最大的河流的了解仍然很差，主要是由于缺乏对水流和河床地形的高分辨率观测。如果没有这种观测，仍然很难模拟大型河流系统的行为并预测其演变。所要求的仪器将支持探索大型河流形态动力学的研究计划。 这项工作围绕着河流科学中三个主要的突出形态动力学问题：1）不稳定的砂床如何抵抗水流并调解洪水，2）复杂的沉积物流动如何雕刻基岩峡谷，以及3）河流如何受到冰形成，破裂和排放的影响。这项研究需要使用适用于河流的海洋学水声仪器对水流进行高分辨率观测。我们请求提供两台双频声学多普勒海流剖面仪和配套的RTK-GNSS设备，这些设备是为海洋环境设计的。每个ADCP都有两套四个不同频率（300/600 kHz和600/1200 kHz）的换能器，在清水中有从几米到一百米的不同剖面范围。较低的频率范围只需要穿透河流中的水柱，强大到足以悬浮砾石大小的颗粒。较高的频率范围在浅流（<5米）中提供了更高的分辨率，其中300/600 kHz ADCP将为每个剖面提供一个或两个点。三个频率的组合允许对速度和声学后向散射进行交错测量，这可用于声学反演，以测量悬浮泥沙浓度、粒度和粒度比泥沙通量。这项研究将产生的河流动力学和洪水过程的新知识对所有加拿大人，特别是管理、养护和保护河流景观的决策者都很有价值。 从来没有一个更紧迫的时间来了解河流如何洪水。在加拿大这样的经济富裕国家，预测河流何时发生洪水，价值数十亿美元的基础设施保护成本。在经济上较贫穷的国家，防洪设施不存在，准确的洪水水位预测是一个生死攸关的问题，包括生存，救援和搬迁计划。

River channels are conduits for water and sediment through landscapes. Their morphology and dynamics result from the interaction of turbulent flow with sediment and a boundary that may be labile, in the case of alluvial rivers, or relatively resistant to erosion, as for bedrock rivers. Prediction of river channel behavior has improved dramatically over the past few decades, in large part because of our ability to test theory and numerical models of river behaviour against high-resolution observations of sediment dynamics, river bed configuration, and turbulent flow. Yet our understanding of the largest rivers on Earth remains poor, largely due to a lack of high-resolution observations of flow and bed topography. It remains difficult to model the behaviour of large river systems and predict their evolution without such observations. The requested instrumentation will support research programs exploring the morphodynamics of large rivers. The work centers around three major outstanding morphodynamic problems in river science: 1) How a labile sand bed resists flow and mediates flooding, 2) How complex sediment-laden flows carve bedrock canyons, and 3) How rivers are impacted by ice formation, breakup and discharge. The research requires high-resolution observations of flow, using oceanographic hydroacoustic instruments adapted for use in rivers. We request two dual frequency acoustic Doppler current profilers (ADCPs) and accompanying RTK-GNSS equipment designed for marine environments. Each ADCP has two sets of four transducers with different frequencies (300/600 kHz and 600/1200 kHz) and different profiling ranges from a few to a hundred meters in clear water. The lower frequency ranges are required simply to penetrate the water column in rivers powerful enough to suspend gravel-sized particles. The higher frequency ranges provide greater resolution in shallow flows (<5m) where the 300/600 kHz ADCP would provide just one or two points per profile. The combination of three frequencies allows for interleaved measurements of velocity and acoustic backscatter, which can be used in acoustic inversions to measure suspended sediment concentration, grain size and grain size specific sediment flux. The new knowledge of river flow dynamics and flood processes that will result from this research is valuable to all Canadians, particularly decision makers who manage, conserve and preserve river landscapes. There has never been a more pressing time to understand how rivers flood. In economically rich countries like Canada, predicting when rivers flood is worth billions of dollars in infrastructure protection costs. In economically poorer countries, where flood defenses are non-existent, accurate flood water level predictions are a matter of life and death when included in survival, rescue, and relocation plans.