Impact of anthropogenic subsidence on relative sea-level rise in the Fraser River delta

Abstract

Subsidence is a common cause of amplifi ed relative sea-level rise, fl ooding, and erosion in coastal environments. In particular, subsidence due to sediment consolidation can play a signifi cant role in relative sea-level rise in large deltas. We use a combination of InSAR (interferometric synthetic aperture radar), leveling, and global positioning system data to map absolute vertical land motion in the Fraser River delta, western Canada. We show that primary consolidation of shallow Holocene sediments is the main cause for the slow subsidence (−1 to −2 mm/a) affecting the delta lowlands. In addition, parts of the delta undergo increased anthropogenic subsidence. Rapid subsidence rates (−3 to −8 mm/a) are associated with recent artifi cial loads and exhibit a fi rst-order exponential decrease with a time constant of ~20 years, consistent with the theory of consolidation. Assuming two sea-level rise scenarios of 30 or 100 cm by the end of the twenty-fi rst century, natural subsidence will augment relative sea-level rise in the Fraser Holocene lowlands by ~50% or ~15%. Anthropogenic subsidence will augment relative sea-level rise by ~130% or ~40%, potentially raising it to as much as 1-2 m. In deltaic, lacustrine, and alluvial environments, anthropogenic sediment consolidation can result in signifi cant amplifi cation and strong spatial variations of relative sea-level rise that need to be considered in local planning.

Detailed quantification of delta subsidence, compaction and interaction with man-made structures: the case of the NCA airport, France

“…4e). These CR values are in the range of what it is observed for modern deltas: 1-2 mm yr −1 for the Fraser, Nile and Mississippi deltas (Mazzotti et al, 2009;Wöppelmann et al, 2013;Törnqvist et al, 2008) and up to 15-18 mm yr −1 in some parts of the Po and Ganges-Brahmaputra deltas (Teatini et al, 2011;Higgins et al, 2014). Contrary to those studies (except for the Po delta that seems to behave similarly), the CR increases until the coastline.…”

“…Since the temporal decrease of subsidence rate typically follows an exponential curve with a relatively short time constant (likely shorter than 100 years) (Terzaghi and Peck, 1967), it seems unlikely that compaction of the basal Pleistocene strata could explain the 4-10 mm yr −1 of compaction rate (CR) observed at the surface. We thus conclude that the subsidence is mainly related to the compaction of the Holocene wedge as inferred for other deltas such as the Po, Mississippi, Fraser or GangesBrahmaputra deltas (Mazzotti et al, 2009;Törnqvist et al, 2008;Teatini et al, 2011;Higgins et al, 2014, e.g.). Moreover, InSAR data show here an increase of the subsidence rate from inland to the coastline that correlates well with the increase of the Holocene sediment thickness.…”

“…Indeed, many of the world's largest river deltas are primarily sinking under the effect of sediment compaction (Syvitski et al, 2009). Examples include the Fraser river delta in Western Canada (Mazzotti et al, 2009), the Mississippi delta in the USA (Törnqvist et al, 2008), the Po delta in Italy (Teatini et al, 2011) or the Ganges-Brahmaputra delta in Bangladesh (Higgins et al, 2014).…”

Land Subsidence over Oilfields in the Yellow River Delta

“…It suggests that other factors like sediment consolidation and loading may also contribute to the total subsidence in this part of the Yellow River delta. These subsidence rates will decrease through time if they are caused by loading [16].…”

“…For river delta studies, InSAR has previously been used to measure subsidence due to sediment consolidation and artificial loading in several deltas, including the Pearl River [14], Nile [15] and Fraser River [16] deltas. In the Yellow River delta, Higgins et al [9] showed subsidence rates as high as 250 mm/yr from InSAR.…”