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Stefano ORLANDINI

Professore Ordinario
Dipartimento di Ingegneria "Enzo Ferrari"

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Pubblicazioni

2023 - Characterization of annual urban air temperature changes with special reference to the city of Modena: a comparison between regression models and a proposal for a new index to evaluate relationships between environmental variables [Articolo su rivista]
Morlini, Isabella; Albertson, Sean; Orlandini, Stefano
abstract

It is commonly recognized that the observed increase in global mean annual air temperature is strongly related to the increase in global carbon dioxide concentration C, and that both these variables are related to global development. It remains, however, unclear the degree to which local mean annual urban air temperature T is affected by local variables such as annual precipitation depth P and urban area extent A. This study assumes that A is a proxy of local development and C is a proxy of global development and investigates the commingled effects of A, P, and C on T by using long-term annual data observed over the years 1881–2019 from the Modena Observatory in Italy. Linear relationships between T, C and A are found to be spurious since all these series have a monotonic increasing trend with time. Parametric analytic models like logistic functions are found to lack flexibility. Smoothing splines can only give insights into the strength of the relationships but not on their shape defining the functional relationship between variables. Advanced nonlinear models like generalized additive models, instead, are found to combine flexibility in a parametric form, and appear therefore to be suitable models for explaining the complex relationships between A, P, and C on T. The different models are evaluated using traditional goodness of fit statistics like R2, AIC, BIC, and a new index of relation IR which is introduced to jointly evaluate the goodness-of-fit of relationships between variables that may either be dependent or independent.

2023 - Modelling local climate change using site-based data [Articolo su rivista]
Morlini, Isabella; Franco-Villoria, Maria; Orlandini, Stefano
abstract

2023 - Thalweg and Ridge Network Extraction From Unaltered Topographic Data as a Basis for Terrain Partitioning [Articolo su rivista]
Moretti, Giovanni; Orlandini, Stefano
abstract

High-resolution grid digital elevation models (DEMs) are increasingly used by scientists and engineers to describe the current state and evolution of Earth and planetary topography. These data, however, are commonly altered by depression filling and grid coarsening procedures. Alteration of observed topographic data may cause significant information loss and limit the capabilities of models. This study shows that physically meaningful thalweg and ridge networks can be extracted automatically from any unaltered high-resolution grid DEM, and that these networks can be used as bases for terrain partitioning. The slopeline network connecting grid cell centers is used to identify ridge points as those grid cell border midpoints and vertices that are not crossed by slopelines. From each ridge point, the average length of the two slopelines extending on the opposite slopes of the ridge until they rejoin is then computed. Based on these lengths, exorheic and endorheic basins are identified. Thalwegs of exorheic and endorheic basins are finally connected through spilling saddles to form the thalweg network. The related ridge network is identified based on neighboring relationships between ridge points. Thalweg and ridge networks are hierarchized using the well-known concept of drainage area and an extended concept of dispersal area to inform terrain partitioning at any level of detail. Observed topographic features are well reproduced by extracted networks. The impact of preserving depressions over mountain areas is evaluated, and the benefits from unstructured terrain partitioning based on thalweg and ridge networks in the description of flood plain inundation are illustrated.

2021 - Failure Probability Analysis of Levees Affected by Mammal Bioerosion [Articolo su rivista]
Balistrocchi, Matteo; Moretti, Giovanni; Ranzi, Roberto; Orlandini, Stefano
abstract

Burrowing mammals often find in levees a suitable habitat. Unfortunately, mammal dens can significantly compromise the functionality of levees by creating preferential flow paths for flood water seeping through the levee bodies, and by causing ultimately levee failures due to excessive seepage and internal erosion. In fact, many levee failures have been connected to the levee weakening caused by mammal dens. Mammal bioerosion significantly increases the failure probability of levees and the related flood risk in densely populated floodplains. Estimating the failure probability of levees affected by mammal bioerosion is therefore a relevant societal need. In the present study levee safety and failure conditions are estimated by combining a fully bivariate statistical description of peak flow discharge and flood duration with a computationally efficient unsteady seepage flow model. The resulting modeling framework incorporates the natural variability of floods and the essential hydraulic properties of disturbed/undisturbed levees. Model results reveal that the return period of levee failure due to excessive seepage reduces from 100 to 9 yr, namely of –91%, when the mammal den extends for 84% of levee thickness. These results can be used to inform levee design and maintenance programs for the safety of societies living in floodplains worldwide.

2019 - Copula-based modeling of earthen levee breach due to overtopping [Articolo su rivista]
Balistrocchi, M.; Moretti, G.; Orlandini, S.; Ranzi, R.
abstract

The level of protection offered by an earthen levee is typically described in terms of flood water level that the levee is capable of containing. If a larger flood occurs, floodwaters exceed the height of the levee and flow over its crest. As the water passes over the top, it may erode the levee, worsening the flooding and potentially causing a breach. In order to determine the annual probability that an earthen levee breaches due to overtopping, multiple flood characteristics such as peak flood water level, or related peak flow discharge, and flood duration need to be characterized statistically by using multivariate statistics. In this study, critical conditions for levee failure are described by using a Clayton copula relating peak flow discharge to flood duration. The obtained model is tested over a real river site located along the Panaro River, in northern Italy, where a 52-year time series of hourly flow discharge and a normal flow rating curve are available. The developed model makes it possible to delimitate the levee failure region within the population of flood events and to statistically describe earthen levee breach due to overtopping. Breach probability is found to be underestimated when the statistical association between peak flow discharge and flood duration is neglected. The proposed copula-based model is therefore important to support the design and construction of earthen levees, and to identify the actions needed to save lives and property when a flood exceeding the levee design limit occurs.

2019 - Cost-Benefit Analysis of Flood-Control and Multipurpose Reservoirs from the Perspective of Society: The Real Case of the Baganza River System in Italy [Abstract in Atti di Convegno]
Orlandini, S.; Moretti, G.
abstract

2018 - Atti del 36º Convegno nazionale di idraulica e costruzioni idrauliche. Ingegneria delle acque: scienza e tecnologia al servizio della comunità [Relazione in Atti di Convegno]
Balistrocchi, Matteo; Ranzi, Roberto; Stefano, Orlandini; Baldassare, Bacchi
abstract

• Le prestazioni della cassa di laminazione sul Panaro sono state stimate tramite approcci diversi. • Una serie di portate lunga 52 anni ha consentito di condurre una simulazione in continuo. • Un metodo di stima stocastico è stato derivato da una distribuzione congiunta di colmi e volumi. • Partendo dalle curve di riduzione delle portate sono stati ricavate piene di progetto. • Il confronto tra simulazioni e metodo probabilistico ha evidenziato una soddisfacente concordanza.

2018 - Efficient use of high-resolution topographic data for the extraction of large river networks [Abstract in Atti di Convegno]
Moretti, G.; Orlandini, S.
abstract

2018 - Flood Routing Efficiency Assessment: an Approach Using Bivariate Copulas [Relazione in Atti di Convegno]
Balistrocchi, Matteo; Ranzi, Roberto; Orlandini, Stefano; Bacchi, Baldassare
abstract

Flood control reservoirs are widely recognized as effective structural practices in order to mitigate the flood risk in natural watersheds. Nevertheless, the flood frequency distribution in the downstream reach is strongly affected by a certain number of characteristics of the upstream flood hydrographs. When a direct statistical method is utilized, a multivariate approach should therefore be utilized to accurately assess reservoir performances. In this paper, a flood frequency distribution of the routed flow discharge is derived from a bivariate joint distribution function ofpeak flow discharges and flood volumes of hydrographs entering the reservoir. Such a joint distribution is constructed by using the copula approach. Reservoir performances are also exploited to categorize event severity and to estimate their bivariate return periods. The method is applied to a real-world case study (Sant’Anna reservoir, Panaro River, northern Italy), and its reliability is verified through continuous simulations. Bearing in mind the popularity that design event methods still have in practical engineering, a final evaluation of the performance assessment achievable by simulations of synthetic hydrographs derived from a flood reduction curve is finally proposed.

2018 - HYDROGRAPHY-DRIVEN COARSENING OF GRID DIGITAL ELEVATION MODELS [Relazione in Atti di Convegno]
Moretti, G.; Orlandini, S.
abstract

2018 - Hydrography-Driven Coarsening of Grid Digital Elevation Models [Articolo su rivista]
Moretti, G.; Orlandini, S.
abstract

A new grid coarsening strategy, denoted as hydrography-driven coarsening, is developed in the present study. The hydrography-driven coarsening is designed to retain the essential hydrographic features of valleys and channels observed in high-resolution digital elevation models: (1) depressions are filled in the considered high-resolution digital elevation model, (2) the obtained topographic data are used to extract a reference grid network composed of all surface flow paths, (3) the Horton order is assigned to each link of the reference grid network, and (4) within each coarse grid cell, the elevation of the point lying along the highest-order path of the reference grid network and displaying the minimum distance to the cell center is assigned to this coarse grid cell center. The capabilities of the hydrography-driven coarsening to provide consistent surface flow paths with respect to those observed in high-resolution digital elevation models are evaluated over a synthetic valley and two real drainage basins located in the Italian Alps and in the Italian Apennines. The hydrography-driven coarsening is found to yield significantly more accurate valley and channel profiles than existing coarsening strategies. In absolute terms, the obtained valleys and channels compare favorably with those observed. In addition, the proposed coarsening strategy is found to reduce drastically the impact of depression-filling in the obtained coarse digital elevation models. The hydrography-driven coarsening strategy is therefore advocated for all those cases in which the relief of the extracted drainage network is an important hydrographic feature.

