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Environmental impact of water exchange blocking in a strait – a multidisciplinary study in the Baltic Sea

Liblik Taavi, Buschmann Fred, Siht Enriko, Kuprijanov Ivan, Väli Germo, Lipp Maarja, Erm Ants, Laanemets Jaan, Eschbaum Redik, Verliin Aare, Saks Lauri, Zekker Ivar

Oceanologia

2024

Vol. 66 (1)

9--25

In this study, we report the environmental impact of water exchange blocking by a 3 km road dam built in 1896 in the shallow Väike Strait, north-eastern Baltic Sea. Using a multidisciplinary measurement campaign and numerical simulations, we show ecological conditions in the strait have considerably altered; the previously free-flowing strait now comprises two bays with separate circulation systems. Water exchange in the area close to the dam has decreased 10–12-fold. Since advection is weakened, exchange with the atmosphere and sediments has a relatively greater role in shaping water characteristics. Consequently, occasional very high sea surface temperature, salinity, and total nitrogen, and strong diurnal cycles in water temperature (>4°C) and dissolved oxygen (>4 mg l−1) were observed near the dam in summer. Oxygen levels are continuously below saturation in winter and concentration occasionally drops to hypoxic levels with ice cover. Nitrogen content in sediments near the dam is 3–4 times higher than in neighboring areas. The dam also modifies sea level, wind wave and suspended matter patterns in the strait. Sediments near the dam show elevated content of hazardous substances likely associated with traffic on the dam road. The phytobenthos community near the dam is dominated by annual green algae, which massively decompose during winter. The dam likely impedes fish migration between suitable feeding and spawning areas, also there have been fish kills caused by rapid fluctuations in sea levels, amplified by dam. The construction of new openings would alleviate negative impacts of the dam.

Assessment of migration conditions for fish swimming through a semi-natural fish pass on the Nidzica River in Bronocice

Plesiński Karol K., Filipczyk Janusz M., Bień Michał M., Karadağ Mustafa

Journal of Water and Land Development

2023

no. 59

54--65

Fish passes are essential elements for maintaining continuity for migrating fish. Without them, fish would be unable to undertake migration to satisfy their basic life needs. These devices must meet a range of requirements related to the size of individual fish pass elements and the hydrodynamic parameters of the flowing water. Despite efforts, it is not always possible to meet these requirements. There are many causes of errors in the design and construction of fish passes, and each case should be assessed individually. The most severe consequence of these errors is the obstruction of fish migrating upstream. In this study, an analysis of the permeability of a semi-natural fish pass was conducted for fish. This assessment was carried out using two methods. In the first approach, the required geometric dimensions of the fish pass elements were determined based on the dimensions of individuals living in the river channel. In the second approach, the dimensions were extracted from publications dedicated to slot fish passes, as the studied object resembles such a design. The analysis revealed that the fish pass does not fulfil its intended role. All fish species living in the Nidzica River channel face difficulties in passing through the fish pass, including the brook trout, for which the object is specifically designed. The main errors stem from the design and construction, resulting in exceeded values, primarily in the hydrodynamic parameters, rendering the fish pass impassable. The study also aimed to develop corrective recommendations considering the latest scientific developments.

Problematyka przywrócenia migracji ryb przez obiekty hydrotechniczne w korytach rzecznych

Wierzbicki M.

Landform Analysis

2013

Vol. 24

107--113

W artykule poruszono problematykę przywrócenia migracji ryb przez obiekty hydrotechniczne w aspekcie oddziaływania piętrzenia na morfologię koryta. Omówiono zmiany jakie mogą nastąpić w korycie rzeki na skutek piętrzenia wody i jej wykorzystania dla celów energetycznych, oraz wpływ, jaki piętrzenie wywiera na warunki migracji organizmów wodnych, głównie ryb. Przedstawiono priorytety oraz założenia projektowe, które powinny spełniać współczesne konstrukcje przepławek tak, aby ich działanie było jak najbardziej efektywne. Na podstawie prac związanych z opiniowaniem dokumentacji projektowych oraz wniosków o dofinansowanie budowy przepławek ustalono, jakie elementy powinny być brane pod uwagę podczas opracowywania koncepcji, projektu oraz użytkowania przyjętego rozwiązania udrożnienia stopnia dla migracji organizmów. Wskazano na potrzebę rzetelnej analizy uwarunkowań formalnoprawnych, środowiskowych i technicznych oraz różnych wariantów rozwiązań.

In this paper aspects of the fish migration trough barrages in context of the barrage influence on river morphology are presented. River morphology changes as the result of the artificial water level increasing and water usage for the power plant are described. Also the barrage influence on fish migration conditions is presented. Fishpass projects priorities and foundations that should be fulfilled to get maximum efficiency are discussed in this paper. On the basis of applications for providing finances of fishpass projects and their realizations, aspects that should be taken into consideration during the conception, project elaborating and the fishpass utilization are specified. The necessity of law regulations and environment and technical aspects adequate analyse is emphasized. Also different versions of available solutions should be analysed.