Page - 1059 - in Book of Full Papers - Symposium Hydro Engineering

1. INTRODUCTION AND BACKGROUND Regular dam safety evaluations are performed on Swedish dams according to the voluntary Dam-Safety Guidelines (RIDAS). Due to recent revisions, deficiencies in structural and hydraulic performance are routinely discovered leading to dam safety upgrades (Yang et al. 2010, 2014). These shortfalls include rock erosion downstream, status of embankment dams, spillway stability and functions of mechanical and electrical systems in addition to spillway discharge capacity (Ygland et al. 2012, Bond et al. 2014). Both Långströmmen and Ramsele are among the candidates for spillway upgrade and renewal. Långströmmen is located on the River Ljusnan in Mid Sweden and was commissioned in 1961. The facility includes more than 2,5 km of embankment dams, owned by the power producer Fortum. The tallest dam sections are placed near the spillway, rising to a height of 29 m. The full retention reservoir level (FRRL) is +279.55 m, with 35 cm of regulation amplitude. Its power plant has two Francis turbines with a gross head of 31.3 m and a turbine flow rate of 100 m3/s. Its annual power production exceeds 250 GWh. dams. Ramsele hydropower plant, owned by Uniper, is located on Faxälven in Northern Sweden and was commissioned 1958. The dam is a 440 m long buttress dam about 40 m high. The full retention reservoir level (FRRL) is +223.50 m, with 50 cm of regulation amplitude. The power station has three Francis turbines with a total output of about 160 MW, a gross head of 79.2 m. Its annual power production is about 870 GWh. Figure 1 shows the location of Långströmmen and Ramsele. 1059