Erosion and progradation in the Atrato River delta: A spatiotemporal analysis with Google Earth Engine

Abstract

The Atrato River Delta in Northwestern Colombia has experienced notable geomorphological changes in its shoreline in recent years. We analyze these changes, associated with erosion and progradation, using Landsat imagery and Google Earth Engine (GEE) algorithms to automatically identify the changes in an annual basis over 33 years (1986–2019). We compare the results with manual delineations on the same imagery using ArcGIS, obtaining similar outcomes, although GEE is much more efficient in processing large amounts of imagery compared with handmade procedures. We identify with good accuracy trends in erosion and progradation areas along the mouths and sides of the delta. Our algorithm performs well at delineating the shorelines, although special care must be taken to clean the images from clouds and shadows that may alter the definition of the shoreline. Results show that the Atrato delta has lost around 10 km2 due to erosion and has gained around 18 km2 in progradation during the period of assessment. Overall, progradation is the dominant process at the delta’s mouths, while erosion is dominant only in areas far from the mouths, which agrees with a river-dominated environment of high sediment loads and is coherent with other studies made in the region. The algorithm in GEE is a versatile tool, appropriate to assess short and long-term changes of coastal areas that do not count with land-based information.

Detection of Coastal Erosion and Progradation in the Colombian ‘Atrato River’ Delta by Using Sentinel-1 Synthetic Aperture Radar Data

“…The same study indicates that progradation in the region amounts to 17 km 2 during the same analyzed period, primarily concentrated in areas like "El Roto" mouth. Despite its formation between the late 19th century and the early 20th century, this is currently the main mouth of the 'Atrato River', showing simultaneous progradation and erosion processes, although progradation dominates due to the substantial sediment contribution of the river [3]. The study also reveals that erosion is concentrated along all coastal areas of the delta, while progradation is focused on the mouths of the 'Atrato River' channels.…”

“…In this delta, a dynamic balance is manifested as a result of the interaction of the processes of erosion/progradation, regional rise in sea level, coastal drift, and extreme events such as storms and rough seas. This causes losses (erosion) and gains (progradation) of land simultaneously in different areas of this mouth, depending on the contributions of sediment from the basin through the main channel, which in turn generate effects on the mangrove ecosystem of the coastal zone, even leading to its possible expansion [3,12]. The trend of sediment contributions from said basin to the Caribbean Sea has increased in recent decades as a result of the economic activities that take place in the basin and, with it, the morphological effects on the delta [13,14].…”

“…This results in a regime with a dry season that is not very intense and is classified as a tropical rainy equatorial forest according to the Köppen-Geiger system [1,2]. These hydrometeorological conditions are associated with persistent cloudiness in the area and recurrent and prolonged rainfall, leading to runoff with sediment transport from the biodiverse jungles of this basin towards its mouth [3].…”

“…In 2023, Sentinel-2a images were used to measure the width of the beach in the southern part of the Baltic Sea, finding some limitations due to cloud cover in satellite data; however, some erosion rates and breach points point to flooding [9]. In 2021, a spatio-temporal analysis of erosion and progradation in the 'Atrato River' (Colombia) delta was performed using Landsat imagery and Google Earth Engine (GEE) to automatically delineate shorelines [3]. These results were compared to manual delineations of the same imagery using ArcGIS with similar outcomes, identifying trends in erosion and progradation with good accuracy along the mouths and sides of the delta.…”

“…Studies such as [3] identified substantial erosion exceeding 10 km 2 through satellite images from the Landsat program (using passive sensing) between 1986 and 2019 in delta areas in contact with the open sea. The same study indicates that progradation in the region amounts to 17 km 2 during the same analyzed period, primarily concentrated in areas like "El Roto" mouth.…”