Application of hydroacoustics and image velocimetry for determining short-term hydraulic changes associated with a dam removal at Hiitola River, Southeast Finland.
- Aalto University, School of Engineering, Department of Built Environment, Finland (kerstin.schlobies@aalto.fi)
A unique large-scale dam removal series with a combined drop height of 18 meters is conducted at Hiitola River, Southeast Finland during the years 2021–2023. Three dams used for power production are replaced by rapids reconnecting longitudinal flows. Here, we concentrate on the hydraulic impacts of the first, lowermost Kangaskoski dam removal site.
Flow features of a river under restoration vary seasonally as well as before and after each dam removal. The magnitude and seasonal variability of flows and the hydraulic capacity of the river to erode and transport the reservoir sediment are crucial in determining the rate of erosion, deposition, and river channel evolution. Thus, the hydrological conditions at Hiitola River upstream, downstream and in the reservoir section of the former Kangaskoski dam, were analyzed using hydroacoustic measurements by a moving-boat ADCP. We used consistent algorithms for quality checking, filtering, and interpolating from QRev software from USGS and automated steps for creating average transects, data post processing and visualization.
The spring and autumn surface flow properties of the 200 m long rapid section constructed in autumn 2021 were derived by using image-based velocimetry approaches from nadir UAV-video data sets. Thus, the following major processing steps were applied: video frame selection, image enhancement, frame stabilization, automatic 3D search area creation, image velocimetry, and statistical outlier filter based on flow characteristics.
The aims are to assess, 1) the spring and autumn variation in discharge, the flow field, and the fluvial forces in 2021 and 2022, and 2) the impact of the Kangaskoski dam and flow routing changes on the flow field and fluvial forces in the three different river zones before and after the removal. Identifying the immediate changes of hydraulics, sediment transport capacity and physical habitat conditions following the step-by-step dam removal and freeing of the Hiitola river may serve as criteria for future dam removal projects.
How to cite: Schlobies, K., Takala, T., Välimäki, J.-M., Pajunen, V. P., and Lotsari, E. S.: Application of hydroacoustics and image velocimetry for determining short-term hydraulic changes associated with a dam removal at Hiitola River, Southeast Finland., EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-3175, https://doi.org/10.5194/egusphere-egu23-3175, 2023.
