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

Subsidence is a common cause of amplified relative sea-level rise, flooding, and erosion in coastal environments. In particular, subsidence due to sediment consolidation can play a significant 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 artificial loads and exhibit a first-order exponential decrease with a time constant of approximately 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-first century, natural subsidence will augment relative sea-level rise in the Fraser Holocene lowlands by approximately 50% or approximately 15%. Anthropogenic subsidence will augment relative sea-level rise by approximately 130% or approximately 40%, potentially raising it to as much as 1-2 m. In deltaic, lacustrine, and alluvial environments, anthropogenic sediment consolidation can result in significant amplification and strong spatial variations of relative sea-level rise that need to be considered in local planning.