Setting Up an Infinite Slope Stability Analysis on a High-Resolution DEM (0.21 × 0.21 m2) of a Mechanically Terraced Slope in Cyprus

For centuries, the landscape of Mediterranean mountains has been shaped by the construction of terraces often supported by dry-stone walls, to allow farming activities. Nowadays, traditional dry-stone wall terraces are often replaced or combined with mechanically constructed terraces. Compared to dry-stone terraces, these behave differently regarding water retention, soil erosion and slope stability. The aims of this study are (i) to characterize a mechanically terraced slope (0.1 km2) partially protected by dry-stone walls and (ii) to set up a high-resolution stability analysis to verify its capabilities in predicting instabilities. The study site is located in the Troodos Mountains (Cyprus). Field observations were made between October 2021 and April 2022. Measurements of depth, hydraulic conductivity and bulk density, as well as the collection of samples for texture analyses, were performed for the physical characterization of soils. The study site was visited after several storms to map areas affected by instabilities. Rainfall was measured by a local meteorological station. A photogrammetric survey was made with a GoPro9 camera mounted on an unmanned aerial vehicle developed by the Unmanned System Research Laboratory of The Cyprus Institute both in firmware and software. The collected data were used as input into FSLAM, an open-source model that couples a simplified hydrologic model with an infinite slope stability analysis. The soil was a loamy sand, with a depth ranging between 0.30 and 0.80 m, an average bulk density of 1.70 g/cm3 and a hydraulic conductivity of 2.05 × 10–3 m/s. From the UAV flights, a DEM with a horizontal resolution of 0.035 m was produced. However, for modelling purposes the DEM was resampled at 0.21 m, to reduce calculation times and avoid high depth-to-length ratios at the single cell (infinite slope assumption). Preliminary results from multiple runs showed that the model responds reasonably well to flow accumulation and variations in soil depth. The model predicts higher instabilities for wetter deep soils. However, at this resolution it was not able to identify specific locations of failure. To improve the model output, FSLAM could be integrated with a routine able to process variable soil depths (now constant within soil units) and to route surface runoff.