Understanding the evolution of sediment connectivity associated with different land use and topographic changes is a prerequisite for a better understanding of sediment budgets and sediment transport ...processes. We used the Index of Sediment Connectivity (IC) developed by Cavalli et al. (2013) based on the original approach by Borselli et al. (2008) to study the effects of decadal-scale land use and topographic changes on sediment connectivity in mountain catchments. The input variables of the IC (i.e. land cover and topography) were derived from historical aerial photos using Structure from Motion-Multi View Stereo algorithms (SfM-MVS). The method was applied in different sub-catchments of the Upper River Cinca Catchment (Central Pyrenees), representative of three scenarios: (a) Land cover changes; (b) Topographic changes in agricultural fields (terracing); and (c) Topographic changes associated with infrastructure (road construction). In terms of land cover changes, results show that although connectivity is increased in some areas due to the establishment of new field crops, for most of the study area connectivity decreased due to afforestation caused by rural abandonment. Topographic changes due to the establishment of agricultural terraces affected connectivity to a larger degree than land cover changes. Terracing generally reduced connectivity due to the formation of flat areas in step-slopes, but in certain points, an increase in connectivity caused by the topographic convergence produced by terraces was observed. Finally, topographic changes associated with road construction greatly modified surface flow directions and the drainage network, resulting in changes in connectivity that may affect erosional processes nearby. The methodology used in this paper allows to study the effects of real decadal-scale land use and topographic changes on sediment connectivity and also evaluating and disentangling those changes. Furthermore, this approach can be a useful tool to identify potential risks associated with morphological and land use changes, involving road infrastructures.
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•Land cover changes have a direct effect on sediment connectivity.•Changes caused by terraces are inferred from the recreation of the terrain without these structures.•Terraces had a larger impact on sediment connectivity than land use change.•The Index of Connectivity is a useful tool to map hot spots in areas where roads are constructed.•Changes on historical sediment connectivity may help understanding catchment-scale sediment supply dynamics.
Coastal dunes result from complex interactions between sand transport, topography and vegetation. However, uncertainty still persists due to limited quantitative analyses, integrating plant ...distribution and morphologic changes. This study aims to assess the initiation and maintenance of feedback processes by analysing the early development stages of incipient foredunes, combining data on the evolution of the plant cover and communities and dune morphology. Over three years, the monitoring of a newly formed dune (1 ha plot) reveals the progressive plant colonisation and the episodic accumulation of sand around vegetated areas controlled by sediment availability. Distinct colonisation rates were observed, influenced by inherited marine conditions, namely topography and presence of beach wrack. Berm-ridges provided elevations above the critical threshold for plant colonisation and surface roughness, aiding sediment accumulation. Beach wrack above this threshold led to rapid expansion and higher plant concentration. In the initial stages, vegetation cover significantly influenced sediment accumulation patterns, with higher accumulation around areas with high plant cover and low slopes or around areas with sparse vegetation but milder slopes. As the dune system matured and complexity grew, the link between vegetation cover and accumulation became nonlinear. Mid to low coverages (5–30 %) retained most of the observed accumulation, especially when coupled with steep slopes, resulting from positive feedbacks between vegetation, topography and sand transport. As foredune developed, vegetation cover and diversity increased while inherited morphologies grew vertically, explaining the emergence of dune ridge morphological types. Flat surfaces lacking wrack materials experienced a three-year delay in colonisation and sand accumulation, leading to the formation of terrace-type incipient foredunes. These observations underline feedback processes during the early stages of dune formation, with physical feedbacks primarily driving initiation and biophysical feedbacks prevailing in subsequent colonisation stages.
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•Natural foredune initiation documented by high-resolution topographic and plant surveys•Marine processes provide the conditions for foredune initiation.•Two morphological types (ridge and terrace) linked to plant colonisation strategies•Sand accumulation is controlled by physical factors during dune initiation.•Biophysical feedbacks control sand accumulation during early development stages.
