Comparative analysis of the differences between using LiDAR and contour-based DEMs for hydrological modeling of runoff generating debris flows in the Dolomites

Present work aims to explore the differences in hydrological modeling when using digital elevation models (DEMs) generated by points from LiDAR surveys and those digitized on the contour lines of the regional technical map (RTM) and their relevance for the simulation of debris flow triggering. Hydrological models for mountainous areas are usually based on digital elevation models (DEMs). DEMs are used to determine the flow path from each pixel, by which the basin is discretized, to the outlet. Hydrological simulations of runoff that triggered debris flows occurred in two rocky headwater basins of Dolomites, Fiames Dimai (area approximately 0.03 km2) and Cancia (area approximately 0.7 km2) are carried out using a DEM-based model designed for simulating runoff that descends from headwater areas. For each basin, the runoff is simulated using DEMs that are generated using points from LiDAR, and those digitized on the contour lines of the regional technical map, respectively. The results show that the peak discharge values corresponding to the simulations carried out using the LiDAR-based DEMs are higher than those corresponding to the simulations carried out using the RTM-based DEMs. Larger differences are observed for the Dimai basin, where the area corresponding to the RTM-based DEM is markedly smaller than the area corresponding to LiDAR-based DEM, whereas for the Cancia basin, the two areas are similar. Both the differences in the peak discharge and the basin area are due to the poor accuracy of the contour-based DEM (i.e., elevation accuracy), that is, a poor representation of the morphological features that leads to errors on the watershed divide and simplifications of the flow paths from each cell to the outlet. This result is highly relevant for estimating the triggering conditions of runoff generated debris flows. An incorrect simulated value of peak discharge can lead to errors both in planning countermeasures against debris flows and in predicting their occurrence

Evaluating the Differences of Gridding Techniques for Digital Elevation Models Generation and Their Influence on the Modeling of Stony Debris Flows Routing: A Case Study From Rovina di Cancia Basin (North-Eastern Italian Alps)

Debris \ufb02ows are among the most hazardous phenomena in mountain areas. To cope with debris \ufb02ow hazard, it is common to delineate the risk-prone areas through routing models. The most important input to debris \ufb02ow routing models are the topographic data, usually in the form of Digital Elevation Models (DEMs). The quality of DEMs depends on the accuracy, density, and spatial distribution of the sampled points; on the characteristics of the surface; and on the applied gridding methodology. Therefore, the choice of the interpolation method affects the realistic representation of the channel and fan morphology, and thus potentially the debris \ufb02ow routing modeling outcomes. In this paper, we initially investigate the performance of common interpolation methods (i.e., linear triangulation, natural neighbor, nearest neighbor, Inverse Distance to a Power, ANUDEM, Radial Basis Functions, and ordinary kriging) in building DEMs with the complex topography of a debris \ufb02ow channel located in the Venetian Dolomites (North-eastern Italian Alps), by using small footprint full- waveform Light Detection And Ranging (LiDAR) data. The investigation is carried out through a combination of statistical analysis of vertical accuracy, algorithm robustness, and spatial clustering of vertical errors, and multi-criteria shape reliability assessment. After that, we examine the in\ufb02uence of the tested interpolation algorithms on the performance of a Geographic Information System (GIS)-based cell model for simulating stony debris \ufb02ows routing. In detail, we investigate both the correlation between the DEMs heights uncertainty resulting from the gridding procedure and that on the corresponding simulated erosion/deposition depths, both the effect of interpolation algorithms on simulated areas, erosion and deposition volumes, solid-liquid discharges, and channel morphology after the event. The comparison among the tested interpolation methods highlights that the ANUDEM and ordinary kriging algorithms are not suitable for building DEMs with complex topography. Conversely, the linear triangulation, the natural neighbor algorithm, and the thin-plate spline plus tension and completely regularized spline functions ensure the best trade-off among accuracy and shape reliability. Anyway, the evaluation of the effects of gridding techniques on debris \ufb02ow routing modeling reveals that the choice of the interpolation algorithm does not signi\ufb01cantly affect the model outcomes

The debris flow occurred at ru secco creek, venetian dolomites, on 4 august 2015: Analysis of the phenomenon, its characteristics and reproduction by models

