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Sea level rise (SLR) due to climate change is expected to alter tidal processes and energy transport, disproportionately affecting coastal communities. Utilizing a nested hydrodynamics model, we provided an integrated investigation of tidal responses to SLR in the Hangzhou Bay (HZB). The scenarios of SLR in the next hundred years count for both non-uniform trends based on historical altimetry data and uniform trends from the latest IPCC projections. In a comparison of model results under different SLR scenarios, we found that the tidal range is amplified by SLR in HZB with stronger amplification at the shallow southern coast. Tidal range change generally increases with the SLR scale; however, neglecting the heterogeneities in the spatial distribution of SLR tends to overestimate the SLR effects. The harmonic analysis illustrates that SLR exaggerates the dominated semidiurnal tides (M2 and S2) but dampens their overtides and compound tides (M4, M6, and MS4), of which M2 amplitude amplification explains 71.2–90.0% of tidal range change. SLR tends to promote tidal energy entering HZB through the Zhoushan Archipelago (ZA) compared to the prototype, while dampened sea-bed roughness and reduced tidal velocity come with a less dissipative environment in HZB, resulting in 6–18% more tidal energy exported upstream. Numerical experiments indicate ZA has significant effects on tidal responses and energy flux generation, therefore, its quantitative influences and physical mechanism are also discussed in this paper. [ABSTRACT FROM AUTHOR]

Hydrodynamic and morphological processes become more complex with large spatial variations after tidal barrier building and estuary restoration. Using a process-based model, responses in the estuary to a two-phase restoration measure in the Shuanglong Estuary are investigated. Numerical modeling indicates that tide-asymmetry in the barraged estuary is the primary factor that determines responses of morphology. After partial absence of tidal flats (first-phase restoration), flood tide-asymmetry is switched to ebb tide-asymmetry in the lower unrestored reach. This induces lower estuary erosion via increased tidal prism, though it is enhanced in the upper widened-deepened restored reach leading to severe siltation. After full restoration (second-phase restoration), current velocities are significantly increased with reduced flood tide-asymmetry. A quantitative comparison of the impact of the cross-sectional profile to net sediment transport shows that a switch from flood-dominated estuary to ebb-dominated estuary can be caused by reshaping the tidal flat which may reduce flood tide-asymmetry. The sediment flushing efficiency after the estuary restoration is further investigated in different sluice discharges with regards to two floodgate operations. Low sluice discharge during ebb tides increases the sediment flushing efficiency, but continuous high sluice discharge contributes to significant improvement of sediment flushing capacity and reduction of flushing duration. We conclude to prevent the flushed sediment from re-deposition into the estuary, a larger flushing capacity discharge released in a short period is required after the second-phase restoration in the Shuanglong Estuary. [ABSTRACT FROM AUTHOR]

The Yangtze River Estuary (YRE) is vulnerable to the accelerated sea level rise (SLR). In this study, a three-dimensional hydrodynamic and salinity transport model, with a high resolution unstructured mesh and spatially varying bottom roughness, is applied to quantify the influences of SLR on saline water intrusion in the YRE. The model has well been validated through observation data of tidal level, flow velocity and direction, and salinity. The performances of four scenarios of the present sea level (PSL) as well as 0.5, 1 and 2 m SLR reveal that (1) the isohaline shifts upstream nonlinearly in the YRE with SLR, and non-uniform in the spatial distribution under the same SLR. The isohalines of 1, 2 and 5 psu near the north bank of the South Branch intrude farther upstream than those near the south bank, and the upstream advance distance of 0.45 psu isohaline is much longer than those of 1, 2 and 5 psu isohalines under the same SLR. (2) The spillover of saline water from the North Branch into the South Branch intensifies with SLR, while the salinity in the lower reach of the North Branch is reduced due to increased low salinity flow from the South Branch and the North Channel caused by SLR. (3) The durations of undrinkable water increase at four reservoirs with SLR, and four reservoirs cannot intake raw drinking-water in the dry season in the 2 m SLR scenario. (4) A regression analysis obtains a quantitative quadratic expression between salinity and SLR. Finally, the effects of the operation of the Three Gorges Reservoir and more SLR scenarios on the salinity, and two different approaches for SLR simulations are also discussed. [ABSTRACT FROM AUTHOR]