Adapting Ligga to higher design flood, spillway channel modification through physical & numerical modeling
2007 (English)Conference paper (Refereed)
As part of Vattenfall’s dam-safety program, Ligga dam is to be rebuilt for higher safety level. Besides diverse measures, the spillway channel will be modified. The channel is bounded by natural bedrock. Spillway operations during the past years have evidenced severe erosion and damages in the fractured rock. Rock instability becomes visible even at moderate spillway discharges 800 – 900 m3/s. The updated design-flood of the dam is in the order of the magnitude of 2000 m3/s. To adapt the dam to the higher flood, the spillway channel has to be re-shaped, so that the flood is safety released and the structural integrity of the embankment dam is maintained. As a cost-effective alternative, excavation is recommended, as a large volume of rock material is required for stabilizing the dam and for replacing the slope protection upstream. To achieve satisfactory flow behaviors, hydraulic model tests are made to examine and optimize excavation possibilities. The re-shaping of the waterway is complicated by the fact that the existing channel bends in plan and the excavation must follow roughly the same curvature. Considerations are also given to exemption of the dam toe from erosion and the forest on the left riverside from being flooded. Computer simulations of water-rock interaction are made with the commercial code UDEC. Against previous flood release records, the numerical model of rock erosion is calibrated and uses measured water level, flow velocity and dynamic water pressure in the model as input data. Results show that the new waterway configuration provides proper flow patterns and the rock foundation after reinforcement is not subjected to unacceptable damage at spillway discharges up to the design flood.
Place, publisher, year, edition, pages
Ligga dam, design flood, model tests, numerical modelling
IdentifiersURN: urn:nbn:se:kth:diva-179785OAI: oai:DiVA.org:kth-179785DiVA: diva2:889450
WaterPower XV, July 2007, Chattanooga, USA
QS 20162015-12-252015-12-252016-01-04Bibliographically approved