Toward understanding the hydrologic, ecologic and community flooding implications of coastal restoration strategies: Sediment diversions

Evaluating the real-world impacts of proposed restoration strategies is a complex process. Typically, restoration is pursued to achieve a number of primary and secondary objectives as most coastal and deltaic areas support a variety of functions and activities with substantial social and economic values. In this analysis, we demonstrate the importance of considering the broad implications of planning and implementing restoration projects. We use a recently developed simplified and computationally efficient biophysical numerical model. The Mid-Barataria Sediment Diversion, a restoration project approximately 60 km down the Mississippi River from New Orleans, Louisiana, USA, offers an opportunity to quantify the benefits and potential impacts of large-scale restoration. Operation plans of the diversion are employed in this analysis to reveal the delicate balance between its potential benefits and possible adverse effects. Evaluation metrics include net land change and landscape evolution, change in salinity and subsequent shift in the distribution of marsh types, long-term change in the hydroperiod and marsh inundation, and change in the flood risk for unique local coastal communities and culture. We also consider subaqueous basin infilling, spatial sediment deposition, and creation of shallow water areas that might be of ecological value. These metrics are evaluated collectively under a set of future scenarios capturing long-term impacts of sea level rise and subsidence. This analysis provides evidence in favor of using a multi-metric approach to holistically evaluate restoration during the planning and design phases, as well as to guide the process of adaptively managing restoration projects post construction.

Keywords: Wetland restoration, Environmental evaluation metrics, Sediment diversions, Operation plans, Morphodynamics, Landscape modeling, Numerical modeling