Tham khảo tài liệu 'hydrodynamics natural water bodies part 8', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 162 Hydrodynamics - Natural Water Bodies Indefinite tracks where one set of particles was tracked for as long as they remained in the reefal bay system - their paths plotted for every three hours they remained. Hourly plotted tracks were used to predict the duration of a reef gyre. Three-hourly tracks were plotted to capture the full horizontal extent of the circulation. Fig. 3. Diagram of the reefal bay dimensions used in calculating the circulatory extent of the bay. The extent BC is calculated as a fraction of the AC distance normal to a line DE joining the land projections. AC is derived from an elliptical approximation of the outer seaward curve of the looping currents. Extents were measured from these plots as a proportion of the linear distance from the shore to the elliptical arc normal to a straight line joining the land projections at the ends of the bay indentation Figure 3 . The ellipse best approximates the seaward edge of the gyre. The elliptical major axis is always equal to or greater than the length of the straight line joining the land projections. Therefore the reef circulation lateral extension Lc is given as the percentage Lc X100 AB 3 Indefinite tracks allowed predictions of the retention ability of gyres. The number of particles remaining around the reef was counted after each 3-hr track run. 5. Results General current flow description based on field measurements Results from fixed S4 current measurements in Wreck Bay Figure 4 showed water flowing through the channel generally exited in a south-south-eastward direction with a deflection southwards when current speeds were high. Mean speed values for channel currents peaked at 22 cm s-1 and flow directions were southward from 173 to 181 . On the western arm speeds averaged 28 cm s-1 with a mean flow direction of 102 and on the eastern arm mean speed was 22 cm s-1 with a flow direction of 290 . Flow persisted southwards out through the channel from the back-reef currents continuously except
