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Liu F.,Sun Yat Sen University | Yang Q.,Sun Yat Sen University | Yang Q.,State and Local Joint Engineering Laboratory of Estuarine Hydraulic Technology | Hu Y.,Sun Yat Sen University | And 2 more authors.
Marine Pollution Bulletin

Five different water samples were collected from the surface to the bottom layers at the Humen river mouth in the Pearl River delta during the flood and ebb tides in August 2011, respectively. Changes in the distribution and characteristics of polycyclic aromatic hydrocarbons (PAHs) were examined to explore their transportation process. More than 62 types of PAHs were detected in the water columns. The mean concentration of the total PAHs ranged from 849.33 to 1370.53. ng/l and from 629.21 to 2019.91. ng/l during the flood and ebb tides, respectively. Furthermore, 2-ring PAHs were the most abundant species, followed by 3-ring PAHs. There were different composition patterns of the PAHs during the flood and ebb tides. And the transportation process of PAHs was influenced by their sources and different estuarine hydrodynamics. Analysis of the sources of the PAHs indicated that the PAHs were derived from primarily petroleum and coal combustion sources. © 2014 Elsevier Ltd. Source

Cai H.,Sun Yat Sen University | Cai H.,State and Local Joint Engineering Laboratory of Estuarine Hydraulic Technology | Savenije H.H.G.,Technical University of Delft | Jiang C.,Yangzhou University | And 3 more authors.
Hydrology and Earth System Sciences

The mean water level in estuaries rises in the landward direction due to a combination of the density gradient, the tidal asymmetry, and the backwater effect. This phenomenon is more prominent under an increase of the fresh water discharge, which strongly intensifies both the tidal asymmetry and the backwater effect. However, the interactions between tide and river flow and their individual contributions to the rise of the mean water level along the estuary are not yet completely understood. In this study, we adopt an analytical approach to describe the tidal wave propagation under the influence of substantial fresh water discharge, where the analytical solutions are obtained by solving a set of four implicit equations for the tidal damping, the velocity amplitude, the wave celerity, and the phase lag. The analytical model is used to quantify the contributions made by tide, river, and tide-river interaction to the water level slope along the estuary, which sheds new light on the generation of backwater due to tide-river interaction. Subsequently, the method is applied to the Yangtze estuary under a wide range of river discharge conditions where the influence of both tidal amplitude and fresh water discharge on the longitudinal variation of the mean tidal water level is explored. Analytical model results show that in the tide-dominated region the mean water level is mainly controlled by the tide-river interaction, while it is primarily determined by the river flow in the river-dominated region, which is in agreement with previous studies. Interestingly, we demonstrate that the effect of the tide alone is most important in the transitional zone, where the ratio of velocity amplitude to river flow velocity approaches unity. This has to do with the fact that the contribution of tidal flow, river flow, and tide-river interaction to the residual water level slope are all proportional to the square of the velocity scale. Finally, we show that, in combination with extreme-value theory (e.g. generalized extreme-value theory), the method may be used to obtain a first-order estimation of the frequency of extreme water levels relevant for water management and flood control. By presenting these analytical relations, we provide direct insight into the interaction between tide and river flow, which will be useful for the study of other estuaries that experience substantial river discharge in a tidal region. © Author(s) 2016. Source

Liu F.,Sun Yat Sen University | Yang Q.,Sun Yat Sen University | Yang Q.,State and Local Joint Engineering Laboratory of Estuarine Hydraulic Technology | Chen S.,East China Normal University | And 3 more authors.
Journal of Asian Earth Sciences

