Search

The characterization of river hydraulics is very important for the definition of many problems connected with flood and morphodynamical models, including the stability of banks, slopes and sediments transport. These physical aspects are often closely related to the observation scale of hydraulic phenomena. The latter has significant value both for the channel and basin scale. This coupling of scales is now possible due to, for example, modern LiDAR detection techniques, in which topographic surveys (DEMs) are predominant, as well as other topographical survey techniques. River scale hydraulic phenomena and their field measurements represent a new paradigm towards the development of computational procedures for the spatio-temporal scale representation of complex hydraulic phenomena. This Special Issue aims to emphasize new numerical techniques and physical measurements in the field of hydraulic observations at laboratory, channel, and basin scale. Applying channel scale, He et al. [1] analyzed the effect of physical factors on the growth of Chlorella vulgaris on enriched media by the use of orthogonal analysis and response surface methodology. In this context, rivers are also viewed as biological coupled systems, and in particular, this study shows that the growth of C. vulgaris can be regulated by changing physical conditions simultaneously, and the optimization of physical conditions can be applied to biomass production, algae prediction, and acid water treatment in rivers [1]. By the use of channel scale, Licciardello et al. [2] introduced a stream hydro-morphological evaluation, analysis, and monitoring system procedure called IDRAIM, which allows us, on the basis of a number of physically based geomorphological descriptors, us to determine the overall state of physical ’equilibrium’ of a river. This is a study case of Dittaino River (Eastern Sicily, Italy). It is very important, because the assessment of a river’s ecological status, including its hydro-morphological and morphological dynamics, which can be used for the implementation of design models and interventions integrating protection and environmental requalification, requires the evaluation of hydro-morphological state changes. As such, the IDRAIM procedure could help in sustainable river management [2]. Rivers also affect urban drainage scales. The transition from confluence situations can highlight critical elements for an adequate design and management. In this context, Zhang and Lin [3] conducted an experimental study on the influence of drastically varying discharge ratios on bed topography and flow structure at urban channel confluences. This study showed that the drastic change in discharge ratio causes secondary scouring to the equilibrium bed topography in the confluence area. The bed surface in the sand hole, a sand bar drops, and the sediment are transported downstream. In this experiment, although local sand hole and sand ridge were formed in the flow recovery zone downstream, the results may be more suitable for urban channel confluence with relatively large width–depth ratio and small- and medium-sized natural channel confluences [3]. At basin scale, Primavera and Florio [4] introduced a new fixed mass algorithm that allows direct determination of the multi-fractal spectrum of a river network. The hybrid procedure, based on parallel computation, makes possible the direct estimation of the multifractal spectrum and the exponents of the singularities, without going through the Legendre transforms. By correctly estimating the scale exponents, i.e., the right-hand side of a spectrum, the maximum singularity index to be used in flood prediction models can be correctly estimated. MIUH (multifractal instantaneous unit hydrograph) is based exclusively on this parameter, so a technique that drastically reduces the computation time of multifractal spectra allows to validate real-time prediction flood procedures based on geomorphological descriptors [4]. Costabile et al. [5] investigated the effects of DEM depression filling on river drainage patterns and surface runoff generated by 2D rain-on-grid scenarios. The analysis, which is interesting from the point of view of morphological scaling, offers criteria for defining scaling effects from the transition of grid-channels to hydraulically active channels. The core of these transitions is based on models characterized by shallow water equations [5].

The dependence of the soil water content ϑ upon the matric potential ψ is studied within a fractal approach that regards the water retention curve as a sequence of well defined fractal regimes. Each of such regimes accounts for a given functional dependence ϑ≡ϑ(ψ), which in turn is characterized by a fractal dimension. The difference between the double fractal (observed into sandy soils) and multifractal (observed into clay soils) regime is explained by recalling that, for a sandy soil, the transition from saturated to dry conditions is driven by a steep reduction of ψ. To the contrary, for a clay (where the change from the highest water contents to the smallest ones is characterized by a large range of the matric potential), the multifractal behaviour is observed. These results are also confirmed by the analysis of experimental data. In particular, we show that the intermediate regime, generally accounting for the fractal multimodality, is due to the sandy nature of the soil at stake, practically immaterial. Finally, we demonstrate that our model can be also regarded as the straightforward generalization of that of Millán and González-Posada (2005).