2017 - Copula-Based Modeling of Flood Control Reservoirs [Articolo su rivista]
Balistrocchi, M.; Orlandini, S.; Ranzi, R.; Bacchi, and B.
abstract

Copulas are shown in this paper to provide an effective strategy to describe the statistical dependence between peak flow discharge and flood volume featuring hydrographs forcing a flood control reservoir. A 52 year time series of flow discharges observed in the Panaro River (Northern Italian Apennines) is used to fit an event-based bivariate distribution and to support time-continuous modeling of a flood control reservoir, located online along the river system. With regard to reservoir performances, a method aimed at estimating the bivariate return period is analytically developed, by exploiting the derived distribution theory and a simplified routing scheme. In this approach, the return period is that of the peak flow discharge released downstream from the reservoir. Therefore, in order to verify the reliability of the proposed method, a nonparametric version of its frequency distribution is assessed by means of continuous simulation statistics. Copula derived and nonparametric distributions of the downstream peak flow discharge are found to be in satisfactory agreement. Finally, a comparison of bivariate return period estimates carried out by using alternative approaches is illustrated.

2017 - Evidence of an emerging levee failure mechanism causing disastrous floods in Italy [Abstract in Rivista]
Orlandini, S.; Moretti, G.
abstract

2017 - Hydrography-driven coarsening of grid digital elevation models [Abstract in Rivista]
Moretti, G.; Orlandini, S.
abstract

2017 - Hydrography-driven coarsening of grid digital elevation models [Abstract in Atti di Convegno]
Moretti, G; Orlandini, S.
abstract

2017 - New metrics for evaluating channel networks extracted in grid digital elevation models [Abstract in Atti di Convegno]
Orlandini, S.; Moretti, G.
abstract

2016 - CONTROL OF COUPLING MASS BALANCE ERROR IN A PROCESS- BASED NUMERICAL MODEL OF SURFACE-SUBSURFACE FLOW INTERACTION [Relazione in Atti di Convegno]
Fiorentini, Marcello; Orlandini, Stefano
abstract

KEY POINTS • Sources of mass balance error in a process-based hydrological model of surface-subsurface flow interaction are investigated to improve the model’s coupling scheme • These sources of mass balance error are identified by using a set of dimensionless indices and the analysis of temporal and spatial patterns of error • A time step control based on a degree of coupling index is proposed and the interpolation algorithm used to pass exchange variables of surface-subsurface flow interaction is improved

2016 - EVIDENCE OF AN EMERGING LEVEE FAILURE MECHANISM CAUSING DISASTRUOS FLOODS IN ITALY [Relazione in Atti di Convegno]
Orlandini, Stefano; Moretti, Giovanni
abstract

KEY POINTS • Burrowing mammals are demonstrated to be a serious threat of earthen levee failure • Internal erosion developing along a den system can cause the collapse of the levee top • Internal flow may be due to direct inflow into the den system or to den wall failure 


2016 - Evidence of an emerging levee failure mechanism causing disastrous foods in Italy [Relazione in Atti di Convegno]
Orlandini, S.; Moretti, G.
abstract

2016 - Relation between grid, channel, and Peano networks in high-resolution digital elevation models [Articolo su rivista]
De Bartolo, Samuele; Dell’Accio, Francesco; Frandina, Giuseppe; Moretti, Giovanni; Orlandini, Stefano; Veltri, Massimo
abstract

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. © 2016. American Geophysical Union. All Rights Reserved.

2015 - Cluster Analysis of Three-Way Atmospheric Data [Relazione in Atti di Convegno]
Morlini, Isabella; Orlandini, Stefano
abstract

Classification of meteorological time series is important for the analysis of the climate variability and climate change. The clustering of several years in groups that are homogeneous with reference to the amount of precipitation and to the atmospheric condition, can aid in understanding the structure of precipitation and may be important in developing hydrological models. In this paper we propose a cluster analysis of multivariate time series based on a dissimilarity measure that considers the functional form of the data. The unit to be classified are 148 years, from 1861 to 2008, and the variables are the values of precipitation, the minimum temperature and the maximum temperature in different occasions (days or months) in the province of Modena (Northern Italy)

2015 - Control of coupling mass balance error in a process-based numerical model of surface-subsurface flow interaction [Articolo su rivista]
Fiorentini, Marcello; Orlandini, Stefano; Paniconi, Claudio
abstract

A process-based numerical model of integrated surface-subsurface flow is analyzed in order to identify, track, and reduce the mass balance errors affiliated with the model’s coupling scheme. The sources of coupling error include a surface-subsurface grid interface that requires node-to-cell and cell-to-node interpolation of exchange fluxes and ponding heads, and a sequential iterative time matching procedure that includes a time lag in these same exchange terms. Based on numerical experiments carried out for two synthetic test cases and for a complex drainage basin in northern Italy, it is shown that the coupling mass balance error increases during the flood recession limb when the rate of change in the fluxes exchanged between the surface and subsurface is highest. A dimensionless index that quantifies the degree of cou- pling and a saturated area index are introduced to monitor the sensitivity of the model to coupling error. Error reduction is achieved through improvements to the heuristic procedure used to control and adapt the time step interval and to the interpolation algorithm used to pass exchange variables from nodes to cells. The analysis presented illustrates the trade-offs between a flexible description of surface and subsurface flow processes and the numerical errors inherent in sequential iterative coupling with staggered nodal points at the land surface interface, and it reveals mitigation strategies that are applicable to all integrated models sharing this coupling and discretization approach.

2015 - Evidence of an Emerging Disturbance of Earthen Levees Causing Disastrous Floods in Italy [Abstract in Atti di Convegno]
Orlandini, Stefano; Moretti, Giovanni
abstract

A levee failure occurred along the Secchia River, Northern Italy, on January 19, 2014, resulting in flood damage in excess of $500 Million (Figure). In response to this failure, immediate surveillance of other levees in the region led to the identification of a second breach developing on the neighboring Panaro River, where rapid mitigation efforts were successful in averting a full levee failure. The paired breach events that occurred along the Secchia and Panaro Rivers provided an excellent window on an emerging disturbance of levees and related failure mechanism. In the Secchia River, by combining the information content of photographs taken from helicopters in the early stage of breach development and 10-cm resolution aerial photographs taken in 2010 and 2012, animal burrows were found to exist in the precise levee location where the breach originated. In the Panaro River, internal erosion was observed to occur at a location where a crested porcupine den was known to exist and this erosion led to the collapse of the levee top. Evidence collected suggested that it is quite likely that the levee failure of the Secchia River was of a similar mechanism as the observed failure of the Panaro River. Detailed numerical modeling of rainfall, river flow, and variably saturated flow occurring in disturbed levees in response to complex hydroclimatic forcing indicated that the levee failure of the Secchia River may have been triggered by direct river inflow into the den system or collapse of a hypothetical den separated by a 1-m earthen wall from the levee riverside, which saturated during the hydroclimatic event. It is important to bring these processes to the attention of hydrologists and geotechnical engineers as well as to trigger an interdisciplinary discussion on habitat fragmentation and wildlife shifts due to development and climate pressures. These disturbances come together with changes in extreme events to inform the broader concern of risk analysis due to floods.

2015 - Evidence of an emerging levee failure mechanism causing disastrous floods in Italy [Articolo su rivista]
Orlandini, Stefano; Moretti, Giovanni; Albertson, John D.
abstract

A levee failure occurred along the Secchia River, Northern Italy, on 19 January 2014, resulting in flood damage in excess of $500 million. In response to this failure, immediate surveillance of other levees in the region led to the identification of a second breach developing on the neighboring Panaro River, where rapid mitigation efforts were successful in averting a full levee failure. The paired breach events that occurred along the Secchia and Panaro Rivers provided an excellent window on an emerging levee failure mechanism. In the Secchia River, by combining the information content of photographs taken from helicopters in the early stage of breach development and 10 cm resolution aerial photographs taken in 2010 and 2012, animal burrows were found to exist in the precise levee location where the breach originated. In the Panaro River, internal erosion was observed to occur at a location where a crested porcupine den was known to exist and this erosion led to the collapse of the levee top. This paper uses detailed numerical modeling of rainfall, river flow, and variably saturated flow in the levee to explore the hydraulic and geotechnical mechanisms that were triggered along the Secchia and Panaro Rivers by activities of burrowing animals leading to levee failures. As habitats become more fragmented and constrained along river corridors, it is possible that this failure mechanism could become more prevalent and, therefore, will demand greater attention in both the design and maintenance of earthen hydraulic structures as well as in wildlife management.

