New Method for Automated Quantification of Vertical Spatio-Temporal Changes within Gully Cross-Sections Based on Very-High-Resolution Models

Abstract

Gully erosion is one of the most prominent natural denudation processes of the Mediterranean. It causes significant soil degradation and sediment yield. Most traditional field methods for measurement of erosion-induced spatio-temporal changes are time and labor consuming, while their accuracy and precision are highly influenced by various factors. The main research question of this study was how the measurement approach of traditional field sampling methods can be automated and upgraded, while satisfying the required measurement accuracy. The VERTICAL method was developed as a fully automated raster-based method for detection and quantification of vertical spatio-temporal changes within a large number of gully cross-sections (GCs). The developed method was tested on the example of gully Santiš, located at Pag Island, Croatia. Repeat unmanned aerial vehicle (UAV) photogrammetry was used, as a cost-effective and practical method for the creation of very-high-resolution (VHR) digital surface models (DSMs) of the chosen gully site. A repeat aerophotogrammetric system (RAPS) was successfully assembled and integrated into one functional operating system. RAPS was successfully applied for derivation of interval (the two-year research period) DSMs (1.9 cm/pix) of gully Santiš with the accuracy of ±5 cm. VERTICAL generated and measured 2379 GCs, along the 110 m long thalweg of gully Santiš, within which 749 052 height points were sampled in total. VERTICAL proved to be a fast and reliable method for automated detection and calculation of spatio-temporal changes in a large number of GCs, which solved some significant shortcomings of traditional field methods. The versatility and adaptability of VERTICAL allow its application for other, similar scientific purposes, where multitemporal accurate measurement of spatio-temporal changes in GCs is required (e.g., river material dynamics, ice mass dynamics, tufa sedimentation and erosion).

A New Systematic Framework for Optimization of Multi-Temporal Terrestrial LiDAR Surveys over Complex Gully Morphology

“…The developed framework was tested on a gully Santiš, located on the SE part of Pag Island, Croatia (Figure 1A,B). Pag Island is known for harsh climatic conditions and absence of vegetation cover that have led to the formation of numerous gullies and other erosional forms [42][43][44]. According to [44], more than 30% of the whole island is characterized by high susceptibility to gully erosion.…”

“…According to [44], more than 30% of the whole island is characterized by high susceptibility to gully erosion. Mean annual precipitation at Pag Island is 977.5 mm and mean air temperature is 15.5 • C, with pronounced seasonal heterogeneity, expressed through variations between very hot and dry summers and rainy springs and autumns [43].…”

“…The second sub-area (SA-2) covers the chosen part of the gully headcut (199.23 m 2 ), where the most intensive traces of headcut uphill regression were noted during the previous field research [43]. For this sub-area, two TLS surveys were conducted, which allowed for (a) validation of the performance of multi-temporal TLS surveys and (b) detection and quantification of spatio-temporal changes.…”

“…Gully Santiš was chosen as the perfect site for testing and validation of the developed framework, due to its complex morphology and rapid soil erosion induced STCs. Gully Santiš was formed predominantly by water erosion in Kalkocambisol soil sediments a few meters deep, which are surrounded and underlined by limestone and dolomite carbonate rocks [43]. The dominant erosion type within gully Santiš is rainfall induced erosion, which causes an annual gully headcut retreat up to 24.85 ± 5 cm year −1 [43].…”

A GIS-Based Spatial Analysis Model Approach for Identification of Optimal Hydrotechnical Solutions for Gully Erosion Stabilization. Case Study

“…The spatial analysis and simulation stage is conditioned by the quality and accuracy of the input databases within the spatial analysis and hydraulic calculation software for simulating the degree of evolution of the ravine. To complete this second stage, the HEC-RAS 5.07 software developed by the US Army Corps of Engineers was used to spatialize the necessary parameters (stream power, max depth, velocity, shear stress, WSE water surface elevation), to analyse stable and critical areas within the analysed ravine as well as for the simulation of the scenarios for different arrangement modes that aim at reducing the erosion within the ravine and, implicitly, its correct arrangement [40,41].…”