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Långbjörn dam - adaptation for safe discharge of extreme floods
Vattenfall R&D.
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2007 (English)Conference paper (Refereed)
Abstract [en]

Långbjörn is a 33 m high embankment dam; its updated design flood is 30% higher than the existing spillway capacity. Based on dam-safety evaluations, several measures are now implemented in order to rebuild the dam according to the updated dam-safety guidelines. The design flood is accommodated by allowing a temporary rise of the water level by 1,3 m above the legal retention reservoir level, which requires heightening and reinforcement of the dam. The large increase in the flood magnitude calls also for examinations of the energy dissipation and flow pattern in the river downstream. The impervious core and dam crest of the dam are heightened to account for the higher reservoir level during extreme floods. To increase stability, new drainage system is added to the existing one, and increased instrumentation of seepage water, slope movement and groundwater stage downstream is suggested. Stability analysis is made for the spillway, which is to be reinforced with e.g. pre-stressed anchors in the dam foundation to increase its stability. The stilling basin with baffle blocks needs repair and reinforcement to safely discharge the higher flood. Extension of he left wall may be necessary to protect the left embankment dam from erosion. Part of the rebuilding measures depends to great extent on how the flow behaves during extreme floods. Hydraulic model tests are therefore made to investigate the energy dissipation and flow pattern downstream. Experiments are made in both fixed and movable bed. Model testing proves to be helpful in the decision making of the dam rebuilding and leads to cost-effective engineering measures.

Place, publisher, year, edition, pages
Keyword [en]
Långbjörn, design flood, spillway, dam rebuilding
National Category
Civil Engineering
Research subject
Civil and Architectural Engineering
URN: urn:nbn:se:kth:diva-179784OAI: diva2:889449
Canadian Dam Association 2007 Annual Conference, Sept 2007, St. John’s, Canada

Qc 20160107

Available from: 2015-12-25 Created: 2015-12-25 Last updated: 2016-01-07Bibliographically approved

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Yang, James
Civil Engineering

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