Tidal flat-wetland systems as flood defenses: Understanding biogeomorphic controls

Coastal managers worldwide increasingly recognize the importance of conservation and restoration of natural coastal ecosystems. This ensures coastal resilience and provision of essential ecosystem services, such as wave attenuation reducing coastal flooding and erosion. In the continuum from unvegetated tidal flats to salt marshes and mangroves, fundamental physical controls as well as biotic interactions, and feedbacks among them, determine morphology and vegetation distribution. Although these processes are well described in established literature, this information is rarely applied to understanding the role of these ecosystems as coastal defense. The focus is often on specific elements of the complex system, such as vegetation structure and cover, rather than on their complex natural dynamics. This review examines whether and how the dynamic nature of tidal flat - wetlands systems contributes to, or detracts from, their role in coastal defense. It discusses how the characteristics of the system adjust to external forcing and how these adjustments affect ecosystem services. It also considers how human interventions can take advantage of natural processes to enhance or accelerate achievement of natural coastal defense.Coastal EngineeringEnvironmental Fluid Mechanic

An Earthen Sill as a Measure to Mitigate Salt Intrusion in Estuaries

At a global scale, deltas are vital economic hubs, in part due to the combination of their access to inland regions via river systems with their proximity to sea. However, with the sea in close vicinity also comes the threat of freshwater contamination by saline seawater, especially during droughts. This study explores the potential of a mitigation measure to estuarine salt intrusion, namely the construction of a (temporary) earthen sill—a measure implemented in the Lower Mississippi River near New Orleans (LA, USA). This study suggests design guidelines on how a sill can be used to mitigate estuarine salt intrusion: the design should focus on the longitudinal placement and the height of the sill, and the mitigating efficiency of the sill reduces with increasing tidal range. Overall, a (temporary) sill has great potential to reduce salt intrusion in salt wedge estuaries if there is sufficient water depth available.Coastal EngineeringCivil Engineering & Geoscience