Application of State of the Art Modeling Techniques to Predict Flooding and Waves for a Coastal Area within a Protected Bay

Abstract

Flood Insurance Rate Maps (FIRMs) are developed by the Federal Emergency Management Agency (FEMA) to provide guidance in establishing the risk to structures and infrastructure from storm surge sand associated waves in the coastal zone. The maps are used by state agencies and municipalities to help guide coastal planning and establish the minimum elevation and construction standards for new or substantially improved structures. A summary of the methods used and a comparison with the results of 2013 FIRM mapping are presented for Warwick, Rhode Island (RI), a coastal community located within Narragansett Bay. Because of its location, Warwick is protected from significant coastal erosion and wave attacks, but is subject to surge amplification. Concerns surrounding the FEMA methods used in the 2013 FIRM analysis are put in context with the National Research Council's (NRC) 2009 review of the FEMA coastal mapping program. New mapping is then performed using state of the art, fully coupled surge and wave modeling, and data analysis methods, to address the NRC concerns. The new maps and methodologies are in compliance with FEMA regulations and guidelines. This new approach makes extensive use of the numerical modeling results from the recent US Army Corp of Engineers, North Atlantic Coast Comprehensive Study (NACCS, 2015). Revised flooding maps are presented and compared to the 2013 FIRM maps, to provide insight into the differences. The new maps highlight the importance of developing better estimates of surge dynamics and the advancement in nearshore mapping of waves in flood inundated areas by the use of state of the art, two-dimensional, wave transformation models.

Land Use and Mitigation Effects on Barrier Beach Erosion in Storms: Case Study in Rhode Island

“…They however neglected stem swaying motiond and inertia forces, and lumped the uncertainty of the stem flexibility and relative velocity between plant and water particles into an empirical drag coefficient (Maza et al, 2013), expressed as, The appeal of this physics-based approach is however mitigated by its applicability. Indeed, the vegetated area needs to be accurately defined with a vegetation density and stem size as well as with a drag coefficient specific to the mechanical properties of the plant (e.g., Stratigaki et al 2011;Maza et al 2013;Vargus-Luna et al 2015). The variety of vegetation and lack of available corresponding drag coefficients prevented us from applying Mendez and Losada's (2004) formulation to our entire site and we only applied it to a small section of the site, covered with tall grass similar to Spartina Alterniflora; for the latter, we used the drag coefficient of Smith et al (2016) based on Anderson and Smith's (2014) experiments, C D = 0.22 + 910/Re.…”

“…Recent studies have assessed the risk posed to coastal communities in RI by the 100-year storm event. While initial 2D modeling following standard procedures predicted potential damage to coastal infrastructures, further studies considering SLR projections and using more accurate wave models showed a dramatic increase in potential damage, due to a significant expansion of the inundation (Grilli et al, 2017; , 2017). To reduce structural damage due to flooding and wave overtopping, several mitigation scenarios were considered, such as rising the First Furnished Floor Elevations (e.g., U.S Corps of Engineer at selected RI South Shore Sites) or beach re-nourishment .…”

STORMTOOLS, Coastal Environmental Risk Index (CERI) Risk and Damage Assessment App

“…These maps are normally provided in the form of BFE maps. However, the FEMA FIRMs have some well documented problems [6,7] for coastal and protected waters in RI [8,9], and in addition do not include the effects of SLR. Damages can be calculated by CERI for low, most likely, and maximum levels for both structure and content, based on the NACCS damage assessment curves [10].…”

“…CERI has been applied to Charlestown and Warwick, RI, with federal funding provided through the Community Development Block Grant (CDBG) Program-Disaster Recovery Hurricane Sandy (HUD) and administered by Rhode Island Office of Housing and Community Development [5]. Charlestown represents a coastal community along the exposed southern RI shoreline [8], while Warwick is inside the more protected Narragansett Bay [9]. Application of CERI to Barrington, Bristol, and Warren, RI, inside Narragansett Bay (a low-lying area, with very high housing density), was recently completed and again funded by HUD-CDBG [11].…”

“…Senior students in the Ocean Engineering program at University of RI (URI) have applied CERI to Matunuck Beach, RI in 2015-2016 [14], to Misquamicut Beach, RI in 2016-2017 [15] to Providence and the Fox Point Hurricane barrier in 2017-2018 [16] and to the Narragansett Bay Commission (NBC) Wastewater Treatment Facility (WWTF), and adjacent above-ground storage tanks (AST) located on Fields Point in 2018-2019 [17]. The development of CERI and its application to coastal communities have been published in the peer-reviewed literature [4,5,8,9,11,18,19] and presented at a number of national conferences (e.g., ASCE Solutions to Coastal Disasters, Estuarine and Coastal Modeling, Coastal Geotools, Northeast Arc User Group Conference). One of the side benefits of CERI is that the data necessary to input to the method and generated as part of its application can be used to provide state-of-the-art flooding maps, equivalent to those developed by FEMA Flood Insurance Rate Maps (FIRMS), but explicitly including the effects of sea level rise (SLR).…”