Coarse sediment grain size variability along gravel-bed rivers via automatic grain size detection (a case study of the Ondava River, Slovakia)

Grain size analysis is the key to understanding the hydraulics and sedimentological properties of river channels. The recent development of new technologies enables the integration of automatic methods for noninvasive monitoring of river channels and river system properties. In this study, the application of photosieving for detecting grain size distribution (GSD) was assessed on the gravel bar of the Ondava River in the Carpathians. The spatiotemporal evolution of gravel bars, as basic sedimentation units of rivers. The photosieving method a combination of BASEGRAIN and Pebble count software revealed that the grain size distribution D50 ranged from 33.1 mm to 76.9 mm and from 31.4 mm to 59.1 mm, respectively. The results were validated via traditional sieving methods. BASEGRAIN demonstrates superior alignment with lab-sieving results, particularly for finer sediment fractions, and is suitable for sediment analyses in environments with a mix of fine to medium grain sizes. In contrast, PebbleCountsAuto is notable for areas with coarse sediment distributions. Automated methods reduce the subjectivity and efforts involved in traditional techniques but require improvement to match the precision and reliability of manual approaches.