Subsidence and relative sea level rise in the Fraser River delta, Greater Vancouver, British Columbia, from combined geodetic data Fraser River, Fraser River Delta, Greater Vancouver Regional District, Vancouver, North Vancouver, Burnaby, Richmond, Delta, Surrey, Langley, Tsawwassen Heights, Point Atkinson sedimentology, surficial geology/geomorphology, tectonics, environmental geology, engineering geology, Holocene, Pleistocene, sea level changes, sea level fluctuations, subsidence, geodesy, geodetic networks, satellite geodesy, radar methods, geological history, sedimentation, coastal environment, coastal management, regional planning, urban planning, deltas, deltaic deposits, glacial tectonics, tectonic history, tectonic setting, mapping techniques, tides, sea level rise, vertical motion, global positioning system, human structures, tide gauges, error analysis, Phanerozoic, Cenozoic, Quaternary We use two independent methods to map the spatial variations in vertical motion of the land surface in the Greater Vancouver Regional District: 1) first-order geodetic levelling in 1958/1959 and 1977, and 2) satellite-based Coherent-Target-Monitoring Interferometric-Synthetic-Aperture RADAR (CTM-InSAR) over the period 1992-1999. The first-order geodetic levelling involves over 60 benchmarks and the CTM-InSAR over 300,000 ground targets. Vertical velocities at five permanent Global Positioning System sites, together with 37 other sites in British Columbia and Washington, are used to align the levelling and CTMInSAR results to the ITRF2000 global reference frame. The combined analysis shows an average subsidence rate in the Holocene delta (Richmond and Delta municipalities) of 1-2 mm/yr compared to uplift of 0-1 mm/yr in the Pleistocene Highlands (Vancouver, Burnaby, Surrey, Tsawwassen Heights). Areas of subsidence coincide with recent (post-glacial) Fraser River Delta sedimentation but there is no significant correlation with known variations in sediment thickness. Localized rapid subsidence areas (>, 4 mm/yr) appear to be associated with sites of relatively recent construction. The BC Ferries Terminal at Tsawwassen, for which historical levelling data and CTM-InSAR are available, exhibits subsidence rates that have diminished from 15 mm/yr in the 1960's and 1970's to 3 mm/yr in the 1990's. More work is needed to determine the effects of the age and size of engineering structures on the observed vertical velocities. The land subsidence map is tied to regional sea level using a subset of collocated tide gauges and GPS stations. This analysis points to a regional Northeast Pacific sea-level rise of 1.8 mm/yr over the 20th century. In contrast, the local tide gauges at Point Atkinson and Vancouver show a low regional sea-level rise of 0.3 mm/yr when combined with our geodetic results. We conclude that the two local gauges are problematic and should not be used for sea-level rise analysis, unless a physical reason for the low rates can be found. Based on the Intergovernmental Panel on Climate Change global predictions, we estimate a future relative sea-level rise (sea-level increase + subsidence) by 2100 of 40-70 cm for most of the Fraser River Delta, and possibly as much as 130 cm in areas that are subsiding rapidly. Source.

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