Coral Reef Restorations Can Be Optimized to Reduce Coastal Flooding Hazards

Abstract

Coral reefs are effective natural coastal flood barriers that protect adjacent communities. Coral degradation compromises the coastal protection value of reefs while also reducing their other ecosystem services, making them a target for restoration. Here we provide a physics-based evaluation of how coral restoration can reduce coastal flooding for various types of reefs. Wave-driven flooding reduction is greatest for broader, shallower restorations on the upper fore reef and between the middle of the reef flat and the shoreline than for deeper locations on the fore reef or at the reef crest. These results indicate that to increase the coastal hazard risk reduction potential of reef restoration, more physically robust species of coral need to be outplanted to shallower, more energetic locations than more fragile, faster-growing species primarily being grown in coral nurseries. The optimization and quantification of coral reef restoration efforts to reduce coastal flooding may open hazard risk reduction funding for conservation purposes.

Designing Coastal Adaptation Strategies to Tackle Sea Level Rise

“…Substantial work has been done on the efficiency of mangroves (McIvor et al, 2013;Möller et al, 2014), salt marshes (Guannel et al, 2016;Leonardi et al, 2018), oyster beds (Morris et al, 2019), and coral reefs (Ferrario et al, 2014;Roelvink et al, 2021) that shows how and under what conditions these ecosystems can attenuate wave power, reduce erosion, and more generally enhance coastal protection. However, the IPCC (2019) shows that accelerated SLR and climate change may lead to significant coastal ecosystem loss by the end of the century.…”

Hurricane Flood Hazard Assessment for the Archipelago of San Andres, Providencia and Santa Catalina, Colombia

“…For model calibration, we focused on bed friction parameters as this parameter does not change from mean to storm conditions (bed friction due to seafloor configurations). Specifically, we calibrated the values of the bed friction coefficient C f , which has been used in the same model for similar sea floor configurations (Roelvink et al, 2021), getting values of 0.01 for the points before x = 3600 m and after x = 7090 m, and values of 0.9 in between, where coral rubble can be found (Díaz et al, 2000). According to the seafloor configuration for other profiles, we extrapolated these results to find the zones of the domain where each C f value applies.…”

A Model-Derived Empirical Formulation for Wave Run-Up on Naturally Sloping Beaches

“…The sum of tides, surge, mean set-up, and the crests of the oscillatory run-up motion are called the TWL. The wave contribution to the TWL may be in the order of 20% [5] on mildly sloping coasts and may be dominant on steeper coasts [6]. While the processes are largely understood and incorporated in numerical models which show considerable skill (e.g., [6,7]), process-based models to compute run-up are not routinely incorporated in forecast systems because of their computational expense.…”

“…The wave contribution to the TWL may be in the order of 20% [5] on mildly sloping coasts and may be dominant on steeper coasts [6]. While the processes are largely understood and incorporated in numerical models which show considerable skill (e.g., [6,7]), process-based models to compute run-up are not routinely incorporated in forecast systems because of their computational expense. Rather, run-up formulas which are based on field observations (e.g., the Stockdon formula [8]) are typically applied [9].…”

“…In the present approach study, we apply the XBeach-NH+ model [18] which is a quasi-two-layer dispersive model which resolves both the incident and infragravity waves up to a relative depth kh of 4. This model has shown good skill in predicting the wave hydrodynamics in field conditions [6] and wave run-up in laboratory conditions [7]. This model, using calibrated settings, is applied to a wide range of geomorphological parameters/coastal types and for a wide range of wave forcing conditions, including obliquely incident waves and wave directional spreading.…”