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Stabilization of ravines, adjacent beaches, and bluffs on Lake Michigan

机译：密歇根湖上山沟，相邻海滩和悬崖的稳定

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This report details the performance of four Illinois coastal restoration and stabilization projects constructed and monitored over 3-15 years. All include integration of native plants with stone into sustainable systems that protect ravines and adjacent coastal beaches from the intense erosional forces of stormwater runoff and storm waves. Prior to urbanization, ravines were metastable and bluffs and beaches eroded slowly. All supported unique plant communities. During the last 125 years, coastal and ravine erosion has accelerated due to loss of protective beaches and an increase in peak stormwater runoff flowing into the ravines. Most of these problems can be attributed to construction and maintenance of harbor entrance channels, impervious structures in the watershed and to the introduction of invasive plants like silver maple and buckthorn. Societal response has typically been to attack the coastal problems with hardened structures of wood, steel and concrete and ignore the problems in the ravines. The result is a lakeshore dominated by hard defensive structures including revetments, groins and seawalls, and ravines with a patchwork of retaining walls, storm sewers, and outfalls. Plant communities have been displaced and many of the structures have failed, in most cases due to flanking or foundation failure. This study quantifies the performance of alternative systems designed to function in concert with natural processes as compared to hardened erosion control structures. Study sites include ravines and beaches in fully urbanized areas of Lake Bluff, Highland Park and Glencoe, and eroding bluffsrnat Foss Park Beach in North Chicago. Systems were monitored for bacterial indicators of sewage pollution (E. coli bacteria), establishment of vegetation, and erosion and sediment loading to Lake Michigan. The most successful ravine projects include removal of invasive plants, restoration of appropriately-sized stream boulders and cobbles (stream armor) with streambanks and ravine slopes further stabilized with stone and native plants. Although water quality improved with reduction of fine sediments and repair of broken sewers, bacterial monitoring was inconclusive. Levels of E. coli bacteria were typically high in the ravines and beach sands and low in Lake Michigan, and appear to be due to diverse animal communities living in the ravines and not necessarily human sewage. Except for periods after heavy rains, the ravines had no effect on E. coli levels in the lake. The lakeshore adjacent to the ravines was successfully stabilized with rocky headlands and pocket beaches, wetlands, and native plants. Results of this report are intended to help planners better manage Great Lakes ravines and coasts with techniques that reduce erosion and restore diverse ecosystems. Based on criteria developed in this study, the Illinois Department of Natural Resources in cooperation with the Lake Michigan Watershed Ecosystem Partnership and Alliance for the Great Lakes has mapped all Lake County ravines to quantify stability and ecological viability. It is anticipated that with the success of the ravine mapping project, mapping the Lake Michigan shoreline for stability and ecological viability will soon follow.
机译：该报告详细介绍了在3到15年内建设和监测的四个伊利诺伊州沿海恢复和稳定项目的绩效。所有这些措施都包括将原生植物和石头整合到可持续的系统中，以保护沟壑和邻近的沿海海滩免受暴雨径流和暴风浪的强烈侵蚀。在城市化之前，沟壑是亚稳态的，虚张声势和海滩慢慢侵蚀。所有受支持的独特植物社区。在过去的125年中，由于失去保护性海滩以及流入峡谷的雨水径流增加，沿海和沟壑的侵蚀加速了。这些问题大多数归因于港口入口通道的建设和维护，流域的不透水结构以及诸如银枫和沙棘等入侵植物的引入。社会反应通常是用硬化的木材，钢和混凝土结构来解决沿海问题，而忽略沟壑中的问题。结果是湖岸被坚硬的防御性结构所支配，包括护岸，腹股沟和海堤以及沟壑，其中有护墙，雨水管道和排污口。植物群落已被迫流离失所，许多建筑物已经失效，在大多数情况下是由于侧翼或地基失效。这项研究量化了与硬化侵蚀控制结构相比，旨在与自然过程协同工作的替代系统的性能。研究地点包括在布拉夫湖，高地公园和格伦科的完全城市化地区的峡谷和海滩，以及北芝加哥福斯公园海滩的布拉夫斯纳特侵蚀地区。监测系统的细菌指标，包括污水污染（大肠杆菌），植被的建立以及侵蚀和向密歇根湖的沉积物。最成功的沟壑项目包括清除外来入侵植物，恢复适当大小的溪流巨石和鹅卵石（溪流护甲）以及溪流和山坡，并用石头和原生植物进一步稳定。尽管水质随着细小沉积物的减少和下水道的修复而得到改善，但细菌监测尚无定论。在山沟和沙滩中，大肠杆菌的水平通常较高，在密歇根湖中则较低，这似乎是由于生活在山沟中的动物群落多种多样，而不一定是人类排泄物。除了大雨过后的时间段，山沟对湖中大肠杆菌水平没有影响。峡谷附近的湖岸已成功地用岩石岬角和口袋海滩，湿地和本地植物稳定下来。本报告的结果旨在通过减少侵蚀和恢复多样化生态系统的技术帮助规划者更好地管理大湖区的峡谷和海岸。根据这项研究制定的标准，伊利诺伊州自然资源部与密歇根湖流域生态系统伙伴关系和大湖区联盟合作，绘制了莱克县所有沟壑的地图，以量化稳定性和生态可行性。可以预期，随着山沟测绘项目的成功，很快将为密歇根湖海岸线测绘稳定性和生态可行性。

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