Chao Sam Ran beach, Phetchaburi is facing with coastal erosion problem leading to loss of local economy and some infrastructures. In 2007-2009, 15 breakwater seawalls were constructed along the coast to mitigate erosion problem. However, the construction of heavy structures into the sea remains controversial that whether or not it can be solved the erosion problem. This study aims to monitor long- and short-terms morphological changes and coastal sediments balance by two approaches. First, analysis in satellite images and aerial photos was carried out in order to monitor horizontal spatial changes by measurement of shoreline moving rates from year 1994 to 2014. This long-term monitoring for 20 years. Second, short-term beach profiling was set up to monitor sediments balance early and during Northeast monsoon. In this study, after-monsoon beach profile was collected and the study area was divided into 3 coastal sectors: north, middle and south. As a result, satellite image and aerial photos interpretation before breakwater construction (year 1994-2006) reveals that the distance of shorelines in the northern part has increased from the reference line (1994 shoreline) with the rates of 1.00 m/year; whereas in the middle part has increased 1.28 m/year and in the south part has decreased 0.71 m/year. During breakwater construction (year 2006-2010), the distance of shorelines in the northern, middle and southern parts has increased with the rates of 3.76, 2.10 and 1.57 m/year, respectively. After breakwater construction (year 2010-2014), shorelines in the northern part has decreased with the rates of 0.37 m/year, whereas in the middle and southern parts has increased with the rates of 0.007 and 1.45 m/year, respectively. Results of beach profiling during monsoon period showed that offshore sediments have transported into nearshore zone and after monsoon period, the beach in northern part was changed to the same as in early monsoon period. Furthermore, there is the scour of sediments at the breakwater base which rip currents may occur.
