A preliminary study of the turbulence features of the tidal bore in the Qiantang River,China

In this paper,the turbulence characteristics of the tidal flow in the Qiantang River,China,the world-famous Qiantang bore,are studied.A detailed field observation at the Yanguan section of the Qiantang River was carried out during the spring tide in October 2010 with a continuous collection of high frequency turbulence data.The data analysis shows that the hydrodynamic processes are characterized by a strong tidal bore.Statistics of the turbulence such as the probability distributions of the turbulent components,the variance terms and the covariance terms are found consistent with those of previous studies of estuaries without the tidal bore.However,along the vertical profile,the distributions of all variables become more scattered downwards.The horizontal turbulence fluctuations are of a similar magnitude while the vertical turbulence has a fluctuation magnitude about 1/3 of that of the horizontal turbulences.The fluctuation strengths and the Reynolds stresses are much larger than those of other estuaries when the bore arrives.The bottom shear stress varies periodically with the tides,less than 0.44 N/m2during the ebb but is increased drastically at the bore arrival,with the maximum being 0.92 N/m2.A good linear relationship is found between the bottom shear stress and the bottom suspended sediment concentration.