A Quang Nam coastline, located in the central of Vietnam, has been strongly affected by severe erosion and accretion due to climate change and human activities. Thus, understanding the causes and mechanisms of coastal morphology changes is essential to offer optimal coastal management and protection solutions. In this research, the Digital Shoreline Analysis System (DSAS) technique developed by the United States Geological Survey was adopted to calculate rate-of-change statistics from multiple historical coastline positions of Quang Nam province extracted from satellite images, i.e., Landsat and Sentinel images from 1990 to 2019. The coastal dynamic was digitized, visualized, and compared by two statistical parameters provided in DSAS, namely End Point Rate (EPR) and Linear Regression Rate (LRR). The final results reveal that the Quang Nam coast experienced remarkable phenomena of erosion and accumulation over the past three decades. The total number of erosional and accretional transects obtained from the EPR results are 401 and 414, with annual change rates of −1.7 and 0.77 m/year, respectively. The LRR parameter was also considered and illustrated a significant correlation with the EPR, as the obtained R² value of 0.96. The lowest value of EPR over the period 1990–2019 is −42.4 m/year, highlighting the most significant erosion at the north of Cua Dai estuary, whereas coastline advance is recorded in the south segment. As a result, this study’s outcomes provide helpful information for better and sustainable coastal management in Quang Nam province of Vietnam.

A friction coefficient f cw is derived for a wave-current coexistent system, by assuming a time-invariant eddy viscosity. It is found that f cw is a function of four parameters, Zn/Z0, ūc/ûw, ϕ and ûw/σZ0 in the case of a rough bottom, or Zn/am, ū0/ûw ϕ and ûwam/v in the case of a smooth bottom. Exact solutions for f cw are given, solved numerically and expressed graphically. Equations which approximate f cw are also derived, by using an asymptotic expansion and an empirically-obtained expression. Several phenomena such as the bottom shear stress, the velocity profile, the condition of incipient movement of sand particles, the sediment transport rate and the size of ripples are expressed in terms of the friction coefficient.