Daniele PINTON, University of Florida, Department of Civil and Coastal Engineering, United States
Alberto CANESTRELLI, University of Florida, Department of Civil and Coastal Engineering, United States
Shengzhuo XU, University of Florida, Department of Civil and Coastal Engineering, United States
A hybrid coastal defense consisting of a salt-marsh system at the seaward side and dykes on the landward side has been globally implemented to improve coastal resilience . In this approach, marshes are valuable ecosystems that dissipate storm surges and have an intrinsic ability to keep up with sea-level rise (SLR) [2,3]. Dykes instead, prevent the surge from penetrating inland . Thus, dyke retreat is now considered a valuable option that allows the creation of new marshland in front of the relocated dyke, thus avoiding blockage and maximizing surge damping. However, dykes can exert a blockage effect, which consists of a water set-up against these structures that can lead to their overtopping . The studies investigating the effect of dyke retreat on surge dissipation do not incorporate the morphodynamic expansion of tidal networks in the de-reclaimed land , which is modeled as an unchannelized marsh . In this work, we implement the morphodynamic model Delft3D and a marsh evolution module to study the formation of tidal networks after dyke retreat and their effect on surge dissipation. We consider different combinations of storm surge peak and duration, sediment input, SLR, dyke retreat, and de-reclaimed land slope. Our results suggest that the century-scale morphodynamic evolution of the marsh is driven by an increase in the tidal prism, which depends on dyke retreat, de-reclaimed land slope, and SLR. Results also show that surge damping is overestimated if the morphodynamic evolution of the tidal network after dyke retreat is neglected since the new creeks favor the landward propagation of the surge. Finally, a genetic machine-learning algorithm is used to determine a relationship between surge dissipation, and the morphological and hydrodynamic properties of the marsh. The relationship indicates that shallow tidal networks, small percentages of channelized area, low surge peaks, and large dyke retreats favor surge damping.
Keywords: Salt marshes|dyke retreat|Delft3D|surge dissipation|coastal resiliency