An Analysis of the Periodic Evolution of the Jingjiang Sandbank in the Tidal Reach of the Yangtze River

The Jingjiang Sandbank (JJS) is located on the bank of the tidal reach in the Yangtze River. It experiences a periodic evolution process of increase, split, migration, and dissipation, which affects the current direction, fish habitat, navigation safety, etc. In this paper, the periodic evolution of the JJS is investigated based on 17 field bathymetric measurements of the river from 1999 to 2017. Firstly, six cycles of the evolution process of the sandbank are described, and the evolution pattern of the split detached bar and the main body of the sandbank are analyzed according to the migration tracks of the detached bars and the historical volume-change of the JJS, respectively. Then an empirical orthogonal function (EOF) is conducted on the historical measurements of the bathymetry. The first four eigenfunctions correspond to the time-averaged bathymetry, the long-term change of the pattern of bathymetry, the periodic change of the JJS, and the downstream migration of the split detached bar, and the periodic change of the rip at the back of JJS. It is pointed out that the construction of two waterway regulation projects might have changed the evolution pattern of the JJS permanently.

Supporting Coastal Resiliency by Investigating Tidal Reach and Inter-Connected Factors in Coastal Georgia

Increasing our understanding of the tidal dynamics, the extent of tidal reach, and storm surge impacts on near-coastal areas of Georgia and South Carolina rivers is a significant research opportunity. It has the potential to yield benefits to sustainable planning, ecosystem protection, and risk management for regulators and state agencies, local municipalities, coastal residents, and other regional stakeholders. This study leveraged existing United States Geological Survey (USGS) water level data for the Savannah River, added additional water level gauges in key areas for less than one year, and analyzed these combined large data sets with modified wavelet analysis and Fourier analysis. One significant outcome of the research included confirmation of river mile 45, historically referred to as Ebenezer Landing, as the head of tide. We also provide information on the dynamics of wave propagation through the near-coastal area of the Savannah River, give indication of critical areas of concern for flooding resulting from interactions between the interconnected factors affecting elevated upstream flows and storm tides, and discuss relevance of study results for various stakeholders.

An improved friction calculation for water level and flow velocity simulation

Flow friction is the key to studying water movement and has been one of the most important research topics in hydraulics and river dynamics. The roughness coefficient in the Manning formula represents friction applied to the flow by channel and changes with the river section characteristics, water level, and flow velocity. However, the Manning formula tends to simulate the friction with little variability, which contributes to large errors in the simulation of water level and flow velocity. To solve this problem, we proposed an improved friction formula based on the relationships between roughness coefficient and energy gradient and developed a differential model of one-dimensional flow with the proposed friction formula. The developed model was tested against both the experimental flood data and observed flow data in Qiantang River, China. The results indicated that the proposed friction formula provides a better simulation of target friction than the original Manning friction formula. The parameters in the proposed friction formula are less sensitive to the river section characteristics. Our results also showed that the developed differential model using the proposed friction formula can simulate the water level and flow velocity well in both the calibration and validation period and can improve the simulation of water level in tidal reach.