Wake region estimations of Vietnam’s artificial reefs considering tropical seawater characteristics

Abstract

Artificial reef (AR) is an important program for restoration and enhancement of marine resources specifically in coastal waters. Currently, ARs in Vietnam (Việt Nam) are reef ball, cylinder reef, and cube reef, which are installed in coastal provinces (e.g. Quang Ninh and Ninh Thuan). This study investigates the three reef types and their wake regions considering tropical seawater temperatures, seasonal water flow variations, and inlet water flow velocities. For the wake region estimations, first, the wake volume is proposed and used to quantitatively represent the wake region estimation by constructing the three reef modules and three reef sets, which are composed of 5×5 flatly-distributed placement models and utilizing the so-called element-based finite volume method. Second, tropical water temperatures (24 and 29C), water flow direction (0, 15, 30, and 45), and inlet velocity variations (1.0, 1.2, 1.4, 1.6, 1.8, and 2.0 m/s) are considered to characterize their effects on the wake volumes. From the results, it is found that the temperature and inlet speed effect are minor in comparison to the flow direction effect on the wake volumes. Among the sets, AR2-set is the most desirable in terms of the size of wake region which has capable of generating the maximum wake volume regardless of the seawater temperature and inlet velocity. In addition, considering the average recirculating flow velocities, AR2-set is preferable because it provides the smallest flow velocities in the wake regions regardless of the variations in seawater temperature and inlet velocity. In other words, AR2-set provides a better size and tranquility in the wake region, which facilitates a shelter, feeding ground, spawning ground, rest area, and/or temporary stopover.