Kondopoga hydroelectric power station is a hydroelectric power station in Kondopoga, utilizing the runoff of the Suna River and Lake Sandal in the Kondopozhsky District of the Republic of Karelia. It is part of the Suna Cascade of hydroelectric power stations, serving as its lower stage.

One of Russia's oldest hydroelectric power stations — construction began in 1916, and the station's completion was carried out under the GOELRO plan, with the first hydro unit commissioned in 1929. During the Great Patriotic War, the station was located in occupied territory and was partially destroyed; in the post-war years, it was restored with equipment replacement. The Kondopoga Hydroelectric Power Station is a cultural heritage site of local significance and is protected by the state. The station's owner is Public Joint-Stock Company TGC-1.

Natural conditions The Kondopoga Hydroelectric Power Station utilizes the runoff of the Suna River, diverted to the Palyeozero Reservoir via the , as well as lateral inflow between the two stations (natural inflow into the Palyeozero and Sandal reservoirs). The catchment area at the station's axis is . In an average water year, the Suna River at the Paleozerskaya Hydroelectric Power Station axis has an average annual flow of 59.3 m3/s, and the lateral inflow between the Paleozerskaya and Kondopoga stations is 10.2 m3/s. The long-term average inflow of Suna water to the Paleozerskaya Hydroelectric Power Station axis is 1879 mill. m3, of which 1806 mill. m3, or 96%, is diverted through the station's turbines and spillway to the lower pool toward the Kondopoga Hydroelectric Power Station. The long-term average volume of lateral inflow between the Paleozerskaya and Kondopoga stations is estimated at 331 mill. m3. The maximum lateral inflow to the Sandal Reservoir (recurrence 0.5%, or once every 200 years) is estimated at 60.6 m3/s; the maximum inflow of water to the Sandal Reservoir from the Palyeozero Reservoir is limited by the channel capacity of the Niva River and amounts to 140 m3/s.Гидроэлектростанции России. [Hydroelectric power plants in Russia]. М.: Типография Института Гидропроект, 1998. pp. 7, 33–34.

Maximum inflows occur from late May to early June during the spring flood, and minimums in March–April. Ice cover forms in November, and the reservoirs clear of ice in May. The maximum wave height in the Sandal Reservoir can reach 1.36 m. The station complex's structures are founded on bedrock (slates); the seismicity of the Kondopoga Hydroelectric Power Station area is 5 points on the MSK-64 scale.Гидроэлектростанции России. [Hydroelectric power plants in Russia]. М.: Типография Института Гидропроект, 1998. pp. 7, 11.

Construction Structurally, the Kondopoga Hydroelectric Power Station is a derivation hydroelectric power station with a non-pressurized headrace derivation in the form of a canal, utilizing the elevation difference between the Sandal Reservoir and Lake Onega. The station uses the runoff from Lake Sandal (converted into a regulating reservoir), as well as most of the Suna River runoff diverted to Palyeozero and then to Lake Sandal via the Paleozerskaya Hydroelectric Power Station. The Kondopoga Hydroelectric Power Station facilities include the Navda and Sopokha dam (forming the Palyeozero and Sandal reservoirs, respectively), a derivation canal with headworks, the station complex (forebay, penstocks, powerhouse, spillway, tailrace canal, 110 kV switchyard). The hydroelectric power station's hydraulic structures are Class III capital structures. The station's installed capacity is , guaranteed capacity is , and the designed average annual electricity generation is 131 mil. kWh. The maximum discharge capacity of the station's structures is 192 m3/s, including through the turbines —120 m3/s— and through the spillway — 72 m3/s.Гидроэлектростанции России. [Hydroelectric power plants in Russia]. М.: Типография Института Гидропроект, 1998. pp. 132-136.Правила использования каскада водохранилищ на р. Суна (Гирвасское, Пальеозерское, Сандальское).[Rules for using the cascade of reservoirs on the Suna River (Girvasskoye, Paleozerskoye, Sandalskoye). ]. М.: Росводресурсы, 2014. pp. 5, 17, 33—34.

Palyeozero Reservoir The Palyeozero Reservoir was formed by raising the level of Palyeozero with the blind Navda dam. The reservoir serves as the lower pool of the Paleozerskaya Hydroelectric Power Station (into which Suna River waters enter after working through the HPP turbines or passing through its spillway). Water discharge from the Palyeozero Reservoir occurs into the Sandal Reservoir through the natural rivers Niva (Nivka) and Tivdiyka.Правила использования каскада водохранилищ на р. Суна (Гирвасское, Пальеозерское, Сандальское).[Rules for using the cascade of reservoirs on the Suna River (Girvasskoye, Paleozerskoye, Sandalskoye)]. М.: Росводресурсы, 2014. P. 5.

The Navda dam is earthen, filled with sand, and has an anti-filtration element — a clay screen. The dam's length is 1500 m, maximum height — 5.4 m, crest width — 7 m, base width — 45 m. The crest elevation is 75.5 m, crest elevation above the normal backwater level of the reservoir — 2 m, head on the dam — 3.4 m. The levee has no water discharge structures; the federal highway Saint Petersburg–Murmansk runs along the dam crest. It was built in 1923–1938 and restored and reconstructed by 1951.Правила использования каскада водохранилищ на р. Суна (Гирвасское, Пальеозерское, Сандальское).[Rules for using the cascade of reservoirs on the Suna River (Girvasskoye, Paleozerskoye, Sandalskoye). ]. М.: Росводресурсы, 2014. P. 17. Coordinates of the central part of the levee: .

