Search

Reliable descriptions of erosion events are foundational to effective frameworks relevant to the fate of tidal landscape evolution. Besides the rhythmic, predictable action of tidal currents, erosion in shallow tidal environments is strongly influenced by the stochastic wave-induced bottom shear stress (BSS), mainly responsible for sediment resuspension on tidal flats. However, the absence of sufficiently long, measured time series of BSS prevents a direct analysis of the combined tide- and wave-driven erosion dynamics and its proper representation in long-term morphodynamic models. Here we test the hypothesis of describing erosion dynamics in shallow tidal environments as a Poisson process by analysing, with the peak-over-threshold theory, the BSS time series computed using a fully coupled, bi-dimensional numerical model. We perform this analysis on the Venice Lagoon, Italy, taking advantage of several historical surveys done in the last 4 centuries, which allow us to investigate the effects of morphological modifications on spatial and temporal erosion patterns. Our analysis suggests that erosion events on intertidal flats can effectively be modelled as a marked Poisson process in different morphological configurations because the interarrival times, durations, and intensities of the over-threshold exceedances are always well described by exponentially distributed random variables. The resulting statistical characterization allows a straightforward computation of morphological indicators, such as the erosion work, and paves the way for a novel synthetic, yet reliable, approach for the long-term morphodynamic modelling of tidal environments. [ABSTRACT FROM AUTHOR]

We propose an experimental setup to measure soil erosion and related it with sediment transport using rainfall simulator on a large plots experimental area. Experiments were carried out in fulfilment of the HERASE project, aimed at investigating the seasonal variations of soil erosion in the Oglio basin, an Alpine and Pre-alpine watershed with an area of about 1800 km2, and maximum elevation of 3.538m a.s.l. Namely some rainfall simulation experiments were carried out to assess water erosion under three different scenarios, on in situ plots having same soil and slope, but with different soil coverage and initial moisture condition. In particular, two experiments were carried out on a grassland plot covering an area of 144m2, one considering an undisturbed initial soil moisture condition and the other on a wet soil. The third experiment plot, having the same soil and slope of the previous, and covering an area of 72m2, was set up in the pine forest underwood area. The duration of the three experiments were respectively of 18 minutes, 30 minutes and 30minutes and rainfall intensity was set equal to 70mm/h, accordingly to a 200 return period storm. The plots were properly designed to ensure a correct as possible measure of surface runoff, and transported sediments were collected at 1 minute steps. Suspended sediment, and particle size analysis were carried out ex-post. Our results show a different behaviour of the two analysed plots, in terms of runoff generation and sediment transport. The runoff peak on grassland ranged from 0.018l/s for the undisturbed condition, to 0.09l/s with wet initial condition, while the peak in sediment transport, slowly delayed with respect to the runoff peak, was 1,7 times bigger in wet conditions. In the third experiment, peak runoff was 0.9l/s (10 times bigger than the peak runoff on wet grassland), and constant until the end of simulated rainfall, and took five minutes to run out (concentration time). The analysis on sediment shows an initial slush, where pine needles composed the majority of sediment. Then, after the sediment reached the peak of 350mg/s after about 9 minutes from the beginning of the experiment, it decreased rapidly to an almost constant value of 50mg/s. Interpretations on experiment results with different formulations and a comparison with similar analyses carried out in the Alpine area of Italy are proposed. [ABSTRACT FROM AUTHOR]

Within river basins, humans require infrastructures to cover their water needs. The basin scale impacts of these infrastructures are difficult, if not impossible, to estimate and therefore medium to long term effects are only partially considered in planning and management decisions.Available morphodynamic models aim at reproducing river shapes as consequences of changes in sediment transport rates, rather than to capture the dynamics of individual particles within the river network. These models are also often calibrated and validated using sediment transport rates measured in specific locations. These measures are affected by a number of drawbacks: they are expensive, characterised by low accuracy and usually limited to a small range of sediment sizes they focus on.Recent studies on sediment attrition claim the existence of a "universal" relation between particles mass loss due to saltation and specific shape indices (Novák-Szabó et al., 2018). Once the universality of this relationship will be confirmed by extensive testing in different real litho-morpho-climatic settings, it will become possible to link measurable properties of sediments (e.g. size, shape and lithology) to their travel distance (Cassel et al., 2018). This will represent a fundamental step towards a deeper understanding of sediment transport in mountain/piedmont rivers.This research aims at the assessment of the applicability of this relationship to estimate sediment travel distance. In order to test the hypothesis of "universality" of the relation between relative mass loss due to attrition and particle shape, we will compare the shape indices of natural sediment characterized by different litho-morphological settings at different distances from their sources.The selected case study is the Cordevole River basin in North-East Italy. Within this watershed, a small tributary, the Sarzana River, is characterized by the presence of localized outcrops of arenite and metabasalts which, given their very localized sources, will be considered as tracers.The methodology that will be applied is based on the analyses of field data collected using UAVs. In the field, samples of sediments including the mentioned tracers have been collected at different distances from their sources and their size and shape has been estimated using digital image processing tools. These data allowed the assessment of quantitative correlation between shape changes and distance travelled for each of the selected lithologies, which will be presented and discussed. [ABSTRACT FROM AUTHOR]