Estimating Bank Erosion Risk from Joint Hydrological and Satellite Image Time Series

Bank erosion is a natural process that is part of the morphological evolution of rivers associated with the hydrological regime and extreme events. However, erosion is sometimes seen as a problem when populations are exposed on the banks. However, in certain circumstances erosion is detonated by anthropogenic causes that induce morphological changes in the short or medium term. Deforestation, for example, generates changes in the hydrological regime that has consequences on the hydrodynamic conditions that may increase the risk of erosion. The risk of bank erosion should be analyzed first from a context of general morphological dynamics rather than from a local context. Certain erosive processes obey a major morphological tendency that may take years or decades and which local manifestation occurs when a population is already close to being affected. This paper shows a methodology to determine the hydrological risk of river bank erosion from correlating hydrological time series with the tendency and bank migration rates determined by satellite image analysis. The methodology was applied in a study sector called Guáimaro located on the Magdalena River, Colombia. This sector, which has presented strong morphological changes in the last two decades, is characterized by meandric segment with the presence of an island and a floodplain of materials with low resistance to erosion. Near the right bank is a population is currently at risk due to erosion. The results showed that the morphological changes are correlated with three important hydrological events that have induced the major migration, and the yearly flow magnitude is associated with the speed of river movement. The method allows the identification of erosion rates and tendency, the temporal trend of proximity to the banks, and the probability of occurrence.