Assessing Land Deformation and Sea Encroachment in the Nile Delta: A Radar Interferometric and Inundation Modeling Approach

Abstract

Persistent scatterer interferometric analyses were conducted on a stack of 84 Environmental Satellite's Advanced Synthetic Aperture Radar scenes spanning 7 years (2004 to 2010) over the entire Nile Delta of Egypt and surroundings (area: 40,416 km2) to monitor the ongoing spatial and temporal land deformation, identify the factors controlling the deformation, and model the interplay between sea level rise and land subsidence to identify areas and populations threatened by sea encroachment by the end of the 21st century. Findings include the following: (1) general patterns of subsidence (average rate: −2.4 mm/year) in the northern delta, near‐steady to slight subsidence in the southern delta (average rate: 0.4 mm/year), separated by a previously mapped flexure zone (minimum width: 20–40 km) undergoing uplift (average rate: 2.5 mm/year); (2) high subsidence rates (up to −8.9 mm/year) over the north central and northeastern delta (area: ~4,815 km2), possibly due to compaction of recent (<3,500 years old), thick (>5 m) silt and clay‐rich Holocene sediments; (3) high subsidence rates (up to −9.7 mm/year) in areas where the highest groundwater extraction rates were reported in southern delta (Menoufia governorate) and in reclaimed desert land in the western delta (Beheira governorate); (4) high subsidence rates (up to −9.7 mm/year) over onshore gas fields, notably the Abu Madi gas field, where high gas extraction rates have been recorded; and (5) using extracted deformation rates, high‐resolution TanDEM‐X digital elevation model, a eustatic sea level rise of 0.44 m, and applying a bathtub inundation model, an estimated 2,660 km2 in northern delta will be inundated by year 2100.

Best Practices for Elevation-Based Assessments of Sea-Level Rise and Coastal Flooding Exposure

“…Despite ample evidence of the significant limitations of global DEMs, especially SRTM, for coastal assessments, they have been used extensively for mapping and describing potential impacts of SLR and coastal flooding, often with assessment parameters (small water level increments and short planning horizons) that fall well within the error bounds of the underlying elevation data (Dasgupta et al, 2008(Dasgupta et al, , 2010Hanson et al, 2010;Curtis and Schneider, 2011;Blankespoor et al, 2014;Hardy and Nuse, 2016;Kopp et al, 2017;Runting et al, 2017;Brown et al, 2018a,b;Gebremichael et al, 2018;Haer et al, 2018;Jevrejeva et al, 2018;Lincke and Hinkel, 2018;Nicholls et al, 2018;Prahl et al, 2018;Rasmussen et al, 2018;Schuerch et al, 2018;Wolff et al, 2018). Some of these studies used a model or database in which the global DEM is embedded, such as the Dynamic Interactive Vulnerability Assessment (DIVA) modeling framework (Hinkel, 2005;Vafeidis et al, 2008), so the inherent vertical uncertainty is contained within model or database components.…”

“…In contrast to global mean SLR scenarios, such projections capture the geographic variation in sea levels and can include factors such as ocean currents and changes in gravity fields (Wuebbles et al, 2017). The importance of using relative SLR rates is well recognized and demonstrated in numerous studies (Spada et al, 2013;Kopp et al, 2014;Nicholls et al, 2014;Slangen et al, 2014;Sweet and Park, 2014;Lentz et al, 2016;Wöppelmann and Marcos, 2016;Antonioli et al, 2017;Davis and Vinogradova, 2017;Gebremichael et al, 2018;Shirzaei and Bürgmann, 2018). (3) Use dasymetric mapping if a coastal assessment includes estimates of impacted population.…”

Surface deformation evolution in the Pearl River Delta between 2006 and 2011 derived from the ALOS1/PALSAR images

“…The geological structure formed by the highly compressible soil layers, however, is inherently unstable. The PRD is mainly composed of soft soil layers with high water content and compressibility, poor permeability, low bearing capacity and shear strength (Gebremichael et al 2018), which easily leads to surface deformation. Most of the soft soil layers formed by sediment deposition are distributed along rivers, so subsidence usually occurs along rivers when those areas were developed by human activities and engineering construction.…”

Novel Quantification of Shallow Sediment Compaction by GPS Interferometric Reflectometry and Implications for Flood Susceptibility

“…Models and data suggest that the rate of shallow subsidence can be greater than current rate of regional and global SLR. This is especially true in coastal plains and river deltas, where close to a billion people live (Gebremichael et al, 2018; Teatini et al, 2011). For example, the average shallow subsidence in the uppermost 5 m of Holocene strata in the Mississippi Delta has been estimated to be 6.4 ± 5.4 mm/yr (Jankowski et al, 2017).…”