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Reservoir construction alters the hydrodynamic characteristics of the flow and sediment regimes, resulting in the enhancement of the hysteresis effect between the flood and sediment peaks. In this study, a 3D numerical model was adopted to investigate the propagation characteristics of sediment peak and the management method of reservoir sediment release. The results indicate that the incoming flow rate and the storage water level have a great influence on the propagation time of the sediment peak, and the incoming flow rate has a large influence on the attenuation rate of the sediment peak while the storage water level and the incoming suspended sediment concentration have a little effect on the attenuation rate of the sediment peak. An empirical formula based on inflow rate, water level elevation, water depth and length and storage capacity of reservoirs was established to predict the lag time between the flood and sediment peaks. The asynchronous movement between the incoming flood and sediment peaks has a clear influence on the propagation characteristics of the sediment peak. The hysteresis effect of the flood and sediment peaks can be fully utilized by reservoir managers to reduce reservoir sedimentation and improve sedimentation distribution.

Downdrift shoreline recession associated with the construction of a shore-crossing hard structure represents one of coastal erosional hotspots that must be addressed for an integrated, sustainable coastal zone management. To prevent siltation within the navigation channel, two rubber-mounted jetties were installed at the Sheyang River mouth on the open mesotidal muddy coast in Jiangsu province, China, in October 2013. The north jetty is 7.9 km long, while the south jetty is 7.8 km long. The net longshore sediment transport is from the north to the south due to flood-tide dominance. As disclosed by high-resolution satellite images, a 36-km-long downdrift shoreline stretch had experienced remarkable retreats at alongshore varying rates by March 2019. The eroding shoreline planform does not resemble a classic “S” shape, a crescentic shape, or a parabolic shape but an irregularly indented curved shape. Transact topographic survey also reveals an almost immediate response of the downdrift coast from the original accretionary scenery to an erosional regime, with the erosion front translocating downcoast at a much faster speed than a normal speed of 1–1.5 km/yr. Using FVCOM and SWAN, 2DH process-based numerical simulations are performed to simulate the flow, the sediment transport, and the yearly-magnitude accretion/erosion distribution in the jetty-affected area by a representative tidal force and an annual-magnitude wave force. The results demonstrate that the reciprocal tidal flow is predominantly responsible for the muddy sediment accretions at downdrift intertidal and surf zones shallower than a 4.0-m isobath, whereas big wind waves play a decisive role in triggering and developing the downdrift erosional process. The predicted spatial extent of the downdrift erosional segment matches closely the actual eroding front. The loss of the net annual longshore sediment transport volume, i.e., 3.08 million m3 due to the blockage by the twin jetties is recovered from a much larger spatial extent than the 36-km-long retreating shoreline stretch. With regard to the Bruun model, the one-line model, the headland-bay model, and the 2DH numerical model, the potential maximum recession length and the planform shape of the downdrift erosional shoreline arc are further elaborated to gain new insights into the spatial and temporal impact of a hard structure on the adjacent shoreline and flat (beach).

There are many reservoirs in China with serious siltation issues which are affecting the function and safety of the reservoirs. Recently, research studies have been carried out regarding siltation loss control and capacity recovery technology due to the decreases in suitable dam sites for establishing reservoirs, and the increasingly serious siltation losses which have been occurring in the present reservoirs. The results of these studies have been of great significance to the partial recoveries of the siltation capacities of reservoirs, improvements in the respective efficiencies of the current reservoirs, and the prolonging of the service life the reservoirs. This study presented a simple review of the previous research findings regarding the current siltation loss situations and controls, as well as the capacity recoveries which have been achieved. Also, this study proposed the urgent need for in-depth examinations to be conducted pertaining to the national investigations of the reservoir siltation status in China, as well as a review of the current mechanisms and control measures for reservoir siltation losses.