Indications of a positive feedback between coastal development and beach nourishment
Beach nourishment, a method for mitigating coastal storm damage or chronic erosion by deliberately replacing sand on an eroded beach, has been the leading form of coastal protection in the United States for four decades. However, investment in hazard protection can have the unintended consequence of encouraging development in places especially vulnerable to damage. In a comprehensive, parcel‐scale analysis of all shorefront single‐family homes in the state of Florida, we find that houses in nourishing zones are significantly larger and more numerous than in non‐nourishing zones. The predominance of larger homes in nourishing zones suggests a positive feedback between nourishment and development that is compounding coastal risk in zones already characterized by high vulnerability.
Population density, housing development, and property values in coastal communities along the U.S. Atlantic and Gulf Coasts continue to increase [National Oceanic and Atmospheric Administration (NOAA), 2013; Carter et al., 2014; National Research Council (NRC), 2014] despite increasing hazard from storm impacts, chronic shoreline erosion, and sea‐level rise [Moser et al., 2014; Wong et al., 2014]. Since the 1970s, beach nourishment, which involves importing sand to widen an eroding beach, has been the main strategy in the United States for protecting coastal properties from hazard damage [NRC, 2014]. However, research into dynamics linking natural hazards, socio‐economic development, and associated risk points to a paradox: investment in hazard protection can have the unintended consequence of encouraging more development in places already vulnerable to damage [Mileti, 1999; Nordstrom, 2000; Turner, 2000; Werner and McNamara, 2007; Cooper and McKenna, 2009; McNamara et al., 2015]. This is a positive feedback, whereby hazard protection drives development and vice versa [Werner and McNamara, 2007]. Initial development may prompt protection, but once the feedback is established, both parts of the system drive—and respond to—each other. Versions of this dynamic have been described for leveed river systems with developed floodplains [Werner and McNamara, 2007; Di Baldassarre et al., 2013]; for wildland–urban interfaces, where wildfire suppression protects development in fire‐prone areas [Gude et al., 2008]; and for developed high‐relief landscapes, where basins are engineered to receive debris flows on mountain flanks [McPhee, 1989; Johnson et al., 1991]. Research into developed coastlines likewise suggests that nourishment protection for high‐value shorefront properties may in turn attract further development [Nordstrom, 2000; Gopalakrishnan et al., 2011; McNamara et al., 2015].
We find that nourishing zones account for more than half of the approximately 1400 km of Florida's coastline fronted by single‐family homes (Table 1). Nourishing zones exceed non‐nourishing zones in total number by nearly 50% (Figure 1a). Total house area and number are both greater in nourishing zones than in non‐nourishing zones (Figures 1a and 1d), and nourishing zones are more densely developed in terms of house area and number per kilometer shoreline (Figures 1e and 1f).