On 4 August 2015, a very high intensity storm, 31.5 mm in 20 min (94.5 mm/h), hit the massif of Mount Antelao on the Venetian Dolomites triggering three stony debris \ufb02ows characterized by high magnitude. Two of them occurred in the historical sites of Rovina di Cancia and Rudan Creek and were stopped by the retaining works upstream the inhabited areas, while the third routed along the Ru Secco Creek and progressively reached the resort area and the village of San Vito di Cadore, causing fatalities and damages. The main triggering factor of the Ru Secco debris \ufb02ow was a large rock collapse on the northern cliffs of Mount Antelao occurred the previous autumn. The fallen debris material deposited on the Vallon d\u2019Antrimoia inclined plateau at the base of the collapsed cliffs and, below it, on the Ru Salvela Creek, covering it from the head to the con\ufb02uence with the Ru Secco Creek. The abundant runoff, caused by the high intensity rainfall on 4 August 2015, entrained about 52,500 m3 of the debris material laying on the Vallon d\u2019Antrimoia forming a debris \ufb02ow surge that hit and eroded the debris deposit covering the downstream Ru Salvela Creek, increasing its volume, about 110,000 m3 of mobilized sediments. This debris \ufb02ow routed downstream the con\ufb02uence, \ufb02ooding the parking of a resort area where three people died, and reached the village downstream damaging some buildings. A geomorphological analysis was initially carried out after surveying the whole basin. All liquid and solid-liquid contributions to the phenomenon were recognized together with the areas subjected to erosion and deposition. The elaboration of pre and post-event topographical surveys provided the map of deposition-erosion depths. Using the rainfall estimated by weather radar and corrected by the nearest rain gauge, about 0.8 km far, we estimated runoff by using a rainfall-runoff model designed for the headwater rocky basins of Dolomites. A triggering model provided the debris \ufb02ow hydrographs in the initiation areas, after using the simulated runoff. The initial solid-liquid surge hydrographs were, then, routed downstream by means of a cell model. The comparison between the simulated and estimated deposition-erosion pattern resulted satisfactory. The results of the simulation captured, in fact, the main features of the occurred phenomenon

Layer-averaged Euler and Navier-Stokes equations

In this paper we propose a strategy to approximate incompressible hydrostatic free surface Euler and Navier-Stokes models. The main advantage of the proposed models is that the water depth is a dynamical variable of the system and hence the model is formulated over a fixed domain.The proposed strategy extends previous works approximating the Euler and Navier-Stokes systems using a multilayer description. Here, the needed closure relations are obtained using an energy-based optimality criterion instead of an asymptotic expansion. Moreover, the layer-averaged description is successfully applied to the Navier-Stokes system with a general form of the Cauchy stress tensor

Permanent mitigation of loss in ultrathin SOI high-Q resonators using UV light

In this paper, we demonstrate strip-loaded guiding optical components realized on a 27 nm ultra-thin SOI platform. The absence of physically etched boundaries within the guiding core suppresses majorly the scattering loss, as shown by us previously for a silicon nitride (Si$_3$N$_4$) platform [Stefan \textit{et. al.}, OL 40, 3316 (2015)]. Unexpectedly, the freshly fabricated Si devices showed large losses of 5 dB/cm, originating from absorption by free carriers, accumulated under the positively charged Si$_3$N$_4$ loading layer. We use 254 nm ultraviolet (UV) light exposures to neutralize progressively and permanently silicon nitride's bulk charge associated with diamagnetic K+defects. This in turn leads to a net decrease of electron concentration in the SOI layer, reducing thus the propagation loss down to 0.9 dB/cm. Detailed MOS-capacitance measurements on test samples were performed to monitor the UV-induced modification of the electronic properties of the system. The evolution of loss mitigation was directly monitored both by Beer-Lambert approach in waveguide transmission experiments, as well as through more accurate cavity linewidth measurements. In the last case, we demonstrate how intrinsic cavity $Q$'s boost from 60,0000 to up to 500,000 after UV treatment. Our results may open routes towards engineering of new functionalities in photonic devices employing UV-modification of space charges and associated local electric fields, unveil the origin of induced optical nonlinearities in Si$_3$N$_4$/Si micro-photonic systems, as well as envisage possible integration of these with ultra-thin SOI electronics.Comment: 8 pages, 5 figure

