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Flow conditions downstream of Bergeforsen dam

Lidén, Erik LU (2012) VVR820 20121
Division of Water Resources Engineering
Abstract
Due to the change in climate the design flow for Bergeforsen dam, located at the Indalsälven river mouth, is being revised from 2300 m3/s to more than 3000 m3/s. The dam needs to be upgraded with a new gated spillway and repaired in order to increase the safety of the dam. Concerns have been raised about the altered flow conditions that will occur downstream of the dam in connection with that the new spillway is constructed and taken into service. These altered conditions could result in an increased risk for erosion of the channel bed as well as a compromise in the safety of the dam and the future operation of the hydropower facility. Therefore, a detailed analysis of the flow downstream of the dam was carried out using the numerical... (More)
Due to the change in climate the design flow for Bergeforsen dam, located at the Indalsälven river mouth, is being revised from 2300 m3/s to more than 3000 m3/s. The dam needs to be upgraded with a new gated spillway and repaired in order to increase the safety of the dam. Concerns have been raised about the altered flow conditions that will occur downstream of the dam in connection with that the new spillway is constructed and taken into service. These altered conditions could result in an increased risk for erosion of the channel bed as well as a compromise in the safety of the dam and the future operation of the hydropower facility. Therefore, a detailed analysis of the flow downstream of the dam was carried out using the numerical modeling program SMS. The velocities, water depths, bed shear stresses and critical particle diameters were simulated with the two-dimensional hydraulic model RMA2. This was done for eight different discharge combinations with flows from the existing and new spillway as well as from the power plant.
From the simulation results, it was concluded that the construction of the new spillway would lead to an increase in velocities, shear stresses and critical particle diameters. The increase was most pronounced in the vicinity of the spillways and the power station outlet. Although no clear information regarding the particle size distribution in the investigated area is available, the bed shear stress and critical particle diameter values in the different zones could be related to each other in order to get a feel for the relative erosion potential. They could also work as an indicator of what kind of erosion protection material that needs to be placed in that particular area in order to prevent future erosion. Topics for further investigations are whether the shallow areas about 200 meters downstream of the existing spillway are sufficiently protected against erosion and what the exact decrease in operational head for the power plant after the construction is.
Regarding the numerical model, the capabilities of RMA2 were not enough to completely reflect the flow conditions, especially in the area around the spillways. Even so, the general flow patterns and trends received from the simulations could function as a good complement to the future tests in the physical hydraulic model in the laboratory at Vattenfall Research and Development in Älvkarleby. (Less)
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author
Lidén, Erik LU
supervisor
organization
course
VVR820 20121
year
type
H3 - Professional qualifications (4 Years - )
subject
keywords
Bergeforsen, Indalsälven, spillway, dam safety, design flow, flow conditions, erosion, SMS, Surfacewater Modeling System, RMA2
report number
1101-9824
ISSN
1101-9824
language
English
id
2796869
date added to LUP
2012-06-19 10:52:14
date last changed
2012-06-19 10:52:14
@misc{2796869,
  abstract     = {Due to the change in climate the design flow for Bergeforsen dam, located at the Indalsälven river mouth, is being revised from 2300 m3/s to more than 3000 m3/s. The dam needs to be upgraded with a new gated spillway and repaired in order to increase the safety of the dam. Concerns have been raised about the altered flow conditions that will occur downstream of the dam in connection with that the new spillway is constructed and taken into service. These altered conditions could result in an increased risk for erosion of the channel bed as well as a compromise in the safety of the dam and the future operation of the hydropower facility. Therefore, a detailed analysis of the flow downstream of the dam was carried out using the numerical modeling program SMS. The velocities, water depths, bed shear stresses and critical particle diameters were simulated with the two-dimensional hydraulic model RMA2. This was done for eight different discharge combinations with flows from the existing and new spillway as well as from the power plant. 
From the simulation results, it was concluded that the construction of the new spillway would lead to an increase in velocities, shear stresses and critical particle diameters. The increase was most pronounced in the vicinity of the spillways and the power station outlet. Although no clear information regarding the particle size distribution in the investigated area is available, the bed shear stress and critical particle diameter values in the different zones could be related to each other in order to get a feel for the relative erosion potential. They could also work as an indicator of what kind of erosion protection material that needs to be placed in that particular area in order to prevent future erosion. Topics for further investigations are whether the shallow areas about 200 meters downstream of the existing spillway are sufficiently protected against erosion and what the exact decrease in operational head for the power plant after the construction is.
Regarding the numerical model, the capabilities of RMA2 were not enough to completely reflect the flow conditions, especially in the area around the spillways. Even so, the general flow patterns and trends received from the simulations could function as a good complement to the future tests in the physical hydraulic model in the laboratory at Vattenfall Research and Development in Älvkarleby.},
  author       = {Lidén, Erik},
  issn         = {1101-9824},
  keyword      = {Bergeforsen,Indalsälven,spillway,dam safety,design flow,flow conditions,erosion,SMS,Surfacewater Modeling System,RMA2},
  language     = {eng},
  note         = {Student Paper},
  title        = {Flow conditions downstream of Bergeforsen dam},
  year         = {2012},
}