Unscreened Water Research Articles

Hydraulics Near Unscreened Diversion Pipes in Open Channels: Large Flume Experiments

AbstractMost of the water diversions on the Sacramento and San Joaquin Rivers (California, United States) and their tributaries are currently unscreened. These unscreened diversions are commonly used for irrigation and are potentially harmful to migrating and resident fishes. A large flume (test section: 18.29 m long, 3.05 m wide and 3.20 m high) was used to investigate the hydraulic fields near an unscreened water diversion under ecologically and hydraulically relevant diversion rates and channel flow characteristics. We investigated all combinations of three diversion rates (0.28, 0.42, and 0.57 m3/s) and three sweeping velocities (0.15, 0.38, and 0.61 m/s), with one additional test at 0.71 m3/s and 0.15 m/s. We measured the three‐dimensional velocity field at seven cross sections near a diversion pipe and constructed regression equations of the observed maximum velocities near the pipe. Because the velocity components in three directions (longitudinal, transverse, and vertical) were significantly greater near the diversion pipe inlet compared with those farther from it, they cannot be neglected in the modeling and design of fish guidance and protection devices for diversion pipes. Our results should be of great value in quantifying the hydraulic fields that are formed around fish guidance devices to design more effective protection for fishes from entrainment into unscreened water‐diversion pipes.

Modified Water Diversion Structures Can Behaviorally Deter Juvenile Chinook Salmon from Entrainment

AbstractJuvenile Chinook Salmon Oncorhynchus tshawytscha traveling in river systems can become entrained by unscreened water diversions when they encounter inflow velocities that exceed their avoidance (i.e., swimming) ability. We tested the efficiency of three devices for deterring fish entrainment; the devices reduced the diversion's maximum inflow velocity by dispersing the inflow across a greater area so as to reduce fish entrainment without causing a decrease in water diversion rates. Tests were performed in a river simulation flume at a 0.15‐m/s sweeping velocity in clear water conditions during the daytime and nighttime as well as in turbid water (daytime) conditions. Water was diverted at a rate of 0.57 m3/s through a 0.46‐m‐diameter pipe. The tested devices included (1) a widened box inlet (1.7 m long × 0.76 m wide × 0.76 m deep) with a trash rack mounted at its entrance (trash rack box), (2) a widened box inlet with a louver array mounted at the entrance (louver box), and (3) a 0.91‐m‐diameter cylinder perforated with 300 evenly spaced, 5‐cm‐diameter holes (perforated cylinder). During 2‐h experiments under daytime conditions, 51.5 of 80 fish (on average) were entrained into the pipe when no device was used (i.e., control), and a fish's mean risk of becoming entrained when passing the pipe once was 14%. The mean entrainment risk during a single pipe passage event was reduced to 7% in the trash rack box treatment (i.e., 50% of the control value), 0.17% in the louver box treatment, and 0.20% in the perforated cylinder treatment. In comparison with the control, the mean number of entrained fish was reduced by 50% in the trash rack box treatment, by 97% in the louver box treatment, and by 93% in the perforated cylinder treatment. These devices also reduced the number of fish that were entrained during darkness or turbid daytime conditions. Our findings suggest that behavioral deterrence devices offer effective, low‐cost alternatives to positive barrier fish screens by protecting juvenile Chinook Salmon from entrainment at water diversion pipes without reducing water pumping efficiency.

Fish-protection devices at unscreened water diversions can reduce entrainment: evidence from behavioural laboratory investigations.

