Sigren, Jacob Marshall (2017-08). Coastal Dunes and Dune Vegetation: Interdisciplinary Research on Storm Protection, Erosion, and Ecosystem Restoration. Doctoral Dissertation.
Thesis
Coastal dunes offer many communities around the world a means to naturally mitigate the damage caused by coastal storms. This dissertation will address some of the knowledge gaps concerning the cost effectiveness of dunes in terms of storm damage mitigation, the role of dune vegetation in erosion resistance during storm surges, and the best techniques for restoring dune vegetation. To determine dune storm damage mitigation value, Hurricane Ike FEMA insurance claims for over one thousand homes in Galveston County, Texas, were analyzed (multivariate regression) with respect to the size of the dunes protecting those homes. The dunes in this area provided over 8 million dollars in protection across the study area during Hurricane Ike. Dunes were generally cost-effective (>$50 of damage mitigation per cubic meter of dune sediment) and were a viable hazard mitigation strategy. With regards to dune vegetation's role in erosion resistance, the effects of different plant features and species on swash hydrodynamics, sediment properties, and erosion was evaluated utilizing multivariate regression and a simulated storm surge/wave attack within a wave flume. Aboveground plant surface area was significantly related to decreased swash flow velocity, turbulent kinetic energy, and wave reflection while fine root biomass density was significantly related to increased sediment shear strength. These results indicated that both above- and below-ground features of plants play a role in reducing dune erosion during storm surges. Lastly, a variety of dune restoration techniques and the broader ramifications of planting vegetation on dune biogeomorphology were evaluated to identify effective dune restoration practices for the Texas Coast. Sargassum baling, useful for transporting the nuisance seaweed from beaches, was minimally impactful on plant growth while using rooted plants and native mycorrhizal fungal inoculations generally increased the accumulation of plant biomass. Dune vegetation planting also initially promoted accretion but lowered plant diversity compared to a naturally colonized dune. The research detailed in this dissertation contributes to the growing body of knowledge concerning engineering with nature and provides additional support for the integration of coastal dune restoration into sustainable coastal hazard mitigation strategies.
Coastal dunes offer many communities around the world a means to naturally mitigate the damage caused by coastal storms. This dissertation will address some of the knowledge gaps concerning the cost effectiveness of dunes in terms of storm damage mitigation, the role of dune vegetation in erosion resistance during storm surges, and the best techniques for restoring dune vegetation. To determine dune storm damage mitigation value, Hurricane Ike FEMA insurance claims for over one thousand homes in Galveston County, Texas, were analyzed (multivariate regression) with respect to the size of the dunes protecting those homes. The dunes in this area provided over 8 million dollars in protection across the study area during Hurricane Ike. Dunes were generally cost-effective (>$50 of damage mitigation per cubic meter of dune sediment) and were a viable hazard mitigation strategy. With regards to dune vegetation's role in erosion resistance, the effects of different plant features and species on swash hydrodynamics, sediment properties, and erosion was evaluated utilizing multivariate regression and a simulated storm surge/wave attack within a wave flume. Aboveground plant surface area was significantly related to decreased swash flow velocity, turbulent kinetic energy, and wave reflection while fine root biomass density was significantly related to increased sediment shear strength. These results indicated that both above- and below-ground features of plants play a role in reducing dune erosion during storm surges. Lastly, a variety of dune restoration techniques and the broader ramifications of planting vegetation on dune biogeomorphology were evaluated to identify effective dune restoration practices for the Texas Coast. Sargassum baling, useful for transporting the nuisance seaweed from beaches, was minimally impactful on plant growth while using rooted plants and native mycorrhizal fungal inoculations generally increased the accumulation of plant biomass. Dune vegetation planting also initially promoted accretion but lowered plant diversity compared to a naturally colonized dune. The research detailed in this dissertation contributes to the growing body of knowledge concerning engineering with nature and provides additional support for the integration of coastal dune restoration into sustainable coastal hazard mitigation strategies.
