Author(s): Hörn Hrafnsdóttir
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Abstract: The Laxá Power Plant III is a 14 MW run-of-the-river plant from 1973, that uses the dam constructed in 1939 for the Laxá Power Plant I. The power plant experienced severe operational and abrasional problems due to ice and sediment transport. In 2016/17, the dam and intake were rebuilt to reduce the operational problems. During the problem analyzing phase, it became clear that the sediment transport is most likely highly linked to the ice slush transport, or more precisely, the resulting ice formations that increase sediment transport capacity considerably. This showed the importance of keeping the intake pond clear of ice formations. The new design features a new outer intake with ice skimming spillway above it and two small sediment traps at the bottom. This paper covers the design considerations for the ice skimming spillway, the velocity within the intake pond, the location of the ice skimming spillway, the formation of the design and areas chosen for supercritical flow. The design time was limited, and no physical model tests were carried out. The design relied on observation of photos and videos of ice transport at the site, as well as knowledge on ice behavior and information from various papers and experience from other sites on ice skimming. Due to this the paper also covers a comparison of the ice skimming facilities at Búrfell Power Plant (built 1969) and the new ice skimming spillway at Laxá Power Plant III (2017). The experience after the first two years in operation was good, even though the ice skimming did not always function due to ice accumulation upstream of the spillway. No operational problems due to ice and sediment around the intake area affected the power production during the first two winters. Some sand and stones still passed through the machinery but very little compared to before. The winter 2019-2020 was extreme in north Iceland, including conditions where the Laxá became porridge like due to ice slush. Such conditions were outside the design scope.
Year: 2020