1,721,469 research outputs found
Il Governo dell'acqua. Ambiente naturale e Ambiente costruito
No full textFinalista 2010 al Premio Galileo per la Divulgazione scientific
Un criterio per la stima degli effetti di non linearità e di varianza in un modello di generazione delle piene
No full textTransport of passive solutes in heterogeneous isotropic porous formations
No full textThe paper deals with the transport of non-reactive tracers in heterogeneous aquifers with a view to the development of dispersion tensor in natural formations. A Monte Carlo numerical scheme is developed to discuss validity and limitations of the existing dispersion theories. The results suggest that quite different velocity of convergence with Monte Carlo runs holds for different orders of spatial moments. This has implications on the spatial extent of the spatial domain for single-realization numerical studies of same type. A comparison of the variance of plumes with the results of Dagan’s linear theory shows an unexpectedly broad validity of field for the theoretical solution (obtained upon a suitable linearization of flow and transport). Reformulation of the same problem with a linearization of the flow equation alone, an assumption commonly accepted in theoretical and numerical studies in this subject, yields deviations from linear theory larger than those induced by a fully nonlinear solution. The interesting consequence, besides casting some doubt on previous conclusions drawn on the limitation of the linear theory based on partially linearized equations, is that the effects on nonlinear terms in the flow and transport equations on the moments of dispersing plumes seem somewhat counteracting thereby yielding to globally consistent formulations
The influence of the form of the log-conductivity covariance on non-Fickian dispersion in random permeability fields
No full textThe paper deals with non-Fickian dispersion of inert solutes in random permeability fields. Attention is focused critically on the statistical characterization of the porous medium which affects pollutant dispersion in groundwater. After a brief account of recent results of stochastic theories of transport in porous media and of the fundamental indications of large-scale field experiments, it is inferred from numerical studies that the particular choice of an analytical form of covariance of log-conductivity has a poor influence on the overall dispersion process. In fact, different covariance structures with the same macroscale (a measure of the distance between two points beyond which the permeability ceases to be correlated) yield very similar dispersion processes. The result has a noteworthy bearing on field studies of pollutant dispersion in groundwater because it underlines the reliability of exponential correlation structures yielding analytical expression for time-varying macrodispersion coefficients
A metacommunity model for the spread of proliferative kidney disease in stream networks
No full textProliferative kidney disease (PKD) affects freshwater salmonid populations in temperate European and North-American rivers. It is caused by the endoparasitic myxozoan Tetracapsuloides bryosalmonae, which exploits freshwater bryozoans as intermediate hosts. Incidence and fish mortality are enhanced by warmer water temperatures. Therefore, environmental change is feared to increase the severity of PKD outbreaks and extend the disease range to higher latitude and altitude regions. Building on a recently developed local model of PKD transmission, a spatially-explicit metacommunity framework is developed to study the spatial effects in the spread of the disease in idealized stream networks. At the local community scale, the model accounts for demographic and epidemiological dynamics of bryozoans and fish. At the network scale, the model couples the dynamics of each community through hydrological transport of parasite spores and fish mobility. The model also explicitly accounts for how habitat characteristics and hydrological conditions change along a river network. The model is applied to synthetic river network replicas derived from Optimal Channel Networks (OCNs), spanning trees known to reproduce all mutually connected scaling exponents of topological and metric features of real rivers. Stability analysis of the local model shows that the introduction of the parasite in a disease-free community is likely to trigger a disease outbreak. Moreover, we show how network connectivity and hydrological conditions critically control the spatial distribution of the prevalence of PKD and the celerity of invasion fronts in the upstream and downstream directions. The developed mathematical model helps further our understanding of the drivers of fish distribution in riverine ecosystems and provide the basis for the development of possible intervention and management tools.ECH
River Networks as Ecological Corridors: Species, Populations, Pathogens
No full textRiver networks are critically important ecosystems. This interdisciplinary book provides an integrated ecohydrological framework blending laboratory, field, and theoretical evidence that changes our understanding of river networks as ecological corridors. It describes how the physical structure of the river environment impacts biodiversity, species invasions, population dynamics, and the spread of waterborne disease. State-of-the-art research on the ecological roles of the structure of river networks is summarized, including important studies on the spread and control of waterborne diseases, biodiversity loss due to water resource management, and invasions by non-native species. Practical implications of this research are illustrated with numerous examples throughout. This is an invaluable go-to reference for graduate students and researchers interested in river ecology and hydrology, and the links between the two. Describing new related research on spatially-explicit modeling of the s..
Transport in the hydrologic response: Travel time distributions, soil moisture dynamics, and the old water paradox
Full text linkWe propose a mathematical framework for the general definition and computation of
travel time distributions defined by the closure of a catchment control volume, where the
input flux is an arbitrary rainfall pattern and the output fluxes are green and blue water
flows (namely, evapotranspiration and the hydrologic response embedding runoff
production through soil water dynamics). The relevance of the problem is both practical,
owing to implications in hydrologic watershed modeling, and conceptual for the linkages
and the explanations the theory provides, chiefly concerning the role of geomorphology,
climate, soils, and vegetation through soil water dynamics and the treatment of the socalled
old water paradox. The work focuses in particular on the origins of the conditional
and time‐variant nature of travel time distributions and on the differences between unit
hydrographs and travel time distributions. Both carrier flow and solute matter transport in
the control volume are accounted for coherently. The key effect of mixing processes
occurring within runoff production is also investigated, in particular by a model that
assumes that mobilization of soil water involves randomly sampled particles from the
available storage. Travel time distributions are analytically expressed in terms of the major
water fluxes driving soil moisture dynamics, irrespectively of the specific model used to
compute them. Relevant numerical examples and a set of generalized applications are
provided and discussed
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