Determination of River Hydromorphological Features in Low-Land Rivers from Aerial Imagery and Direct Measurements Using Machine Learning Algorithms

Abstract

Hydromorphology of rivers assessed through direct measurements is a time-consuming and relatively expensive procedure. The rapid development of unmanned aerial vehicles and machine learning (ML) technologies enables the usage of aerial images to determine hydromorphological units (HMUs) automatically. The application of various direct and indirect data sources and their combinations for the determination of river HMUs from aerial images was the main aim of this research. Aerial images with and without the Sobel filter, a layer of boulders identified using Yolov5x6, and a layer of direct measurements of depth and streamflow velocity were used as data sources. Three ML models were constructed for the cases if one, two, or three data sources were used. The ML models for HMU segmentation were constructed of MobileNetV2 pre-trained on ImageNet data for the feature extraction part and U-net for the segmentation part. The stratified K-fold cross-validation with five folds was carried out to evaluate the performance of the model due to the limited dataset. The analysis of the ML results showed that the measured metrics of segmentation using direct measurements were close to the ones of the model trained only on the combination of boulder layer and aerial images with the Sobel filter. The obtained results demonstrated the potential of the applied approach for the determination of HMUs only from the aerial images, and provided a basis for further development to increase its accuracy.

The impact of the geographical environment on the hydromorphological conditions of watercourses in southern Poland

“…In the case of lowland rivers, a dominance of laminar flow is observed and this in turn translates into habitats for macrophytes and macroinvertebrates (Guareschi et al 2014, Kujanová et al 2018, Vilenica et al 2022). The selected river sections were therefore characterised by a relatively high diversity and abundance of hydromorphological units compared to the other sections (Akstinas et al 2022).…”

“…River hydromorphology assessed by direct measurement is a time-consuming and costly procedure, yet the most accurate one (Akstinas et al 2022). There are multiple methods for hydromorphological assessment.…”