Non-Uniform Sediment Transport Downstream from Reservoir

The transport characters of non-uniform sediment before and after the reservoir operation are compared and analyzed. Field data from the Three Gorges Reservoir (TGR), Danjiangkou, and Sanmenxia reservoir indicate that the transport character of coarse particle is various in different reaches. Before the reservoir operation, the dramatic decrease of the hydraulic condition in some reaches is the main reason to cause the coarse particle deposited. After the reservoir operation, almost all grain sized sediment may be eroded, when the reach is eroded seriously. However, the transport character of the coarse particle will be consistent with what it was before, when the reach is not eroded seriously. The deposition amount will be less than its pre-dam value, and it will tend to decrease with the time going on. Erosion of fine particle results from its unsaturation. Longdistance erosion downstream from reservoir is caused by shortage of the supply from riverbed, especially the shortage of fine particle.

Channel erosion and its impact on environmental flow of riparian habitat in the Middle Yangtze River

Evaluating environmental flow(EF)is pivotal for conserving and restoring riverine ecosystems.Yet,prevalent EF evaluations presume that a river reach's hydraulic conditions are exclusively governed by inflow discharge,presupposing a state of equilibrium in the river channel.This presumption narrows the scope of EF evaluations in expansive alluvial rivers like the Middle Yangtze River(MYR),characterized by marked channel alterations.Here we show the profound channel erosion process and its impact on EF requirements for riparian habitats within the MYR.Our research unveils that:(i)pronounced erosion has led to a mean reduction of 1.0-2.7 m in the riverbed across four sub-reaches of the MYR;(ii)notwithstanding a 37-107%increase in minimal discharges post the Three Gorges Project,the lowest river stages at some hydrometric stations diminished owing to bed erosion,signifying a notable transformation in MYR's hydraulic dynamics;(iii)a discernible rightward shift in the correlation curve between the weighted useable area and discharge from 2002 to 2020 in a specific sub-reach of the MYR,instigated by alterations in hydraulic conditions,necessitated an increase of 1500e2600 m^(3)s^(-1)in the required EF for the sub-reach;(iv)it is deduced that macroinvertebrate biomass rapidly decreases as the flow entrains the riverbed substrate,with the maximum survivable velocity for macroinvertebrates being contingent on their entrainment threshold.These findings highlight the importance of incorporating channel morphological changes in devising conservation strategies for the MYR ecosystem.

A novel two-way method for dynamically coupling a hydrodynamic model with a discrete element model(DEM)

The effect of floating objects has so far been little considered for hazard risk assessment and structure design, despite being an important factor causing structural damage in flood-prone and coastal areas. In this work, a novel two-way method is proposed to fully couple a shock-capturing hydrodynamic model with a discrete element model （DEM） for simulation of complex debris-enriched flow hydrodynamics. After being validated against an idealized analytical test, the new coupled model is used to reproduce flume experiments of floating debris driven by dam-break waves. The numerical results agree satisfactorily with the experimental measurements, demonstrating the model＇s capability and efficiency in simulating complex fluid-debris interactions induced by violent shallow flows.