Abstract
Abstract. The "Wild Moselle" regional nature reserve extends over 13 km at the western foothills of the Vosges Mountains (France). The hydrological regime of the river is characterized by high flow in winter and spring and low flow in summer. Its average slope is 0.12 % and its average bankfull width is 60 m. The coarse sediment load comes mainly from bank erosion. Although this sector is relatively less affected by past or present human activities, the propagation of morphodynamic adjustments initiated by actions carried out both upstream and downstream of this sector impacts the current functioning of the river. These erosion waves converge today towards the central part of the reserve, which led to the collapse of the central pier of the Bainville-aux-Miroirs bridge during a 2-year flood in 2011, and could induce potential risks of defluviation which may destabilize infrastructures. In this context, the study carried out aims to characterize and anticipate the morphodynamic evolutions of the Moselle to be able to propose scenarios of management and restoration of the lateral mobility of the river. For this purpose, a 2D hydro-sedimentary model is being built over the entire reserve, combined with a detailed morpho-sedimentary monitoring. In order to improve the understanding of the lateral migration of the Moselle River, a photogrammetric monitoring was carried out along the concave bank of the most active meander of the studied sector. To follow this morphological evolution more closely, it was decided to establish a 4D GIS. The objective of this monitoring is to compare the rate of bank retreat with hydrodynamic parameters in order to estimate the geotechnical properties of the bank. Comparison of the observed and modelled bank retreat must thus allow these different parameters to be calibrated in the hydro-sedimentary model. As part of this work, this paper aims to highlight the use of 4D GIS to monitor bank retreat at the scale of a meander bend and is divided into three different parts: (i) a state of art to situate the study into the current knowledge and technologies, (ii) a presentation of the study area and the measurements carried out and (iii) a description of the different 3D or 4D data produced and the consequent spatial analyses.
Highlights
Data management and representation have made great progress last decades notably in moving from 2D to 3D and integrating time
Pfeifer (2007) defines terrestrial laser scanning as a data acquisition technique using laser light to directly measure, in a regular frame, the coordinates of 3D points on surfaces at an Earth position
Laser-scanning of an area using a laser scanner, whether terrestrial or aerial, provides 3D point clouds of the entire area with a configurable point density depending on the equipment and the recording conditions
Summary
Data management and representation have made great progress last decades notably in moving from 2D to 3D and integrating time. Photogrammetry has become a widely used technique even for local scale mapping applications This technique allows the user to obtain 3D data from an area of interest. Photogrammetry by UAV is interesting in sites requiring rapid intervention, including the case of inspection and monitoring (Murtiyoso et al, 2017) (Jaud et al, 2014) It is possible, from images with well-defined overlapping areas, to determine the relief and contours of an object or territory in the form of point clouds obtained from dense matching techniques. By comparison with a reference model, topographic and/or height changes can be quantified and represented This was used to evaluate the accuracy of digital surface model (DSM) of river-channel morphology derived from. This paper is divided into three parts which: (i) describe steps from photogrammetric monitoring to point of clouds construction, (ii) present a method to extract bank profiles and (iii) show how to integrate photogrammetric data into a GIS including other topo-bathymetric data
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