Evaluating the efficacy of natural flood defense systems: coastal hydrodynamic, wave, and vegetation measurements in Chesapeake Bay

Coastal areas in the Mid-Atlantic regions of the US are threatened by flooding due storm surge and sea level rise (SLR). With more than 7,000 miles of shoreline and a projected 2.0 to 4.2 feet of SLR over this century, Maryland is one of the most vulnerable states to coastal flooding. Also, with its proximity to open ocean and large bodies of water, as the case of Chesapeake Bay, several communities are exposed to coastal flood hazard due to sea level rise, as storm surge, flooding and erosion. While hard structures have long been used for coastal flood protection, several scientific studies showed that the natural ecosystems, such as wetlands and marshes, can reduce the impacts of storm surge by attenuating water levels, waves, and erosion.

However, when faced with an opportunity to adopt nature-based solutions as part of a community resilience strategy, local decision makers express doubt as to the efficacy of natural habitats to reduce the impacts of coastal flooding and sea level rise. In this project, the George Mason University, Maryland’s Department of Natural Resources, and the Maryland/DC Chapter of The Nature Conservancy are working together to investigate the effectiveness of natural habitats for coastal flood protection. The collaborative project aimed to measure the hydrodynamics of storm surge and waves inside Maryland’s marshes and the attenuation of waves and currents.

The project conducted hydrodynamic, topographic and vegetation surveys at the selected coastal marshe in the Deal Island during the summer and fall of 2018. The hydrodynamic data collection consists of measuring water levels and waves data using low frequency pressure transducer (Hobo onset U20L-01, U20-001-01 Ti and U20-001-04), high frequency pressure sensors (Trublue 255) and Acoustic Doppler Current Profiles (Aquadopp Nortek 2Mhz). The measurements focused on two distinct cross shore transects in the marsh and dune areas. Additionally, vegetation characteristics impacting flow over the marsh were surveyed in the study site three times during the monitoring period. A topo-bathymetric survey was also conducted and all the equipment locations were recorded with GPS. A multi-media survey documented the environmental changes over the monitoring period at two location in the study site. All the field measurements are completed and the processed data are uploaded here. The data analyses is now underway and supporting a numerical modeling implementation in the study site. This work will be carried out during the spring of 2019 and we expect will also leverage results for the final journal publication.

美国中大西洋地区的沿海区域正受到风暴潮与海平面上升（Sea Level Rise, SLR）引发的洪涝威胁。马里兰州拥有超过7000英里的海岸线，预计本世纪内海平面将上升2.0至4.2英尺，是受沿海洪涝影响最严重的州之一。此外，由于毗邻开阔大洋与切萨皮克湾等大型水体，该州多个社区因海平面上升、风暴潮、洪涝及海岸侵蚀面临沿海洪水风险。长期以来，硬质防护结构一直被用于沿海防洪，但多项科学研究表明，湿地、沼泽等自然生态系统可通过削弱水位、海浪及侵蚀作用，缓解风暴潮带来的影响。

然而，当地方决策者有机会将基于自然的解决方案纳入社区韧性战略时，他们对自然栖息地缓解沿海洪涝与海平面上升影响的有效性持怀疑态度。本项目由乔治梅森大学、马里兰州自然资源部以及马里兰州/哥伦比亚特区自然保护协会合作开展，旨在探究自然栖息地用于沿海防洪的实际效果。该合作项目旨在测量马里兰州沼泽内部的风暴潮与波浪水动力特性，以及波浪和海流的衰减效应。

项目于2018年夏秋两季，在迪尔岛选定的沿海沼泽地开展了水动力、地形及植被调查。水动力数据采集工作采用低频压力传感器（Hobo Onset U20L-01、U20-001-01 Ti及U20-001-04）、高频压力传感器（Trublue 255）以及声学多普勒流速剖面仪（Acoustic Doppler Current Profiles, Aquadopp Nortek 2Mhz），对水位与波浪数据进行测量。测量聚焦于沼泽与沙丘区域的两条跨岸断面。此外，研究团队在监测期内三次对影响沼泽地表水流的植被特征开展了调查。本次调查还开展了地形-水深测量，并通过全球定位系统（Global Positioning System, GPS）记录了所有设备的布设位置。研究团队通过多媒体调查记录了监测期内研究区域两处点位的环境变化情况。所有野外测量工作均已完成，处理后的数据已上传至本平台。目前数据分析工作正在进行中，同时将支撑研究区域的数值模拟工作。该模拟工作将于2019年春季开展，研究团队预计还将基于本项目成果撰写最终期刊论文。