The frequency and intensity of heavy rainfall on the Chinese Loess Plateau (CLP) are increasing due to global climate change, which has caused severe soil erosion. However, precise evaluation of ...heavy rainfall-induced soil erosion, deposition, and related topographical changes at the catchment scale is lacking, and there is uncertainty as to how effectively trees can inhibit erosion, especially during heavy rainfall. In this study, we selected a pair of catchments with afforestation and natural grassland restoration on the CLP. Precise evaluation of erosion and topographic changes induced by heavy rainfall was conducted based on airborne light detection and ranging (LiDAR) data. In the grassland catchment, the gully bed area increased by 17.6 %, the gully slope and inter-gully land area decreased by 1.4 %, and the length of the gully shoulder line decreased by 4.4 %. Conversely, the forestland catchment experienced a decrease in gully bed area of 8.8 %, an increase in gully slope area of 5.3 %, a decrease in inter-gully land area of 9.9 %, and a decrease in the length of the gully shoulder line of 11.4 %. Following heavy rainfall, both catchments experienced a substantial increase in terrain relief. Soil erosion in the gully slope accounted for >90 % of the total erosion in both catchments, while deposition in the same area contributed to >75 % of the total deposition. The grassland catchment experienced a unit area erosion of 233,908 m3 km−2, which was 4.7 times greater than that of the forestland catchment (49,768 m3 km−2). In both catchments, erosion predominantly transpired in the steep slope region adjacent to the gully shoulder line, accounting for >15 % of the gully slope erosion area. The grassland catchment exhibited a continuous distribution pattern of erosion and deposition, whereas the forestland catchment exhibited a scattered and intertwined distribution pattern. This study is essential for further research on erosion and topographic changes induced by extreme weather events and to determine appropriate measures.
•Rainstorm erosion was observed on the Loess Plateau;•Compared to the grassland catchment, the forestland catchment substantially reduced unit area erosion;•The terrain relief increased after rainstorm erosion in both catchments;•Grassland and forestland catchments showed different patterns of erosion and deposition;•Both catchments experienced different changes in gully landform evolution.
The estimation of the volume of volcanic flows during an ongoing eruption is challenging but this information is crucial for improving risk assessment and for forecasting future events. Although ...previous studies have shown the ability of TanDEM-X satellite data to derive the thickness and the volume of lava flow fields during effusive eruptions, the method has not been explored yet for pyroclastic flows. Using bi-static interferometry, we produce TanDEM-X DEM on Fuego volcano (Guatemala) to measure the significant topographic changes caused by the 3rd June 2018 eruption, which destroyed the town of San Miguel Los Lotes. We estimate the volume of the Pyroclastic Density Currents (PDCs) to be 15.1 ± 4.2 × 106 m3. The deposits are likely to be the source of lahars during future rainy seasons. We identify the main channel of deposition (positive elevation changes) and the source region of pyroclastic material, areas of significant substrate erosion, and vegetation destruction (negative elevation changes). Our results show that the June 3rd 2018 pyroclastic flow was predominantly composed of material which had gravitationally collapsed from a location close to the vent. The eroded material increased the volume of the flow (bulking) and likely caused the run-out distance of the 2018 PDC to be larger than previous eruptions (1999–2017). This study highlights the potential of remote sensing techniques for actively monitoring topography changes in inaccessible locations and to rapidly derive deposit volumes.
•Our study shows the benefit of TanDEM-X high-resolution DEMs for deriving the thickness and the volume of Pyroclastic Density Currents (PDCs) emplaced during the 2018 deadly eruption of Fuego volcano (Guatemala).•In addition to Sentinel-2 optical imagery used for mapping the PDCs facies, the TanDEM-X DEMs difference provides the spatial distribution of positive and negative topographic changes associated with the flow emplacement.•During the 2018 eruption, most of the PDC material originated from bulking and erosion processes occurring at the upper slopes of the volcano, which increases the volume and more importantly the mobility of the flow, as deposits reached up to 12 km from the summit.•Our study points out the importance of the monitoring of mass accumulation/collapse at the summit of steep-sided stratovolcanoes using remote sensing techniques, as it contributes to improve the assessment and the mitigation of hazards related to PDCs and lahars.
•UAV surveys can be used for evaluating long-term hillslope morphology evolution.•Successive landslides influence frequency distributions of topographic features.•Successive landslides gradually ...reduce slope gradient, roughness and local relief.•The slope gradient changes with elevation.
