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Sediment concentration usually increases during the reservoir sediment flushing or natural floods, which may result in acute hypoxia stress and death of fishes in river reaches. Deceased fishes often appeared during periods of the reservoir sediment flushing in the Yellow River. To assess the quantitative impacts of high sediment concentration on carp, the suspended sediment concentration‐exposure duration model (SEV model) was applied and revised. With data from field surveys conducted during the sediment flushing of the Xiaolangdi Reservoir, the sediment flushing in 2009 was assessed as having no lethal effect. However, for the flushing in 2010, the fish mortality rate was assessed to be less than 20%. By analysing the data from experiments that exposed carps to different sediment concentrations, the SEV model tended to underestimate the acute impact of high sediment concentration (>30,000 mg/l). The SEV model was revised by refitting with experimental data. The comparison between the models showed that the severity effect values (SEVs) calculated by the revised model were closer to actual observations. The revised model was validated with data from previous field surveys. This research could provide a scientific basis for river sediment management and eco‐friendly reservoir sediment flushing operations.

In fishway design, the combination of fish swimming behaviors and suitable fishway hydraulic characteristics increases the fish passage efficiency. In this study, the most representative grass carp among the “four major Chinese carps” was selected. Under conditions similar to the time period for feeding migration, juvenile grass carps were targeted to study the swimming characteristic indicators (i.e., critical and burst swimming speeds) and swimming behaviors that were closely associated with fishway hydraulic design using the incremental water velocity method in a homemade test water tank. (1) The study results reveal that both the absolute critical (Ucrit) and burst (Uburst) swimming speeds increased linearly with increasing body length and both the relative critical (U’crit) and burst (U′burst) swimming speeds decreased linearly with increasing body length. There existed a quantitative relationship between Uburst and Ucrit, which could facilitate the fishway hydraulic design. (2) This study analyzed the effects of water velocity changes on fish swimming behaviors and proposed a classification method for four fish swimming behaviors—swimming freely, staying, dashing at a long distance, and dashing at a short distance—of tested fish during the process of adapting to water velocity changes interspersed with one another. The entire swimming process under the incremental water velocity was divided into four stages. (3) This study suggests that the maximum water velocity of the mainstream in a fishway using grass carp as the major passage fish should not exceed 52–60% Uburst at stage 1. For the high-water velocity areas of a fishway, such as vertical slots and orifices, the optimal water velocity should not be higher than 76–79% Uburst at stage 2 and should absolutely not exceed 90–96% Uburst at stage 3.

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Hydromorphology is a major component of riverine ecosystems. Therefore, proper assessments of the status quo, as well as the detection of pressures in river basins, are of high relevance. Process-based morphological methods have been developed, relying on a broad data basis and resulting in suitable instruments, such as the Morphological Quality Index (MQI). In this study, the hydromorphological status of the Nanxi river system in Eastern China was assessed by an adapted application of the MQI. Adaptations and amendments in the methodical approach were developed in cycles and carried out to transfer the well-approved method for European river systems to another geographical setting. The strengths of the tested approach are the few data requirements, the applicability for modified river basins, and the decoupling of historical information. The assessment of 161 river kilometers resulted in a hydromorphological status quo with the focus being a relative comparison of different sections ranging from “moderate” to “bad”, with an average classification of a “poor” state. On the one hand, the results build the basis for future restoration and river management planning, specifically, and on the other hand, they create a foundation for the development of an assessment method fitted for modified river systems conditions.