On the morphological evolution of restored banks

Abstract

In recent years, many riverbanks in Europe had their protections removed to reactivate natural erosion processes and improve riparian habitats. Yet, other river functions may be affected, such as navigation and flood conveyance. The quantification and prediction of erosion rates and volumes is then relevant to manage and control the integrity of all river functions. This work studies the morphological evolution of riverbanks along two restored reaches of the Meuse River in the Netherlands, which are taken as case studies. This river is an important navigation route and for this its water level is strongly regulated with weirs. Through aerial photographs and two airborne LIDAR surveys, we analysed the evolution over nine years of restoration and reconstructed the topography along 2.2 km. of banks. An extraordinary low-water level after a ship accident provided the opportunity to observe and measure the bank toe. The banks show a terrace of erosion close to the normally regulated water level, highly irregular erosion rates up to 7 m/year, embayments evolving with upstream and downstream shifts, and sub-reaches with uniform erosion. Probable causes of erosion include ship-waves, high water flows and water level fluctuations. Distinct patterns might be explained by the presence of riparian trees and soil strata of different compositions. These intriguing case studies will continue to be studied to disentangle the role of different erosion drivers, predict erosion magnitudes and establish whether bank erosion will stop or continue in the future.