2014 - Analytical basis for determining slope lines in grid digital elevation models [Articolo su rivista]
Orlandini, Stefano; Moretti, Giovanni; Gavioli, Andrea
abstract

[1] An analytical basis for the determination of slope lines in grid digital elevation models is provided by using the D8-LTD method (eight slope directions, least transverse deviation). The D8-LTD method’s capability to predict consistently exact slope lines as the grid cell size goes to zero is shown analytically by applying mathematical analysis methods. The use of cumulative, least transverse deviations is found to be the key factor allowing for globally unbiased approximations of slope lines. The D8-LTD method’s properties are also demonstrated numerically by using digital elevation models of a synthetic sloping surface obtained from the Himmelblau function. It is shown that slope lines obtained from the D8-LTD method can approximate the exact slope lines as close as desired by selecting a grid cell size that is small enough. In contrast, the standard D8 method is found to produce significantly biased results even when small grid cells are used. The D8-LTD method outperforms the D8 method over a wide range of grid cell sizes (up to 20 m in this application), beyond which grid cell size becomes too large to validly represent the underlying sloping surface. It is therefore concluded that the D8-LTD method should be used in preference to the standard D8 method in order to obtain slope lines that are only limited in reliability by the detail of topographic data, and not by the accuracy of the slope direction method applied.

2014 - Control of mass balance error in a detailed model of surface-subsurface flow interaction [Abstract in Atti di Convegno]
Fiorentini, Marcello; Orlandini, Stefano
abstract

Several process-based catchment-scale hydrologic models have been developed in recent years to describe the interactions and feedbacks between different components of the water cycle, but few studies have considered the sources of coupling error in these models. In this work we analyze the sequential iterative coupling scheme of the distributed model CATHY (CATchment HYdrology) in order to identify the different sources of mass balance error and to examine how these are influenced by topography, hydraulic properties, and atmospheric forcing. A pair of adimensional indices that quantify the degree of coupling and of flux partitioning is presented. Our analysis shows that mass balance errors increase during the flood recession limb because of the exchange of information between surface and subsurface water flow. Surface water propagation is cell centered, while the subsurface flow equation is solved on the vertices of surface cells. Evaluation of surface pressure heads and exchange fluxes is critical on this staggered surface-subsurface mesh, especially during transitions from unsaturated to saturated conditions and vice versa. A modified version of the flux exchange algorithm is introduced that considers the effective availability of water on surface cells. The performance of the model is also improved by introducing a heuristic procedure to control and adapt the time step interval. Starting from numerical stability and convergence constraints, this procedure varies the computational interval as a function of the rate of change of surface saturation via the coupling degree index. A final improvement made to the sequential coupling scheme in CATHY is to solve the surface routing equation after rather than before the subsurface module. We find that the modified version improves the water balance by more than 50% in most of the tests considered for a simple v-shaped catchment. The results so far obtained for the synthetic v-catchment indicate the need for a more comprehensive analysis including real catchments.

2013 - Cluster analysis of three-way atmospheric data [Abstract in Atti di Convegno]
Morlini, Isabella; Orlandini, Stefano
abstract

Classification of meteorological time series is important for the analysis of the climate variability and climate change. The clustering of several years in groups that are homogeneous with reference to the amount of precipitation and to the atmospheric condition, can aid in understanding the structure of precipitation and may be important in developing hydrological models. In this paper we propose a cluster analysis of multivariate time series based on a dissimilarity measure that considers the functional form of the data. The unit to be classified are 148 years, from 1861 to 2008, and the variables are the values of precipitation, the minimum temperature and the maximum temperature in different occasions (days or months) in the province of Modena (Northern Italy)

2013 - Robust numerical solution of the reservoir routing equation [Articolo su rivista]
Fiorentini, Marcello; Orlandini, Stefano
abstract

The robustness of numerical methods for the solution of the reservoir routing equation is evaluated. The methods considered in this study are: (1) the Laurenson–Pilgrim method, (2) the fourth-order Runge–Kutta method, and (3) the fixed order Cash–Karp method. Method (1) is unable to handle nonmonotonic outflow rating curves. Method (2) is found to fail under critical conditions occurring, especially at the end of inflow recession limbs, when large time steps (greater than 12 min in this application) are used. Method (3) is computationally intensive and it does not solve the limitations of method (2). The limitations of method (2) can be efficiently overcome by reducing the time step in the critical phases of the simulation so as to ensure that water level remains inside the domains of the storage function and the outflow rating curve. The incorporation of a simple backstepping procedure implementing this control into the method (2) yields a robust and accurate reservoir routing method that can be safely used in distributed time-continuous catchment models.

2013 - Technical Report of the Project: Climate Change and Human Impacts on the Sustainability of Groundwater Resources: Quantity and Quality Issues, Mitigation and Adaptation Strategies in the Toledo River Basin (Brazil) [Monografia/Trattato scientifico]
Cusi, Alice; Fiorentini, Marcello; Moretti, Giovanni; Orlandini, Stefano; Bley, Cicero J. r.; Rafael González Hernando de, Aguiar; Salvatore, D'Angelo
abstract

A distributed physically-based hydrological model named CATHY (CATchment HYdrology) is used to perform a detailed analysis of the Toledo River basin response to climate projections. CATHY couples a subsurface module, described by a three-dimensional Richards equation, with a surface module, led by a one-dimensional diffusion wave equation. Dynamical coupling is achieved by means of a switching in boundary conditions, from a Dirichlet to a Neumann condition and vice versa. Future climate scenarios are determined from historical time series of daily rainfall and temperature in the study area by applying changes compatible with predictions made by the Intergovernmental Panel on Climate Change (IPCC). A twenty-year simulation is run under four future scenarios and the results are compared with those obtained under an unaltered scenario. It is found that the rise or the lowering of water table level is generally not uniform across the basin, being more significant in the uppermost areas. This suggests that measures of adaptation to climate change effects could be practiced by selecting suitable cultures across drainage basins, especially in the areas where the impact of climate change are most significant.

2012 - ASSESSMENT OF CLIMATE CHANGE IMPACTS IN A BRAZILIAN CATCHMENT USING A DETAILED HYDROLOGICAL MODEL [Relazione in Atti di Convegno]
Cusi, Alice; Fiorentini, Marcello; Moretti, Giovanni; Orlandini, Stefano; Bley, C. J. r.; R., Gonzáles; S., D'Angelo
abstract

A distributed physically-based hydrological model named CATHY (CATchment HYdrology) is used to perform a detailed analysis of the response of Toledo River basin (Paranà, Brazil) to climate projections. CATHY couples a subsurface module, described by a three-dimensional Richards equation, with a surface module, led by a one-dimensional diffusion wave equation. Dynamical coupling is achieved by means of a switching in boundary conditions, from a Dirichlet to a Neumann condition and vice versa. Future climate scenarios are determined from historical time series of daily rainfall and temperature in the study area by applying changes compatible with predictions made by the Intergovernmental Panel on Climate Change (IPCC). A twenty-year simulation is run under four future scenarios and the results are compared with those obtained under an unaltered scenario. It is found that the rise or the lowering of water table level is generally not uniform across the basin, being more significant in the uppermost areas. This suggests that measures of adaptation to climate change effects could be practiced by selecting suitable cultures across drainage basins, especially in the areas where the impact of climate change are most significant.

2012 - Evaluation of flow direction methods against field observations of overland flow dispersion [Relazione in Atti di Convegno]
Orlandini, Stefano; Moretti, Giovanni; Corticelli, Mauro Alessandro; Santangelo, Paolo Emilio; Capra, Alessandro; Rivola, Riccardo; Albertson, John D.
abstract

The D8, D8-LTD, D∞-LTD, D∞, MD∞, and MD8 flow direction methods are evaluated against field observations of overland flow dispersion obtained from novel experimental methods. Thin flows of cold water were released at selected points on a warmer slope and individual overland flow patterns originating from each of these points were observed using a terrestrial laser scanner and a thermal imaging camera. Land microtopography was determined by using laser returns from the dry land surface, whereas overland flow patterns were determined by using either laser returns or infrared emissions from the wetted portions of the land surface. Planar overland flow dispersion is found to play an important role in the region lying immediately downslope of the point source, but attenuates rapidly as flow propagates downslope. In contrast, existing dispersive flow direction methods are found to provide a continued dispersion with distance downslope. Predicted propagation patterns, for all methods considered here, depend critically on the size h of grid cells involved. All methods are found to be poorly sensitive in extremely fine grids (h ≤ 2 cm), and to be poorly specific in coarse grids (h = 2 m). Satisfactory results are, however, obtained in grids having resolutions h that approach the average flow width (50 cm), with the best performances displayed by the MD8 method in the finest grids (5 cm ≤ h ≤ 20 cm), and by the MD∞, D∞, and D∞-LTD methods in the coarsest grids (20 cm < h ≤ 1 m).

2012 - Evaluation of flow direction methods against field observations of overland flow dispersion [Articolo su rivista]
Orlandini, Stefano; Moretti, Giovanni; Corticelli, Mauro Alessandro; Santangelo, Paolo Emilio; Capra, Alessandro; Rivola, Riccardo; Albertson, John D.
abstract

The D8, D8-LTD, D∞-LTD, D∞, MD∞, and MD8 flow direction methods are evaluated against field observations of overland flow dispersion obtained from novel experimental methods. Thin flows of cold water were released at selected points on a warmer slope and individual overland flow patterns originating from each of these points were observed using a terrestrial laser scanner and a thermal imaging camera. Land microtopography was determined by using laser returns from the dry land surface, whereas overland flow patterns were determined by using either laser returns or infrared emissions from the wetted portions of the land surface. Planar overland flow dispersion is found to play an important role in the region laying immediately downslope of the point source, but attenuates rapidly as flow propagates downslope. In contrast, existing dispersive flow direction methods are found to provide a continued dispersion with distance downslope. Predicted propagation patterns, for all methods considered here, depend critically on the size h of grid cells involved. All methods are found to be poorly sensitive in extremely fine grids (h ≤ 2 cm), and to be poorly specific in coarse grids (h = 2 m). Satisfactory results are, however, obtained in grids having resolutions h that approach the average flow width (50 cm), with the best performances displayed by the MD8 method in the finest grids (5 ≤ h ≤ 20 cm), and by the MD∞, D∞, and D∞-LTD methods in the coarsest grids (20 cm < h ≤ 1 m).

