Frequent changes in the tide levels in estuaries cause constant changes in the hydraulics of fish passage systems, with important effects on successful fish passage and swimming behavior. In most cases, Japanese eels often have low passage rates in engineered fishways because of their special habits. In this study, we established a 1:4 scaled-down weir-hole combination bulkhead fishway, studied the effects of different tidal differences and water depths on the passage rates and swimming behavior of yellow-phase Japanese eels, and analyzed the response of the Japanese eels to the hydraulic factors by superimposing their swimming trajectories and the flow field simulation results. We found that the passage rate of the eels decreased from 68.18% to 50.00% and 45.45% under extreme high tide differences and extreme low tide differences, respectively. The eels tended to use the low-velocity area to climb up the wall, and when crossing the mainstream, the yellow-phase Japanese eels preferred the area with a flow velocity of 0.1~0.36 m/s and a turbulent kinetic energy range of 0.001~0.007 m2/s2. Their upstream swimming speed was maintained at a range of 0.1~0.3 m/s.

No abstract

Downstream of the sluice gate or weir, wave-type flows inevitably occur in stilling basins with no tailwater. This paper aims to investigate the hydraulic performance of wave-type flows at a sill-controlled stilling basin through experimental research. The flow pattern, bottom pressure profiles along the stilling basin, and the air concentrations on the bottom and the sidewall were examined in five sill-controlled stilling basins by altering the sill position and the height. The results show that wave-type flow patterns contain submerged and non-submerged jumps, which are relevant to ambient pressure head and air entrainment. The bottom pressure profiles are related to larger pressure fluctuations at large unit discharges and two peak pressure values in the vicinity of the sill. The air concentrations on the bottom and the sidewall decrease with the increasing unit discharge. The flow zone in the vicinity of the sill should be focused upon concerning protection against cavitation damage because of the slight air entrainment and significant pressure fluctuations. These findings advance our understanding of wave-type flows, and their ambient pressure heads and air entrainment are useful for designing the sill-controlled stilling basin in hydraulic engineering.

In this pilot study, the performance of an “ultrafiltration (UF) + nanofiltration (NF)” advanced treatment process in improving drinking water quality was investigated. The membrane performance and effluent qualities of three commercial NF membranes (Dow Filmtec NF270-400, VONTRON TAPU-LS, and GE Osmonics-HL8040F 400) were evaluated, and the reasons for the difference in effluent quality of these three NF membranes were analyzed. The results showed that UF as a pretreatment process could provide NF with stable and qualified influent. After passing through the UF unit, the turbidity of raw water decreased by 88.6%, and the SDI value was less than 3. Due to the small pore size of NF membranes, organics and polyvalent ions in raw water were further removed. With a water recovery of 90%, the conductivity, chemical oxygen demand (CODMn), and hardness of NF effluent are significantly improved. The three commercial NF membranes showed different performance advantages. Among them, Dow Filmtec NF270-400 had the best desalting performance, VONTRON TAPU-LS had the highest retention rate of organic matter, and GE Osmonics-HL8040F 400 had significantly advanced softening performance. Thanks to the combination of the UF membrane and NF membrane, membrane fouling was effectively inhibited, and drug consumption was within an acceptable range. The operation costs of these three NF membranes were 0.165, 0.179, and 0.171 USD per ton of produced water, respectively. The results showed that the UF + NF process is an ideal technology for advanced treatment in water plants.