Diversion (i.e. extraction) of water from rivers and estuaries can potentially affect native wildlife populations if operation is not carefully managed. For example, open, unmodified water diversions can act as a source of injury or mortality to resident or migratory fishes from entrainment and impingement, and can cause habitat degradation and fragmentation. Fish-protection devices, such as exclusion screens, louvres or sensory deterrents, can physically or behaviourally deter fish from approaching or being entrained into water diversions. However, empirical assessment of their efficacy is often lacking or is investigated only for particular economically or culturally important fishes, such as salmonids. The Southern population of anadromous green sturgeon (Acipenser medirostris) is listed as threatened in California, and there is a high density of water diversions located within their native range (the Sacramento-San Joaquin watershed). Coupled with their unique physiology and behaviour compared with many other fishes native to California, the green sturgeon is susceptible to entrainment into diversions and is an ideal species with which to study the efficacy of mitigation techniques. Therefore, we investigated juvenile green sturgeon (188-202 days post-hatch) in the presence of several fish-protection devices to assess behaviour and entrainment risk. Using a large experimental flume (∼500 kl), we found that compared with an open diversion pipe (control), the addition of a trash-rack box, louvre box, or perforated cylinder on the pipe inlet all significantly reduced the proportion of fish that were entrained through the pipe (P = 0.03, P = 0.028, and P = 0.028, respectively). Likewise, these devices decreased entrainment risk during a single movement past the pipe by between 60 and 96%. These fish-protection devices should decrease the risk of fish entrainment during water-diversion activities.

Efficacy of a sensory deterrent and pipe modifications in decreasing entrainment of juvenile green sturgeon (Acipenser medirostris) at unscreened water diversions.

Water projects designed to extract fresh water for local urban, industrial and agricultural use throughout rivers and estuaries worldwide have contributed to the fragmentation and degradation of suitable habitat for native fishes. The number of water diversions located throughout the Sacramento-San Joaquin watershed in California's Central Valley exceeds 3300, and the majority of these are unscreened. Many anadromous fish species are susceptible to entrainment into these diversions, potentially impacting population numbers. In the laboratory, juvenile green sturgeon (Acipenser medirostris) have been shown to have high entrainment rates into unscreened diversions compared with those of other native California fish species, which may act as a significant source of mortality for this already-threatened species. Therefore, we tested the efficacy of a sensory deterrent (strobe light) and two structural pipe modifications (terminal pipe plate and upturned pipe configuration) in decreasing the entrainment of juvenile green sturgeon (mean mass ± SEM = 162.9 ± 4.0 g; mean fork length = 39.4 ± 0.3 cm) in a large (>500 kl) outdoor flume fitted with a water-diversion pipe 0.46 m in diameter. While the presence of the strobe light did not affect fish entrainment rates, the terminal pipe plate and upturned pipe modifications significantly decreased the proportion of fish entrained out of the total number tested relative to control conditions (0.13 ± 0.02 and 0.03 ± 0.02 vs. 0.44 ± 0.04, respectively). These data suggest that sensory deterrents using visual stimuli are not an effective means to reduce diversion pipe interactions for green sturgeon, but that structural alterations to diversions can successfully reduce entrainment for this species. Our results are informative for the development of effective management strategies to mitigate the impacts of water diversions on sturgeon populations and suggest that effective restoration strategies that balance agricultural needs with conservation programmes are possible.

Assessing Juvenile Chinook Salmon Behavior and Entrainment Risk near Unscreened Water Diversions: Large Flume Simulations

AbstractJuvenile Chinook Salmon Oncorhynchus tshawytscha from California's Central Valley must pass thousands of unscreened water diversion pipes during their out‐migration to the Pacific Ocean. The number of fish that become entrained into (drawn through) these diversions at different hydraulic and environmental conditions is currently unknown. We tested the ability of juvenile Chinook Salmon to avoid entrainment into a 0.46‐m‐diameter unscreened water diversion pipe while swimming in a large‐river‐simulation flume. Fish swimming experiments were conducted at 0.15, 0.38, and 0.61 m/s sweeping velocities (simulating the river current) with 0.42 and 0.57 m3/s water diversion rates during the day and at 0.15 and 0.61 m/s with a diversion rate of 0.57 m3/s in turbid water and during the night. The number of fish entrained during day experiments ranged from 0.8% (SE, 0.3) to 8.5% (SE, 0.3). The percentage of pipe passage events resulting in fish entrainment nearly doubled at the 0.57 m3/s water diversion rate (1.7%) compared with that at 0.42 m3/s (0.9%). In clear water conditions during the day, more fish became entrained at the higher water diversion rate (0.57 m3/s) and slower sweeping velocity (0.15 m/s), with fish entrainments starting 38.6 cm (SE, 1.6) from the center of the pipe inlet, where fish experienced an increased velocity gradient and a mean resultant velocity of 0.74 m/s. Fish entrainment was strongly influenced by the number of pipe passages per experiment, rather than by swimming orientation or time spent in the flume. More fish were entrained at the faster sweeping velocity (0.61 m/s) in turbid water during the day and at night, indicating that juvenile Chinook Salmon may use nonvisual guidance (e.g., lateral line system) to avoid water diversions in slower currents. These results help to provide a scientific basis for protecting out‐migrating juvenile Chinook Salmon exposed to unscreened water diversions.