The Yellow, Yangtze and Pearl Rivers supply over 90% of the sediment flux from China to the western Pacific Ocean. Trends and abrupt changes in the water discharge and sediment load of the three rivers were examined and compared based on data updated to the year 2011 at the seasonal and annual scales. The total water discharge from the three rivers shows a statistically insignificant decreasing trend with a rate of 0.62×109m3/a, and the total sediment load shows a statistically significant decreasing trend at a rate of 31.12×106t/a from the 1950s to 2011. The water discharge of the entire Yellow River and the upstream portion of the Yangtze River shows significant decreasing trends, and that of the mid-lower stream of Yangtze River and the entire Pearl River shows insignificant trends. The sediment loads in the three river basins all show significant decreasing trends at the annual and seasonal scales, and a dramatic decrease in the 2000s resulted in a more obvious decreasing trend over the studied period. From the 1950s to the 2000s, the contribution of sediment flux from the Yellow River to the ocean decreased from 71.8% to 37.0%, and the contributions of the Yangtze and Pearl Rivers increased from 24.2% and 4.0% to 53.0% and 10.0%, respectively. Inter-annual variations in water discharge and sediment load were affected by climate oscillations, such as the El Niño/Southern Oscillation, and the long-term decreasing trend in sediment load was primarily caused by human activities. Dam constructions and soil conservation projects were the major causes of sediment reduction. From the 1970s to the 2000s, the decrease in total sediment load from the three rivers caused by climate change and human activities was 2.24×108t/a (23.0%) and 7.5×108t/a (77.0%), respectively. In the coming decades, the sediment flux from the three rivers into the sea will decrease further with intensifying human activities, resulting in many challenges for the management of river basins and river deltas. © 2014 Elsevier Ltd. Source

Liu F.,Sun Yat Sen University | Yuan L.,Sun Yat Sen University | Yuan L.,State and Local Joint Engineering Laboratory of Estuarine Hydraulic Technology | Yang Q.,Sun Yat Sen University | And 5 more authors.

In this paper, temporal variations in the hydrological process of the Pearl River delta (PRD) are examined based on monthly datasets for water discharge, sediment load and suspended sediment concentration (SSC) since the 1950s using the methods of power spectrum analysis and Fourier transform. In addition, the underlying causes of the variations are examined to address the influence of diverse human activities on hydrological process. The results indicate that (1) for the monthly low pass filtering series with a timescale of more than 8a, the water discharge from the Pearl River increased insignificantly with an average rate of 1.66m3/s per year, whereas the sediment load and SSC decreased significantly with an average rate of 18.54kg/s and 0.002kg/m3 per year, respectively, between 1957 and 2009; (2) decadal change in the water discharge of the Pearl River can be identified with low periods in 1950s-1972, 1984-1992 and 2003-2009 and high periods in 1973-1983 and 1993-2002, which is in good agreement with precipitation changes. Decadal change in the sediment load generally differed among three tributaries. For the West River and the North River, before the 1970s, no significant change in the sediment load can be observed because of the balanced influences of dam construction and deforestation. In the 1980s, a significant increase occurred because deforestation exceeded dam construction. Since the 1990s, large reservoirs were constructed in the West River and North River basins. And total deposition rate of all the reservoirs in two river basins was estimated to be 168.8×106m3/a in the 1990s and reached to 881.1×106m3/a in the 2000s, respectively. The influences of dam construction and soil conservation have outweighed the impact of deforestation, which has resulted in a significant decrease in the sediment load. For the East River, since the dam construction in 1960, the influence of deforestation on the sediment load did not outweigh the influence of the dam construction, which gradually decreased the sediment load; (3) for the PRD, temporal change in the water discharge and sediment load in the West River and North River deltas correspond well with the change in the water discharge and sediment load upstream of the West River and the North River before the 1990s. Due to the uneven down-cutting of the riverbed in the upper PRD since the mid-1980s, which is primarily caused by intensified sand excavation from the river channel, the divided flow ratio and divided sediment ratio at Sanshui station in the North River delta increased by 7.8% and 7.7%, respectively, in the 1990s-2000s compared with the 1960s-1980s. Therefore, the water discharge and sediment load in the North River delta increased by 57.0% and 12.2%, respectively. These changes have resulted in morphological changes in the PRD and caused many environmental problems across the PRD, which should be paid special attention. © 2013 Elsevier B.V. Source

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