2012 - Evaluation of flow direction methods against field observations of overland flow dispersion [Abstract in Rivista]
Orlandini, Stefano; Moretti, Giovanni; Corticelli, Mauro Alessandro; Santangelo, Paolo Emilio; Capra, Alessandro; Rivola, Riccardo; D. Albertson., John
abstract

Despite the broad effort made in grid-based distributed catchment modeling to account for planar overland flow dispersion, actual dispersion experienced by overland flow along a natural slope has not been measured so far, and the ability of terrain analysis methods to reproduce this dispersion has not been evaluated. In the present study, the D8, D8-LTD, D$infty$-LTD, D$infty$, MD$infty$, and MD8 flow direction methods are evaluated against field observations of overland flow dispersion obtained from novel experimental methods. Thin flows of cold (2--10$^circ$C) water were released at selected points on a warmer (15--30$^circ$C) slope and individual overland flow patterns originating from each of these points were observed using a terrestrial laser scanner and a thermal imaging camera. Prior to each experimental water release, a ScanStation C10 terrestrial laser scanner by Leica Geosystems was used to acquire a point cloud having average density of 25~points/cm$^2$. This point cloud was used to generate alternative grid-based digital elevation models having resolution $h$ ranging from 1~cm to 2~m. During the experiments, an Avio Advanced Thermo TVS-500EX camera by Nippon Avionics was used to monitor land surface temperature with resolution better than $0.05^circ$C. The overland flow patterns were also found to be discernible in terrestrial laser scanner reflectance signal acquired immediately following the flow experiments. Overland flow patterns were determined by considering contrasted temperature and reflectance of the dry and wetted land surface portions. Predicted propagation patterns and observed flow patterns were compared by considering the fractions of flow released at the point source that propagates through the grid cells. Predictions of these quantities were directly provided by flow direction methods and by related flow accumulation algorithms. Suitable data for the comparison were derived from observed overland flow patterns by assuming a uniform distribution of flow along each cross section. Planar overland flow dispersion is found to play an important role in the region lying immediately downslope of the point source, but attenuates rapidly as flow propagates downslope displaying a nearly constant width of about 50~cm. In contrast, existing dispersive flow direction methods are found to provide a continued dispersion with distance downslope. Predicted propagation patterns, for all methods considered here, depend critically on $h$. All methods are found to be poorly sensitive in extremely fine grids ($h leq 2$~cm), and to be poorly specific in coarse grids ($h = 2$~m). Satisfactory results are, however, obtained when $h$ approaches the average flow width, with the best performances in terms of Pearson correlation coefficient displayed by the MD8 method in the finest grids ($5~{ m cm} leq h leq 20~{ m cm}$), and by the MD$infty$, D$infty$, and D$infty$-LTD methods in the coarsest grids ($20~{ m cm} < h leq 1~{ m m}$). The results obtained in this study suggest further testing of terrain analysis methods with longer flow patterns and coarser grids. Scale issues affecting the relation between land surface microtopography, dispersion, and size of grid cells involved need then to be addressed to provide a hydrologic model of flow partitioning along the slope directions identified by terrain analysis methods.

2012 - NUMERICAL SOLUTION OF THE RESERVOIR ROUTING EQUATION [Relazione in Atti di Convegno]
Fiorentini, Marcello; Orlandini, Stefano
abstract

Numerical methods for the solution of the reservoir routing equation are critically reviewed. The methods considered in this study are: (1) the Laurenson-Pilgrim method, (2) the fourth-order Runge-Kutta method, and (3) the fixed order Cash-Karp method. Method (1) does not handle complex outflow rating curves in which discharge may decrease with water level. Method (2) is found to crash under critical conditions occurring especially when large time steps (greater than 10 min in this application) are used at the beginning of the inflow rising limbs and at the end of the inflow recession limbs. Method (3) is computationally intensive and it does not solve the limitations of method (2) mentioned above. In this study it has been found that the limitations of method (2) can be efficiently overcome by reducing the time step in the critical phases of the simulation so as to allow water level to remain within the domains of definition of the storage function and of the outflow rating curve. With this control, the Runge-Kutta method ensures robust and accurate descriptions of reservoir dynamics and it is therefore expected to be suitable for use in distributed catchment models.

2011 - Idrologia superficiale della Valchiavenna: Simulazione delle correnti diffuse e canalizzate [Capitolo/Saggio]
Orlandini, Stefano
abstract

Il presente studio illustra le attività di campo e modellistiche svolte nell'ambito del progetto di ricerca "La Valchiavenna: Un bacino pilota per il controllo dell'ambiente alpino" al fine di migliorare la descrizione delle correnti superficiali che si attuano sui versanti e nei canali.

2011 - On the prediction of channel heads in a complex alpine terrain using gridded elevation data [Articolo su rivista]
Orlandini, Stefano; P., Tarolli; Moretti, Giovanni; G., Dalla Fontana
abstract

Threshold conditions for channel initiation are evaluated by using gridded elevation data derived from a lidar survey, a reliable algorithm for the determination of surface flow paths, and field observations of channel heads for a study area located in the eastern ItalianAlps. These threshold conditions are determined by considering the channel heads observed across a portion of the study area and computing the related values of (1) drainage area A, (2) area-slope function AS^2, with S being the local slope, and (3) Strahler order omega* of surface flow paths extracted from gridded elevation data. Attention is focused on the dependence of the obtained threshold values on the size of grid cells involved and on the ability of the identified threshold conditions to provide reliable predictions of channel heads across the entire study area. The results indicate that the threshold values of A, AS^2, and omega* are all significantly dependent on grid cell size, and the uncertainty in the determination of threshold values of omega* is significantly smaller than that affecting the determination of threshold values of A and AS^2. The comparison between predicted and observed channel heads indicates that the considered methods display variable reliability and sensitivity over different drainage basins and grid cell sizes, with a general tendency to predict more channelheads than can be observed in the field. Acceptable predictions are normally obtained where channel heads are formed essentially by surface runoff. More comprehensive methods seem, however, to be needed to predict channel heads affected by groundwater seeping upward.

2010 - Identification and prediction of channel heads from gridded elevation data [Abstract in Rivista]
Orlandini, Stefano; Moretti, Giovanni; P., Tarolli; G., Dalla Fontana
abstract

See the file in PDF provided as attachment.

2010 - On predicting channel initiation from gridded elevation data [Relazione in Atti di Convegno]
P., Tarolli; G., Dalla Fontana; Moretti, Giovanni; Orlandini, Stefano
abstract

Three threshold conditions for channel initiation are evaluated by using gridded elevation data derived from a detailed lidar survey, a reliable algorithm for the determination of surface flow paths, and accurate field observations of channel heads for a study area located in the eastern Italian Alps. These three threshold conditions are determined by considering part of the observed channel heads and computing for them the related values of (1) the drainage area A, (2) the monomial area-slope function AS2 of the drainage area A and the local slope S, and (3) the Strahler order ω* of surface flow paths extracted from gridded elevation data. Attention is focused on the dependence of the obtained threshold values on the size of grid cells involved, and on the ability of threshold conditions to predict channel heads. The results indicate that (i) the uncertainty in the threshold values of the Strahler order ω* is significantly smaller than that affecting the threshold values of the drainage area A and the area-slope function AS2, (ii) threshold values of A, AS2, and ω* are all significantly dependent on grid cell size, and (iii) the threshold values of the Strahler order ω* follow quite well a power function relationship of grid cell size. The comparison between predicted and observed channel heads, performed on three different drainage basins, indicates that Strahler classification of surface flow paths and pruning of exterior links provide a sound basis for the determination of channel heads formed essentially by surface erosion. In addition, it reveals that more comprehensive methods are needed to predict channel heads affected by groundwater seeping upwards in areas characterized by strong geologic controls.

