This study is motivated by the need to understand the temperature dynamics and warm-water temperature withdrawal. This study also recognizes the need for an environmental assessment of the proposed temperature control schemes at New Fengman Dam. An unsteady three-dimensional (3D) non-hydrostatic model is used in the present study to predict the hydrodynamics and thermal dynamics in the forebay and intakes of the New Fengman Dam. The numerical model is validated using hydrodynamic data collected from a 1:120 entire physical model and 1:30 local model in the present paper. The numerical and experimental results indicate that the Stop Log Gate has no effect on warm-water withdrawal. After dam reconstruction, the reservoir release temperatures can be increased from 4.0 °C to 6.0 °C to improve the habitat of native fishes. The cancellation of the Stop Log Gate program is recommended; the old dam meets the performance objectives for temperature increase.

Due to the complex structure and the multiformity of boulder arrangements, there is currently no perfect design criterion for nature-like fishways. This paper proposes four types of nature-like fishways arranged with an impermeable partition wall (IPW), a semi-permeable partition wall (SPPW) or a fully permeable partition wall (FPPW). The hydraulic characteristics of these fishways were investigated experimentally. The results show that the discharge of the fishway arranged with a FPPW was almost twice that of an IPW fishway, and the discharge of a SPPW fishway was between the two extremes. The mean flow velocity of the FPPW fishway was larger than that of the other schemes. For the fishway arranged with an IPW, the flow information was basically consistent with that of the engineered technical fishway. In the FPPW or SPPW fishway, there was more abundant flow information and no obvious recirculation zones in the fishway pool, and these conditions are suitable for migratory fish moving up- and downstream. Notably, for the fishway arranged with two fish passages, two mainstreams were formed in the pool, which divided the flow pattern of the pool into three flow regions. A weak recirculation area was formed in the low-velocity region, which facilitates swimming for migratory fish. According to this comprehensive comparative study, the SPPW fishway with two fish passages had low discharge, abundant flow information and favorable fish migration characteristics; thus, it is the optimal fishway scheme among those studied in this paper.

To imitate the constraints of topographic conditions, turning pools with different angles, such as 90° and 180°, are set in fish passage arrangements. If the mainstream in the turning pool is close to the wall and the recirculation zone is too large, it will have an adverse effect on fish migration. Taking the 180° turning pool as an example, five types of arrangements without and with additional rectifier baffles are proposed to optimize the body shape of the turning pool. A three-dimensional numerical simulation method is used to compare and analyze the different arrangement schemes. The results show that adding rectifier baffles can adjust the flow structure in the 180° turning pool. The arrangement adding rectifier baffles at the two three-equidistant points of the 180° turning pool and tilting 15° inward outperforms others in this study. This arrangement can center the mainstream, reduce turbulent kinetic energy, significantly decrease the flow velocity along the course, downscale the recirculation zone, and decrease the overall flow velocity.

When fish swim upstream in the long-distance fishways, fatigue may occur, thereby affecting their passage efficiency and passage time. Therefore, constructing suitable resting pools within the fishway is essential. In this study, a diversion pile was introduced into the resting pool of the vertical solt fishway while altering its installation position. A three-dimensional re-normalization group k– ε turbulent mathematical model was then employed to analyze how the diversion pile with distinct positions affects the hydraulic characteristics in the resting pool under different slope conditions. The results show that with the diversion pile at the two-thirds position of the partition wall’s sidewall in the resting pool, the mainstream is effectively regulated to the central position, accompanied by a small degree of meandering. Under such an arrangement, although the diversion pile has an impact on the turbulent kinetic energy in the resting pool across various slope conditions, the influence is insignificant. Therefore, it is recommended to install the diversion pile at the two-thirds position of the partition wall’s sidewall in the resting pool, which can adjust the hydraulic characteristics of the resting pool and provide a large range of low-velocity areas for fish to rest, thereby facilitating the passage efficiency.