Tresna Dam

The earth dam at Tresna closes the Soła valley between the Żywiec Basin and the Little Beskids and has held back Lake Żywiec since the mid-1960s. It rises 39 m above the valley floor and is over 300 m long, and building it meant flooding entire villages. It is the first and highest step of the Soła cascade – the only place in Poland where three dams stand on such a short stretch of river.

History: an answer to the flood

The first test drilling for the dam took place in 1952, but it was the catastrophic flood of 1958 that pushed the project ahead. Work began in 1960 and, delayed by further floods, ended in 1966; the hydropower plant followed a year later, and the reservoir was formally put into service in 1967. Villages including Zadziele and Stary Żywiec, as well as parts of Tresna and Zarzecze, disappeared under water.

The dam in numbers

• type: earth dam with a clay core, built from local gravel and cobbles; the seal reaches into bedrock and an inspection and grouting gallery,
• height above the valley floor: 39 m, length: about 300–310 m (sources differ), crest width: 10 m,
• three-pipe bottom outlet with a capacity of 730 m³/s,
• hydropower plant at the dam: 21 MW,
• Lake Żywiec: capacity 94.6 million m³, about 6.6 km long, 33.7 km of shoreline, maximum depth 26.8 m.

The complex is more than the main dam: side dams stand in the upper reaches of the reservoir, and six pumping stations drain the low-lying land behind the embankments. The main task of the whole system is to protect the Soła valley from floods and to store water.

The Soła cascade

Tresna is the top step of the cascade. Below lies Lake Międzybrodzie, held back by the concrete dam at Porąbka, built in 1921–1936, with Mount Żar and its pumped-storage power station rising above it. Lowest of all is the Czaniec earth dam of 1958–1966, whose reservoir supplies drinking water to cities including Bielsko-Biała. The cascade evens out the flow of the upper Vistula, protects against floods, supplies water to part of Silesia and generates electricity.

Interesting facts

The reservoir is slowly silting up – estimates suggest it could lose about half its capacity within some 70 years of construction. In dry 2015 the water level dropped by around 2 m, exposing large parts of the lake bed. By the bridge in Wilczy Jar near Oczków, a plaque recalls the disaster of 15 November 1978, when two buses taking miners to the Brzeszcze colliery fell from the bridge into the lake; 30 people died.

Tripto tip

The dam is a working hydraulic structure – the interior of the dam and power plant is not open to visitors, and everything is seen from outside, with no tickets or opening hours. A stop takes 20–30 minutes; combine it with a walk by the lake in Tresna, where there are holiday resorts. Tresna lies in the Czernichów municipality, about 3 km from Żywiec and 17 km from Bielsko-Biała. Nearby, plan Mount Żar above Lake Międzybrodzie, the Porąbka dam and nearby Żywiec.