anna chiara Bixio - Academia.edu (original) (raw)
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Papers by anna chiara Bixio
Water Resources Research, 2005
Theoretical and Applied Climatology
This paper deals with precipitation events, particularly the problem of recognising events indivi... more This paper deals with precipitation events, particularly the problem of recognising events individually, of distinguishing one local meteorological/precipitation event from another. The final aim was to arrive at a more appropriate conceptualization of “distance” between individual annual events. A criterion for identifying annual precipitation events, inside a 5 min-timestep series of pluviometric data, was proposed. Using this numerical criterion, a series of annual distances between events were obtained and compared with those obtained by other two known and applied statistical methods. This comparison would be important for linking the so-called statistical methods to the real data of the series, analysed through a numerical process. This would make it possible to provide a kind of “measure” for the understanding of real data via a statistical model. Results showed that distances between events, obtained through numerical analyses, are almost always different from those obtained by statistical methods. The supposed Poisson-process, generally matched to, and widely applied in the field of rainfall data, showed some contradiction with the analysis conducted in this paper. The so-called Lag method shows a numerical method type distribution, but produces some important internal deviations from numerical results. It seems that the method proposed in this paper can reproduce the real distances between events more realistically compared to the statistical methods considered here. Exponential distribution does not seem highly performing, at least in the case of the annual analysis, with series of a 5-min time-step resolution, obtained from rain gauges installed in the Veneto Region of Italy. It is believed that the numerical criterion presented in this paper can be considered adequate for determining the distances between events, within an annual time-window.
A distributed catchment scale numerical model for the s imulation of coupled surface runoff and s... more A distributed catchment scale numerical model for the s imulation of coupled surface runoff and subsurface flow is presented. Starting from ra infall(evaporation) records, the model first determines the infiltration (exfiltration) r ates in the soil, by evaluation of the soil field capacity at the specific conditions as calc ulated from the three-dimensional solution of the variably-saturated groundwater flow model ( Richards’ equation). The flow rate that remains or returns to the surface, the so called overland flow, is then routed via a diffusion wave surface runoff model based on a Muskingum-Cunge scheme with variable parameters. Both hillslope and channel flow ar e described, and a special algorithm is used for the simulation of pools/lakes effec ts on storm-flow response. The importance of including detailed subsurface flow descript ion in catchment simulations is shown on a simple testcase characteri zed by the presence of a central depression.
Water Resources Research, 2005
1] Vegetation affects the mean and turbulent flow structure in surface water bodies, thus impacti... more 1] Vegetation affects the mean and turbulent flow structure in surface water bodies, thus impacting the local transport processes of contaminants and sediments. The present paper explores the capability of two different mathematical models to predict fully developed one-dimensional open channel flow in the presence of rigid, complex-shaped vegetation with leaves, submerged or emergent. The flow is described by applying two different turbulence closure schemes, both of which are based on the Boussinesq eddy viscosity model: a suitably modified k À e model and a two-layer model based on the mixing length approach. To describe the turbulence structure within and above the canopy a turbulent kinetic energy budget equation was added to the two-layer model. The results of the models were compared with experimental data where simple cylinders, plastic plant prototypes, or real plants, all arranged in a scattered pattern, were employed. Since good agreement between the results of the models and measurements was found in comparing velocity and turbulent shear stress, the models could potentially be used to assess vegetative resistance. Significant disagreement was found when comparing measured and computed eddy viscosity distributions, streamwise turbulence intensity, and most of the terms comprising the turbulent kinetic energy budget. Citation: Defina, A., and A. C. Bixio (2005), Mean flow and turbulence in vegetated open channel flow, Water Resour. Res., 41, W07006,
Water Resources Research, 2005
Theoretical and Applied Climatology
This paper deals with precipitation events, particularly the problem of recognising events indivi... more This paper deals with precipitation events, particularly the problem of recognising events individually, of distinguishing one local meteorological/precipitation event from another. The final aim was to arrive at a more appropriate conceptualization of “distance” between individual annual events. A criterion for identifying annual precipitation events, inside a 5 min-timestep series of pluviometric data, was proposed. Using this numerical criterion, a series of annual distances between events were obtained and compared with those obtained by other two known and applied statistical methods. This comparison would be important for linking the so-called statistical methods to the real data of the series, analysed through a numerical process. This would make it possible to provide a kind of “measure” for the understanding of real data via a statistical model. Results showed that distances between events, obtained through numerical analyses, are almost always different from those obtained by statistical methods. The supposed Poisson-process, generally matched to, and widely applied in the field of rainfall data, showed some contradiction with the analysis conducted in this paper. The so-called Lag method shows a numerical method type distribution, but produces some important internal deviations from numerical results. It seems that the method proposed in this paper can reproduce the real distances between events more realistically compared to the statistical methods considered here. Exponential distribution does not seem highly performing, at least in the case of the annual analysis, with series of a 5-min time-step resolution, obtained from rain gauges installed in the Veneto Region of Italy. It is believed that the numerical criterion presented in this paper can be considered adequate for determining the distances between events, within an annual time-window.
A distributed catchment scale numerical model for the s imulation of coupled surface runoff and s... more A distributed catchment scale numerical model for the s imulation of coupled surface runoff and subsurface flow is presented. Starting from ra infall(evaporation) records, the model first determines the infiltration (exfiltration) r ates in the soil, by evaluation of the soil field capacity at the specific conditions as calc ulated from the three-dimensional solution of the variably-saturated groundwater flow model ( Richards’ equation). The flow rate that remains or returns to the surface, the so called overland flow, is then routed via a diffusion wave surface runoff model based on a Muskingum-Cunge scheme with variable parameters. Both hillslope and channel flow ar e described, and a special algorithm is used for the simulation of pools/lakes effec ts on storm-flow response. The importance of including detailed subsurface flow descript ion in catchment simulations is shown on a simple testcase characteri zed by the presence of a central depression.
Water Resources Research, 2005
1] Vegetation affects the mean and turbulent flow structure in surface water bodies, thus impacti... more 1] Vegetation affects the mean and turbulent flow structure in surface water bodies, thus impacting the local transport processes of contaminants and sediments. The present paper explores the capability of two different mathematical models to predict fully developed one-dimensional open channel flow in the presence of rigid, complex-shaped vegetation with leaves, submerged or emergent. The flow is described by applying two different turbulence closure schemes, both of which are based on the Boussinesq eddy viscosity model: a suitably modified k À e model and a two-layer model based on the mixing length approach. To describe the turbulence structure within and above the canopy a turbulent kinetic energy budget equation was added to the two-layer model. The results of the models were compared with experimental data where simple cylinders, plastic plant prototypes, or real plants, all arranged in a scattered pattern, were employed. Since good agreement between the results of the models and measurements was found in comparing velocity and turbulent shear stress, the models could potentially be used to assess vegetative resistance. Significant disagreement was found when comparing measured and computed eddy viscosity distributions, streamwise turbulence intensity, and most of the terms comprising the turbulent kinetic energy budget. Citation: Defina, A., and A. C. Bixio (2005), Mean flow and turbulence in vegetated open channel flow, Water Resour. Res., 41, W07006,