Assessment of Restoration Effects in Riparian Wetlands using Satellite Imagery. Case Study on the Lower Danube River

To better understand the outcomes of river restoration, our paper analyzes the variability of the water content in a restored riparian wetland. We focused our demonstration on the case study of the Babina Islet located in the northern Danube Delta. This site was restored in 1994 by opening levees to regain the pristine hydrological regime with both flooding and dry phases depending on the water level of the Danube River. We monitored the wetland by using the Normal Difference Water Index (NDWI) estimated on Landsat scenes for the period 1984–2020. When compared to pre-restoration conditions, we found an increase of the surface-water area. The maximum surface-water area corresponded to the restoration works. Post-implementation of the restoration solution in 1994, the surface-water area is decreasing. The surface-water area pre-restoration is smaller than the surface-water area in present-day conditions, similar to the control site (Small Islet of Brăila), thus confirming the role of hydrology in maintaining the effects of restoration works. Moreover, we detected the increase of drought area since 1984 on both the restored and the control site. This finding appears to be a new challenge for restoring the riparian wetlands of the Lower Danube River. Our paper recommends the use of standardized indicators via satellite remote sensing to understand riparian wetlands functioning at large scale, which could help to design a coherent strategy of river restoration.