Toward Sustained Monitoring of Subsidence at the Coast Using InSAR and GPS: An Application in Hampton Roads, Virginia

Hampton Roads is among the regions along the U.S. Atlantic Coast experiencing high rates of relative sea level rise. Partly to mitigate subsidence from aquifer compaction, Hampton Roads is injecting treated wastewater into the underlying aquifer. However, the GPS (Global Positioning System) station spacing (similar to 30 km) is too coarse to capture the spatial variability of subsidence and potential uplift from the injection. We present a cost-effective workflow for generating an InSAR (interferometric synthetic aperture radar) and GPS combined displacement product. We leverage a live, open-access archive of InSAR products generated from Sentinel-1 data. We find an overall subsidence rate of-3.6 +/- 2.3 mm/year with considerable spatial variability. The effects of groundwater injection are currently below detection. The workflow presented here is an asset for sustained monitoring of the injection effort and regional subsidence that is applicable along the U.S. coasts for assisting in mitigation and adaptation of relative sea level rise. Plain Language Summary Hampton Roads in coastal Virginia is among the regions experiencing high rates of relative sea level rise. This rate exceeds the global average primarily due to ongoing land subsidence. In part to reduce this subsidence, Hampton Roads has begun injecting treated wastewater into the underlying aquifer. However, the rate of subsidence and potential uplift from the injection is not uniform but varies spatially, such that the existing network of sensors is unsuitable for monitoring. Here we implement a cost-effective approach for ongoing monitoring that leverages publicly available data products derived from the Sentinel-1 satellite. Overall, we find that Hampton Roads is sinking at a rate of -3.6 +/- 2.3 mm/year, with considerable differences at the neighborhood scale. The effects of the injection cannot yet be seen but will have a larger impact at the surface as more wastewater is injected at full-scale facilities later this year. The workflow presented here is a valuable asset for sustained monitoring of the injection effort and regional subsidence that can be applied along the U.S. coasts for assisting in mitigation and adaptation of relative sea level rise.