Landslides are recognized as dominant geomorphic events of morphological evolution in most mountainous and hilly landscapes. However, the lack of multitemporal high-resolution topographic data has resulted in a lack of quantitative estimates of topographic changes influenced by successive landslides. Taking a typical hillslope with successive loess landslides in the Heifangtai loess tableland, China, as an example, we conducted four unmanned aerial system (UAS) surveys and created corresponding high-resolution digital elevation models (HRDEMs) and orthophotos. We found that multitemporal UAS surveys have become a powerful new approach for addressing local topographic changes and evolution over a relatively long time series. Moreover, landslides can leave persistent geomorphic imprints on hillslope topography. The frequency distributions of topographic indexes are significantly influenced by successive landslides. The mean slope gradient, roughness and local relief decreased with successive landslide occurrences, whereas the mean topographic wetness index (TWI) increased. However, the mean slope aspect was almost unchanged by successive landslides. Furthermore, analysis of the coefficient of variation demonstrates that the frequency distribution of the slope gradient becomes more dispersed with landslide occurrences, while the slope aspect and TWI become more concentrated. The slope gradient changes with elevation. More broadly, this study provides new insights into the prediction of the local topographic feature changes and morphology evolution trends caused by successive landslides.
Morphologic and topographic changes of tidal flats can be key indicators for monitoring environmental changes and sea level rise. Recently, a number of studies have been performed to estimate ...temporal topographic changes in tidal flats based on the waterline method using a number of remote sensing data that were acquired at different tidal heights. However, the effect of seasonal variation has not been taken into consideration, nor been understood so far. In this study, 18 scenes of Landsat TM and ETM+ data, covering the period 2003–2004, and corresponding tidal gauge observation data, were used to estimate seasonal topographic variations in two major tidal flats in Gomso and Hampyeong Bay in the southern part of the west sea of South Korea, using the waterline method. Our results showed that the summer deposition was dominant in Gomso Bay with overall average seasonal topographic increase of approximately 18.6 cm. In contrast, Hampyeong Bay showed more dominant summer erosion with overall average seasonal topographic subsidence of about 5.0 cm. In addition, the net overall sedimentation budget was estimated as 6,308,047 m3 and -2,210,986 m3 in Gomso and Hampyeong Bay, respectively. The results also indicates that although both bays of Gomso and Hampyeong are classified as semi-enclosed tidal flat, the sedimentary facies caused by formation geometry and sediment type led to different topographic changes. The results demonstrate that the amount of seasonal topographic variations is not negligible and are expected to improve the accuracy of topographic change derived by the waterline method.
A multi-temporal LiDAR study of an active landslide at Montaguto (Italy) is presented. Four LiDAR-derived Digital Terrain Models acquired on May 2006, July 2009, April 2010 and June 2010 are used. ...The interpretation of selected morphometric parameters (surface roughness, residual topographic surface) and the statistical analysis of the temporal variations of such parameters allowed the reconstruction and tracking of the landslide. The landslide boundary monitoring was achieved and zones of uplift and subsidence, volumes of removed and/or accumulated material, and average rates of vertical and horizontal displacement (retreat rate of the crown and advancement rate of the toe) were estimated. Deformation structures (scarps, cracks, folds) affecting the landslide in different times were also mapped; some of such structures represent precursors of impending instability processes or give information on the mechanism of emplacement. Various types of activity (e.g. rock-fall, flow) and geometry (e.g., channelized flow) are recognized and zones whose topographic features change with time due to artificial drainage and earth handling/removal work were detected. The LiDAR-derived information allows us to decipher the kinematics of the landslide. The results provide new insight on the use of airborne LiDAR in the monitoring strategies of gravity-controlled processes.
► Multi-temporal Lidar data allow us to track the evolution of a landslide. ► We examine topographic changes and provide estimates of volume changes and velocity. ► We decipher the kinematics of the landslide using morphometric parameters. ► The results provide new insight on the monitoring of gravity processes.
On September 14, 2019, a reactivated landslide with a volume of 1.3 × 10
7
m
3
occurred in Changhe Town, Tongwei County, Gansu Province, China. As a result, a provincial highway, brickfield, and ...bridge were destroyed. Based on field investigation, interferometric synthetic aperture radar (InSAR) as well as unmanned aerial vehicle (UAV) photogrammetry, high-resolution remote sensing imagery, and digital elevation model, we addressed the surface displacement, travel distance, topographic changes, and causative factors of the Changhe landslide. The result shows the combination of ascending and descending orbit datasets can not only be used to monitor the landslide surface displacement but also to verify the deformation results. This landslide is a typical retrogressive landslide where large pre-failure deformation exists in the lower part of the landslide body. We detected the surface travel distance of the landslide and found spatial differences exist in the surface travel distance of the landslide. The deposit volume slightly exceeds erosion volume due to decompaction during the landslide. The frequency distribution of the basic topographic factors before and after the landslide is different, which indicates that the landslide event significantly changed the local topography and geomorphology. This study provides an insight into the spatiotemporal evolution of the landslide and has practical importance for early warning of landslides and risk mitigation.
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