Hydraulic and Hydrologic Characteristics of Effective Sea Lamprey Barriers
2024-06
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Hydraulic and Hydrologic Characteristics of Effective Sea Lamprey Barriers
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2024-06
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A network of 494 lowermost barriers on tributaries of the Laurentian Great Lakes prevent invasive sea lamprey from accessing upstream spawning habitat. Most of the lowermost barriers are low-head dams that are designed to maintain a minimum vertical separation of 45 cm between the barrier crest and the downstream water level. Many barriers are unable to maintain the design criteria for all flows, yet still effectively prevent sea lamprey passage. The fact that some barriers continue to block sea lamprey passage even when inundated (i.e., the downstream water level rises above the barrier crest) suggests other hydraulic conditions near the barrier may limit passage. However, little is known about the in situ hydraulic conditions downstream of these barriers. It was hypothesized that barrier efficacy is partially dependent on downstream hydraulic characteristics related to velocity and turbulence. A physical modeling laboratory study was conducted with three sea lamprey barriers of varying historical efficacies. Experiment 1 used an Acoustic-Doppler Velocimeter (ADV) to provide a quantification of the hydraulic characteristics downstream of these barriers. Experiment 2 used a force sensor to quantify the vertical forces at the riverbed. The results of Experiment 1 showed that mean longitudinal velocity averaged across a horizontal upper cross section was strongly correlated with barrier efficacy. This variable was interpreted as a marker of large-scale turbulence. Experimental trials that yielded a mean longitudinal velocity less than 1.3 m/s were effective, while ineffective barriers had values greater than 1.3 m/s. Other highly correlated variables included energy dissipation rate and eddy length scale in the vertical direction. These three variables, along with hydraulic head and the gravitational constant, were combined to form a dimensionless barrier number. The barrier number can be used to categorize barrier efficacy, and ineffective barrier trials generally had higher barrier numbers than effective barrier trials. In Experiment 2, the calculated upward pressure exerted on the riverbed peaked at -0.44 kPa. Since sea lamprey can produce suction pressures that overcome the -0.44 kPa peak pressure, the vertical upward pressures downstream of barriers are not likely capable of detaching a sea lamprey from the riverbed. Vertical force at the riverbed, therefore, is not likely an important variable to barrier efficacy. Together, the two experiments present a unified conclusion that the conditions near the riverbed are not as important to barrier efficacy as the conditions higher above the riverbed at 50% of the crest height. An improved understanding of how existing barriers block sea lamprey movement will aid in the design of future effective sea lamprey barriers.
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University of Minnesota M.S. thesis. June 2024. Major: Civil Engineering. Advisors: Vaughan Voller, Miki Hondzo. 1 computer file (PDF); xi, 82 pages.
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Reynolds, Kassandra. (2024). Hydraulic and Hydrologic Characteristics of Effective Sea Lamprey Barriers. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/265102.
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