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Effects of structurally-engineered beaches on coastal processes and shores of the Great Lakes

机译：结构化海滩对大湖沿岸过程和海岸的影响

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Impacts of coastal structures on America's shores and beaches represent a scientific, economic and engineering challenge to assure that our beaches are protected and sustained. Coastal professionals go to great lengths to properly design, build, monitor, and maintain engineered beaches. However, the beach has a powerful and visceral connection to human nature that makes us all personally and emotionally sensitive to possible threats, proposed changes, and, ultimately, loss of this important component of human well-being. Inadvertent sand starvation and loss of beaches downdrift of 19th- and 20th-century harbor structures has left many people with a natural aversion to "engineered structures." Despite that, a common solution to eroding beaches downdrift of harbors was construction of groins and groin fields that functioned like smaller versions of the harbor breakwaters trapping sand on their updrift sides. Sand bypassing and nourishment of downdrift beaches, introduced in most cases more than 50 years after harbor construction, was generally "too little and too late" to keep groin fields filled with sand.rnToward the end of the 20th century, coastal scientists and engineers, recognizing the reduced effectiveness of groins on sediment-starved coasts, began designing and constructing nearshore stone breakwaters and headlands that are better able to hold sand. These projects were typically filled (premitigated)rnwith sand to minimize downdrift problems. Breakwater projects designed to protect beaches in the Great Lakes, including the first designed by the U.S. Army Corps of Engineers are reviewed, and several are examined in detail. These include public and private beaches on the south shore of Lake Erie, the north shore of Lake Ontario near Toronto, and the west shore of Lake Michigan north of Chicago. The largest is a 55-breakwater system designed to protect the state park at Presque Isle in Lake Erie (58 were originally designed and approved).rnMonitoring and examination of historic air photos has shown that attached and detached breakwaters and armored headlands, if built well within the surf zone, have minimal impacts on downdrift beaches and shores. Exceptions are temporary interruption of the littoral drift when structures are built without being adequately filled (nourished) with sand, or interruptions to planned nourishment due to lack of funding. In Illinois, state regulators adopted a requirement that any structure that may trap sand be pre-mitigated with the anticipated sand fill quantity plus a 20% overfill of new sand to assure no negative impact.rnImportantly, access to Google Earth on the Internet has allowed citizens and scientists to view and monitor the coast in a historical context, unbiased by a lack or misunderstanding of scale or perceived bias of coastal "experts."
机译：沿海结构对美国海岸和海滩的影响代表了确保我们的海滩得到保护和维持的科学，经济和工程挑战。沿海专业人士竭尽全力正确设计，建造，监控和维护工程海滩。然而，海滩与人性之间有着强大而内在的联系，这使我们所有人对可能的威胁，拟议的变化以及最终丧失人类福祉的这一重要组成部分在个人和情感上都很敏感。 19世纪和20世纪港口结构的疏忽造成的沙子匮乏和海滩失落使许多人对“工程结构”产生了自然厌恶。尽管如此，侵蚀港口顺流而下的海滩的一种常见解决方案是建造腹股沟和腹股沟田，其功能类似于较小型的港口防波堤，将防砂堤困在其上游侧。在大多数情况下，在港口建设后的50多年中，引入绕沙和对下漂流海滩进行养分通常是“太少太晚了”，以至于腹股沟田无法充满沙子。rn在20世纪末，沿海的科学家和工程师们，由于认识到腹股沟在沉积物匮乏的海岸上的有效性降低，因此开始设计和建造能够更好地容纳沙子的近岸石材防波堤和岬角。这些项目通常都用沙子填充（首选）以最大程度地减少下漂问题。审查了旨在保护大湖地区海滩的防波堤项目，其中包括美国陆军工程兵团设计的第一个防波堤项目，并对其中一些进行了详细检查。这些包括伊利湖南岸，多伦多附近的安大略湖北岸和芝加哥以北密歇根湖西岸的公共和私人海滩。最大的是有55个防波堤系统，旨在保护伊利湖普雷斯克岛的州立公园（最初设计和批准了58个）。rn对历史航空照片的监视和检查显示，如果建造得当，可以附加和分离防波堤和装甲岬角。在冲浪区内，对漂流海滩和海岸的影响最小。例外情况是，在建造结构时未充分填充（养育）沙子时临时中断了沿岸漂流，或由于缺乏资金而中断了计划的营养。在伊利诺伊州，州监管机构采用了一项要求，即必须使用预期的填沙量加上20％的新填沙量来预先缓解可能捕集沙子的任何结构，以确保不会造成负面影响。重要的是，互联网上的Google Earth访问已被允许公民和科学家在历史背景下查看和监视海岸，而没有受到规模的缺乏或误解或海岸“专家”的偏见。

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