Shoreline Identification Bias: Theoretical and Measured Value for Meso-Tidal Beaches in Kuala Nerus, Terengganu (Malaysia)

Abstract

Shoreline change analysis frequently begins with feature identification through visual interpretation (proxy-based shoreline) or the intersection of a specific tidal zone (datum-based shoreline). Using proxy-based shoreline information, this study quantifies the distance between proxy-based and datum-based shoreline data, which is defined as the proxy-datum bias. The study was conducted at meso-tidal beaches in Kuala Nerus, Terengganu, Malaysia, with morphodynamic responses to northeast and southwest monsoons. The high-water line (HWL) shoreline (proxy-based) was determined using ortho-rectified aerial images captured by an unmanned aerial vehicle (UAV). By contrast, the mean high-water (MHW) shoreline (datum-based) was determined using measured beach profiles adjusted with the Peninsular Malaysia Geodetic Vertical Datum (DTGSM). The theoretical proxy-datum bias was approximated using the best estimate (median) for the beach slope, wave height, and wave period from the estimated total water level (TWL) model. Based on the study, the recorded horizontal proxy-datum bias for the research area was up to 32 m. This study also discovered that the theoretical assumption of the proxy-datum bias based on the TWL model yields values comparable to those of the measurements, with a narrower distinction in bias for steeper beach slopes than the obtained results. The determined proxy-datum bias value can benefit future shoreline change studies as it could be incorporated to either proxy-based shorelines by shifting the shoreline seaward or to datum-based shorelines by shifting the shoreline landward in order of the bias value. The seasonal monsoon’s effect on beach profiles should be considered when calculating bias values and conducting potential shoreline change rate studies.

Keywords

Shoreline evolution / Datum / Beach profile / Unmanned aerial vehicle / Monsoon