This report presents the results of a laboratory study evaluating the survival, injury, and scale loss of fish exposed to a Passavant-Geiger Multi-Disc (Geiger) screen specifically designed to protect juvenile and adult fish. Information in this report increases the performance database for this technology. The data presented provide a basis upon which to estimate the potential for these screens to meet the proposed Environmental Protection Agency (EPA) Clean Water Act §316(b) Existing Facilities Rule (the Rule) as the Rule relates to impingement mortality.
Modified traveling band screens with fish protection features are one option for meeting the impingement mortality reduction standard in the proposed Rule under the streamlined compliance approach. The extent to which new traveling screen designs such as the Geiger screen will be included in the streamlined approach, however, is not known. In general, there are limited biological performance data for these screens upon which to demonstrate their similarity to other modified traveling band screens. Since the Rule is scheduled to be finalized in June 2013, a laboratory evaluation was considered to be the only approach that could develop a substantial quantity of new data under various conditions to assess the Geiger screen’s comparative performance compared to modified traveling band screens.
To expand the database of biological performance data for Geiger screens
To determine the effect of approach velocity, screen mesh type, and fish length on species-specific rates of fish survival, injury, and scale loss for Geiger screens
To achieve these objectives, a Geiger screen was installed in a large hydraulic test flume, and six species of juvenile and adult freshwater fish of varying lengths were exposed to the impingement and collection process and subsequently evaluated for survival, injury, and scale loss. During the study, two mesh types were used: 2.0-mm stainless steel (2.0-mm mesh) and 9.5-mm drilled plastic (9.5-mm perforated mesh).
A total of 105 treatment and control replicates involving over 24,600 fish were tested over 31 days between July 13 and September 19, 2012. The median unadjusted survival rate for all species and velocities tested was 95.7%. For most species, survival was significantly correlated to velocity, with a decrease in survival as velocity increased. The velocity effects were often specific to the species and mesh type tested. For most combinations of species and mesh types, survival was significantly correlated to fish length, with larger fish surviving better than smaller fish. In some cases, there were differences in survival associated with mesh type. In all cases when this was true, the survival was higher with the 2.0-mm mesh than the 9.5-mm perforated mesh. For golden shiner with the 9.5-mm perforated mesh and bluegill with the 2.0-mm mesh, control mortality was about 8%, indicating that some of the mortality observed was not likely attributable to the impingement process.
Fish injury followed a trend similar to survival. Injury was species-specific, with some fish exhibiting higher rates of injury than others. Fish length was a significant predictor of injury for four of the six species tested, with larger fish exhibiting fewer injuries than smaller fish. In most cases, mesh type was not a significant predictor of injury. In almost all cases, increases in velocity significantly increased the number of injuries. The most common injury types observed were bruising and fin damage. Since the severity of injuries was not recorded, it is not possible to determine if these injuries were ephemeral or could result in a reduction in fitness of the impinged fish.
As with injury and survival, rates of scale loss were variable by species. In general, scale loss increased with increases in velocity. In all cases, larger fish exhibited less scale loss than smaller fish. In some cases, there were differences in scale loss between mesh types. When differences by mesh size were detected, the fish tested with the 2.0-mm mesh exhibited less scale loss than those tested with the 9.5-mm perforated mesh.
Overall, the fundamental design (traveling, through-flow screen) and function (two-step fish and debris removal) of Geiger and Ristroph screens are similar and substantial disparity in their performance with regard to fish impingement survival in the field would not be expected. The results of this study do not alter this expectation.
Applications, Value, and Use
This report provides power generators with data on the ability of Geiger screens to maximize impingement survival of juvenile freshwater fish. In addition, these data are now available to inform the EPA rulemaking process with scientifically defensible research results from testing Geiger screens with different mesh types in the laboratory to determine the survival, injury, and scale loss of fish.