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Assessing Ways to Protect Shorelines Against Flooding and Erosion by New High-Fidelity Numerical Models

Stefano Brizzolara, MIT Sea Grant and MIT
Monday, June 16 @ 12:15pm


About 3 billion people in the world live in coastal areas. Just in Europe each year up to 2.5 million people could be affected by coastal flooding (Nicholls, RJ, 2006), and about 20% of coastal wetlands could disappear by 2080 (Nicholls, RJ 2004). Coastal and near-shore marine ecosystems are vulnerable to a host of climate change-related effects including increasing air and water temperatures, ocean acidification, changes in runoff from the land, sea-level rise, and altered currents, increased storm intensity in some regions (U.S. Global Change Research Program - 2009 Report). The coastal areas are particularly vulnerable to the impact of global change, it is expected that these may entail, among other things, an increase in floods and extreme events and accelerated coastal erosion (Nicholls, RJ 2004).

MIT Sea Grant is developing new multi-fidelity numerical simulation models for the prediction of wave flooding due to extreme events in a sensible coastal stretches of Massachusetts. By these simulation tools it will be possible to systematically and scientifically assess the efficacy of different types of innovative underwater protection structures to mitigate flooding risk and reduce beach erosion problems.

We will present some examples of the new protection structures realized in successful beach restoration projects in the North Tyrrenum sea which were designed and optimized by the accurate numerical modeling of costal hydrodynamic processes (Brizzolara & Stura, 1998; Brizzolara & Brizzolara, 2004).

The integrated simulation model will couple a high fidelity Smoothed Particle Hydrodynamic (SPH) numerical solver in the near shore domain with a time or spectral domain deterministic model to predict the wave shoaling with tide/current/wind effects from the offshore to the surf region. Among the existing wave transformation models, we will particularly consider the FVCOM developed at UMass Darmouth and WHOI, which is a well validated 3D offshore hydrodynamic model that has been recently integrated with a third generation spectral wave model (SWAVE), supported also by MIT-SG and successfully applied to Massachusetts coast.; and Mike21 NSW and BW models of the Danish Hydraulic Institute, that have been extensively validation for different coastal hydraulic problems and effectively used to design the two mentioned interventions.

The new high-fidelity model based on an enhanced version of the SPH solver (Monaghan, 1992), highly parallelized on GPGPU cards, will efficiently eliminate most of the empiricism currently utilized at various levels, allowing a significant step forward in the accurate assessment of the resilience properties of different coastal structures, building and infrastructures. The model, in fact, will be capable of accurately reproducing the wave propagation and the run up phenomena on sloped beach (Angelini R.R & Brizzolara S. 2014) and to supplying impact forces and water elevation in complex topographies and/or urbanized areas of the coast, evolving the physical processes from the most general (and best known) offshore conditions where the spectral or time domain wave transformation model is applied. Over all the SPH model can be used to define the shape, the dimension and the response of the multi-function submerged coastal structures and to study the innovative system for energy production from wave or current.

The coupled model is expected to bring a major step forward in the prediction of nearshore hydrodynamic processes with respect to the current state of the art (Wolf et al., 2008; Zhang et al., 2004). A much higher fidelity to the real physical processes will be achieved, allowing for important non-linear interaction effects due to complex bathymetries and rigid coastal profiles (i.e. wall overtopping and dune breaching) that are not currently considered by any state of the art code.

Angelini R. R, Brizzolara S. (2014) Numerical Modeling of Breaking Periodical Waves on a Sloped Beach Profile by SPH. ISOPE 2014 TPC 1127.
Brizzolara E., Stura S. (1998). Beach Restoration project on the littoral of Loano (SV) Italy. (in Italian)
Brizzolara E., Brizzolara S. (2002). Hydraulic design of the protected beach nourishment project in Varazze (SV), Italy. (in Italian)
Monaghan J.J. (1992). Smoothed particle hydrodynamics Ann. Rev. Astron. Astrophys. 30 543–74
Nicholls, R. J. (2004). "Coastal flooding and wetland loss in the 21st century: Changes under the SRES climate and socio-economic scenarios." Global Environmental Change 14, 69–86.
Nicholls, R.J. and R.S.J. Tol. 2006. Impacts and responses to sea-level rise: a global analysis of the SRES scenarios over the twenty-first century. Phil. Trans. R. Soc. A 2006 364.
U.S. Global Change Research Program (USGCRP) - 2009 Report
Wolf, J. (2008). Coastal flooding: impacts of coupled wave–surge–tide models, Nat Hazards, 49 (2), 241–260.
Zhang H., Ole S. Madsen, S.A. Sannasiraj, Eng Soon Chan (2004) Hydrodynamic model with wave–current interaction in coastal regions, Estuarine, Coastal and Shelf Science, Volume 61,2, pp. 317-324, ISSN 0272-7714, 10.1016/j.ecss.2004.06.002