Observations and Modelling of Freeze-up Processes in Rivers

当北方河流的水超级冷却到略低于零度时，被称为Frazil的微小冰粒会在水流的湍急部分形成。几乎所有形式的河冰都起源于碎屑，其形成和演化是冰冻过程中的主要河冰过程。过冷水中的脆性颗粒很容易附着在自然和人造表面上。它们可能会粘在床上，形成锚冰，或者相互粘连，形成絮状物，最终在表面变成大的冰沙球，冻结在一起，形成“奶油平底锅”，最终形成冰盖。数值河冰模型包括模拟冻结过程的算法，但由于缺乏现场数据可供比较，其准确性尚不清楚。尽管近年来在开发精确的测量技术方面取得了进展，但仍然非常需要更多的现场测量。为了满足这一需求，我提出了一个雄心勃勃的现场测量计划，旨在显著增加我们对关键冻结过程的了解，并使用产生的数据来评估当前用于模拟这些过程的算法的准确性。这项拟议研究的长期目标是提高我们对河流冰的形成及其对河流生态、水力学和地貌的影响的了解。拟议研究计划的短期目标是：(1)继续调查河流中悬浮冰的产生、运输和去向；(2)调查锚冰的性质及其对河流生态和水力学的影响。(三)确定锚冰排沙对河流泥沙收支的影响。(四)评估河冰过程模型准确模拟冰冻的能力。三名博士生和两名硕士研究生将合作开展这项拟议的研究。这些学生将接受关于使用各种复杂的现场仪器、先进的数据处理方法和数值建模的培训。实地测量将在两条河流的多个冬季进行。河冰过程模式River1D将应用于这两条河流，并将通过比较模型预测和现场测量来评估其模拟冰冻过程的准确性。理科硕士学生将收集和平河表面冰层状况的数字图像，并使用机器学习技术进行分析。他们的目标是获得对释放的锚定冰盘输送的泥沙数量的准确估计。提高我们准确监测和预测河流冻结过程的能力，将对沿河流修建的基础设施的规划、设计、建设和运营产生重大影响。它还将加强我们评估寒冷地区项目的环境影响和更准确地评估气候变化对北方河流冻结过程的影响的能力。

Tiny ice particles, called frazil, form in the turbulent portions of the flow in northern rivers when the water supercools to just below zero degrees. Virtually all forms of river ice originate from frazil and its formation and evolution are the dominant river ice processes during freeze-up. Frazil particles in supercooled water readily adhere to natural and man-made surfaces. They may stick to the bed, forming anchor ice, or to each other, creating flocs that ultimately become large slush balls at the surface, freeze together into `frazil pans,' and eventually form the ice cover. Numerical river ice models include algorithms for simulating freeze-up processes but their accuracy is unknown due to a lack of field data to compare with. Although progress has been made in recent years to develop accurate measurement techniques there is still a great need for additional field measurements. To address this need, I propose an ambitious program of field measurements designed to significantly increase our knowledge of key freeze-up processes, and to use the resulting data to assess the accuracy of the algorithms currently used to model these processes. The long-term goal of the proposed research is to improve our understanding of how river ice forms, and its impacts on river ecology, hydraulics, and geomorphology. The short-term objectives of the proposed research program are to:    (1)Continue investigating the generation, transport, and fate of suspended frazil ice in rivers    (2)Investigate the properties of anchor ice and its impact on the ecology and hydraulics of rivers.    (3)Determine the impact of rafting of sediment by anchor ice on the sediment budget of rivers.    (4)Assess the ability of river ice process models to accurately model freeze-up. Three PhD and two MSc students will collaborate on the proposed research. The students will receive training on the use of a wide variety of sophisticated field instrumentation, advanced data processing methods and numerical modelling. Field measurements will be conducted over multiple winters on two rivers. River1D, a river ice processes model, will be applied to both rivers and its accuracy simulating freeze-up processes will be assessed by comparing model predictions to field measurements. The MSc students will gather digital images of surface ice conditions on the Peace River and analyze them using machine learning techniques. Their goal is to obtain accurate estimates of the amount of sediment transported by released anchor ice pans. Improving our ability to accurately monitor and predict freeze-up processes in rivers will have a significant impact on the planning, design, construction and operation of infrastructure built along rivers. It will also enhance our ability to assess the environmental impacts of cold region projects and more accurately assess the impact of climate change on freeze-up processes in northern rivers.