Coastal Erosion Control Management Through Thin Layer Placement for Sustained Living Shorelines

This presentation explores research determining the optimal thin layer placement application depths for maintaining black needle rush (Juncus Roemerianus) vegetation survival in the northern Gulf of Mexico's coastal wetlands. These wetlands safeguard against erosion, sea level rise, and storms while providing vital ecosystem services. However, their degradation, driven by accelerated sea level rise, intensified storms, and erosion in this region, poses significant risks. The study employed a raised brackish water pool housing 84 experimental units with dredged material from Mobile Bay and black needle rush plugs. Experimental units were subjected to simulated tidal conditions with varying thin layer placement depths from 6-14 inches. Vegetation health indicators like stem measurements, biomass, and soil compaction were monitored over 9 months. Results will guide managing aging living shoreline projects cost-effectively by informing vegetation re-establishment strategies. This minimizes coastal erosion, land loss, and the need for costlier hard armoring, extending these critical protective barriers' functional lifespan against rising seas and storms.

Full Abstract: Coastal wetlands, recognized as highly productive ecosystems, play a vital role in safeguarding against erosion, sea level rise, and storm events, while performing nutrient removal, improving water quality, and serving as crucial habitats for fisheries. Human communities along coastlines rely on these services, yet the degradation of coastal areas poses risks to both these services and property. Particularly in the northern Gulf of Mexico, elevated rates of sea level rise, intensified storm events, and erosion are key contributors to substantial land loss. The objective of this research is to determine the optimal thin layer placement depth needed to maintain black needle rush (Juncus Roemerianus) vegetation survival in the northern Gulf of Mexico. A raised pool filled with brackish water was used to house 84 experimental units filled with beneficial use dredged material from Mobile Bay. Each experimental unit had a 12 in. (30 cm) diameter and started with five, 2 in. (5 cm) Black Needle Rush (Juncus Roemerianus) plant plugs planted in a domino five pattern. This experiment was designed in two phases. Phase I was the first four months, where plants were given time to establish themselves. Phase II was where plants were subjected to sea level rise and various thin layer placement (TLP) depths. Phase I diurnal tidal heights ranged between 3 in. (7 cm) and 13 in. (33 cm) and increased to 11 in. (28 cm) and 21 in. (53 cm) during Phase II to imitate Gulf of Mexico tidal conditions. All experimental units were constructed of a polypropylene fabric to allow for free-flowing water through the experimental units and were filled with an average dredged soil depth of 13 in. (33 cm). TLP depths consisted of 6, 8 ,10, 12, and 14 in. (15, 20, 25, 30, 36 cm) where the control did not contain any additional sediment. Soil compaction, stem length, stem width, stem count, stem biomass, and root biomass samples have been monitored to track plant health over 9 months. Final data will be collected in mid-June that will complete research for this study. Building back coastlines that are being lost due to erosion or sea level rise can be expensive. The results from this study will provide critical guidance on managing and maintaining existing living shoreline projects as they approach the end of their design life. Identifying the optimal thin layer placement depths will inform strategies to ensure vegetation can be re-established cost-effectively, minimizing further coastal erosion and land loss from rising sea levels. This improved understanding will enhance the ability to maintain the protective services provided by living shorelines, preventing the need for more costly hard armoring or reconstruction. Extending the functional lifespan of living shorelines through sustainable maintenance techniques is vital for communities seeking to combat coastal land loss while operating within budgetary constraints.