2010 - Role of hydraulic geometry in flood wave propagation [Abstract in Rivista]
Orlandini, Stefano
abstract

The role of hydraulic geometry in flood wave propagation is investigated by using a diffusion wave model with inertial effects. Power function relationships W = a’ Q^b’ and kS = r’ Q^y’ are used to reproduce the at-a-station variations of water-surface width W and Gauckler-Strickler conductance coefficient kS (the inverse of Manning resistance coefficient) with flow discharge Q. Downstream variations of coefficients a’ and r’ are not considered in this study. The considered hydraulic geometry relationships are incorporated into a diffusion wave model in which the term (1 − Ve^2), Ve being the Vedernikov number, multiplies the Hayami’s diffusivity Q/(2 W S0), S0 being the channel bed slope. This mathematical model is solved numerically by using a matched artificial diffusivity method. Numerical experiments are carried out by evaluating peak attenuation and mean peak celerity of flood waves propagating along channel reaches characterized by coefficients a’ and r’ equal to the average values observed in natural rivers, by all the combinations of exponents b’ and y’ laying in the range 0–0.5, and by values of S0 laying in the range 0.000125–0.032. It is found that: (1) peak attenuation and mean peak celerity display the minimum values for b’ = 0.5 and y’ = 0, (2) for high values of y’, Ve displays values greater than 1 indicating physical instability of flood waves, and (3) around the condition b’ = 0 and y’ = 0, for high values of Q/W and low values of S0, the Peclet number Pe (evaluated over the channel reach length) displays values less than 2 indicating unrealistic hydraulic diffusion (more storage effects than those produced by a reservoir). The region of the plane b’y’ representing relevant flood waves lays therefore between the instability region Ve > 1, where unstable flood waves are physically possible but rarely observed in natural channels and not reproducible with the considered model, and the region of unrealistic diffusion Pe < 2, where numerical solutions are possible but physically questionable. In this region, peak attenuation and mean peak celerity are found to be more sensitive to variations in y’ than in b’. The developed diffusion wave model provides a reliable description of the advection and diffusion processes determining travel times and storage variations at the channel reach scale, with clear implications for reproducing surface flows and their interaction with the subsurface. The obtained results indicate that stream channel geometry plays a critical role in runoff propagation, and thus caution must be exercised in river engineering when altering shape and resistance to flow of channels. In addition, they suggest that the developed model can be usefully combined with field data to understand how kinematic wave celerity and hydraulic diffusivity scale when mountain streams and hillslope rivulets are considered, a challenge for the definition of a new generation of distributed models that are really based on physics at all the spatial and temporal scales characterizing the different processes that occur within the drainage basin.

2010 - Surface-subsurface flow modeling with path-based runoff routing, boundary condition-based coupling, and assimilation of multisource observation data [Articolo su rivista]
M., Camporese; C., Paniconi; M., Putti; Orlandini, Stefano
abstract

A distributed physically based model incorporating novel approaches for the representation of surface-subsurface processes and interactions is presented. A path-based description of surface flow across the drainage basin is used, with several options for identifying flow directions, for separating channel cells from hillslope cells, and for representing stream channel hydraulic geometry. Lakes and other topographic depressions are identified and specially treated as part of the preprocessing procedures applied to the digital elevation data for the catchment. Threshold-based boundary condition switching is used to partition potential (atmospheric) fluxes into actual fluxes across the land surface and changes in surface storage, thus resolving the exchange fluxes, or coupling, between the surface and subsurface modules. Nested time stepping allows smaller steps to be taken for typically faster and explicitly solved surface runoff routing, while a mesh coarsening option allows larger grid elements to be used for typically slower and more compute-intensive subsurface flow. Sequential data assimilation schemes allow the model predictions to be updated with spatiotemporal observation data of surface and subsurface variables. These approaches are discussed in detail, and the physical and numerical behavior of the model is illustrated over catchment scales ranging from 0.0027 to 356 km2, addressing different hydrological processes and highlighting the importance of describing coupled surface-subsurface flow.

2009 - Cell Size Dependence of Threshold Conditions for the Delineation of Drainage Networks from Gridded Elevation Data [Abstract in Atti di Convegno]
Tarolli, P.; Dalla Fontana, G.; Moretti, G.; Orlandini, S.
abstract

2009 - Comment on "Global search algorithm for nondispersive flowpath extraction" by Kyungrock Paik [Articolo su rivista]
Orlandini, Stefano; Moretti, Giovanni
abstract

Paik [2008] presents a new algorithm for the extractionof surface flow paths from gridded elevation data,arguing that ‘‘significant improvement over the limitationof D8 and D8-LTD [methods] can be achieved using a new and simple idea without introducing any model parameter’’ [Paik, 2008, paragraph 9]. However, all Paik’s [2008] arguments against Orlandini et al.’s [2003] D8-LTD method can be shown to be unsubstantial merely on the basis of geometrical considerations. The purpose of the present comment is to point out that (1) an analytical background to support the decision to set the dampening factor equal to 1 in the D8-LTD method does exist and (2) results obtained from incorrect implementations of the D8-LTDmethod are used in the investigation of Paik [2008]. Further considerations on Paik’s [2008] analysis of the D8-LTD method are also provided.

2009 - Determination of surface flow paths from gridded elevation data [Articolo su rivista]
Orlandini, Stefano; Moretti, Giovanni
abstract

Surface flow paths are obtained from gridded elevation data by connecting grid cell centers along predetermined flow directions. These flow directions are commonly determined using single and multiple flow direction algorithms. It remains, however, unclear whether multiple flow direction algorithms, which introduce artificial dispersion, can be used to describe surface flow paths and gravity-driven processes across a terrain without causing unrealistic flow dispersion. To explore this issue, a unified algorithm for the determination of flow directions has been developed, and new methods for the validation of the resulting surface flow paths are introduced. The unified algorithm makes it possible, by setting appropriate parameters, to perform local or path-based analyses and to experiment with different combinations of single and multiple flow directions in a morphologically significant manner. The new validation methods use drainage systems delineated from contour elevation data as a reference and take into consideration the overlap between these systems and those obtained from gridded elevation data. The unified algorithm is presented, and the results are evaluated for selected case studies in order to provide guidance on the use of surface flow path algorithms based on gridded elevation data.

2009 - Identification of surface flow paths, slopes, and channel networks from gridded elevation data [Abstract in Rivista]
Orlandini, Stefano; Moretti, Giovanni; P., Tarolli; G., Dalla Fontana
abstract

Stream channels enhance the hydrological connectivity between land surface elements. The representation and prediction of stream channels in drainage basins has therefore been a perennial concern in geomorphology, with implications for understanding of drainage basin origin, scale and morphology, basin hydrology, and effects of natural and man-induced process changes. The channel (or stream) network is defined by channels with well-defined banks and sources. In theory, the channel network includes all the minor rills which are definite watercourses, even including all the ephemeral channels in the furthermost headwaters. In practice, the direct survey of all channels is normally a prohibitive task, and the detail with which the channel network is represented is dependent on the scale of the map used to trace the channels. In actual fact, the headward limits of the blue lines do not reflect any statistical characteristic of streamflow occurrence, but they are drawn to fit a rather personalized aesthetic. On the other hand, the explicit description of the mechanisms determining the channel heads is a nontrivial task since it requires complex fluvial and/or landsliding processes to be considered singly or in combination. However, the increasing availability of highly accurate digital elevation data derived from LiDAR surveys, reliable terrain analysis methods, and observations collected in the field or remotely, offers new potential for developing and/or evaluating prediction models for channel initiation. In addition to detailed models, simpler generalizations from field facts can be sought by incorporating the broad features of climate, topography, and geology. In the present study, methods for the determination of surface flow paths are briefly reviewed. Three methods for the prediction of channel networks are then evaluated by using gridded elevation data derived from high-precision LiDAR surveys, a reliable algorithm for the determination of surface flow paths, and accurate field observations of channel heads for sites located in the eastern Italian Alps. These three methods are based on different threshold conditions for channel initiation, defined in terms of: (1) drainage area, (2) monomial function of drainage area and local slope, and (3) Strahler order of surface flow paths extracted from gridded elevation data. Attention is especially focused on the dependence of threshold conditions on the size of grid cells involved. The results indicate that: (i) all threshold conditions for channel initiation are grid cell size depended, (ii) the methods based on drainage area and Strahler order provide robust predictions of channel heads, and (iii) the threshold in the Strahler order of surface flow paths extracted from gridded elevation data follows quite well a scaling relation of grid cell size. The analysis carried out shows that the considered methods may provide a sound rationale for the prediction of channel heads formed essentially by surface erosion, but it reveals that more comprehensive methods are needed to predict channel heads influenced by groundwater seeping upwards.

2008 - Automatic delineation of drainage basins from contour elevation data using skeleton construction techniques [Relazione in Atti di Convegno]
Moretti, Giovanni; Orlandini, Stefano
abstract

New methods for automatic delineation of drainage basins from contour elevation data are presented. As a fundamental preprocessing step, the points defining a set of contour lines are used to compute the Delaunay triangulation, the Voronoi diagram, and other structures known in computational geometry as the crust and the skeleton (or medial axis transform). By exploiting the skeleton extracted from contour lines, a recursive algorithm is then developed to solve critical topographic structures such as ridges, saddles, and peaks in a fully automated and accurate manner. Finally, the algorithm is further extended to deal with the construction of flow nets. The proposed methods are able to process automatically complex topographic structures and to produce results comparable to those that can be interpreted visually from contour lines.

2008 - Automatic delineation of drainage basins from contour elevation data using skeleton construction techniques [Articolo su rivista]
Moretti, Giovanni; Orlandini, Stefano
abstract

New methods for automatic delineation of drainage basins from contour elevation data are presented. As a fundamental preprocessing step, the points defining a set of contour lines are used to compute the Delaunay triangulation, the Voronoi diagram, and other structures known in computational geometry as the crust and the skeleton (or medial axis transform). By exploiting the skeleton extracted from contour lines, a recursive algorithm is then developed to solve critical topographic structures such as ridges, saddles, and peaks in a fully automated and accurate manner. Finally, the algorithmis further extended to deal with the construction of flow nets. Numerical experiments based on high-accuracy contour elevation data of real terrains show that the proposed methods are able to process automatically complex topographic structures andto produce results comparable to those that can be interpreted visually from contour lines. The gain in accuracy over current state-of-the-art solutions is generally found to be significant and to increase as the contour interval increases.

