Gully erosion can reach alarming dimensions, and in several cases contributes significantly to soil loss and sediment yield in catchments. The studied example is one of the largest known gully networks in the world (its surface area is approximately 0.5 million m² and volume 5 million m³), more than twice as large compared to the largest gullies described in peer-reviewed literature. To improve gully management strategies, it is not only critical to understand the factors that lead to erosion, but also to identify the extent of in-channel erosional and depositional features. Few studies consider in-channel patterns of erosion and deposition within gully systems. This study utilises a fixed-wing Unmanned Aerial Vehicle (UAV) and Structure-from-Motion (SfM) photogrammetry to create a high resolution orthomosaic and Digital Surface Model (DSM) to determine the position and spatial extent of erosional and depositional features within a large gully network in South Africa. Formation of such a large gully in relation to a relatively small drainage area is unusual but can be explained by the presence of dispersive soils and regional landscape incision. Longitudinal and cross-sectional profiles indicate that the gully network consists of three channel types (i.e. V-shaped, U-shaped and trapezoidal), each with a unique combination of erosional and depositional features. This study demonstrates the value of identifying and mapping of intra-gully features to better understand sediment transfer within the gully network to implement appropriate restoration strategies, which in this instance should focus on depositional zones to enhance channel decoupling.

中文翻译：

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使用无人机摄影测量法对南非最大的有记录的沟壑网络进行沟内测绘：对恢复策略的启示

沟壑侵蚀可以达到惊人的程度，在某些情况下会显着导致集水区的土壤流失和泥沙产量。所研究的例子是世界上已知最大的沟壑网络之一（其表面积约为 50 万平方米^，体积为 500 万平方米）)，比同行评审文献中描述的最大沟壑大两倍多。为了改进沟壑管理策略，不仅要了解导致侵蚀的因素，而且要确定河道内侵蚀和沉积特征的程度。很少有研究考虑沟渠系统内侵蚀和沉积的通道内模式。本研究利用固定翼无人机 (UAV) 和运动结构 (SfM) 摄影测量来创建高分辨率正射镶嵌和数字表面模型 (DSM)，以确定侵蚀和沉积特征的位置和空间范围。南非的大型沟壑网络。相对较小的流域形成如此大的沟壑是不寻常的，但可以通过分散土壤和区域景观切口的存在来解释。纵向和横截面剖面表明，沟网由三种渠道类型（即V型、U型和梯形）组成，每种渠道都具有独特的侵蚀和沉积特征组合。本研究证明了识别和绘制沟内特征的价值，以更好地了解沟网内的沉积物转移，以实施适当的恢复策略，在这种情况下，应侧重于沉积区以加强渠道脱钩。每一个都具有独特的侵蚀和沉积特征组合。本研究证明了识别和绘制沟内特征的价值，以更好地了解沟网内的沉积物转移，以实施适当的恢复策略，在这种情况下，应侧重于沉积区以加强渠道脱钩。每一个都具有独特的侵蚀和沉积特征组合。本研究证明了识别和绘制沟内特征的价值，以更好地了解沟网内的沉积物转移，以实施适当的恢复策略，在这种情况下，应侧重于沉积区以加强渠道脱钩。