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Monitoring underwater nourishments using multibeam bathymetric and backscatter time series
Coastal Engineering ( IF 4.4 ) Pub Date : 2020-06-01 , DOI: 10.1016/j.coastaleng.2020.103666 Timo C. Gaida , Thaiënne A.G.P. van Dijk , Mirjam Snellen , Tommer Vermaas , Chris Mesdag , Dick G. Simons
Coastal Engineering ( IF 4.4 ) Pub Date : 2020-06-01 , DOI: 10.1016/j.coastaleng.2020.103666 Timo C. Gaida , Thaiënne A.G.P. van Dijk , Mirjam Snellen , Tommer Vermaas , Chris Mesdag , Dick G. Simons
Natural and man-induced coastal erosion endanger life and environment in coastal areas worldwide. For sedimentary barrier coasts, beach and underwater nourishments are an efficient coastal protection strategy. To optimize nourishments and to understand their impact on the marine environment, monitoring strategies are required. In this study, we investigate the potential of multibeam echosounder (MBES) data, providing both bathymetry and backscatter (BS), for monitoring the evolution of the nourished sediment and morphodynamics over time. A time series of seven MBES measurements, as well as two sets of box cores, vibrocores and seismic data were acquired of a channel-side nourishment near the Wadden Sea island Ameland (The Netherlands), between April 2017 and May 2019. In general, a high confidence of the acoustic reliability of the BS time series measurements is demonstrated. The unsupervised Bayesian classification method, supported by ground-truthing, is employed to produce a time series of sediment maps, revealing sediments ranging from sandy mud to sand with varying amounts of shell fragments. Based on the sediment maps, the nourished sediment could be distinguished from the natural sediment. Within one year, the shell-rich pre-nourishment seabed is recreated by washing out finer sediments, which are deposited towards the main tidal channel. Using the seismic data and vibrocores, the shell-rich pre-nourishment seabed could be identified in the subsurface after being buried by the nourishments, supporting the general findings. Furthermore, a rapid development of steep bedforms with increasing sediment sorting is observed in parts of the nourished areas. This study shows that high-resolution sediment maps obtained from a time series of MBES BS together with bathymetry reveal morphodynamic and sedimentary processes of nourishment evolution and can advance underwater nourishment strategies.
中文翻译:
使用多波束测深和反向散射时间序列监测水下营养
自然和人为引起的海岸侵蚀危及全球沿海地区的生命和环境。对于沉积屏障海岸,海滩和水下营养是一种有效的海岸保护策略。为了优化营养并了解它们对海洋环境的影响,需要采取监测策略。在这项研究中,我们调查了多波束测深仪 (MBES) 数据的潜力,提供水深测量和反向散射 (BS),用于监测营养沉积物和形态动力学随时间的演变。在 2017 年 4 月至 2019 年 5 月期间,在瓦登海岛 Ameland(荷兰)附近的河道边养料中获得了七个 MBES 测量值的时间序列,以及两组箱形岩心、振动岩心和地震数据。总的来说,证明了 BS 时间序列测量的声学可靠性的高可信度。由地面实况支持的无监督贝叶斯分类方法用于生成沉积物图的时间序列,揭示从砂质泥土到具有不同数量贝壳碎片的沙子的沉积物。根据沉积物图,可以将滋养沉积物与天然沉积物区分开来。在一年之内,通过冲刷沉积在主要潮汐通道上的更细的沉积物,可以重建富含贝壳的营养前海床。使用地震数据和振动岩心,可以在被营养物掩埋后在地下识别富含贝壳的营养前海床,支持一般发现。此外,在部分滋养区观察到随着沉积物分选的增加,陡峭的床形迅速发展。这项研究表明,从 MBES BS 的时间序列中获得的高分辨率沉积物图连同水深测量揭示了营养演化的形态动力学和沉积过程,并可以推进水下营养策略。
更新日期:2020-06-01
中文翻译:
使用多波束测深和反向散射时间序列监测水下营养
自然和人为引起的海岸侵蚀危及全球沿海地区的生命和环境。对于沉积屏障海岸,海滩和水下营养是一种有效的海岸保护策略。为了优化营养并了解它们对海洋环境的影响,需要采取监测策略。在这项研究中,我们调查了多波束测深仪 (MBES) 数据的潜力,提供水深测量和反向散射 (BS),用于监测营养沉积物和形态动力学随时间的演变。在 2017 年 4 月至 2019 年 5 月期间,在瓦登海岛 Ameland(荷兰)附近的河道边养料中获得了七个 MBES 测量值的时间序列,以及两组箱形岩心、振动岩心和地震数据。总的来说,证明了 BS 时间序列测量的声学可靠性的高可信度。由地面实况支持的无监督贝叶斯分类方法用于生成沉积物图的时间序列,揭示从砂质泥土到具有不同数量贝壳碎片的沙子的沉积物。根据沉积物图,可以将滋养沉积物与天然沉积物区分开来。在一年之内,通过冲刷沉积在主要潮汐通道上的更细的沉积物,可以重建富含贝壳的营养前海床。使用地震数据和振动岩心,可以在被营养物掩埋后在地下识别富含贝壳的营养前海床,支持一般发现。此外,在部分滋养区观察到随着沉积物分选的增加,陡峭的床形迅速发展。这项研究表明,从 MBES BS 的时间序列中获得的高分辨率沉积物图连同水深测量揭示了营养演化的形态动力学和沉积过程,并可以推进水下营养策略。