2008 - Collecting a multi-disciplinary field dataset to model the interactions between a flood control reservoir and the underlying porous aquifer (abstract) [Abstract in Atti di Convegno]
Borgatti, L.; Corsini, A.; Chiapponi, L.; D'Oria, M.; Giuffredi, F.; Lancellotta, R.; Mignosa, P.; Moretti, G.; Orlandini, S.; Pellegrini, M.; Remitti, F.; Ronchetti, F.; Tanda, M.; Zanini, A.
abstract

2008 - On the determination of surface flow paths from gridded elevation data [Abstract in Rivista]
Orlandini, Stefano; Moretti, Giovanni
abstract

Multiple flow direction algorithms are commonly thought to be a useful means for determining drainage areas from gridded elevation data. It remains however unclear whether these algorithms can be used to describe surface flow paths and gravity-driven processes across a terrain without causing unrealistic artificial dispersion of flow. To explore this issue, a unified algorithm for the determination of flow directions is developed and new methods for the validation of surface flow paths are introduced. The unified algorithm allows, by setting appropriate parameters, to perform local or path-based analyses, and to experiment different combinations of single and multiple flow directions in a morphologically significant manner. The new validation methods use drainage systems delineated from contour elevation data as a reference and consider the overlapping between these drainage systems and the corresponding drainage systems obtained from gridded elevation data. A purely morphologic analysis is carried out. The obtained results suggest that dispersive methods may be preferred over nondispersive methods if the computation of the spatial pattern of drainage area, especially along divergent terrains, is the main focus. On the other hand, the results reveal that path-based nondispersive methods should be preferred over dispersive methods if the delineation of drainage systems and surface flow paths is an important focus. Path-based nondispersive methods are found to be a reliable means for the determination of surface flow paths from gridded elevation data, and to provide therefore a sound basis for the distributed description of gravity-driven processes. Future work is needed to formulate models of physical dispersion for water, sediments and solutes upon this purely morphologic basis.

2008 - On the determination of surface flow paths from gridded elevation data [Relazione in Atti di Convegno]
Orlandini, Stefano; Moretti, Giovanni
abstract

Multiple flow direction algorithms are commonly thought to be a useful means of determining drainage areas from gridded elevation data. It remains however unclear whether these algorithms can be used to describe surface flow paths and gravity-driven processes across a terrain without producing excessive artificial dispersion of flow. To explore this issue, a unifying algorithm for the determination of flow directions is developed and new methods for the validation of surface flow paths are introduced. The unifying algorithm allows, by setting appropriate parameters, to perform local or path-based analyses, and to experiment different combinations of single and multiple flow directions in a morphologically significant manner. The new evaluation methods designate the drainage systems delineated from contour elevation data as a reference and consider the overlapping between these drainage systems and the corresponding drainage systems obtained from gridded elevation data. Results from numerical experiments indicate that multiple flow direction algorithms are useful to describe the between-cell variation of drainage areas across divergent slopes, but reveal that path-based single flow direction algorithms are more effective to describe surface flow paths across both convergent and divergent terrains.

2007 - Automatic delineation of drainage basins from contour elevation data using skeleton construction techniques [Abstract in Rivista]
Moretti, Giovanni; Orlandini, Stefano
abstract

A new method for automatic delineation of drainage basins from contour elevation data is presented. As a preprocessing step, contour line vertices are used to construct Delaunay and Voronoi diagrams along with other useful structures known in computational geometry as the crust and the skeleton or medial axis transform. Using the skeleton of contour lines, a recursive algorithm is then developed to solve critical topographic structures such as ridges, saddles, and peaks in a fully-automated and accurate manner. Numerical experiments based on high- accuracy contour elevation data of real terrains (generated from LiDAR surveys) show that the proposed method is able to process automatically any topographic structure and to produce results that are comparable to those that can be interpreted visually from contour lines. The gain in accuracy over state-of-the-art solutions is generally found to be significant and to increase as the contour interval increases. Finally, it is shown how the proposed method can be easily applied to construct accurate flow nets in a fully-automated manner. Skeleton construction techniques allow the morphological information implicitly present in contour elevation data to be explicitly revealed and appropriately processed by a computer program, and therefore appear useful means for improving the accuracy with which physiographic features of drainage basins are determined. The proposed method can be used to advance the construction of flow nets and contour-based digital elevation models (as outlined in this study) and to test the reliability of algorithms for the analysis of more efficient and straightforward, gridded or triangulated, elevation data (as shown in a companion study).

2007 - Le alluvioni del Po nel secolo XIX: Alla ricerca delle cause [Capitolo/Saggio]
B., Bacchi; Orlandini, Stefano; Pellegrini, Maurizio
abstract

Il Capitolo 10, "Le alluvioni del Po: Alla ricerca delle cause", scritto da Baldassare Bacchi, Stefano Orlandini e Maurizio Pellegrini, cerca di dare una risposta al quesito che si erano posti gli ingegneri idraulici dell’Ottocento su quali fossero le cause delle tante piene del Po e dei suoi affluenti e per quale motivo, già dal 1705, ogni piena superasse il livello delle precederti, con una tendenza che sarebbe si sarebbe invertita solo dopo il 1951. Il dibattito scientifico fu aspro, con toni anche duri, come nel contrasto che oppose il Lombardini al Brighenti, studioso autorevole, questo ultimo, proveniente dall’ex legazione pontificia bolognese. Per il Lombardini non c’erano dubbi: la causa del fenomeno delle piene sempre più aggressive era da ricondurre all’intenso disboscamento nei bacini idrografici, un processo che si intensificò ulteriormente con la diffusione delle macchine a vapore. Il Manfredi intervenne nella disputa suggerendo un’ipotesi, quella di una tendenza di lungo periodo all’aumento delle precipitazioni, che il Lombardini ritenne inconsistente. D’altra parte, come ci ricorda Baldassare Bacchi nel Capitolo 8, mancavano in quel periodo misure sistematiche delle precipitazioni e delle portate dei corsi d’acqua. In assenza di questi dati diventa problematico anche oggi dare una risposta argomentata al quesito iniziale. L’orientamento attuale, in ogni modo, è quello di considerare con attenzione i cambiamenti climatici che si ebbero durante quei secoli. Dal 1580 circa, Alpi e Appennini furono interessati da un periodo freddo e piovoso, che in Nord Europa era iniziato già più di un secolo prima. È ragionevole pensare che, per effetto del cambiamento di clima, aumentassero le portate di piena dei corsi d’acqua, non solo del Po, ma di tutti i fiumi italiani ed europei. Aumento delle precipitazioni e disboscamento concorsero a incrementare sensibilmente il trasporto solido (i detriti asportati dalla montagna e trasportati dalla corrente fluviale sino al mare), con conseguente innalzamento del fondo dell’alveo. Nel Po si era aggiunto, peraltro da molti secoli, l’effetto di un potente fattore antropico: l’uomo per recuperare nuovi spazi all’agricoltura aveva arginato il fiume, costringendolo entro spazi sempre più ristretti; la massa d’acqua incanalata raggiungeva in tempi più brevi l’alveo della bassa pianura, da cui esondava per la più ridotta efficienza idraulica dell’alveo stesso a trattenerla. La grande pensilità del Po, dopo l’ansa di Viadana e Guastalla, decretava, infine, un rischio idraulico elevatissimo per le campagne latistanti; è sufficiente ricordare qualche “numero”: circa 1000 chilometri quadrati di campagne rimasero allagati nel 1705 e nel 1951 e circa 830 chilometri quadrati nel 1872. (Tratto dalla "Guida alla lettura," di Ireneo Ferrari e Maurizio Pellegrini, p. 9-14.)

2007 - Sulle origini e gli sviluppi dell’idrometria del fiume Po [Capitolo/Saggio]
Orlandini, Stefano
abstract

"Sulle origini e gli sviluppi dell’idrometria del fiume Po" è il titolo del Capitolo 9, scritto da Stefano Orlandini, che sviluppa, in pratica, i temi affrontati nel capitolo precedente. La trattazione riguarda principalmente la descrizione dei contenuti degli elaborati tecnici della Commissione Brioschi, che costituiscono una sorta di manuale illustrato per la determinazione delle scale delle portate, da prendere come esempio per tutte le sezioni di misura del Po. Lo strumento utilizzato, come si legge anche nel capitolo scritto da Bacchi [Capitolo 8], consisteva in scale idrometriche semplici ma molto belle: erano incise nella pietra del Biancone veronese. La sezione di misura sperimentale era ubicata in Provincia di Ferrara, presso Fossadalbero, circa 7 km a valle di Pontelagoscuro. La Commissione aveva compreso che per potere studiare la dinamica fluviale fosse indispensabile misurare le portate, per seguire la propagazione delle piene lungo l’asta fluviale, per capire le cause della frequenza di questi eventi e della crescita continua dei livelli idrometrici. L’illustrazione delle tecniche di misura e dei contenuti delle tavole è accompagnata da una breve storia degli strumenti di rilevamento e dei loro ideatori. Anche questo capitolo contribuisce significativamente alla conoscenza dei progressi tecnici e scientifici che hanno segnato l'evoluzione dell’idraulica padana. Il contributo di Stefano Orlandini costituisce, dunque, non solo un'interessante rassegna dell'idraulica padana nel corso del tempo, ma accenna anche alle tecniche di misura attuali sul Po e su quelle impiegate negli Stati Uniti, il paese all’avanguardia per l’idraulica fluviale, e a quello che si potrebbe fare nel Po. (Tratto dalla "Guida alla lettura," di Ireneo Ferrari e Maurizio Pellegrini, p. 9-14.)

