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Vaikasas, S., Lithuanian Univ. of Agriculture, Kaunas (Lithuania). Water Management Inst. | Palaima, K., Lithuanian Univ. of Agriculture, Kaunas (Lithuania). Water Management Inst.

After a 16-m high dam was constructed and a 297-ha pond was arranged in the River Šušvė nearby Angiriai in 1980, the previous natural flow regime of the river has changed: 15500000 m3 of water accumulated above the dam is not discharged via a natural bed, but through two 1.5x1.5 m bottom orifices, and flood discharges (up to Q1% = 296 m3 sE-1) are directed into the lower reach through a 16-m high shaft spillway of floods. Such arrangement of the Angiriai dam ensured it to become an essential obstacle for migrating fish. In 2000, after the arrangement and operation of Angiriai hydro-electric power station, the water regime downstream the dam has been changed and new hydrological pulses as well as ecosystem biodiversity are to be adapted. Thus, the operation of Angiriai HPS on the River Šušvė generating hydroelectric power can have adverse effect on the river habitats and hydro ecological connectivity. To evaluate the effect, the eco-hydraulic water regime measurements in 2005 in a lower stretch with and without turbines operating were made. The study results showed that artificial water levels fluctuation (≈ 4 m hrE-1) induced by Angiriai hydro-electric power station as well as the discharge flowing through the bottom orifices due to high velocities (13–14 m sE-1) and temperature differences could create stressful situations for young fish in the lower bank. According to the data of soil texture of the Šušvė River, the bed armoring process is going on below the Angiriai HPS is quasistable and no impact of HPS operation is found.

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