Evaluation of Gully Monitoring Techniques: The Case of the Metropolitan Region of Manaus, Amazonas, in the Amazon Region

In Manaus, studies on gullies have been conducted since the mid-1990s, and several of them have employed monitoring techniques. This article aims to address and describe the monitoring techniques used in the gullies of the Metropolitan Region of Manaus (MRM). Analysis of the studies revealed that the monitoring activities primarily aimed to estimate erosion rates, predict their evolution, understand their mechanisms and processes, and assess the resulting environmental and social consequences. The analyzed monitoring techniques can be grouped into four categories based on instrument usage: 1) tape measure, compass, survey forms, and sketches; 2) planimetric surveys; 3) satellite imagery and Google Earth; 4) high-resolution aerial imagery via unmanned aerial vehicles (UAVs). It was concluded that the use of more modern monitoring techniques, such as UAV imagery, does not necessarily exclude the use of simpler procedures, such as survey forms, tape measures, and compasses. Additionally, the combination of different techniques can contribute to a more detailed morphometric characterization of the monitored gully, as well as its associated secondary features.