Effects of the Zebra Mussel (Dreissena polymorpha Pallas) on Protozoa and Phytoplankton from Saginaw Bay, Lake Huron

Direct effects of the grazing activities of the zebra mussel, Dreissena polymorpha, on the natural assemblage of planktonic protozoa and algae from Saginaw Bay, Lake Huron, were studied in September and October 1994. Water and mussels collected from two eutrophic sites were incubated in an outdoor “natural light” incubator at ambient temperature for 24 hours. Experiments were conducted in 4-L bottles with screened (40 or 53-μm net) or unscreened water and with and without mussels. Despite relatively high growth rates of protozoa on both dates, mussels lowered protozoan numbers by 70–80% and reduced the species richness of the protozoan community by 30–50%. Large heterotrophic flagellates were reduced up to 100% while peritrichous ciliates attached to the colonies of blue-greens were reduced only by 50%. Dreissena selectively removed nanoplanktonic Cryptomonas and Cyclotella, but had no significant effect on the predominant phytoplankton species, Microcystis. Overall, Dreissena clearance rates were low in the presence of this cyanophyte species. We conclude that zebra mussels, in regions where they are abundant, can cause significant changes in composition of both the protozoan and phytoplankton communities.

Significance of planktonic ciliated protozoa in the Lower St. Lawrence Estuary: comparison with bacterial, phytoplankton, and particulate organic carbon

To investigate the potential role of microzooplankton as trophic links in the Lower St. Lawrence Estuary (LSLE, ca 48'50' N, 68 10' W), the importance of ciliate carbon biomass (CilC) was evaluated in relation to bacterial (BactC), phytoplankton (PhytoC), and particulate organic (POC) carbon, from May to September 1992. These variables generally peaked in the upper 10 m of the water column. Their seasonal peaks occurred in June and July when water temperature and stratification index were at their highest levels. CilC averaged 22, 8, and 4 % of BactC, PhytoC, and POC, respectively. Compared to bacteria, ciliates appeared able to respond more rapidly to an increase in phytoplankton biomass, and were under higher predation pressure. Ciliates were dominated by individuals with sizes (19 to 187 pm) up to 15 times larger than that of the blooming diatoms. Direct observations revealed protozoan individuals with up to 10 ingested bloom-forming algal cells within their body. Microzooplankton grazing rates (estimated In July 1992 using a dilution technique) in unscreened water samples from the depth of maximum chlorophyll a concentration represented up to 70% (mean & SD = 54 * 21 %) of the phytoplankton growth rates. Microzooplankton grazing rates in prescreened (

The Fishery Development Program in the Lower Columbia River

The gradual decline of the Columbia River salmon fishery has been brought about through deforestation, pollution, over-fishing, unscreened water diversions, and construction of dams within the watershed. The latter is believed to be the major contributing factor. Present water-development programs of the U. S. Bureau of Reclamation and the Corps of Engineers have accelerated the organization of a conservation plan for the maintenance of the salmon and steelhead fishery before the proposed dams bring about further diminution of the runs. This plan, endorsed and supported by federal planning agencies, consists of the maximum development and management of the fish runs in tributaries of the lower Columbia River basin. To effectuate this program approximately a 10-year period and 20 million dollars will be required, of which one million dollars have been appropriated for expenditure in fiscal year 1949. Essentially, the program is based on the cooperative efforts of the States of Oregon and Washington and the U. S. Fish and Wildlife Service in (1) removal of obstructions to permit passage of fish, (2) abatement of pollution, (3) screening of water diversions and construction of fishways, (4) transplantation of upriver runs, (5) extension of artificial propagation, and (6) establishment of fish refuges in which conflicting developments would not be permitted. There is sufficient reason to believe that with the effectuation of this program, the populations of salmon and trout in the Columbia River and its tributaries can be maintained.