| Large dams
The early Swedish buttress dams resemble massive dams, while later ones resemble an Ambursen dam. Storfinnforsen is an example of a Swedish buttress dam.
Concrete was often essential for the early Swedish embankment dams. Until the 1950s, large embankment dams in Sweden were constructed as diaphragm embankments, with a central watertight diaphragm of either concrete or wood. The thin diaphragm wall was often placed in or adjacent to a core of clay or till. The old dam at Porjus is an example of such a dam and was among the first large embankment dam completed in Sweden.
Embankment dams pave the way for fast hydropower expansion – 1950s
to 1980 The large-scale hydropower development took until after the Second World War to start. At this time, engineers had developed new techniques for building embankment dams using modern principles, and there were plenty of international examples of successful earth and rock fill dams. The construction of the first large embankment dams in Sweden without a central diaphragm began in the early 1950s, and by the 1960s, the country had shifted to almost exclusively build large dams as earth fill and rock fill dams with a core made of till. However, concrete was still commonly used for spillway structures, intakes, waterways, and engine houses. The cross-section of a typical modern Swedish embankment dam consists of several zones with different functions. At the centre is a core of compacted till with low hydraulic conductivity. On both sides of the core, filters made of sand and gravel protect the core material from internal erosion. The support fill creates the dam’s stability and is the main load-bearing zone. The dam is protected from waves, precipitation and run-off, and ice by rip rap at the crest and slopes.
Economic and legal considerations have shaped a tradition of wanting to be able to discharge a 100-year flood with the reservoir at the normal retention water level. Consequently, passive discharge solutions such as overflow weirs that require temporarily raising the reservoir level have often not been used. Instead, a typical discharge structure in a Swedish dam facility is a concrete structure with two or three gate openings equipped with vertical lift gates or radial gates. Large-scale hydropower development peaked during the 1950s-1970s. In the 1970s, the Swedish
government announced the protection of four major rivers from hydropower development, signaling the beginning of the end of large-scale hydropower development in Sweden. The most profitable falls had already been developed, and new hydroelectric plants were completed at a decreasing rate thereafter. Instead, to meet the continued increasing demand for electricity, Sweden started its nuclear power programme during the 1970s. This period also saw the rise of large-scale tailing dams. Prior to the 1950s, most of the ore extracted in Sweden was used directly, resulting in a limited amount of waste. As production ramped up, mining activities increased, and new techniques were introduced, large-scale tailing dams became necessary. While the first tailing management facility was constructed in 1930, it wasn’t until the 1950s that this type of facility was used on a larger scale to accommodate the growing volume of mine tailings. The design of the early tailings dams was strongly influenced by the embankment dams used by the Swedish hydropower industry, as described above. Sweden’s topography is ideal for valley or side-hill impoundments, with deposition typically occurring from a single discharge point uphill from the dam structure. This resulted in water and slime accumulating against the dam face. Since the dams were designed to hold water and Sweden has high precipitation rates, the tailings ponds often stored significant volumes of water.
Above: Discharge through the newly renovated bottom outlet at Storfinnforsen. The photo also shows the concrete dam with the insulation wall Photo: Uniper
Below: Section through the Trängslet embankment dam showing the impervious core made of till, surrounded by three filter layers of varying characteristics (fine, medium and coarse) and rock fill shoulders. The illustration does not show the new downstream toe berm, but it can be seen in the photo. The dam was constructed using 7.2Mm³ of material, which includes 4.5Mm³ rock fill, 1.2Mm³ filter, and 1.5Mm³ till. The dam is founded on bedrock consisting of syenite, porphyry, and at some locations, diabase
www.waterpowermagazine.com | May 2023 | 23
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