Detecting riverbank changes with remote sensing tools. Case study: Aggitis River in Greece

Abstract

Fluviogeomorphologic processes such as bank erosion and deposition affect and change the shape and condition of river and stream channels. Erosion and deposition rates are dependent on many natural (e.g. climate, geology, vegetation, topography) and anthropogenic (e.g. dams, bridges, gabions, straightening, wildfires etc.) factors. Alterations to these factors disrupt the rivers/streams dynamic equilibrium and they respond by altering their shape, formation or even location. These changes might be slow or rapid but can cause serious problems to infrastructures and lead to loss of human lives. For the more effective and sustainable management of rivers or stream and in general watersheds, new innovative methods are needed to monitor and understand these fluviogeomorphologic processes. Remote sensing tools can be utilized to monitor, predict and measure such changes in rivers and streams. Free satellite images and ortho-maps generated by airplanes have been used worldwide to map geomorphologic changes through time. Ortho-images captured by drone flights are more effective because their higher spatial resolution they provide compared to satellite or airplane images can provide more details on the river or stream. The use of drone images can be low cost, thus provide an effiecint way to map riverbank changes in targeted reaches that face erosional or depositional problems. This study used remote sensing tools to identify river banks changes by combining free satellite, aerial and low flight drone images. The study areas were reaches along Aggitis River in northern Greece. Firstly, free satellite and Google Earth images were utilized to map the entire watershed and find at a large scale the potential riverbank reaches that have had changes (erosion and/or deposition). Secondly, drone flights were executed to acquire high resolution images at a specific location (having erosion). Through these images, it was determined more accurately if accelerated bank erosion or deposition were occurring. Overall, these remote sensing tools proved to be a quick and low-cost methodology that allows identifying and measuring stream bank changes over many years but also over short periods of time (e.g. after a flood event). In addition, the methodology enables us to locate the areas with the greatest potential of erosion and deposition where nature-based solution should be implemented to stabilize stream banks, reduce erosion or deposition rates and mitigate nonpoint source pollutants. This paper was presented at the MONITOX International Symposium “Deltas and Wetlands”, Tulcea, Romania, 15-17 September, 2019.