ABSTRACT

This research explores intra-gully sediment volume changes of a massive gully network (42 ha) located in the Eastern Cape, RSA, in response to high rainfall events during a three-year study period (2017–2020). Unmanned aerial vehicles (UAVs) and photogrammetric processing were used to generate high resolution digital surface models (DSMs). Volumetric calculations were run to estimate the extent of gully expansion within the system to determine intra-gully changes and sediment erosion over the study period. The gully was categorised into four zones based on predominant structure and processes. These are the Extension Zone, Expansion Zone, Transport/Deposition Zone and the Side Branches. Rainfall data from a rainfall station (10 km away) was used to investigate the correlation between rainfall depth, rainfall intensity, and flow accumulation over two wetter years and one drier year with gully expansion experienced during these periods. The gully network encountered a total gully sediment volume erosion of 104,489 m³ (6.01%) over the study period. Nineteen high to extreme intensity (>20 mm per day) rainfall events produced the runoff necessary for gully expansion during the 2017 and 2018 hydrological years. Notably, lower gully growth was recorded in the Expansion and Transport/Deposition Zones during the subsequent below average hydrological year in 2019–2020.

摘要

本研究探讨了位于南非共和国东开普省的一个大型沟渠网络（42 公顷）的沟壑内沉积物体积变化，以响应三年研究期间（2017-2020 年）的高降雨事件。无人机（UAV）和摄影测量处理用于生成高分辨率数字表面模型（DSM）。通过体积计算来估计系统内沟壑扩张的程度，以确定研究期间沟壑内的变化和沉积物侵蚀。根据主要结构和过程，沟渠被分为四个区域。这些是扩展区、扩张区、运输/沉积区和侧支线。使用雨量站（10公里外）的降雨数据来研究降雨深度、降雨强度、以及两年多雨年和一年多雨年的流量累积以及在此期间经历的沟壑扩张。沟网共遭遇沟谷泥沙量侵蚀104,489 m³ (6.01%) 在研究期间。2017年和2018年水文年，19次高强度至极端强度（每天>20毫米）降雨事件产生了沟渠扩张所需的径流。值得注意的是，在随后的 2019-2020 年低于平均水平的水文年份中，扩张区和运输/沉积区的沟壑增长速度较低。