ABSTRACT Gu, J.; Zhu, J., and Lyu, H., 2021. Observation and analysis of water and salt transports in the North Branch of the Changjiang Estuary. Journal of Coastal Research, 37(3), 518–527. Coconut Creek (Florida), ISSN 0749-0208. The North Branch (NB) is the first-order bifurcation of the Changjiang Estuary and is an extremely shallow water channel. The greatest characteristic of saltwater intrusion is the saltwater spillover from the NB into the South Branch (SB). A field observation was conducted in the NB from 21 to 27 February 2017 to understand the water current and salinity variation. The residual unit width water and salt fluxes, as well as their decomposed terms, were calculated to discuss the mechanisms of water and salt transport. The tidal and vertical variations in ebb and flood duration, current velocity, and salinity during the neap-middle-spring tide were presented and dynamically analyzed in detail. The direction of the Eulerian water and salt transports and tidal pumping salt transport varied by site, vertical layer, and tidal type, whereas the Stokes drift water and salt transports were landward. During neap tide, the total residual water and salt fluxes in the upper layer of the whole NB were seaward transported because of the runoff effect; the total water and salt fluxes in the lower layer were landward in the lower-middle and lower reaches of the NB, reflecting the existence of a two-layer estuarine circulation. During the moderate tide, the total residual water and salt fluxes were seaward in the whole NB except in the lower layer in the low reaches of the NB, which were landward due to the strong baroclinic effect. During the spring tide, all the total residual water and salt fluxes were landward because some flood water flowed into the SB, resulting in an imbalance between the flood and ebb water volumes in the NB. The dynamic processes of water and salt transport from the NB into the SB during spring tide were revealed by the observation and flux decomposition method.

ABSTRACT Chen, Q.; Zhu, J.; Lyu, H., and Chen, S., 2019. Determining critical river discharge as a means to provide water supply security to the Changjiang River Estuary, China. Journal of Coastal Research, 35(5), 1087–1094. Coconut Creek (Florida), ISSN 0749-0208. Shanghai is one of the six cities worldwide experiencing severe water shortage in the 21st century. To solve the water supply shortage problem, a strategic water source transfer from the Huangpu River to the Changjiang Estuary has been completed; approximately 80% of the supply of fresh water in Shanghai is taken from the water sources in the estuary, but the estuary experiences saltwater intrusion during periods of low river discharge, e.g ., the dry season. The reservoirs cannot take water if the salinity is higher than 0.45 psu at the water intakes. The longest water residence time of the Chenhang Reservoir (CHR) is 7 days; thus, the CHR will experience water supply problems if the duration of saltwater intrusion is longer than 7 days. In this study, saltwater intrusion was simulated, and the critical river discharge was ascertained under different river discharge conditions using the improved Estuarine, Coastal, and Ocean Model, semi-implicit. The saltwater spillover from the North Branch arrived in the middle reaches of the South Branch during the subsequent moderate tide and neap tide, threatening the water intake of the CHR. During a period of spring–neap tides, the longest periods for which the CHR could not take water from the Changjiang Estuary were 5.0, 6.5, and 8.2 days under river discharge conditions of 11,500, 10,000, and 9000 m 3 /s, respectively. The saltwater intrusion increased when the river discharge declined, and the availability of useable freshwater resources in the estuary became severe. By finely adjusting the river discharge in the model, the authors found that the critical river discharge was 9500 m 3 /s. If the amount of river discharge reaches 9500 m 3 /s, the Shanghai government can ask the Changjiang Water Resources Committee to discharge more water from the Three Gorges Reservoir to restrain the saltwater intrusion and ensure water security in the megalopolis of Shanghai.

ABSTRACT Lyu, H. and Zhu, J., 2019. Impacts of tidal flat reclamation on saltwater intrusion and freshwater resources in the Changjiang Estuary. Journal of Coastal Research, 35(2), 314–321. Coconut Creek (Florida), ISSN 0749-0208. A well-validated numerical model, residual water and salt transport, and the water diversion ratio between channels as well as their variations were used to simulate and analyze the impacts of the tidal flat reclamation project in the Eastern Hengsha Shoal (RP-EHS) on saltwater intrusion and freshwater resources. The RP-EHS is the largest tidal flat reclamation project in the Changjiang Estuary and has significantly changed the local topography. The RP-EHS results in a net transection water flux increase in the North Channel and decreases in the South Channel, North Passage, and South Passage, which weaken the saltwater intrusion in the North Channel and enhance the saltwater intrusion in the South Channel, North Passage, and South Passage. The saltwater intrusion in the North Branch and the saltwater spillover from the North Branch into the South Branch were increased after the establishment of the RP-EHS. There are three reservoirs in the Changjiang Estuary, which provide more than 80% of the freshwater to Shanghai. Because the saltwater sources of the reservoirs mainly originate from the saltwater spillover, the salinity at the water intakes of the three reservoirs slightly increased after the project, which means that the project is unfavorable for water resources in the Changjiang Estuary. The reservoirs are important for Shanghai's water supply, and the impacts of the tidal flat reclamation on water resources should receive greater attention to ensure water safety.