Wave Characteristics at the South Part of the Radial Sand Ridges of the Southern Yellow Sea

Based on one-year wave field data measured at the south part of the radial sand ridges of the Southern Yellow Sea, the wave statistical characteristics, wave spectrum and wave group properties are analyzed. The results show that the significant wave height （H1/3） varies from 0.15 to 2.22 m with the average of 0.59 m and the mean wave period （Tmean） varies from 2.06 to 6.82 s with the average of 3.71 s. The percentage of single peak in the wave spectra is 88.6 during the measurement period, in which 36.3% of the waves are pure wind waves and the rest are young swells. The percentage with the significant wave height larger than 1 m is 12.4. The dominant wave directions in the study area are WNW, W, ESE, E and NW. The relationships among the characteristic wave heights, the characteristic wave periods, and the wave spectral parameters are identified. It is found that the tentative spectral model is suitable for the quantitative description of the wave spectrum in the study area, while the run lengths of the wave group estimated from the measured data are generally larger than those in other sea areas.

The reverse sediment transport trend between abandoned Huanghe River(Yellow River) Delta and radial sand ridges along Jiangsu coastline of China——an evidence from grain size analysis

To reveal the sediment transporting mechanism between the abandoned Huanghe River （Yellow River） Delta and radial sand ridges, “End Member” Model and grain size trend analysis have been employed to separate the “dynamic populations” in the surficial sediment particle spectra and to determine the possible sediment transporting pathway. The results reveal four “dynamic subpopulations”（EM1 to EM4） and two reverse sediment transporting directions： a northward transport tend from the radial sand ridges to mud patch, and a southward transport trend in deep water area outside the mud patch. Combined with the published hydrodynamic information, the transporting mechanism of dynamic populations has been discussed, and the main conclusion is that the transporting of finer subpopulations EM1 and EM2 is controlled by the “anticlockwise residual current circulation” forming during tidal cycle, which favor a northward transporting trend and the forming of mud patch on the north of radial sand ridges, while the transporting of coarser EM3 is mainly controlled by wind driven drift in winter, which favors a southward transporting direction.

Mathematical model of wave transformation over radial sand ridge field on continental shelf of South Yellow Sea

According to a deformed mild-slope equation derived by Guang-wen Hong and an enhanced numerical method, a wave refraction-diffraction nonlinear mathematical model that takes tidal level change and the high-order bathymetry factor into account has been developed. The deformed mild-slope equation is used to eliminate the restriction of wave length on calculation steps. Using the hard disk to record data during the calculation process, the enhanced numerical method can save computer memory space to a certain extent, so that a large-scale sea area can be calculated with high-resolution grids. This model was applied to wave field integral calculation over a radial sand ridge field in the South Yellow Sea. The results demonstrate some features of the wave field： （1） the wave-height contour lines are arc-shaped near the shore; （2） waves break many times when they propagate toward the shore; （3） wave field characteristics on the northern and southern sides of Huangshayang are different; and （4） the characteristics of wave distribution match the terrain features. The application of this model in the region of the radial sand ridge field suggests that it is a feasible way to analyze wave refraction-diffraction effects under natural sea conditions.

The evolution characteristics of main waterways and their control mechanism in the radial sand ridges of the southern Yellow Sea

The comparison of the underwater topographic data in recent four decades shows that main waterways of the radial sand ridges area in the southern Yellow Sea tend to gradually migrate southward（scour depth and southward extension of the main channels in Xiyang, southward approach of Lanshayang Waterway and Xiaomiaohong Waterway on South Flank）. Although there are various hypotheses about the cause and mechanism of the overall southward migration of the radial sand ridges, no universal and reliable understanding has been obtained so far. The mechanism of this process becomes a challenging problem which serves a key issue in the morphodynamics of the radial sand ridges and the harbor construction in this area. On the basis of the shoreline positions and underwater terrains at different development stages of the Huanghe Delta coast in northern Jiangsu Province, China since the northward return of the Huanghe River and flowed into the Bohai Sea,combined with the tidal wave numerical simulation study, the characteristics and hydrodynamic changes of the tidal wave system in the southern Yellow Sea at different evolution stages are investigated. It is shown that due to the shoreline retreat and the erosion of underwater delta, tidal current velocity is enhanced, and the enhanced area gradually migrates southward. It is revealed that this southward migration of a large-scale regional hydrodynamic axis is possibly a dominant mechanism leading to the overall southward migration of the radial sand ridges.

