Coastlines are commonly defined as the line of contact between land and water (Alesheikh et al., 2007). They are considered one of the most important linear features on the surface of the earth, as almost half of the world’s population resides within 150 kilometers of a shore (Alesheikh et al., 2007; Xue et al., 2009). A combination of human and natural processes have contributed to the erosion of coastlines over time (Chaibi & Sedrati, 2009). Natural causes of coastline erosion include the dynamics of sediment transfer along a beach, long-term shoreline evolution, sea level rise, and large-scale erosion caused by high magnitude storms (Hsu et al., 2007). Human causes, on the other hand, include sand-mining close to the shoreline, construction of coastal structures, tourism and the encroachment of human development towards shorelines (Hsu et al., 2007).
Human developmental projects, such as upstream dams, cause reduced sediment supply at river mouths near coastlines, which can contribute to coastal erosion (Xue et al., 2009). Additionally, development and infrastructure built to support tourism along coastlines causes significant changes in shoreline morphology (Ferrer-Valero et al., 2017). Tourists themselves even contribute to the removal of sand from beaches (Xue et al., 2009). Furthermore, urbanization near coasts leads to deforestation and construction which contributes to shoreline changes and subsequent erosion (Xue et al., 2009). Therefore, increasing development and human activity both place greater pressure on coastlines, making them more vulnerable to erosion.
Efforts are made worldwide to prevent erosion by using shoreline hardening techniques, which involve the implementation of structures, such as seawalls or revetments, along coastlines (Coyne et al., 1998; Gittman et al., 2016). Shoreline hardening is used to prolong human activity and protect infrastructure along coastlines, however, it restricts sand transport, which starves beaches of their natural sediment supply, eventually leading to total coastal erosion (Bush et al., 1996; Gittman et al., 2016; Hanson & Kraus, 1986). For example, a study conducted by Chaibi and Sedrati (2009) analyzing shoreline change along Moroccan coasts found that the use of shoreline hardening disrupted the equilibrium state of sediment transfer along a beach in Tangier Bay. The result was that the eastern side of the beach experienced more erosion than usual (Chaibi & Sedrati, 2009).
Despite the vast amounts of research conducted surrounding coastlines, there are still some gaps to be addressed. Census data would allow for a better understanding of the various human processes that contribute to coastal vulnerability, and accurate models of socioeconomic activities could be used in conjunction with data regarding physical characteristics of coastlines to better manage coastal erosion (Boruff et al., 2005). GIS applications are crucial in analyzing spatial patterns and trends. Saravanan et al. (2014) discuss how GIS can be used to combine different spatial data regarding coastal erosion to map out areas of high concern. They found that the presence of barrier islands, river inputs and wave patterns caused the erosion that further depended on coastal configuration (Saravanan et al., 2014). Therefore, it was very beneficial and useful that the erosion hazard maps showed the usefulness of geospatial technologies in the coastal management system and served as a tool to initiate and implement coastal management programs (Saravanan et al., 2014). A more detailed analysis, involving multiple spatial variables, is required to determine the most sustainable way of addressing coastal erosion in areas that need it most.
Purpose of Research
The purpose of this research is to develop a vulnerability index model using GIS to identify areas of human development in Oahu and Kauai that contribute to coastal erosion.
Objective 1: Identify socioeconomic variables that contribute to coastal erosion.
Objective 2: Develop a coastal vulnerability index model to identify areas of human development that contribute to coastal erosion.
Objective 3: Apply coastal vulnerability index model to coastal areas in Oahu and Kauai to identify coastlines vulnerable to erosion aggravated by human activity.
Objective 4: Compare resulting maps and analyze strengths and weaknesses of a human-induced coastal vulnerability index.