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

漂浮的河流羽流是河流排入大陆架的淡水的结果，是世界沿海海洋中普遍存在的特征。河流羽流是海岸环流和海洋地球化学循环的重要组成部分，是陆源碳、营养盐和其他陆地成分进入海岸海洋的重要通道。大量的理论，实验室和数值研究指出，在设置散装羽流属性，如跨海岸羽流的范围和沿海电流传输的河口的深度和宽度的重要性。此外，最初的羽流结构和随后对外部强迫（风，波浪，环境陆架环流）的反应在很大程度上是由外流。自19世纪80年代后期以来，哥伦比亚河下游河口（LCRE）经历了持续的工程改造，在哥伦比亚河口建造码头和疏浚航道，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（CRP）系统提供了一个独特的和新颖的试验平台，研究控制河口，羽流和沿海海洋之间的耦合的基本物理过程，同时提供有价值的见解和提高集体的理解人类对LCRE/CRP系统的影响。该项目解决了如何人为施加的变化，河流流量，几何形状，形态，和通道方向的LCRE在过去的130年中，影响或改变，占主导地位的物理过程，控制混合，结构和运输在整个耦合河流河口海岸海洋系统。由于羽流是陆地/海洋沉积物、营养物和其他标量交换的主要环节，因此更好地了解羽流动力学的历史变化将拓宽我们对沿海生态系统长期变化的理解。CRP的位置和结构也有重要的影响生殖策略的哥伦比亚河鲑鱼种群。该项目的结果将在哥伦比亚河口会议上向当地和区域利益攸关方和管理人员传播，在该会议上，项目主管将努力发展有益的跨学科合作。该项目的主要假设是基本的羽流特征-出口处的水力控制、中场羽流尺寸、分层、羽流夹带率以及与上升流风的相互作用-已经从根本上改变。将使用利用19和21世纪测深和潮汐数据开发和校准的哥伦比亚河下游河口现有的历史和现代数值模型。敏感性研究将改变强迫参数，如河流流量，潮汐和风通过其历史范围，结果将使用无量纲数字和通过质量/动量/能量守恒的方法进行分析。因为美国几乎所有的主要河流出口（和世界）已经修改，拟议的案例研究将形成一个模板，用于了解其他地点的变化;特别是，由于哥伦比亚河系统跨越了潮汐振幅和河流流量方面的大参数空间，拟议的研究将涵盖边界条件（分层的和部分分层的条件;水流;几何学）在其他主要河流出口处发现的。此外，历史变化如此之大，以至于出现了明显的对比（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。在气候变化方面，人为变化的影响也很重要：河流流量和深度的历史变化为了解海平面上升和水文模式改变造成的未来变化提供了一个模板。拟议的研究将是一个关键的一步，在推进对俄勒冈州/华盛顿海岸的人类引起的影响的知识，同时解决的基本问题的作用，外流控制羽流结构和运输，因为它在大陆架上蔓延和演变。

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.