When designing a fish collection system for fishpass facilities, considering the approach–avoidance behavior of fish under different flow velocities and light colors, is essential to ensure a good fishpass efficiency. In this study, a generalized physical model for a fish collection system entrance, including the fish collection system channel, the fish luring channel, and the mainstream channel was designed. Grass carp, a representative fish of “four major Chinese carps”, was selected as the research object, and the approach–avoidance behavior of 660 juvenile grass carps (8–12cm), under different flow velocity and light color at a water temperature of 28 ± 1 °C, were investigated. Three general indicators that reflect the fish-luring ability of a fish collection system were proposed, including the optimal flow velocity at the fish collection system entrance, the optimal ratio between the flow velocities at the entrances of the fish luring channel and the fish collection system channel, and the optimal light colors for approach–avoidance behaviors of the fish. Results indicate that (1) there was an optimal flow velocity (approximately 0.3 m/s) at the fish collection system entrance; (2) there existed an optimal ratio (approximately 2.3:1) between the flow velocities at the entrances of the fish luring channel and the fish collection system channel; (3) there were different approach–avoidance behaviors of the fish to various light colors, and the percentages of successful migration of the juvenile grass carps were 0.4%, 0.57%, 0.88%, and 1.43% of that obtained under natural light, when red, white, green, and blue light were used, respectively, at the fish collection system entrance, indicating that the juvenile grass carps would avoid the red light while approaching the blue light. The three proposed general indicators are the keys in the design of a fish collection system entrance, for successful migration of grass carps. The generalized physical model and the experimental devices and methods will provide important references for studying a fish collection system entrance for other fish species.

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.

The Beijing-Tianjin-Hebei (Jingjinji) region is the most densely populated region in China and suffers from severe water resource shortage, with considerable water-related issues emerging under a changing context such as construction of water diversion projects (WDP), regional synergistic development, and climate change. To this end, this paper develops a framework to examine the water resource security for 200 counties in the Jingjinji region under these changes. Thus, county-level water resource security is assessed in terms of the long-term annual mean and selected typical years (i.e., dry, normal, and wet years), with and without the WDP, and under the current and projected future (i.e., regional synergistic development and climate change). The outcomes of such scenarios are assessed based on two water-crowding indicators, two use-to-availability indicators, and one composite indicator. Results indicate first that the water resources are distributed unevenly, relatively more abundant in the northeastern counties and extremely limited in the other counties. The water resources are very limited at the regional level, with the water availability per capita and per unit gross domestic product (GDP) being only 279/290 m³ and 46/18 m³ in the current and projected future scenarios, respectively, even when considering the WDP. Second, the population carrying capacity is currently the dominant influence, while economic development will be the controlling factor in the future for most middle and southern counties. This suggests that significant improvement in water-saving technologies, vigorous replacement of industries from high to low water consumption, as well as water from other supplies for large-scale applications are greatly needed. Third, the research identifies those counties most at risk to water scarcity and shows that most of them can be greatly relieved after supplementation by the planned WDP. Finally, more attention should be paid to the southern counties because their water resources are not only limited but also much more sensitive and vulnerable to climate change. This work should benefit water resource management and allocation decisions in the Jingjinji region, and the proposed assessment framework can be applied to other similar problems.

The decrease in periodic scouring of pulsed flows in regulated rivers can result in algal communities dominated by filamentous algae, not available as food sources for fish and macroinvertebrates. To study the pulsed flow velocity required to scour benthic algae from natural river beds, the removal effects on the algal biomass and resistances of different species were tested in a laboratory flume at different velocities of 0.8, 1.1, 1.4, 1.7, and 2.0 m/s. The removal of total algal biomass showed a significant positive relationship with increasing velocities, which reached 22% at 2.0 m/s. The biomass removal of green algae and diatoms was higher than that of blue–green algae. The flow velocity at 1.4 m/s had a clear removal effect on filamentous algae. The velocity higher than 1.7 m/s caused a significant increase in the removal percentage of total biomass dominated by diatoms and blue–green algae. To reduce the filamentous algae and retain the diatoms and blue–green algae, a range of near bed flow velocity was suggested to be 1.4–1.7 m/s. This range could serve as a reference for required pulsed flow velocity to reduce the growth of excessive or nuisance periphyton.