We study the scale dependence of the saturated hydraulic conductivity Ksthrough the effective porosity neby means of a newly developed power-law model (PLM) which allows to use simultaneously measurements at different scales. The model is expressed as product between a single PLM (capturing the impact of the dominating scale) and a characteristic function κ⋆accounting for the correction because of the other scale(s). The simple (closed form) expression of the κ⋆-function enables one to easily identify the scales which are relevant for Ks. The proposed model is then applied to a set of real data taken at the experimental site of Montalto Uffugo (Italy), and we show that in this case two (i.e. laboratory and field) scales appear to be the main ones. The implications toward an important application (solute transport) in Hydrology are finally discussed. Copyright © 2016 John Wiley & Sons, Ltd.

The topological interconnection between grid, channel, and Peano networks is investigated by extracting grid and channel networks from high-resolution digital elevation models of real drainage basins, and by using a perturbed form of the equation describing how the average junction degree varies with Horton-Strahler order in Peano networks. The perturbed equation is used to fit the data observed over the Hortonian substructures of real networks. The perturbation parameter, denoted as “uniformity factor,” is shown to indicate the degree of topological similarity between Hortonian and Peano networks. The sensitivities of computed uniformity factors and drainage densities to grid cell size and selected threshold for channel initiation are evaluated. While the topological relation between real and Peano networks may not vary significantly with grid cell size, these networks are found to exhibit the same drainage density only for specific grid cell sizes, which may depend on the selected threshold for channel initiation.

Solute transport takes place in heterogeneous porous formations, with the log conductivity, Y = ln K, modeled as a stationary random space function of given univariate normal probability density function (pdf) with mean 〈Y〉, variance σY2, and integral scale IY. For weak heterogeneity, the above mentioned quantities completely define the first-order approximation of the longitudinal macrodispersivity αL = σY2 IY. However, in highly heterogeneous formations, nonlinear effects which depend on the multipoint joint pdf of Y, impact αL. Most of the past numerical simulations assumed a multivariate normal distribution (MVN) of Y values. The main aim of this study is to investigate the impact of deviations from the MVN structure upon αL. This is achieved by using the concept of spatial correlations of different Y classes, the latter being defined as the space domain where Y falls in the generic interval [Y,Y + DY]. The latter is characterized by a length scale γ(Y), reflecting the degree of connectivity of the domain (the concept is similar to the indicator variograms). We consider both "symmetrical" and "non-symmetrical" structures, for which γ(Y′) = γ(-Y′) (similar to the MVN), and γ(Y′) ≠ γ(-Y′), respectively, where Y′ = Y - 〈Y〉. For example, large Y zones may have high spatial correlation, while low Y zones are poorly correlated, or vice versa. The impact of γ(Y) on αL is investigated by adopting a structure model which has been used in the past in order to investigate flow and transport in highly heterogeneous media. It is found that the increased correlation in the low conductive zones with respect to the high ones generally leads to a significant increase in aL, for the same global IY. The finding is explained by the solute retention occurring in low Y zones, which has a larger effect on solute spreading than hi h Y zones. Conversely, αL decreases when the high conductivity zones are more correlated than the low Y ones. Dispersivity is less affected by the shape of γ(Y) for symmetrical distributions. It is found that the range of validity of the first-order dispersivity, i.e., αL = IYσY2, narrows down for non-symmetrical structures. © 2010 by the American Geophysical Union.

In this paper, the authors, present last results on a low cost method to monitoring Passive-Optical-Network, which it uses Fiber-Bragg-Gratings and a modified Optical-Time-Domain-Reflectometer, and a remote power supply of Optical-Network-Terminals by a bivalent-use cable.

A clear statement in these lines textually cited (Byers et al., 1938) defines the framework of this special issue: “True soil is the product of the action of climate and living organism upon the parent material, as conditioned by the local relief. The length of time during which these forces are operative is of great importance in determining the character of the ultimate product. Drainage conditions are also important and are controlled by local relief, by the nature of the parent material or underlying rock strata, or by the amount of precipitation in relation to rate of percolation and runoff water. There are, therefore, five principal factors of soil formation: Parent material, climate, biological activity, relief and time. These soil forming factors are interdependent, each modifying the effectiveness of the others.” Due to these various processes associated to its formation and genesis soil dynamics reveals high complexity that creates several levels of structure using this term in a broad sense