Constructed oyster reefs (CORs) provide shore protections and habitats for fish and shellfish communities via wave energy attenuation. However, the processes and mechanism of CORs on wave attenuation remain unclear, thus limiting the effective assessment of CORs for shoreline protection. This paper presents results of a field investigation on wave characteristics and wave spectral variations along a shoreline with CORs in an estuary with a large tidal range as well as large wind waves and swell energy. Six pressure transducers were deployed from January 31 to April 2, 2018, in Gandy’s Beach, New Jersey, in upper Delaware Bay. CORs were constructed at the study site in 2016 as living shoreline structures after Hurricane Sandy. The data collected from the study site exhibits the wave variations and spectral characteristics over the span of 2 months, including four winter storms (i.e., nor’easters). The spatial variations of wave heights measured on both sides of CORs show a strong dependence on the ratio between the freeboard of CORs and the offshore wave heights. Due to the large tidal range (> 2 m), the crests of CORs remain submerged over 85% of the time. The submerged CORs only provide partial attenuation of wave energy. The wave environment in the estuary is complex, especially during nor’easters. For instance, winds with rapid changing fetches could lead to bi-modal wind seas. Due to the complex wave spectra, the bulk wave heights such as the significant wave heights cannot be adopted to adequately reveal the capacity of CORs to attenuate wave energy. Spectral analysis is conducted to investigate the spatial and temporal variations of wave energy in targeted frequency bins. The spectral analysis results reveal the energy transfer from the primary waves to the high harmonics after waves propagate over the submerged CORs. Moreover, it is found that swell energy originated from the Atlantic Ocean can penetrate CORs without any dampening even when CORs are emergent. This study could help resource managers for in-depth evaluation of living shoreline effectiveness and improvement of living shoreline structures such as CORs.

中文翻译：

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活生生的海岸线在上特拉华湾的风浪的野外观测

人造牡蛎礁（CORs）通过波能衰减为鱼类和贝类群落提供了海岸保护和栖息地。但是，CORs对波衰减的过程和机制仍不清楚，因此限制了对海岸线保护的CORs的有效评估。本文介绍了在潮汐范围大，风浪和膨胀能量大的河口沿岸带CORs的沿岸线的波特征和波谱变化的野外调查结果。从2018年1月31日至4月2日，在特拉华湾上游的新泽西州甘迪海滩部署了六个压力传感器。CORs于2016年在研究现场建造，是飓风桑迪之后的活动海岸线结构。从研究地点收集的数据显示了2个月跨度内的波变化和频谱特征，包括四场冬季风暴（即“诺伊斯特”风暴）。在COR两侧测量的波高的空间变化显示出对COR的干舷与离岸波高之比的强烈依赖性。由于潮汐范围大（> 2 m），COR的波峰在超过85％的时间内仍被淹没。浸没的COR仅提供部分波能衰减。河口的海浪环境十分复杂，尤其是在诺伊斯特山脉地区。例如，取水速度快速变化的风可能导致双峰风海。由于波谱复杂，无法采用体波高（例如有效波高）来充分显示CORs衰减波能的能力。进行频谱分析以研究目标频点中波能量的时空变化。频谱分析结果表明，当波在水下COR上传播时，能量从一次波传递到高次谐波。而且，已经发现，即使当COR出现时，源自大西洋的膨胀能量也可以穿透COR而没有任何衰减。这项研究可以帮助资源管理者深入评估生活中海岸线的有效性并改善生活中海岸线的结构，例如COR。