Have large scale river plumes and coastal circulation patterns been fundamentally altered by historic estuary outlet modifications?

浮力的河流羽流是由河流排放到大陆架上的轻淡水形成的，是世界沿海海洋中普遍存在的特征。河流羽流是沿海环流和生物地球化学循环的重要组成部分，是陆源碳、营养物质和其他陆源成分进入沿海海洋的重要通道。大量的理论、实验室和数值研究都指出，河口的深度和宽度对于确定大块羽流特性（如跨岸羽流范围和海岸流输送）的重要性。此外，最初的羽流结构和随后对外部强迫（风、波、周围陆架环流）的响应在很大程度上是由外流决定的。自19世纪80年代末以来，下哥伦比亚河河口（lre）经历了持续的工程改造，在哥伦比亚河口建造了码头和疏浚航道，使出口深度和宽度都改变了近50%。历史和现代的LCRE/哥伦比亚河羽流（CRP）系统为研究控制河口、羽流和沿海海洋之间耦合的基本物理过程提供了一个独特而新颖的测试平台，同时提供了有价值的见解，并提高了对LCRE/CRP系统的人类影响的集体理解。该项目研究了在过去130年里，人类对河流流量、几何形状、形态和河道方向的改变是如何影响或改变了控制整个河流-河口-沿海耦合海洋系统混合、结构和运输的主要物理过程的。由于羽流是陆地/海洋交换沉积物、营养物质和其他标量的主要环节，因此更好地了解羽流动力学的历史变化将扩大我们对沿海生态系统长期变化的理解。此外，CRP的位置和结构对哥伦比亚河鲑鱼种群的繁殖策略具有重要意义。该项目的成果将在哥伦比亚河河口会议上传播给当地和区域的利益攸关方和管理人员，在该会议上，pi将努力发展有益的跨学科合作。该提案支持两名早期职业科学家和一名研究生。该项目的主要假设是，羽流的基本特征——出口的水力控制、中部羽流大小、分层、羽流夹带率以及与上升风的相互作用——已经从根本上改变了。将使用现有的哥伦比亚河河口下游的历史和现代数值模型，这些模型是根据19世纪和21世纪的测深和潮汐数据开发和校准的。敏感性研究将通过历史范围改变强迫参数，如河流流量、潮汐和风，结果将使用无量纲数字和质量/动量/能量守恒方法进行分析。由于美国（和世界）几乎所有的主要河流出口都已被修改，因此拟议的案例研究将形成一个模板，以了解其他地区的变化；具体来说，由于哥伦比亚河系统在潮汐振幅和河流流量方面跨越了一个很大的参数空间，因此拟议的研究将涵盖其他主要河流出口的边界条件（分层和部分分层条件；电流；几何形状）。此外，历史的变化是如此之大，以至于会出现明显的对比（历史与现代）。可以说，哥伦比亚河羽流是美国进行此类研究的最佳地点。在气候变化的背景下，人为变化的影响也很重要：河流流量和深度的历史变化为理解海平面上升和水文模式改变造成的未来变化提供了模板。拟议的研究将是推进人类对俄勒冈/华盛顿海岸影响的知识的关键一步，同时解决流出控制对羽流结构和运输的作用的基本问题，因为它在大陆架上扩散和演变。

Buoyant river plumes, the result of the light fresh water discharged by rivers onto the continental shelf, are ubiquitous features in the world's coastal oceans. River plumes are vital components of the coastal circulation and biogeochemical cycles, serving as essential conduits to the coastal ocean for terrigenous carbon, nutrients, and other terrestrial constituents. Numerous theoretical, laboratory, and numerical studies point out the importance of the depth and width of the estuary mouth in setting bulk plume properties such as the cross-shore plume extent and coastal current transport. Additionally, the initial plume structure and subsequent response to external forcing (winds, waves, ambient shelf circulation) is largely set by the outflow. Since the late 1880's, the Lower Columbia River Estuary (LCRE) has experienced continual engineering modifications and the construction of jetties and the dredging of navigation channels at the mouth of the Columbia River that have altered both outlet depth and width by nearly 50%. The historical and modern LCRE/Columbia River Plume (CRP) systems provide a unique and novel testbed for examining the fundamental physical processes governing the coupling between the estuary, plume and coastal ocean while providing valuable insight and improve the collective understanding of the human impacts on the LCRE/CRP system. The project addresses how human-imposed changes to the river flow, geometry, morphology, and channel orientation of the LCRE over the last 130 years have impacted, or altered, the dominant physical processes that control the mixing, structure, and transports over the entire coupled river-estuary-coastal ocean system. Because plumes are a primary link in the land/ocean exchange of sediments, nutrients, and other scalars, a better understanding of historical changes to plume dynamics will broaden our understanding of long-term change to coastal ecosystems. The position and structure of the CRP additionally has important implications for reproductive strategies for the Columbia River salmon populations. The results of the project will be disseminated to local and regional stakeholders and managers at the Columbia River Estuary Conference where PIs will work to develop beneficial interdisciplinary collaborations. The proposal supports two early-career scientists and graduate student.The main hypothesis of the project is that basic plume characteristics - hydraulic control at the outlet, mid-field plume size, stratification, plume entrainment rates, and interaction with upwelling winds - have been fundamentally altered. The existing historical and modern numerical models of the Lower Columbia River Estuary, which have been developed and calibrated using 19th and 21st century bathymetry and tide data, will be used. Sensitivity studies will alter forcing parameters such as river flow, tides, and wind thru their historical range, and results will be analyzed using non-dimensional numbers and thru conservation of mass/momentum/energy approaches. Because nearly all major river outlets in the US (and the world) have been modified, the proposed case-study will form a template for understanding changes in other locations; specifically, since the Columbia River system straddles a large parameter space in terms of tidal amplitudes and river flow, the proposed research will cover the boundary conditions (stratified and partially stratified conditions; currents; geometry) found at other major river outlets. Moreover, the historical changes have been so large that they will allow clear contrasts (historic vs. modern) to emerge. Arguably, the Columbia River Plume is the best location in the U.S. for such a study. The effects of anthropogenic changes are also important in the context of climate change: historical changes to river flow and depth provide a template for understanding future changes due to sea-level rise and altered hydrological patterns. The proposed research will be a critical step in advancing the knowledge of the human-induced impacts on the Oregon/Washington coast while simultaneously addressing fundamental questions on the role of outflow controls on plume structure and transports as it spreads and evolves on the continental shelf.