Towards an Integrated Assessment of Sea-Level Observations Along the U.S. Atlantic Coast

Sea levels are rising globally due to anthropogenic climate change. However, local sea levels that impact coastal ecosystems often differ from the global trend, sometimes by a factor of two or more. Improved understanding of this regional variability provides insights into geophysical processes and has implications for coastal communities developing resilience to ongoing sea-level rise. This dissertation conducts an investigation of sea level and its contributing processes at multiple spatial scales. Focusing on primarily interannual time-scales and data-driven approaches, new data sources and technologies are utilized to reduce current uncertainties. First, sea-level trends are assessed over the global ocean and at coastlines using data from the recently launched ICESat-2 satellite. These trends agree well with independent measurements, while also filling observational gaps along undersampled coastlines and at high-latitudes. Next, the spatial focus is narrowed to the U.S. East Coast, which is experiencing exceptionally high rates of relative sea-level rise, largely due to land subsidence. By incorporating new state-of-the-art estimates of land-ice melt, an existing Bayesian hierarchical space-time model is expanded to assess the relative contributions of sea surface height and vertical land motion to 20th century relative-sea level change. Model results confirm previous findings that identified regional-scale geological processes as the primary driver of spatial variability in East Coast relative sea level. By rigorously quantifying uncertainties, constraints are placed on the current state of knowledge with clear directions for future research. Finally, small-scale vertical land motion in Hampton Roads, VA is investigated using the remote-sensing technology of Interferometric Synthetic Aperture Radar (InSAR). Two different data sources and processing strategies are implemented which independently reveal substantial rates of vertical land motion that vary over short spatial scales. The results highlight the importance of vertical land motion in exacerbating negative impacts of relative sea-level rise such as flooding and inundation. Overall, this study leverages new spaceborne sensors, an innovative statistical model, and state-of-the-art processing strategies to enhance our understanding of ongoing sea-level change

Precipitation and Sea Level Rise Impacts on Groundwater Levels in Virginia Beach, Virginia

Global sea level rise (SLR) is one of the most immediate impacts of climate change, and poses a significant threat to low-lying coastal communities worldwide. The metropolitan region of Hampton Roads in Southeastern Virginia is one such community, and one where knowledge surrounding SLR is rapidly accumulating. However, most of the research is focused exclusively on surface water processes despite the presence of a shallow groundwater table closely connected to them. SLR will continue to cause the groundwater table to increase in tidally influenced areas of Hampton Roads, and thereby decrease storage capacity of the unsaturated zone. This study investigates the spatial and temporal response of the groundwater table to SLR and precipitation. We choose a tidal watershed, West Neck Creek, in Hampton Roads was chosen to conduct a conceptual yet realistic simulation of the hydrologic cycle using historical precipitation data with SLR scenarios from 0 m (current) to 2 m in 1 m intervals. Groundwater infiltration from the land surface, recharge, and evapotranspiration are modeled using the Unsaturated-Zone Flow package with MODFLOW-NWT. Groundwater rise is simulated by increasing the stage of the tidal stream that drains the watershed. Precipitation and overland runoff are simulated using the surface water model SWMM. The two models are coupled to permit the exchange of boundary condition values at each time step.An ensemble approach is taken to test model sensitivity to a variety of parameters. The findings of the study demonstrated the potential for the effects of SLR-induced groundwater rise to become a damaging hazard to Virginia Beach communities and ecosystems. Most of the potential damages arose from increased interactions of groundwater levels with subsurface infrastructure. Additional runoff was found to be of lesser concern, because the prevalent soils in West Neck Creek are characterized by slow infiltration rates. The results of the sensitivity analysis provided encouraging results, in that changes in parameters did not have excessively large effects on forcing variables. Overall, this study provides a foundation to guide future scientific and engineering efforts to mitigate and adapt to the increasing threat of SLR-induced groundwater rise