Historical reconstruction of shoreline evolution at the Nam Dinh Coast, Vietnam

ABSTRACT Hai Hau, located in northern Vietnam, has suffered from severe coastal erosion with a retreat rate reaching 20 m/yr in recent years. Based on a systematic review of the literature, the shoreline recession trend along the Hai Hau is associated with the decline of water and sediment discharged from the So River, assumed to be active after a great flood in 1787, resulting in channel bifurcation and abandonment of the former channel. A historical analysis of the shoreline evolution of approximately a thousand years (the year 1000 – present) was conducted along this scenario using a modified one-line model. The simulated shorelines agreed well with the results of carbon-14 dating analysis, the historical reference points and shoreline positions extracted from the old maps, and the recently measured shoreline change derived from Landsat imagery. The present study demonstrates that the erosion at the Hai Hau has been ongoing from the end of the 18th century rather than the beginning of the 20th century, as proposed by some previous works. We regard the combined effects of the decrease in river sediment load, and other processes (subsidence and sea level rise (SLR)) are the major causes of long-term erosion on Hai Hau Coast.