Analysis and modelling of surface runoff triggering debris flows

In the Dolomites, short-duration and high-intensity rainfalls produce abundant surface runoff in headwater catchments. These discharges often trigger debris flows on the scree slopes placed at the base of rock cliffs. With the aim to quantify the discharges delivered by these headwater catchments and associated rainfalls, we built a measuring facility at the outlet (elevation 1770 m a.s.l.) of a rocky channel incised on the Dimai Peak, near Cortina d'Ampezzo (Belluno province) in the Venetian Dolomites (North Eastern Italian Alps). The channel delivers surface runoff gathered by a small impervious headwater catchment (area ~0.032 km^2, average slope ~320%). The facility consists of a monitoring station equipped with a rain gauge, and trapezoidal-shape waterproof basin, closed by a sharp-crested weir. The recorded rainfalls allow us to verify the features that lead to runoff discharges or mass transport events. In the period 2011-2017, among the measured discharges, about fifteen runoff events were considered as significant. These observations provide a unique opportunity for improving knowledge about the hydrological response of a rocky headwater catchment. The recorded hydrographs show impulsive shapes, with a sudden raise up to the discharge peak, generally followed by a likewise rapidly decreasing tail. Furthermore, the discharges can be used to calibrate and validate hydrological models. We show that the observations can be modelled by means of a distributed hydrological model, assuming that the excess rainfall is accurately evaluated. More specifically, we show that the combination of the Soil Conservation Service Curve-Number (SCS-CN) procedure with constant routing velocities results in an underestimation of the flow peak and a delayed time of peak. Better predictions of the peak of discharge, its timing, and the impulsive shape of the hydrographs could be obtained by coupling the SCS-CN method with a simplification of the Horton equation, and simulating the routing of runoff along the channel network by means of a matched diffusivity kinematic-wave model. The reliability of the method is tested by comparing simulated and observed timings of hyper-concentrated runoff or debris flow triggering in two neighbouring dolomitic watersheds

Cardiac motion assessement from echocardiographic image sequences by means of the structure multivector

International audienceWe recently contributed an algorithm for the estimation of cardiac deformation from echocardiographic image sequences based on the monogenic signal. By exploiting the phase information instead of the pixel intensity, the algorithm was robust to the temporal contrast variations normally encountered in cardiac ultrasound. In this paper we propose an improvement of that framework making use of an extension of the monogenic signal formalism, called structure multivector. The structure multivector models the image as the superposition of two perpendicular waves with associated amplitude, phase and orientation. Such a model is well adapted to describe the granular pattern of the characteristic speckle noise. The displacement is computed by solving the optical flow equation jointly for the two image phases. A local affine model accounts for typical cardiac motions as contraction/expansion and shearing; a coarse-to-fine B-spline scheme allows for a robust and effective computation of the model parameters and a pyramidal refinement scheme helps deal with large motions. Performance was evaluated on realistic simulated cardiac ultrasound sequences and compared to our previous monogenic-based algorithm and classical speckle tracking. Endpoint-error was used as accuracy metric. With respect to them we achieved error reductions of 13% and 30% respectively

Coupling of Photonic Waveguides to Integrated Detectors Using 3D Inverse Tapering

We report on the design, fabrication, and characterization of a Silicon Nitride (SiN)-based integrated photonic chip in which the dielectric waveguides are coupled to photodetectors integrated homogeneously into the Silicon substrate. The photonic-electronic coupling was realized by a 3D inverse tapering of SiN waveguides. The novelty of our approach consists in tapering the waveguide in the vertical direction by means of an engineered wet chemical etching. This allows for a smooth transition from a full-height to an arbitrarily thin waveguide thickness at the detector location, expanding adiabatically the optical mode towards the latter. The measured chips showed a responsivity $R\approx 109~\mu$A/mW and a corresponding quantum efficiency of $16\%$ at an excitation wavelength of $850$~nm. Our technological solution offers a versatile method for a top-down monolithic integration of lightwave circuitries with substrate-located photon sensing devices