The study on the bottom friction and the breaking coefficient for typhoon waves in radial sand ridges—the Lanshayang Channel as an example

Owing to the interactions among the complex terrain, bottom materials, and the complicate hydrodynam-ics, typhoon waves show special characteristics as big waves appeared at the high water level （HWL） and small waves emerged at low and middle water levels （LWL and MWL） in radial sand ridges （RSR）. It is as-sumed that the mud damping, sandy bed friction and wave breaking effects have a great influence on the typhoon wave propagation in this area. Under the low wave energy, a mud layer will form and transport into the shallow area, thus the mud damping effects dominate at the LWL and the MWL. And high Collins coef-ficient （c around 1） can be applied to computing the damping effects at the LWL and the MWL. But under the high wave energy, the bottom sediment will be stirred and suspended, and then the damping effects disappear at the HWL. Thus the varying Collins coefficient with the water level method （VCWL） is imple-mented into the SWAN to model the typhoon wave process in the Lanshayang Channel （LSYC） of the RSR, the observed wave data under “Winnie” （“9711”） typhoon was used as validation. The results show that the typhoon wave in the RSR area is able to be simulated by the VCWL method concisely, and a constant wave breaking coefficient （γ） equaling 0.78 is better for the RSR where wide tidal flats and gentle bed slopes exist.

Detrital Zircon Geochronology of the Radial Sand Ridge System of Jiangsu Coast, East China: Implication for Sediment Provenance

The radial sand ridge system （RSRS） located at Jiangsu coast of China attracts much attention on its origin and mechanic of formation for its special structure and potential land resource. Due to complicated hydrodynamic condition, the Jiangsu RSRS is a hot debated on its potential sources, Yangtze River or Yellow River？ We collected ten sand samples from surface sediments along the west coast of Bohai Sea and Yellow Sea from the modern Yellow River estuary to Yangtze River estuary in summer, 2013. The samples are analyzed by method of detrital zircon age for source identification of the RSRS sediments. The U-Pb age spectra of detrital zircon grains of the samples show a wide range from Cenozoic to Late Archean with several age peaks. Comparing the age spectra between the Yangtze River and the Yellow River, the detrital zircons have younger age （〈100 Ma） group in the Yangtze River. These age distribution of the Jiangsu coastal RSRS sediments are similar to that of the Yangtze River, but different from the Yellow River. The samples located adjacent to the old Yellow River Delta show more wide-range age distribution, implying a compounded origination from the both rivers. Based on these findings it is proposed that, contrary to common opinion, the main sediment source of the Jiangsu RSRS is the Yangtze River, rather than the Yellow River. By implication, there should be evidence of hydrodynamic mechanics of oceanic currents and tidal motion. This aspect awaits confirmation in future research.

Wave-induced flow and its influence on ridge erosion and channel deposition in Lanshayang channel of radial sand ridges

Very limited modeling studies were available of the wave-induced current under the complex hydrodynamic conditions in the South Yellow Sea Radial Sand Ridge area（SYSRSR）. Partly it is due to the difficulties in estimating the influence of the waveinduced current in this area. In this study, a coupled 3-D storm-surge-wave model is built. In this model, the time-dependent varying Collins coefficient with the water level method（TCL） are used. The wave-flow environment in the Lanshayang Channel（LSYC） during the ＂Winnie＂ typhoon is successfully represented by this model. According to the modelling results, at a high water level（HWL）, the wave-induced current similar to the long-shore current will emerge in the shallow area of the ridges, and has two different motion trends correlated with the morphological characteristics of the ridges. The wave-induced current velocity could be as strong as 1 m/s, which is at the same magnitude as the tidal current. This result is verified by the bathymetric changes in the LSYC during the ＂Matsa＂ typhoon. Thus, the wave-induced current may be one of the driven force of the ridge erosion and channel deposition in the SYSRSR. These conclusions will help to further study the mechanism of the ridge erosion and channel deposition in the SYSRSR.

Tide simulation using the mild-slope equation with Coriolis force and bottom friction

Since the mild-slope equation was derived by Berkhoff （1972）,the researchers considered various mechanism to simplify and improve the equation,which has been widely used for coastal wave field calculation.Recently,some scholars applied the mild-slope equation in simulating the tidal motion,which proves that the equation is capable to calculate the tide in actual terrain.But in their studies,they made a lot of simplifications,and did not consider the effects of Coriolis force and bottom friction on tidal wave.In this paper,the first-order linear mild-slope equations are deduced from Kirby mild-slope equation including wave and current interaction.Then,referring to the method of wave equations’ modification,the Coriolis force and bottom friction term are considered,and the effects of which have been performed with the radial sand ridges topography.Finally,the results show that the modified mild-slope equation can be used to simulate tidal motion,and the calculations agree well with the measurements,thus the applicability and validity of the mild-slope equation on tidal simulation are further proved.