Grundlagen der Ethohydraulik

Horizontal bar rack bypass systems (HBR-BS) are characterized by a horizontal bar rack (HBR) with narrow clear bar spacing of 10–20 mm and an adjacent bypass (BS) to efficiently protect and guide downstream moving fish at water intakes. The small bar spacing may lead to operational challenges, such as clogging and high head losses. This study investigated whether combining an HBR with a low-voltage electric field (e-HBR) allows one to increase the clear bar spacing while maintaining a high standard of fish protection and guidance efficiency. To this end, an HBR-BS with 20 mm bar spacing and an e-HBR-BS with 20 and 51 mm bar spacing were tested with spirlin (Alburnoides bipunctatus) and European eel (Anguilla anguilla) in a laboratory flume. The racks were electrified with 38 V pulsed direct current. The protection efficiency of the e-HBR with 51 mm was 96% for spirlin and 86% for eels, which are similar results to those of the HBR with 20 mm. Some eels passed through the e-HBR, but only when they were parallel to the rack. Fish injuries of variable severeness due to the electrification were observed. The results highlight the potential of hybrid barriers for the protection of downstream moving fish. However, fish injuries due to electricity may occur; and reporting applied voltage, electrode geometry, resulting electric field strength and the pulse pattern of the electrified rack setup is necessary to ensure comparability among studies and to avoid injuries.

Section: Statistical Analysis and Data Limitationscontrasting

confidence: 49%

“…This is a simplification, as fish may have been affected by the behavior of other fish of the same group. No schooling behavior was observed in any of the eel experiments, which is typical for eels [33]. In most eel experiments, several minutes passed between the downstream passage of different individuals.…”

Section: Limitations Of the Statistical Analysismentioning

confidence: 81%

Protection and Guidance of Downstream Moving Fish with Electrified Horizontal Bar Rack Bypass Systems

Meister

Moldenhauer-Roth

Beck

et al. 2021

“…Continuous monitoring with the VAKI Riverwatcher can be an important tool to aid in researching fish population size and also to evaluate the potential relationships between abiotic factors and fish migration, as every passage record is associated with a direction, date, time, and water temperature. Longterm monitoring efforts encompass seasonal, environmental, and population variation, and trends or responses by fish populations to such variations can be used to identify parameters that influence migration behavior [48]. Several installations within a river system provide additional opportunity for the fine-scale analysis of migration rates in order to determine the proportion of migrating individuals within a population or estimate distribution or mortality between separate monitoring stations.…”

Section: Discussionmentioning

confidence: 99%

Monitoring of Fish Migration in Fishways and Rivers—The Infrared Fish Counter “Riverwatcher” as a Suitable Tool for Long-Term Monitoring

Haas,

Thumser,

Hellmair

et al. 2024

With the globally increasing awareness regarding the interconnectivity between freshwater ecosystems, projects for re-establishing connectivity with fishways as well as stock management are increasing. To ensure the quality and impact of such projects and for extending the scientific state of knowledge on this topic, a detailed monitoring of these measures is mandatory. Automatic, passive, and contactless counting devices can play a major role in these long-term monitoring projects, both for animal protection (non-invasive methods) and technical issues (comparatively low-cost systems in terms of time). Infrared fish counters can be used in a variety of fisheries applications and have proven particularly valuable in situations when long-term or continuous monitoring in lotic systems is required. Herein, we describe the function and technical capabilities of the VAKI Riverwatcher fish counter, provide information regarding its installation, and highlight some specific, practical applications of this technology. We discuss how the Riverwatcher can be used to validate the functionality of fish passage structures and to provide abundance estimates of migratory fish populations. Finally, we call attention to the challenges associated with operating monitoring equipment in variable river systems and briefly discuss potential sources of error that can influence the monitoring results and approaches to minimize or alleviate these errors.

“…To achieve an escape into the right direction, the flow velocity must not exceed the swimming capabilities of the target fish species [14]. As a general rule, these systems are only applicable where the average flow velocities (v A ) do not exceed v A = 0.5 m/s [4] so the fish has enough time to react to the stimulus [21] and is not drifted through the barrier [3]. Sometimes, even lower values for a proper function of a behavioral barrier in downstream direction are recommended in the literature (0.3 m/s) [14].…”

Section: Introductionmentioning

confidence: 99%

Retrofitting of Existing Bar Racks with Electrodes for Fish Protection—An Experimental Study Assessing the Effectiveness for a Pilot Site

Haug

Auer

Frees

et al. 2022

Downstream-migrating fish in rivers tend to follow the main current, and are in danger of swimming through the turbines at run-of-river hydropower plants, possibly causing high mortality rates. To avoid these losses, fish must be prevented from entering the turbines. Most existing vertical bar rack systems (used for turbine protection) however usually do not ensure proper fish protection due to large bar spacings. FishProtector technology enables the retrofitting of existing bar racks (i.e., the mechanical barrier) with additional electrodes to create a hybrid barrier. The induced electric field in the water aims to create a behavioral barrier to prevent fish passage through the bar rack. In this study, ethohydraulic experiments to investigate the effect of such a behavioral barrier on fish were performed. In detail, the fish-protection rate at a bar rack with a bar spacing of 30 mm was tested in five different scenarios: (i) a bar rack without electrodes (reference), and four electrified setups with electrode spacings of (ii) 80 mm, (iii) 120 mm, (iv) 160 mm, and (v) 200 mm. A flow velocity of 0.23 m/s was chosen to replicate the situation at a planned pilot site. The study was conducted in an outdoor laboratory flume using small fish of several local riverine species, mostly cyprinids and minnows. The results show that the mean fish-protection rate in the experiments could be increased from 62% in the reference setup up to 96% in the electrified setups.