Evaluation of Downstream Passage Alternatives for Shortnose Sturgeon

摘要

A laboratory evaluation was conducted for the Holyoke Gas & Electric Department in a large flume at Alden Research Laboratory to determine the engineering and biological criteria necessary to guide shortnose sturgeon to a 2-ft square bottom bypass entrance in a 10-ft wide section of steel bar rack with 2-in clear spacing. Tests were conducted with yearling shortnose sturgeon (mean length:332 mm) in a 80 ft L × 20 ft W × 8-ft D test flume. A constant approach velocity of approximately 2.2 ft/s was maintained at the face of the bar rack for all trials. All test fish were fitted with externally attached PIT tags to track fish movements at two locations upstream of the bar rack and in the bypass. Test conditions included bypass entrance velocities of 1, 2, 5, and 6.2 ft/s. In addition, trials were conducted under nighttime light conditions with and without illumination of the bypass entrance. Finally, based on the bottom-oriented behavior of sturgeon, additional trials were conducted to determine the effectiveness of bottom-mounted guidance ridge structures for guiding sturgeon towards the bypass entrance. The ridges were two 1.5 × 0.75-in plywood strips angled from each flume wall downstream towards the bypass entrance. Data were collected with submersible video cameras (day tests), a DIDSON acoustic camera (night tests), and a PIT tag system. Effectiveness of each test condition was measured as the percent excluded from entrainment, the percent bypassed, and the overall bypass efficiency (number bypassed divided by the total entrained and bypassed combined). Percent excluded, percent bypassed, and bypass efficiency generally increased with increasing bypass entrance velocities, but peaked at 5 ft/s. At 5 ft/s, 82% of sturgeon were excluded, 33% were bypassed, and a bypass efficiency of 64.3% was achieved. Trials conducted at night at a bypass entrance velocity of 5 ft/s without illumination of the bypass entrance achieved a higher percent bypassed (67%) and bypass efficiency (70%), but a lower percent excluded (71%). Illumination of the bypass entrance did not increase bypass use at night. Trials conducted at 5 ft/s with bottom-mounted guidance ridges yielded the highest percent excluded (87%) and bypass efficiency (74%). Video, DIDSON, and PIT tag data indicated that sturgeon passed downstream more quickly at higher bypass entrance velocities and at night. The bottom-mounted guidance ridges were effective in delaying downstream passage, minimizing entrainment, and increasing bypass use. With additional testing of alternative designs, guidance ridges leading to a bottom bypass may have potential to improve downstream passage of sturgeon at hydro project intakes.