2006 - Field determination of the spatial variation of resistance to flow along a steep Alpine stream [Articolo su rivista]
Orlandini, Stefano; C., Boaretti; V., Guidi; G., Sfondrini
abstract

Accurate field data have been collected along the Febbraro River (central Italian Alps) during quasi-steady, low-flow conditions to investigate the spatial variations of hydraulic and geomorphologic quantities potentially affecting resistance to flow. Detailed uncertainty analysis and weighted least-squares fitting of simple power function relationships to field-derived data are carried out to identify possible interdependencies between observed variables. Mean flow velocity is found to depend on water-surface slope, bed material particle size, and upstream drainage area, whereas its dependence on hydraulic depth appears less susceptible to quantification. Upstream drainage area is found to explain the variations of hydraulic depth, water-surface slope, Gauckler-Strickler conductance coefficient, and (although less significantly) flow discharge. Specifically, a highly significant positive dependence of the Gauckler-Strickler conductance coefficient on the upstream drainage area is found to exist, although anomalies in the variations of hydraulic depth and flow discharge are observed along the stream. The combined use of uncertainty analysis, hydraulic equations, and geomorphological relationships allows a possible characterization of resistance to flow along a steep Alpine stream and, perhaps more importantly, provides useful guidelines for future investigative efforts.

2006 - Sulla dimensione rappresentativa delle aree scolanti nei modelli distribuiti di drenaggio urbano [Relazione in Atti di Convegno]
Orlandini, Stefano; Moretti, Giovanni; M., Mambretti; F., Zanolla; P., Pedrazzoli; M., Cingi
abstract

La presente nota illustra i risultati di esperimenti numerici svolti applicando un modello distribuito di drenaggio all’abitato di Guastalla (Reggio Emilia) al fine di valutare l’influenza del dettaglio nella rappresentazione delle aree scolanti sulla risposta idrologica dei sistemi urbani complessi. I meccanismi di generazione e di propagazione del deflusso sulle aree scolanti sono descritti utilizzando il metodo CN e lo schema della corrivazione con curva tempo-area lineare, rispettivamente. Il dettaglio nella rappresentazione delle aree scolanti è variato attraverso la progressiva aggregazione delle classi di uso del suolo disponibili e delle aree scolanti associate ai pozzetti del sistema. I risultati indicano che il numero di aree scolanti, ovvero la loro dimensione media, ha una maggiore influenza sulla risposta idrologica del sistema rispetto a quella connessa alla rappresentazione dell’uso del suolo. Nel caso reale esaminato, una dimensione media delle aree scolanti pari a circa mezzo ettaro consente una rappresentazione ragionevolmente accurata dei processi idrologici all’interno del sistema di drenaggio.

2005 - Il Pianeta Acqua nel Continente Agricoltura (Congresso Nazionale dell’Associazione Italiana delle Società Scientifiche Agrarie – AISSA) [Altro]
Stanca, Am; Arru, Laura; Bignami, Cristina; Conte, Angela; Endrighi, Emiro; Franchini, ; Lofiego, D; Manicardi, Gian Carlo; Orlandini, Stefano; Pellegrini, ; Ulrici, Alessandro; Bacarella, Borin; Dazzi, Espen; Gallerani, Giupponi; Magnani, ; Pecchioni, Nicola; Poni, Rossi; Zanni,
abstract

Nell’era della specializzazione nel settore della Ricerca Scientifica, il Convegno ha l’ambizione di mettere insieme i singoli componenti del mondo scientifico agrario, di farli interagire tra di loro e di tentare di affrontare il problema Acqua in modo interdisciplinare. L’avanzamento delle conoscenze sul ruolo dell’acqua nel “Continente Agricoltura” garantirà ricadute di notevole interesse a breve, medio e lungo termine, per migliorare ulteriormente l’interazione “Organismi viventi di interesse agrario e forestale - Terreno – Atmosfera”. L’obiettivo finale è infatti quello di assicurare per il futuro uno sviluppo sostenibile, grazie alla razionale gestione di un fattore ambientale ed economico primario, l’Acqua.

2004 - Determinazione sperimentale della resistenza allo scorrimento idrico superficiale lungo un torrente alpino [Relazione in Atti di Convegno]
Orlandini, Stefano; C., Boaretti; V., Guidi; G., Sfondrini
abstract

Nella presente nota vengono illustrati e discussi i risultati sperimentali raccolti nel bacino del torrente Febbraro (Valchiavenna, Alpi Centrali) al fine di studiare la variazione spaziale della resistenza allo scorrimento idrico superficiale. Sono state selezionate dodici sezioni fluviali e, in ciascuna di esse, sono state condotte accurate misure per la determinazione delle pendenze longitudinali dell’alveo e della corrente, della geometria idraulica della sezione, della composizione del materiale d’alveo e della velocità media della corrente. Le misure acquisite sono state utilizzate per verificare l’affidabilità delle equazioni di Darcy-Weisbach e Gauckler-Manning-Strickler combinate con espressioni dei coefficienti di resistenza o di conduttanza proposte in letteratura per la descrizione delle correnti fluviali montane. In particolare, è stato verificato un metodo basato sulla combinazione dell’equazione di Gauckler-Manning-Strickler con relazioni fluviali di natura geomorfologica. Nel caso esaminato, tale metodo permette di identificare una legge di variazione del coefficiente di conduttanza di Gauckler-Strickler con l’area di drenaggio altamente significativa, nonostante la legge di variazione della portata con l’area di drenaggio non sia riprodotta in modo altrettanto significativo.

2003 - Path-based methods for the determination of nondispersive drainage directions in grid-based digital elevation models [Articolo su rivista]
Orlandini, Stefano; Moretti, Giovanni; M., Franchini; B., Aldighieri; B., Testa
abstract

Path-based methods for the determination of nondispersive drainage directions ingrid-based digital elevation models are presented. These methods extend the descriptivecapabilities of the classical D8 method by cumulating the deviations between selected andtheoretical drainage directions along the drainage paths. It is shown that either angular ortransversal deviations can be employed. Accordingly, two classes of methods designatedD8-LAD (eight drainage directions, least angular deviation) and D8-LTD (eight drainagedirections, least transversal deviation) are developed. Detailed tests on four syntheticdrainage systems of known geometry and on the Liro catchment (central Italian Alps)indicate that the proposed methods provide significant improvement over the D8 methodfor the determination of drainage directions and drainage areas.

2002 - A Nondispersive Method for the Determination of Drainage Directions in Grid-based Digital Elevation Models (abstract) [Abstract in Rivista]
Orlandini, S.; Moretti, G.; Franchini, M.; Aldighieri, B.; Testa, B.
abstract

2002 - On the spatial variation of resistance to flow in upland channel networks [Articolo su rivista]
Orlandini, Stefano
abstract

Detailed field measurements of channel properties and flow characteristics collectedin the Ashley and Cropp catchments (New Zealand) are used to investigate the spatialvariation of resistance to flow across upland channel networks. The application of theDarcy-Weisbach equation and semilogarithmic flow resistance relationships reveals thatmean flow velocities calculated from local measurements of bed material particle size,hydraulic depth, and channel bed slope may be inaccurate. The Manning-Gauckler-Strickler equation with resistance coefficient independent of bed material particle size isfound to be relatively more reliable but not sufficiently general to reproduce the spatialvariation of resistance to flow across a complex channel network. A new methodology isdeveloped by combining a hydraulic equation of the Manning-Gauckler-Strickler type, aflow discharge-upstream drainage area relationship, and geomorphological fluvialrelationships for mean flow velocity, Gauckler-Strickler resistance coefficient, hydraulicdepth, and friction slope. This methodology is found to improve the reproduction of thespatial variation of mean flow velocity across the Ashley catchment and appears of generalapplicability for the parameterization of resistance to flow in distributed catchmentmodels.

