Sequences of repeated bathymetric surveys through time have been successfully used to document the morphodynamical evolution of coastal environments within historical times. Most chronobathymetric sequences have a restricted temporal coverage, as surveys rarely date back earlier than the 19th century. The aim of this study is to explore the potential of older lead line depth measurements as a reliable source of bathymetric data. A late 17th century marine chart of the Pertuis Charentais (France) was used as a test case. High-resolution scans of the chart sheets were retrieved from a public online digital library. A rare manuscript contemporary to the chart was obtained from the French National Archives, in order to constrain the methodology used to acquire depth measurements. A spatially explicit bathymetry covering 1500 km² was reconstructed from the interpolation of about 4600 georeferenced depth soundings. Vertical error was estimated by assuming the equivalence of depth values between the late 17th century and the recent (1960) bathymetries above subtidal rocks outcropping on the seafloor. Documentary data indicated that the chart author did not acquire depth measurements on purpose but instead collected data taken by local sailors and coasting pilots over an unknown period of time, probably ranging from a few years to a few decades. The large vertical error estimated to $\pm$ 4.5 m mainly resulted from the lack of tide correction. Bathymetric difference maps could not be computed, but despite these weaknesses, the large-scale sediment infilling of the area and the long-term evolution of an estuarine sandbank could be documented, in agreement with previous works. Beyond its utility for local studies, this article provides insights into the processing of depth measurements acquired long before modern hydrography surveys, and demonstrates that such old marine charts deserve consideration, provided conditions are met for their critical assessment.

经过一段时间的重复测深调查序列已成功用于记录历史时期内沿海环境的形态动力学演变。大多数测时序列的时间覆盖范围有限，因为调查很少可以追溯到19世纪。这项研究的目的是探索潜在的较旧的铅线深度测量作为测深数据的可靠来源。测试用的是17世纪晚期Pertuis Charentais（法国）的海图。从公共的在线数字图书馆中检索了图表的高分辨率扫描图。该图表的稀有手稿是从法国国家档案馆获得的，以限制用于获取深度测量值的方法。覆盖1500 km的空间明确的测深法从大约4600个地理参考深度探测的插值中重建了^2个。垂直误差是通过假设17世纪后期和最近（1960年）潮下带露出海底岩石的水深之间的等值深度来估计的。文献数据表明，图表作者并非有意获取深度测量值，而是收集了当地水手和滑行飞行员在未知时间段内（可能从几年到几十年不等）获取的数据。大的垂直误差估计为$\pm$4.5 m主要是由于缺乏潮汐校正。尽管无法计算出测深图，但尽管存在这些缺点，但与以前的工作相一致，该区域的大规模沉积物填充和河口沙洲的长期演变仍可记录在案。除了将其用于本地研究之外，本文还提供了对在现代水文学测量之前很久就获得的深度测量值进行处理的见解，并证明只要满足关键评估条件，此类旧海洋图值得考虑。