Measuring seasonal bedload transport rates in a sub-arctic river using image processing techniques

Accurately predicting, modelling and measuring bedload transport rate remains a challenge even after a century of research and various approaches. Traditionally measurements of bedload transport rate in field setting have been done with labor-intensive and difficult to use mechanical equipment such as bedload samplers or traps. Mechanical devices are often intrusive, meaning that the devices’ presence can influence the shape of riverbed and the measured bedload transport rate during the measurement. These devices are also limited in their capability to capture the spatial and temporal fluctuations of bedload transport and only describe dimensionless mean transport rate from a point or a section. Image processing techniques such as particle image velocimetry and optical flow combined with background subtraction and image labeling methods enable continuous, non-intrusive two-dimensional bedload velocity and bedload transport rate measurements over large areas. These image processing techniques have been previously successfully applied in lab conditions to measure bedload transport rates from video data sets but not in field conditions.

The focus of this study is 1) to apply image processing techniques to underwater video data sets to measure seasonal bedload transport rates in various sediment transport conditions and 2) to understand and compare the seasonal variation in bedload transport measured with image processing techniques and traditional mechanical measurements.

To cover various sediment transport conditions, the study is based on field data collected over various years (2021-2024), seasons (winter, spring, autumn), and flow conditions (open channel and ice-covered) at sub-arctic Pulmanki river, which is in northern Finland (~70°N latitude) and drains to the Arctic Sea. The novel results are presented and show that the method is promising in enhancing the understanding of sediment transport processes and the seasonal transported amounts in sub-arctic river conditions.