Study on the Two Patters of Vertical Velocity Profile of Tidal Current and Their Law in Estuary and Coastal Waters

Many scholars at home and abroad have studied tidal velocity profile in estuarine and coastal waters. The results show that velocity profile of tidal current often deviated obviously from the traditional logarithmic profile, due to the flow including wind-driven current, wave-driven current, salinity and so on. In estuarine waters, runoff should be included as a component. In this paper, two patters of vertical velocity profile of tidal current are firstly divided, that are monotone increasing I-velocity profile (during flood tide and ebb tide stage) and non-monotone increasing II -velocity profile (during slack tide stage). Then, by use of variable fractal dimension to obtain the law of II-velocity profile, the results show that: (1)The II -velocity vertical profile does express a first-order accumulated variable-dimensional fractal phenomenon. (2) Through of the fractal dimension, the various formula fitting II-velocity profile were compared, and the results showed that, in practical applications of engineering, cubic function formula is the best fit as the measured data have been verified. Finally, the cubic function formula is applied to flow separation of II -velocity measured in Yangtze River. By the easily separation of the measured flow, we can not only get a reasonable surface flow velocity, such as wind-driven current, runoff, salinity, as well as their driving force weight in the hydrodynamic of estuarine and coastal waters, but also gain the data of bed roughness length and sea surface wind speed, providing reasonable border conditions of the seabed and sea surface for the hydrodynamic numerical simulation in estuarine and coastal waters.