1,721,014 research outputs found
Analysis of topographic and climatic control on rainfall-triggered shallow landsliding using a quasi-dynamic wetness index
No full textA model for the prediction of both topographic and climatic control on shallow landslide initiation processes in hilly mountainous terrain is proposed. The model develops upon a theory for coupled shallow subsurface flow and landsliding of the soil mantle previously proposed by Montgomery and Dietrich [Water Resour. Res. 30 (1994) 1153]. The model uses a 'quasi-dynamic' wetness index to predict the spatial distribution of soil saturation in response to a rainfall of specified duration. The rainfall predicted to cause instability in each topographic element is characterised by duration and frequency of occurrence. The incorporation of a rainfall frequency-duration relationship into assessment of landslide hazard provides a practical way to include climate information into estimation of the relative potential for shallow landsliding. The model is applied to a mountain experimental basin where high-resolution digital elevation data are available: the Cordon catchment (5 km2), in north-eas..
Snowmelt modelling by combining air temperature and a distributed radiation index
No full textHigh spatial variability in snowmelt phenomena was observed in the experimental watershed of the upper Cordevole (7 km2), in the Dolomites. Snowmelt depends, at a point scale, on available energy, which in turn is heavily affected by slope, aspect and shading effects of the site. A distributed hourly model of snowmelt was set up as a geographical information system (GIS) module. The model accumulates snowfall for each raster element (20 m x 20 m) using a tem- perature threshold. It simulates snowmelt using air temperature and a radiation index consist- ing of daily average values of clear sky radiation that have cumulated at selected dates since 21 December. It should be underlined that the only relevant calibration parameter of the model is the combined snowmelt factor, which is unique for the whole basin. The clear sky radiation maps were computed for a selected period of the year, based on the watershed digital terrain model and the solar path sampled at very short intervals. When run for a season, the model produces snow water equivalent maps at given dates. The model was validated, with satisfac- tory results, by comparing these maps with 60 snow covered area surveys and related water equivalent measures collected in six snowmelt seasons from 1986 to 1991. The classical tem- perature index approach to snowmelt modelling does not allow the full variability over the basin to be taken into account. Besides, it seems important to point out that this fully dis- tributed approach allows us to avoid the use of snow covered area (SCA) depletion curves, the definition of which still proves a troublesome task
Automatic measurement of glacier ice ablation using thermistor strings
Full text linkIn this work we tested the suitability of thermistor strings as automatic tools for the continuous
measurement of glacier ice ablation. Experimental data collected in summer 2017 over an Italian
glacier provided ice ablation readings with accuracy similar to manual measurements with ablation
stakes and other automatic systems, like the draw-wire method and the Bøggild ablatometer.
Thermistor strings have potential for future applications in remote glacier monitoring, thanks to their
flexibility, simple construction, and robustness
4D-SFM photogrammetry for monitoring sediment dynamics in a debris-flow catchment: Software testing and results comparison
Full text linkIn recent years, the combination of Structure-from-Motion (SfM) algorithms and UAV-based aerial images has revolutionised 3D topographic surveys for natural environment monitoring, offering low-cost, fast and high quality data acquisition and processing. A continuous monitoring of the morphological changes through multi-temporal (4D) SfM surveys allows, e.g., to analyse the torrent dynamic also in complex topography environment like debris-flow catchments, provided that appropriate tools and procedures are employed in the data processing steps. In this work we test two different software packages (3DF Zephyr Aerial and Agisoft Photoscan) on a dataset composed of both UAV and terrestrial images acquired on a debris-flow reach (Moscardo torrent - North-eastern Italian Alps). Unlike other papers in the literature, we evaluate the results not only on the raw point clouds generated by the Structure-from-Motion and Multi-View Stereo algorithms, but also on the Digital Terrain Models (DTMs) created after post-processing. Outcomes show differences between the DTMs that can be considered irrelevant for the geomorphological phenomena under analysis. This study confirms that SfM photogrammetry can be a valuable tool for monitoring sediment dynamics, but accurate point cloud post-processing is required to reliably localize geomorphological changes
Evaluating the influence of forest roads on shallow landsliding
No full textThis study investigates how subsurface flowpaths are altered by forest roads and how these changes influence shallow landslid- ing susceptibility in steep, forested landscape. A simple conceptual model of the effect of forest roads on hillslope subsurface flow is developed. The model is incorporated into a hydro-geomechanical, threshold-based model for slope instability. In the model, the occurrence of shallow landsliding is evaluated in terms of drainage areas, ground slope and soil properties (i.e., hydraulic conductivity, bulk density, and friction angle). Model results allow to quantify the influence of roads on shallow landsliding hazard across a landscape and to generate hypotheses about the broader geomorphic effect of roads.
