Drivers of Coastal Shoreline Change: Case Study of Hon Dat Coast, Kien Giang, Vietnam

Abstract

Coastal shorelines are naturally dynamic, shifting in response to coastal geomorphological processes. Globally, land use change associated with coastal urban development and growing human population pressures is accelerating coastal shoreline change. In southern Vietnam, coastal erosion currently is posing considerable risks to shoreline land use and coastal inhabitants. The aim of this paper is to quantify historical shoreline changes along the Hon Dat coast between 1995 and 2009, and to document the relationships between coastal mangrove composition, width and density, and rates of shoreline change. The generalized linear mixed-effects models were used to quantify the major biophysical and land-use factors influencing shoreline change rates. Most significant drivers of the rates of change are cutting of mangroves, the dominant mangrove genus, changes in adjacent shoreline land use, changes of shoreline land cover, and width of fringing mangroves. We suggest that a possible and inexpensive strategy for robust mangrove shoreline defense is direct mangrove planting to promote mangrove density with the presence of breakwater structures. In the shorter term, construction of coastal barriers such as fence-structured melaleuca poles in combination with mangrove restoration schemes could help retain coastal sediments and increase the elevation of the accretion zone, thereby helping to stabilize eroding fringe shorelines. It also is recommended that implementation of a system of payments for mangrove ecosystem services and the stronger regulation of mangrove cutting and unsustainable land-use change to strengthen the effectiveness of mangrove conservation programs and coastal land-use management.

Appendices

Appendix 1

See Table 5.

Table 5 Summary of coastal datasets used in generalized linear mixed-effects modeling, derived from Duke and others (2010), pp 34–37

Appendix 2: Coastal Erosion Severity Classification

The classification of coastal erosion severity to coastal land cover, adjacent shoreline land use and adjacent coastal development in this study was adapted from Pendleton and others (2010), Ozyurt and Ergin (2010) and Hai-Hoa and others (2010a, b) with appropriate modification for study sites. The ranges from 1 to 5 for coastal erosion severity were based on coastal shorelines experiencing with erosion and accretion rates derived from the GIS application. The negative and positive values indicated the intensity of erosion and accretion, respectively. As a result, the rates of coastal change were less than or equal to −2.0 m year⁻¹, assigned as very high severity (5), −2.0 < rate ≤ −1.0 year⁻¹ as high severity (4), −1.0 < rate ≤ 1.0 year⁻¹ as moderate severity (3), 1.0 < rate ≤ 2.0 year⁻¹ as low severity (2), and rate > 2.0 year⁻¹ as very low severity (1).

Appendix 3

See Table 6.

Table 6 Erosion severity rankings to adjacent land use in Hon Dat (expressed in length, km)

In this Appendix, an overall classification of coastal erosion is relatively low severity to adjacent shoreline land uses and adjacent coastal development. Indeed, the percentage of coastal sections with rankings of very high (5) and high severities (4) over study sites was 15.5 %, equivalent to 8.0 km. The remaining length of coastal sections (43.4 km) was ranked as moderate, low, and very low severities to adjacent land uses and adjacent coastal development, making up 84.5 % of total surveyed coastline (50.3 km).

Appendix 4

See Table 7.

Table 7 Generalized linear mixed-effects modeling used to calculate the rates of coastal shoreline change

Appendix 5

See Fig. 7.