Project
Field Investigation of Hydrologic and Hydraulic Characteristics of Effective Sea Lamprey Barriers
Physical barriers are essential to the sea lamprey (Petromyzon marinus) control program, preventing adult lamprey from reaching spawning habitat in Great Lakes tributaries and reducing the amounts of chemical lampricides needed to treat streams infested with sea lamprey larvae. Sea lamprey barriers are designed to maintain a 45-cm vertical differential between crest and tailwater elevations for the highest flood frequency event feasible. Once flows exceed the design flood flow, the barrier loses its 45-cm differential, and sea lamprey blocking efficacy will typically decrease. Some barriers, however, continue to be effective even when the vertical differential is lost. Exploring why barriers remain effective despite the inability to meet design criteria could provide insights for future barrier designs. Our laboratory work proved strong evidence that high streamwise velocities with elevated flow instabilities (i.e., turbulence) may hinder sea lamprey passage at barriers that exceed the design conditions. The study also resulted in the generation of a dimensionless Barrier (Bn) number representing the ratio of turbulent kinetic energy dissipation within the barrier and the potential energy difference across the barrier. Barrier numbers below a value of 5 x 10-4 are associated with conditions where a barrier is effective. These findings have helped refine our hypothesis that the efficacy of a sea lamprey barrier significantly correlates to stream hydrology variations (e.g., frequency and intensity of flooding), downstream hydraulic characteristics (energy dissipation rates, maximum velocities in the downstream direction, and turbulence intensities), channel geometry, and stream bed characteristics. We conducted the initial experiments under laboratory and simplified conditions using historic records of escapement that could not be assigned to specific flow events. To test our hypothesis under more realistic conditions, we propose field measurements of the key hydraulic variables near two existing barriers with concurrent monitoring of sea lamprey escapement using acoustic telemetry.