Wetland Accretion Rate Model for Ecosystem Resilience and its Application to Coastal Transportation Infrastructure Along Alabama State Route 180

Abstract

Fort Morgan Road (SR-180) on Alabama’s Gulf Coast is a vital coastal roadway impacted by severe storms, high groundwater table, and future sea-level rise (SLR). The area surrounding SR-180 supports a variety of ecological habitats for natural and nature-based features (NNBF). This study focuses on the effects of SLR (ESLR) on surface transportation infrastructure and the ability of NNBF to mitigate those effects. NNBF combine ecological with conventional designs and are expected to change substantially over their lifespan through natural processes. To inform modeling of NNBF scenarios, we applied the Wetland Accretion Rate Model for Ecosystem Resilience (WARMER) to vegetated areas of proposed NNBF. WARMER predicts changes in marsh surface elevation relative to mean sea-level (MSL) through its cohort tracking method to capture critical marsh accretion processes. We parameterized WARMER using marsh sediment cores collected by previous studies in Bon Secour Bay paired with NOAA predictions for SLR in the northern Gulf Coast. Four coastal salt marsh vegetation species were analyzed in WARMER to predict their effectiveness when incorporated into NNBF design. Mean annual accretion rates computed by WARMER during the 150-year simulation were 14.10 mm/yr for C. mariscus, 13.26 mm/yr for J. roemerianus, 11.61 mm/yr for S. patens, and 14.31 mm/yr for T. domingensis. Under low and intermediate-low SLR scenarios, the NNBF increases elevations for all marsh species. With intermediate SLR, only T. domingensis remains above SLR. Under the intermediate-high and high scenarios, the NNBF will become inundated within 22 years and 11 years, respectfully, for all species. Marsh surface elevations from WARMER will be used in the ongoing NOAA ESLR project as inputs for hydrologic and hydrodynamic (H & H) modeling of Fort Morgan Peninsula. WARMER will also be used to predict how NNBF will evolve as part of a dynamic system while informing the better design of NNBF to improve coastal transportation infrastructure resilience.