Incorporating Future Infrastructure Decisions Into Salt Marsh Migration Models (Final Report)

Sea level rise affects both coastal development and coastal ecosystems by increasing flooding and erosion. The impacts to human infrastructure and ecosystems are often assessed separately, when in fact they are highly intertwined. Coastal salt marshes may persist under rising seas by migrating landward; however, land management decisions, including armoring coastal properties, may prevent this inland migration, essentially squeezing salt marshes between hard upland barriers and the rising sea. These land management decisions might significantly affect marsh habitat but are not currently accounted for in projections of salt marsh persistence. The goal of this study was to examine the interactions between land management and salt marsh migration under rising sea level. We developed improved modeling tools that specifically account for these interactions to provide more realistic projections of how salt marsh habitat on the Georgia coast might evolve in the future. First, we used a detailed census of existing coastal armoring to develop a logistic regression equation that estimates the probability of armoring for individual coastal parcels. We also simulated future urbanization using the SLEUTH urban growth model. These models were both incorporated into the Sea Level Affecting Marshes Model (SLAMM)to simulate future marsh migration under sea level rise while accounting for urbanization and coastal armoring decisions. We found that sea level rise effects were generally larger than the effects of armoring and urbanization on future salt marsh extent. Armoring and urbanization did restrict salt marsh migration, especially in already developed areas (e.g. the Savannah region). These differences were much smaller for the whole Georgia coast because there are (and are projected to remain) large undeveloped areas where uninhibited marsh migration is allowed. This research provides a more realistic understanding of the interplay2between sea level rise, land management, and salt marsh migration and can inform effective and sustainable coastal management. Methods: This research yielded two major outputs. First, was the development of a logistic regression equation that can predict the probability that a coastal parcel will be armored now or in the future. The second output was the development of an integrated modeling approach to incorporate the effects of armoring and future urbanization on salt marsh migration on the Georgia Coast.