Coastline evolution rates of Portugal

Regional/global-scale information on coastline rates of change and trends is extremely valuable, but national-scale studies are scarce. A widely accepted standardized methodology for analysing long-term coastline change has been difficult to achieve, but is essential to conduct an integrated and holistic approach to coastline evolution and hence support coastal management actions. Additionally, databases providing knowledge on coastline evolution are of key importance to support both coastal management experts and users.
The main objective of this work is to present the first systematic, global and consistent long-term coastline evolution data of Portuguese mainland low-lying sandy.
The methodology used quantifies coastline evolution using an unique and robust coastline indicator (the foredune toe), which is independent of short-term changes.
The dataset presented comprises: 1) two polyline sets, mapping the 1958 and 2010 sandy beach-dune systems coastline, both optimized for working at 1:50 000 scale or smaller, and 2) one polyline set representing long-term change rates between 1958 and 2010, estimated at each 250 m.
Results show beach erosion as the dominant trend, with a mean change rate of -0.24 ± 0.01 m/year for all mainland Portuguese beach-dune systems. Although erosion is dominant, this evolution is variable in signal and magnitude in different coastal sediment cell and also within each cell. The most relevant beach erosion issues were found in the coastal stretches of Espinho - Torreira and Costa Nova - Praia da Mira, both at sub-cell 1b; Cova Gala - Leirosa, at sub-cell 1c and Cova do Vapor - Costa da Caparica, at cell 4. Cells 1 and 4 exhibit a history of major human interventions interfering with the coastal system, many of which originated and maintained a sediment deficit. In contrast, cells 5 and 6 have been less intervened and show stable or moderate accretion behaviour.

区域乃至全球尺度的海岸线变化速率与趋势信息具有极高的科研与应用价值，但国家级尺度的相关研究仍较为匮乏。尽管建立一套广泛认可的长期海岸线变化分析标准化方法颇具挑战，但此类方法对于开展海岸线演化的集成化、整体性研究，进而支撑海岸管理实践至关重要。此外，收录海岸线演化相关研究成果的数据库，对于海岸管理从业者与相关应用用户均具有关键支撑作用。
本研究的主要目标是提供首套系统性、全球性且一致性良好的葡萄牙本土低平沙质海岸线长期演化数据集。
本研究所用方法通过一种独特且稳健的海岸线指标——前滩沙丘脊（foredune toe）——量化海岸线演化过程，该指标不受短期海岸变化的干扰。
本次发布的数据集包含以下内容：1）两组折线数据集（polyline set），分别绘制了1958年与2010年的沙质海滩-沙丘系统海岸线，二者均适配1:50000及更小比例尺的应用需求；2）一组折线数据集，表征了1958年至2010年间每250米间隔处的长期海岸线变化速率。
研究结果显示，海滩侵蚀为该数据集覆盖区域的主导演化趋势，葡萄牙本土所有海滩-沙丘系统的平均变化速率为-0.24±0.01米/年。尽管侵蚀占据主导地位，但不同海岸沉积物单元（coastal sediment cell）内部及单元之间，海岸线演化的方向与强度均存在显著差异。侵蚀问题最为突出的海岸段包括：位于子单元（sub-cell）1b的埃斯皮纽（Espinho）-托雷拉（Torreira）段与科斯塔诺瓦（Costa Nova）-米拉海滩（Praia da Mira）段；位于子单元1c的科瓦加拉（Cova Gala）-莱罗萨（Leirosa）段；以及位于单元4的科瓦杜瓦波尔（Cova do Vapor）-卡帕里卡海岸（Costa da Caparica）段。单元1与单元4曾遭受大规模人类活动干预，干扰了海岸系统的自然演化过程，其中多数活动导致并持续加剧了海岸沉积物亏缺。与之形成对比的是，单元5与单元6受人类活动干预程度较低，海岸演化呈现稳定或轻度淤积的态势。