Abstract Coastal and estuarine wetlands provide a range of important ecosystem services, but are currently being damaged and degraded due to human activities, reduced sediment supply and sea level rise. Managed realignment (MR) is one approach used to compensate for the loss of intertidal habitat, however saltmarshes in MR sites have been recognised to have lower biodiversity than natural environments. This has been associated with differences in the physical functioning including the sediment structure, reduced hydraulic connectivity, and lower topographic variability such as the abundance of intertidal creek networks. Intertidal morphology, including creek networks, play an important role in supporting and regulating saltmarsh environments through the supply of sediment, nutrients and water, and in draining intertidal marshes. However, there is a lack of empirical data on the formation and evolution of topographic features and variability in saltmarsh environments. This is likely to be due to creek networks in natural marshes already being in a state of quasi-equilibrium, making MR sites an ideal environment to investigate creek development. However, traditional remote sensing techniques (such as LiDAR) tend to be relatively expensive, infrequent and at a coarse resolution meaning small, but important (cm-scale), changes are often missed. This study advances the ability to detect these small scale changes by demonstrating the suitability and potential applications of using the emerging photogrammetric method Structure-from-Motion (SfM) on images taken using a small-Unmanned Aerial System (sUAS). Three surveys from a rapidly changing, near-breach site were taken at the Medmerry Managed Realignment Site in July 2016, September 2017 and July 2018. A suitable degree of confidence was found between the modelled surface and independent check points (vertical root-mean-square-errors of 0.0245, 0.0704 and 0.1571 for 2016, 2017 and 2018 respectively). DSMs of Difference (DoD) analysis was performed to evaluate elevation change, with areas experiencing up to 85 cm of accretion between 2016 and 2018. However, when considering the error associated with both surveys, between 2016 and 2017, only 34.39% of the survey area experienced change above the level of detection (LoD). In contrast, 76.97% experienced change greater than the LoD between 2017 and 2018. Stream order analysis classified the creek networks into five orders in 2016 and four orders in 2017 and 2018, with 2016 having a higher abundance (291 in 2016 compared to 117 (2017) and 112 (2018)) and density (0.44 m/m2 in 2016 compared to 0.27 m/m2 in both 2017 and 2018) of creek networks. These results provide an innovative high resolution insight into the evolution of restored intertidal wetlands, and suggest that SfM analysis of images taken using a sUAS can be a useful tool with the potential to be incorporated into studies of MR and natural saltmarsh sites. sUAS analysis can, therefore, advance the management of these environments to ensure the provision of ecosystem services and to protect against future anthropogenic activity, sea level rise and climate change.

中文翻译：

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使用小型无人机系统对潮间带湿地恢复计划进行高分辨率分析

摘要 沿海和河口湿地提供了一系列重要的生态系统服务，但由于人类活动、沉积物供应减少和海平面上升，目前正在遭受破坏和退化。管理重整 (MR) 是一种用于补偿潮间带栖息地丧失的方法，但已认识到 MR 站点中的盐沼生物多样性低于自然环境。这与物理功能的差异有关，包括沉积结构、水力连通性降低和地形变异性较低，例如潮间带小溪网络的丰富度。潮间带形态，包括小溪网络，在通过提供沉积物、养分和水以及排干潮间带沼泽地支持和调节盐沼环境方面发挥着重要作用。然而，缺乏关于盐沼环境中地形特征和变异性的形成和演变的经验数据。这可能是由于天然沼泽中的小溪网络已经处于准平衡状态，使 MR 站点成为研究小溪发展的理想环境。然而，传统的遥感技术（如 LiDAR）往往相对昂贵、不频繁且分辨率粗糙，这意味着很小但很重要（厘米级）的变化经常被忽略。本研究通过展示使用新兴摄影测量方法 Structure-from-Motion (SfM) 对使用小型无人机系统 (sUAS) 拍摄的图像的适用性和潜在应用，提高了检测这些小规模变化的能力。三项调查来自瞬息万变的，2016 年 7 月、2017 年 9 月和 2018 年 7 月在 Medmerry Managed Realignment Site 拍摄了接近突破点。在建模表面和独立检查点之间发现了合适的置信度（垂直均方根误差为 0.0245、0.0704 2016 年、2017 年和 2018 年分别为 0.1571）。执行差异 DSM (DoD) 分析以评估海拔变化，2016 年至 2018 年期间，该地区经历了高达 85 厘米的增生。然而，考虑到与两次调查相关的误差，2016 年至 2017 年期间，仅占调查的 34.39%区域经历了高于检测水平 (LoD) 的变化。相比之下，76.97% 的变化大于 2017 年至 2018 年的 LoD。 流阶分析将溪流网络分为 2016 年的五个订单和 2017 年和 2018 年的四个订单，2016 年具有更高的溪流网络丰度（2016 年为 291 比 117（2017）和 112（2018））和密度（2016 年为 0.44 m/m2，而 2017 和 2018 年均为 0.27 m/m2）。这些结果提供了对恢复的潮间带湿地演变的创新高分辨率洞察，并表明对使用 sUAS 拍摄的图像进行 SfM 分析可以成为一种有用的工具，有可能被纳入 MR 和天然盐沼遗址的研究中。因此，sUAS 分析可以推进对这些环境的管理，以确保提供生态系统服务并防止未来的人为活动、海平面上升和气候变化。这些结果提供了对恢复的潮间带湿地演变的创新高分辨率洞察，并表明对使用 sUAS 拍摄的图像进行 SfM 分析可以成为一种有用的工具，有可能被纳入 MR 和天然盐沼遗址的研究中。因此，sUAS 分析可以推进对这些环境的管理，以确保提供生态系统服务并防止未来的人为活动、海平面上升和气候变化。这些结果提供了对恢复的潮间带湿地演变的创新高分辨率洞察，并表明对使用 sUAS 拍摄的图像进行 SfM 分析可以成为一种有用的工具，有可能被纳入 MR 和天然盐沼遗址的研究中。因此，sUAS 分析可以推进对这些环境的管理，以确保提供生态系统服务并防止未来的人为活动、海平面上升和气候变化。