Predicting the Hydraulic Influence of Hydropower Operations on Upstream Aquatic Habitat

• Author / Creator

  Langford, Mathew T

• The development of hydropower facilities greatly affects the morphology of regional water resources, as well as the physical, chemical and biological factors of upstream aquatic ecosystems. Evaluating the environmental impacts of hydropower operations is important in a regulatory context. Of particular interest is investigating fish entrainment risk, which has been identified as one of the key impacts of hydropower generation on the productivity and biodiversity of aquatic species. Entrainment results when fish of the upstream reservoir are passed through the turbines of a dam. The risk of fish entrainment at a particular facility is correlated with the effect of intake withdrawals on the flow and thermal structures of the forebay. Developing an understanding of the upstream hydraulics at hydropower dams is a key component of studying fish entrainment risk. Deep lakes and reservoirs in northern climates have a dimictic stratification cycle and generally thermal stratification develops in later summer and fall. Some reservoirs can be approximated by a distinct two-layer stratification profile, with a sharp temperature change at the thermocline; however this is not the case for all reservoirs. The shape of the thermal profile is controlled by solar insolation as well as surficial wind mixing, a lack of which may result in a less distinct hyperbolic thermal profile. The vertical density distribution of a stratified reservoir may limit the elevation at which water is withdrawn at hydropower facilities, known as selective withdrawal. When evaluating the physical impacts of hydropower generation on the upstream forebay (hydraulic and thermal characteristics), it is important to not only look at the direct impacts to fish, but also the impacts to the geometry of the forebay itself. The potential for sediments to deposit on the reservoir bed, or be entrained into the flow is a dynamic process that can lead to significant changes in reservoir bathymetry over time. The coarseness of the bed material also has an impact on fishes habitat use (i.e. fish fry commonly inhabit gravel beds). Determination of the wall shear stress induced by hydropower flows may dictate the bed form’s dynamics upstream of a facility, the anticipated substrate size and potential habitat utilization adjacent to the intake. The objectives of this thesis are to use numerical modelling to evaluate the impact of hydropower operations on erosion and sedimentation patterns, thermal structure and flow field upstream of hydropower facilities. This knowledge can then be applied in the context of evaluating fish entrainment risk. CFD models have been used to simulate the flow field in the forebay of Aberfeldie Dam on the Bull River, Mica Dam on the Columbia River and Revelstoke Dam on the Columbia River in British Columbia, Canada. These sites include both shallow and deep reservoirs as well as run-of-the-river and storage reservoirs. These models were verified through detailed hydroacoustic field measurements at both Aberfeldie and Mica Dams. This thesis outlines methodologies for completing CFD modelling as well as complex acoustic studies upstream of hydropower facilities. At Aberfeldie Dam, a large scour hole has been created due to increased velocities induced by the intakes. The CFD solver shows that flow-induced bed shear stress causes a seasonally fluctuating, dynamic bed form. The modelled velocity field has been used to evaluate the entrainment risk of mountain whitefish and westslope cutthroat trout based on swimming mechanics and life stage. CFD modelling proves to be a promising tool for evaluating fish entrainment risk and the effectiveness of potential mitigation measures and management options. The Mica Dam CFD model evaluated the upstream hydraulics under varying discharges and reservoir levels. The results highlight how intake selection may suppress vortex formation and limit the size of the entrainment risk zone. A potential flow solution was applied to predict the velocity field induced by Mica Dam. Despite the simplicity of the solution the velocities compared well with the more complex CFD model, even with rotational flows. At Mica and Revelstoke Dams, the thermal profile has distinct impacts on the upstream flow field. The inclusion of thermal stratification greatly increases the entrainment risk volume for smaller fish, while having negligible impacts on the risk zone for larger fish. Additionally it was found that CFD modelling is effective at predicting the impact of forebay stratification on discharge temperature.

• Subjects / Keywords

  • Erosion and Sedimentation
  • Hydropower
  • Fish Entrainment
  • Thermal Stratification
  • Hydraulic Engineering
  • Computational Fluid Dynamics

• Graduation date

  Spring 2016

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3319S98Z

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.