Analysis on distribution characteristics of velocities over depth in a coastal area

Abstract

Based on the continuous Acoustic Doppler Current Profiler (ADCP) data at two stations in the Strait of Georgia, Canada, spatiotemporal variation characteristics of the eastern and northern velocity component over depth was analyzed, and dominant tidal components M2, K1 and O1at each layer were extracted through tidal current harmonic analysis. Main results are: (1) The vertical flow velocity in the study area has significant stratification, and the flow velocity generally decreases with the increase of water depth. Analysis of standard deviation of the flow in direction of east–west (u) and north–south​ (v) components shows that the standard deviation of u component at station 1 varied from 76.24 cm/s to 10.12 cm/s at depth of 20 m or more, while the standard deviation of v component varied from 99.65 cm/s to 11.6 cm/s. The standard deviation of component u at station 2 varied from 51.73 cm/s to 9.68 cm/s. While the standard deviation of component v changes from 93.56 cm/s to 11.39 cm/s, and the standard deviation below 20 m does not change significantly. It indicates that the velocity variation over depth is bounded at 20 m, the above gradient is relatively large, and the below gradient is relatively small; (2) Tidal pattern coefficient F of station 1 is 1.06, and that of station 2 is 1.15, both are 0.5<F≤2.0, thus, this area was dominated by the irregular semi-diurnal tide. The averaged value of the shallow water tide influence coefficient G is 0.084 and 0.063 at station 1 and 2, respectively, both are greater than 0.04. This indicates that the shallow water tide is significant in tidal currents; (3) The tidal current ellipse of the two stations is a reciprocating flow as a whole. The flow is dominated by M2 component, followed by K1 and O1. The surface tidal ellipse is larger than other layers. This research can provide theoretical basis and reference significance for the evaluation and utilization of tidal current energy.