Terrestrial Laser Scanning for the Detection of Coarse Grain Size Movement in a Mountain Riverbed

Abstract

Fluvial transport is a natural process that shapes riverbeds and the surrounding terrain surface, particularly in mountainous areas. Since the traditional techniques used for fluvial transport investigation provide only limited information about the bed load transport, recently, laser scanning technology has been increasingly incorporated into research to investigate this issue in depth. In this study, a terrestrial laser scanning technique was used to investigate the transport of individual boulders. The measurements were carried out annually from 2011 to 2016 on the Łomniczka River, which is a medium-sized mountain stream. The main goal of this research was to detect and determine displacements of the biggest particles in the mountain riverbed. The methodology was divided into two steps. First, the change zones were detected using two strategies. The first strategy was based on differential digital elevation model (DEM) creation and the second involved the calculation of differences between point clouds instead of DEMs. The experiments show that the second strategy was more efficient. In the second step, the displacements of the boulders were determined based on the detected areas of change. Using the proposed methodology, displacements for individual stones in each year were determined. Most of the changes took place in 2012-2014, which correlates well with the hydrological observations. During the six-year period, movements of individual particles with diameters less than 0.8 m were observed. Maximal displacements in the observed period reached 3 m. Therefore, it is possible to determine both vertical and horizontal displacement in the riverbed using multitemporal TLS.

Automatic Segmentation of Individual Grains From a Terrestrial Laser Scanning Point Cloud of a Mountain River Bed

“…Another alternative technique is terrestrial photogrammetry. However, it provides less accurate description of the grain geometry than laser scanning [8], which also agrees with a statement by Schwendel and Milan [25] that "river reaches with high spatial heterogeneity are challenging for Structure from Motion processing". This may lead to improper identification of corresponding grains during further analyzes.…”

“…This may lead to improper identification of corresponding grains during further analyzes. A detailed discussion on alternative measurement techniques and their usefulness for river bed mapping is provided in Walicka et al [8].…”

“…Delineating one small point cloud per particles offers the possibility to monitor sediment transport on the level of individual grains, as suggested in [8]. It requires multiple measurement campaigns and a method to match point clouds of (moved) grains between epochs [7].…”

“…Whereas during the spring, high water flows occur that cause intensified displacement of the grains. A detailed description of the test site is provided in Walicka et al [8].…”

Reconstruction of River Topography for 3D Hydrodynamic Modelling Using Surveyed Cross-Sections: An Improved Algorithm

“…Airborne interferometric radar and its data products, such as Shuttle Radar Topography Mission (SRTM) 1 arc-second global DEM [8], have been widely used to represent large scale dry areas, while light detection and ranging (LiDAR) nowadays is often used to generate topographic maps with higher resolution [9]. For example, aerial laser scanning (ALS) and terrestrial laser scanning (TLS) were used to generate DEMs for geomorphology studies of river systems [10,11]. Unfortunately, both aforementioned techniques are unable to measure the submerged riverbed (channel zone) topography because radar signals cannot penetrate the water surface and the latter still has limitations in bathymetry applications [12][13][14].…”