Towards principles and policy levers for advancing living shorelines.

Living shorelines are often better alternatives to stabilize shorelines and reduce dangerous erosion compared to traditional hard armoring practices such as bulkheads and seawalls. Increasing the use of living shorelines will require policy innovation and new approaches to shoreline management, however. Informed by a comparative legal analysis, this article identifies "policy levers" through four categories that demonstrate critical aspects of the human dimension in the estuarine management context that, to greater and lesser extents, promote or inhibit the implementation of living shorelines. Specifically, these categories include: erosion and flood control; neighboring stabilization structures; rebuild policies and sea-level rise projections; and jurisdictional boundaries. The article concludes that the policy levers that are the most optimal baseline choices to advance living shorelines include prohibiting shoreline stabilization in areas where erosion is controlled and bank loss mitigated; eliminating hard armoring as the default erosion and flood control stabilization preference; prohibiting "gap-filling" policies that connect or "align" existing, legal seawalls or armoring; requiring living shorelines in areas where a minimum percentage (10-25%) of the tidal shoreline is already armored; and requiring the replacement of hard armoring with living shorelines when repair is required or certain sea-level rise projections are met. Because modeling frameworks incorporating policy simulations would allow coastal scientists and managers to better visualize how and to what extent policy choices advance or inhibit the adoption of living shorelines, identifying and understanding such policy levers is a critical first step to utilize modeling frameworks to simulate and evaluate how certain legal regimes either promote or inhibit the use of living shorelines for shoreline stabilization in estuarine environments.

Shifting landscapes of risk: Quantifying pluvial flood vulnerability beyond the regulated floodplain.

Floods are recognized as the costliest type of natural hazard both worldwide and in the United States, with projected increases in frequency and magnitude in the absence of effective adaptation strategies. In the fall of 2018, Hurricane Florence made landfall in southeastern North Carolina, USA, bringing record rainfall and resulting in widespread inundation that impacted many areas outside of the federally designated Special Flood Hazard Area (SFHA). Much of this flooding was from inland pluvial inundation, which is an understudied component of coastal risk and vulnerability assessments primarily due to the scarcity of infrastructure data and historically lower flooding recurrence rates. This has resulted in severe damages in areas that residents and local officials considered at low risk from flooding. Using nearly-coincident high-spatial, high-temporal resolution CubeSat satellite imagery, we quantified the areal extent of post-Hurricane Florence floodwater within and beyond the 100-year floodplain (SFHA) and the proportion of residential structures exposed to flooding within an eight-county study area. We propose a novel approach to estimate flood risk resulting from this singular event (termed an actualized risk index) when compared to a published empirical model of vulnerability. We show that 24.3% of detected floodwater was outside the 100-year floodplain, 43.4% of exposed residential structures are outside the 100-year floodplain, and communities of highest vulnerability are not only along the coast but also inland along the Cape Fear, Northeast Cape Fear, Trenton, and Neuse Rivers. This suggests that the SFHA may not adequately show the spatial distribution of pluvial flood risk in riverine areas, and that misunderstanding of this risk has led to a pattern of development in which houses have a higher than expected risk of flooding. Moreover, this additional flood risk may disproportionately affect lower-income residents of these largely rural areas. These results have important implications in light of recent policy guidance in southeastern USA states that mandate that predictive coastal vulnerability assessments to sea level rise be conducted relative to 100-year SFHA zones.

Frontiers in assessing septic systems vulnerability in coastal Georgia, USA: Modeling approach and management implications.

Threats to public health and environmental quality from septic systems are more prevalent in areas with poorly draining soils, high water tables, or frequent flooding. Significant research gaps exist in assessing these systems' vulnerability and evaluating factors associated with higher rates of septic systems replacement and repair. We developed a novel GIS-based framework for assessing septic system vulnerability using a database of known septic system specifications and a modified Soil Topographic Index (STI) that incorporates seasonal high groundwater elevation to assess risks posed to septic systems in coastal Georgia. We tested the hypothesis that both the modified STI and septic system specifications such as tank capacity per bedroom and drainfield type would explain most of the variance in septic system repair and replacement using classification inference tree and generalized logistic regression models. Our modeling results indicate that drainfield type (level vs. mounded) is the most significant variable (p-value < 0.001) in predicting septic systems functionality followed by septic tank capacity per bedroom (p-value < 0.01). These show the importance of septic system design regulations such as a minimum requirement for horizontal separation distance between the bottom of trenches and seasonal water table, and adequate tank capacity design. However, for septic systems with a mounded drainfield and a larger tank capacity per bedroom, the modified STI representing hydrological characteristics of septic system location is a significant predictor of a high septic system repair and replacement rate. The methodology developed in this study can have important implications for managing existing septic systems and planning for future development in coastal areas, especially in an environment of rapid climatic change.