Modelling results are compared with field data collected in four sites located in north-eastern Italy. Observed landslide patterns are broadly consistent with model estimates, a finding that underscores the utility of this simple approach for predicting the geomorphic effects of forest roads constructed on steep slopes. The approach used in this study may be useful for defining criteria for road design that reduce the effects of roads on geomorphic processes
Automatic recognition of road and pathway induced slope instabilities by high resolution topography
No full textDownstream hydraulic geometry relationships: Gathering reference reach-scale width values from LiDAR
No full textThis paper examines the ability of LiDAR topography to provide reach-scale width values for the analysis of downstream hydraulic geometry relationships along some streams in the Dolomites (northern Italy). Multiple reach-scale dimensions can provide representative geometries and statistics characterising the longitudinal variability in the channel, improving the understanding of geomorphic processes across networks. Starting from the minimum curvature derived from a LiDAR DTM, the proposed algorithm uses a statistical approach for the identification of the scale of analysis, and for the automatic characterisation of reach-scale bankfull widths. The downstream adjustment in channel morphology is then related to flow parameters (drainage area and stream power). With the correct planning of a LiDAR survey, uncertainties in the procedure are principally due to the resolution of the DTM. The outputs are in general comparable in quality to field survey measurements, and the procedure allows the quick comparison among different watersheds. The proposed automatic approach could improve knowledge about river systems with highly variable widths, and about systems in areas covered by vegetation or inaccessible to field surveys. With proven effectiveness, this research could offer an interesting starting point for the analysis of differences between watersheds, and to improve knowledge about downstream channel adjustment in relation, for example, to scale and landscape forcing (e.g. sediment transport, tectonics, lithology, climate, geomorphology, and anthropic pressure)
4D-SFM PHOTOGRAMMETRY FOR MONITORING SEDIMENT DYNAMICS IN A DEBRIS-FLOW CATCHMENT: SOFTWARE TESTING AND RESULTS COMPARISON
Full text linkIn recent years, the combination of Structure-from-Motion (SfM) algorithms and UAV-based aerial images has revolutionised 3D topographic surveys for natural environment monitoring, offering low-cost, fast and high quality data acquisition and processing. A continuous monitoring of the morphological changes through multi-temporal (4D) SfM surveys allows, e.g., to analyse the torrent dynamic also in complex topography environment like debris-flow catchments, provided that appropriate tools and procedures are employed in the data processing steps. In this work we test two different software packages (3DF Zephyr Aerial and Agisoft Photoscan) on a dataset composed of both UAV and terrestrial images acquired on a debris-flow reach (Moscardo torrent – North-eastern Italian Alps). Unlike other papers in the literature, we evaluate the results not only on the raw point clouds generated by the Structure-from- Motion and Multi-View Stereo algorithms, but also on the Digital Terrain Models (DTMs) created after post-processing. Outcomes show differences between the DTMs that can be considered irrelevant for the geomorphological phenomena under analysis. This study confirms that SfM photogrammetry can be a valuable tool for monitoring sediment dynamics, but accurate point cloud post-processing is required to reliably localize geomorphological changes
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