At normal backwater level, the Palyeozero Reservoir has an area of , length of 22.6 km, maximum width of 8.8 km, maximum depth of 74 m. The total and useful capacity of the reservoir is 2000.5 and 158.5 mil. m3, respectively. The reservoir is transit; artificial runoff regulation is not performed due to the absence of regulating structures (only natural regulation determined by the discharge capacity of the Niva River outlet). The normal backwater level elevation is 72.5 m above sea level (per the Baltic system of heights), dead storage level—71 m; forced backwater level is not provided.Правила использования каскада водохранилищ на р. Суна (Гирвасское, Пальеозерское, Сандальское).[Rules for using the cascade of reservoirs on the Suna River (Girvasskoye, Paleozerskoye, Sandalskoye). ]. М.: Росводресурсы, 2014. pp. 25-26.

Sandal Reservoir

The Sandal Reservoir was formed by raising the level of Lake Sandal with the blind Sopokha dam, which blocks the outlet of the Sandalka River. The reservoir serves as the upper pool of the Kondopoga Hydroelectric Power Station; water discharge from the reservoir occurs into Lake Onega through the HPP turbines and spillway.Правила использования каскада водохранилищ на р. Суна (Гирвасское, Пальеозерское, Сандальское).[Rules for using the cascade of reservoirs on the Suna River (Girvasskoye, Paleozerskoye, Sandalskoye). ]. М.: Росводресурсы, 2014. P. 11.

The Sopokha dam is earthen, filled with sand and loam, protected from filtration by a buttress drainage and drainage ditch. The dam's length is 1427 m, maximum height—5.2 m, crest width — 3.5 m, base width — 33 m. The crest elevation is 64 m, crest elevation above the normal backwater level — 1.45 m, head on the dam — 3.75 m. The upstream slope is secured with stone paving. Initially, the dam had a spillway into the Sopokha River, but it is now filled in. It was built in 1926 and reconstructed in 1938 with an increase in height.Правила использования каскада водохранилищ на р. Суна (Гирвасское, Пальеозерское, Сандальское). [Rules for using the cascade of reservoirs on the Suna River (Girvasskoye, Paleozerskoye, Sandalskoye).]. М.: Росводресурсы, 2014. P. 18.

Coordinates of the central part of the dam: .

The Sandal Reservoir incorporated Lake Sandal (whose level was raised by , as well as Nigo Lake and Gabo Lake, which became bays of the reservoir. At normal backwater level, the Sandal Reservoir has an area of , length of 41.7 km, maximum width of 7.3 km, maximum depth of 58 m. The total and useful capacity is 1780 and 298 mil. m3, respectively, allowing for seasonal regulation (the reservoir is filled during flood and drawn down during low-water period) and partial long-term regulation (filled in wet years and drawn down in dry years). The normal backwater level elevation is 62.55 m, dead storage level—60.9 m, forced backwater level—.Правила использования каскада водохранилищ на р. Суна (Гирвасское, Пальеозерское, Сандальское).[Rules for using the cascade of reservoirs on the Suna River (Girvasskoye, Paleozerskoye, Sandalskoye). ]. М.: Росводресурсы, 2014. pp. 3, 23, 26–27

Derivation The Kondopoga Hydroelectric Power Station's derivation is intended to convey water from the Sandal Reservoir to the station complex. It includes a derivation canal and headworks located within the urban development of the city of Kondopoga.Правила использования каскада водохранилищ на р. Суна (Гирвасское, Пальеозерское, Сандальское).[Rules for using the cascade of reservoirs on the Suna River (Girvasskoye, Paleozerskoye, Sandalskoye)]. М.: Росводресурсы, 2014. P. 101.

The derivation canal is open, non-pressurized, self-regulating, constructed in a half-cut–half-embankment, with a maximum discharge capacity of 200 m3/s. Length, per various sources, , top width 34 m, bottom width 9.6 m, depth . The canal dams have a maximum height of 7.99 m, crest elevation— (elevation above NBL—. The canal slopes are secured with stone paving with gunite. The canal contains a water intake for the pulp and paper mill, crossed by several bridges and urban utility crossings.Правила использования каскада водохранилищ на р. Суна (Гирвасское, Пальеозерское, Сандальское).[Rules for using the cascade of reservoirs on the Suna River (Girvasskoye, Paleozerskoye, Sandalskoye)]. М.: Росводресурсы, 2014. pp. 19, 101.Гидроэлектростанции России. [Hydroelectric power plants in Russia]. М.: Типография Института Гидропроект, 1998. pp. 132–136.

The headworks are located at the beginning of the derivation canal and are intended to block the canal during its draining. It is a reinforced concrete surface dock-type water intake with one 11 m span opening, closed by a 5-section flat sliding metal gate, with a cable hoisting mechanism of 12 t capacity. The intake length is 32 m, width—23.4 m, height—11.1 m; the Saint Petersburg–Murmansk railway passes along the headworks abutments.Правила использования каскада водохранилищ на р. Суна (Гирвасское, Пальеозерское, Сандальское).[Rules for using the cascade of reservoirs on the Suna River (Girvasskoye, Paleozerskoye, Sandalskoye). ]. М.: Росводресурсы, 2014. P. 101. Coordinates of the headworks: .

Station complex

The station complex includes a forebay with water intake, penstocks, spillway, powerhouse, tailrace canal, and open switchyard (OSY) 110 kV.Правила использования каскада водохранилищ на р. Суна (Гирвасское, Пальеозерское, Сандальское).[Rules for using the cascade of reservoirs on the Suna River (Girvasskoye, Paleozerskoye, Sandalskoye)]. М.: Росводресурсы, 2014. pp.102-104.Гидроэлектростанции России. [Hydroelectric power plants in Russia]. М.: Типография Института Гидропроект, 1998. pp.132-136.