Hydraulic Modelling of a Regulated River Reach on Different Scales to Evaluate Its Inherent Environmental Conditions

Hydraulic modelling can be an important tool to assess ecological status of rivers and to evaluate where and how measures should be implemented to maximize their impact. This is becoming increasingly important in regulated rivers since hydropower's ability to balance intermittent electricity sources such as wind- and solar power is resulting in more frequent starts and stops of the power plants, which in turn is affecting the local environmental conditions. The resulting flow fields from the modelling can, for instance, be used to classify biologically important areas in rivers. Several relevant flow parameters can be predicted and applied, e.g depth and water velocities can be used to estimate habitat for specific fish species or the variation in water levels can be used to evaluate the risk of stranding for fish in different life stages. This work specifically involves numerical modelling of a heavily regulated reach in the Lule River in northern Sweden. Models are created in 1D, 2D and 3D to show strengths and weaknesses in the different modelling techniques. To ensure that the models capture reality, measurements of water levels and temperatures in the reach are performed using pressure/temperature loggers for validation purposes. River velocities are also measured with an Acoustic Doppler Current Profiler which are mainly used to validate the 3D model. The results derived using the different modelling methods are all shown to be useful depending on relevant application.