Mapping and study of morphological monitoring of the beaches of Lorient Agglomeration

Lorient Agglomeration has 132 km of coastline, one of the major attractions of its territory. In response to the vulnerability of this space and the anthropogenic and natural pressures of this coastline, Lorient Agglomeration has launched a monitoring programme whose first phase (1999-2013) was to bring together the information on the different parameters that affect the evolution of the coastline, to identify signs of erosion* and to estimate the degree of sensitivity of the coastal fringe. As a result of this operation, a photographic monitoring tool was put in place. Several further studies have thus been carried out, in particular on Kerguelen, for example. However, these qualitative data do not allow quantitative monitoring. Thus, the objective of this study is to launch multi-year monitoring on the beaches of Lorient Agglomeration showing signs of erosion, based on a bi-annual topo-bathymetric survey and particle size analyses*. These constant and regular data will help to better understand the hydrosedimentation* of its beaches over the long term and to define the best management and/or development tools. **Collection context** Bathymetric surveys take place offshore towards the foreshore and at high tide, and surveys topographics at low seas, in order to obtain a cover allowing the setting data. High tidal coefficients are preferred for interventions. The interpretation of topo-bathymetric data should be an aid to managers to determine the most appropriate accommodations to combat against coastal erosion and the risk of flooding. Monitoring of topo-bathymetric data will allow as campaigns to know the characteristics of each site and to understand the sediment movements in the profile at different time scales. **Collection method** The topo-bathymetric readings were made by the firm Ingeo. The method used is as follows: The bathymetric reading is carried out using a multibeam probe* high definition, coupled for the exhaustive topography of the foreshore* with a LiDAR survey*, rigged on the roof of a 4x4. Topographical and bathymetric coasts are reported to zero of the lowest seas. Reminder: I.G.N 69 = CM + 2.63. Taking into account the extent of topo-bathymetric surveys of longitudinal profiles have been realised. These have been set to the particle size sampling profiles, the positioning of which is stipulated in the IGO report. For this first campaign, the analysis of topobathymetric surveys was based on the range profiles that were also used for particle size sampling and on the analysis of isobath 0 CM, considered here (taking into account SHOM and Candhis data on the sector)as a depth close to the limit of action of the houles. For more information, see [the metadata on the Isogeo catalog](https://open.isogeo.com/s/0bd17a2a330842c68ec4a412d1df6824/AiCyPK6W8fg012l-vHV0s5tPry5b0/r/32e90f95741e4d0ba494120a85f57cb5).洛里昂城市圈（Lorient Agglomeration）拥有132公里海岸线，这是其辖区内最主要的景观之一。 针对这片海岸带的脆弱性，以及该海岸线面临的人为与自然压力，洛里昂城市圈启动了一项监测计划，其第一阶段（1999-2013年）旨在整合影响海岸线演变的各类参数信息，识别侵蚀（erosion*）迹象，并评估海岸带的敏感程度。 通过该阶段工作，一套摄影监测工具得以部署。后续又开展了多项研究，其中尤以凯尔盖朗（Kerguelen）地区的相关研究为典型。 然而，这些定性数据无法支持定量监测工作。因此，本研究的目标是基于每半年一次的地形-水深测量（topo-bathymetric survey）与粒度分析（particle size analyses*），对洛里昂城市圈范围内出现侵蚀迹象的海滩启动长期监测工作。 这些持续且规律的观测数据，将有助于更深入地理解海滩长期的水动力沉积过程（hydrosedimentation*），并为制定最优的海岸管理与开发方案提供依据。 **采集背景** 水深测量作业在近岸向岸区域及高潮位期间开展，地形测量则在低潮时段进行，以获取完整覆盖的数据。作业优先选择高潮位系数较高的时段实施。 地形-水深数据的解译可为管理者提供决策辅助，帮助其确定对抗海岸侵蚀与洪涝风险的最优适配方案。 地形-水深监测数据将随历次测量作业逐步完善各站点的特征信息，并阐明不同时间尺度下剖面内的沉积物运移规律。 **采集方法** 本次地形-水深测量由Ingeo公司完成，采用的技术方案如下： 水深测量使用高清多波束测深仪（multibeam probe*），而潮间带（foreshore*）的全覆盖地形测量则通过搭载激光雷达扫描（LiDAR survey*）的四驱车完成。 海岸带地形与水深数据均以最低潮位的零点为基准。 备注：法国国家地理信息局（IGN）69坐标系 = CM + 2.63。 考虑到本次地形-水深测量的覆盖范围，已布设了纵向剖面。这些剖面与粒度采样剖面一一对应，其位置依据IGO报告中的规定确定。 在本次首阶段测量中，地形-水深测量的分析以用于粒度采样的纵向剖面以及0厘米等深线（isobath 0 CM）的分析为基础——结合法国海军海洋水文与地理研究所（SHOM）及坎迪斯（Candhis）的区域数据，该等深线被视为接近波浪作用极限的水深阈值。 如需更多信息，请参阅[Isogeo目录元数据](https://open.isogeo.com/s/0bd17a2a330842c68ec4a412d1df6824/AiCyPK6W8fg012l-vHV0s5tPry5b0/r/32e90f95741e4d0ba494120a85f57cb5)。