2002 - Un metodo non dispersivo per la determinazione delle direzioni di drenaggio nei modelli digitali del terreno su griglia rettangolare [Relazione in Atti di Convegno]
Orlandini, Stefano; Moretti, Giovanni; M., Franchini; B., Aldighieri; B., Testa
abstract

Nella presente nota viene proposto un metodo non dispersivo per la determinazione delle direzioni di drenaggio nei modelli digitali del terreno su griglia rettangolare. Seguendo l’impostazione di Tarboton (1997), la topografia locale viene descritta congiungendo il centro della cella centrale con quelli delle celle di contorno inquadrate dauna finestra mobile 3 × 3, in modo da formare otto faccette triangolari. La direzione teorica di drenaggio viene quindi definita come quella di massima pendenza identificabile su tali faccette. Tale direzione può assumere valori variabili con continuità tra 0 e 2π radianti e generalmente non coincide con nessuna delle otto direzioni principali di drenaggio definibili collegando il centro della cella centrale con quello delle celle di contorno. Nel classico metodo D8 proposto da O’Callaghan & Mark (1984) la direzione di drenaggio coincide con una delle otto direzioni principali ed assicura la minima deviazione angolare tra direzione determinata e direzione teorica. Nel presente studio viene proposta una strategia basata sul concetto di deviazione trasversale tra centro della cella drenante (posta a valle di quella di riferimento) e direzione teorica di drenaggio. In questo metodo le deviazioni trasversali vengono sommate algebricamente lungo il percorso di drenaggio e, ad ogni passo, la direzione di drenaggio viene determinata minimizzando il modulo della deviazione trasversale cumulata. Tale metodo è denominato D8-LTD (otto direzioni possibili, least transversal deviation). Le sue capacità descrittive sono valutate su quattro sistemi di drenaggio sintetici con geometria nota, mentre la robustezza del metodo è verificata attraverso l’applicazione al caso reale del bacino del fiume Liro (Valchiavenna, Alpi Centrali).

2001 - Multivariate analysis of radar images for environmental monitoring [Articolo su rivista]
Morlini, Isabella; Orlandini, Stefano
abstract

The identification of the relationship between radar reflectivity factor Z, expressed in mm6 m-3, and rainfall intensity R, expressed in mm h-1, is crucial for both the calibration and operational phases. The Marshall and Palmer relationship, which links together Z at the lowest constant altitude plan position indicator (CAPPI) level and R, is commonly used in operational hydrology. This relation is of the form Z = aR^(b). Coefficients a and b reflect the dependence of Z from the number and size distribution of meteors present in the volumes scanned by radar beam. However, as a and b (which depend on the type of precipitation) are affected by great variability and both Z and R are affected by errors, detailed statistical analyses of the Z-R relationship may help improving the operational capabilities of weather radar. In this framework, the aim of the paper is twofold: (1) to develop a non-parametric approach which is more flexible and offers more generalisation capabilities than the MP relationship;(2) to use a vector of all 11 reflectivity factors at different CAPPI levels. For this purposes, three kinds of neural networks are developed: the multi-layer perceptron, radial basis function networks and Bayesian networks. Models are trained and tested using a real data set of reflectivity observed by the Monte Grande weather radar (Teolo, Italy) and rainfall intensity measured at five rain gauges in the Cortina d’Ampezzo area (Northern Italian Dolomites), during the June 12, 1997 storm event (from 11.15am to 12.00pm). Reflectivity data are given at 11 CAPPI levels with 15-minute time resolution. Rainfall intensity data are measured at 5-minute time resolution and are averaged over the 15-minute time intervals of radar data to constitute integrated measurements.

2000 - Artificial neural network estimation of rainfall intensity from radar observations [Articolo su rivista]
Orlandini, Stefano; Morlini, Isabella
abstract

Artificial neural networks are used to identify the relationship between weather radar observations of the reflectivity factor Z and rain gauge measurements of rainfall intensity R. These networks are trained and tested using a real data set of reflectivity observed by the Monte Grande weather radar (Teolo, Italy) and rainfall intensity measured by five rain gauges in the Cortina d’Ampezzo area (Italian Dolomites). A principal components analysis is also carried out to investigate the correlation between the Z values at 11 constant altitude plan position indicator levels and to synthesise these values into fewer orthogonal input variables for the networks. Besides the widely used Marshall-Palmer relationship, linear models and flexible discriminants like generalised additive models are used as a benchmark against which the predictive performances of the neural models are measured.Volumetric scans of radar reflectivity Z and gage measurements of rainfall intensity R are used to explore the capabilities of three artificial neural networks to identify and reproduce the functional relationship between Z and R. The three networks are a multilayer perceptron, a Bayesian network, and a radial basis function network. For each of them, numerical experiments are conducted incorporating in the network inputs different descriptions of the space-time variability of Z. Space variability refers to the observations of Z along the vertical atmospheric profile, at 11 constant altitude plan position indicator levels, namely ZT=(Z1,...,Z11). Time variability refers to the observations of Z at the time intervals prior to that for which the estimate of R is provided. Space variability is evaluated by performing a principal component analysis over standardized values of Z, namely Z~, and the first two principal components of Z~ (which describe 91% of the original variance) are used to synthesize the elements of Z into fewer orthogonal inputs for the networks. Network predictions significantly improve when the models are trained with the two principal components of Z~ with respect to the case in which only Z1 is used. Increasing the time horizon further improves the performances of the Bayesian network but is found to worsen the performances of the other two networks.

2000 - Effect of wind on precipitation intercepted by steep mountain slopes [Articolo su rivista]
Orlandini, Stefano; A., Lamberti
abstract

A simple and efficient formulation is developed to describe the effects of wind speed and directionon ground level precipitation intercepted by steep mountain slopes. A 3D rainfall field is reproduced frommeasurements of (vertical) precipitation intensity, wind speed, and wind direction. The Marshall-Palmer dropsize distribution is used to express the volumetric precipitation water content as a function of measured precipitationintensity, and raindrops are assumed to move horizontally with the measured wind speed and direction.Land topography is described using digital elevation model data, and local contributions to ground level precipitationare calculated as the interception of the obtained 3D rainfall field by horizontal and vertical surfacesthat constitute the elemental land surface systems. The developed formulation is tested at the Acquabona andFiames mountain slopes, located in the Northern Italian Dolomites, near the town of Cortina d’Ampezzo, wheredebris flow phenomena often occur. Simulation results are corroborated, although in an indirect and approximatemanner, by field estimates of debris flow volumes delivered by the considered mountain slopes in response tomonitored storm events. Although more accurate and comprehensive validation is needed, the developed formulationappears to constitute a useful diagnostic tool for providing interpretation of storm-flow hydrographsdelivered by steep mountain slopes in response to storm precipitations affected by wind.

2000 - Neural network identification of Z-R relationships [Relazione in Atti di Convegno]
Orlandini, Stefano; Morlini, Isabella
abstract

Rainfall is one of the most difficult elements of hydrologic cycle tomeasure and forecast. This is due to the tremendous range of variability it displays over a wide range of scales both in space and time. Weather radar constitutes an attractive possibility for improving the description of rainfall fields. Radar emits electromagnetic energy in narrow bands.From the reflected energy that returns to the transmitter it is possible to obtain measurements of the rainfall field. In practice, the exclusive use of radar is yet to be achieved and rain gauge or other punctual systems are required to calibrate radar. The identification of the relationshipbetween radar reflectivity factor and rainfall intensity is crucial for both thecalibration and operational phases. In this framework, the aim ofthe paper is twofold:(1) to develop a non-parametric approach which is more flexible and offersmore generalisation capabilities than the Marshall and Palmer relationship, and(2) to use a vector of all 11 reflectivity factors at different CAPPI levels.For this purposes, three kinds of neural networks (NNs) are developed:the multi-layer perceptron (MLP), radial basis function networks (RBFNs)and Bayesian networks (BNs) Models are trained and tested using a real data set of reflectivity observedby the Monte Grande weather radar (Teolo, Italy) and rainfall intensitymeasured at five rain gauges in the Cortina d'Ampezzo area (NorthernItalian Dolomites), during the June 12, 1997 storm event(from 11.15am to 12.00pm).

2000 - Physically-based distributed model for coupled surface runoff and subsurface flow simulation at the catchment scale [Relazione in Atti di Convegno]
A. C., Bixio; M., Putti; Orlandini, Stefano; C., Paniconi
abstract

The interactions between surface and subsurface hydrologic processes are important in many waterresource applications and require modeling approaches capable of treating these processes in an integrated manner. We describe a distributed, physically-based model that couples a three-dimensional subsurface flow module to a DEM-based one-dimensional surface routing module and resolves in a detailed manner the exchange of flux and head information between the two regimes. The coupled model can treat flow in saturated and variably saturated porous media, surface runoff, channel flow, and storage in lakes and other topographic depressions. The algorithm that handles the exchange between the surface and subsurface components is described in detail, and an illustrative test case is presented.

2000 - Stima della relazione tra riflettività radar e precipitazione al suolo mediante reti neurali [Relazione in Atti di Convegno]
Orlandini, Stefano; Morlini, Isabella
abstract

Motivated by a real world problem, this study develops a neural network approach to identify and evaluate the relationship between atmospheric radar reflectivity and ground level rainfall intensity. Rainfall is one of the most difficult elements of hydrologic cycle to measure and forecast. This is due to the tremendous range of variability it displays over a wide range of scales both in space and time. Weather radar constitutes an attractive possibility for improving the description of rainfall fields as it can provide high resolution images in space and time of the atmospheric reflectivity over large areas. Radars emit short pulses of energy in the radio-frequency portion of the electromagnetic spectrum, which are focused by the antenna into a narrow beam. From the backscattering energy of the hydrometeors that returns to the transmitter it is possible to obtain estimates of the rainfall field. Radar data are displayed on constant altitude plan position indicators (CAPPIs) levels. The empirical Marshall–Palmer (MP) relationship is normally used in operational hydrology to link together the reflectivity factor Z at the lowest CAPPI level and rainfall intensity R at the ground level. The coefficients reflect the dependence of Z from the number and size distribution of meteors present in the volumes scanned by radar beam. The MP relationship needs a careful preprocessing phase to remove known anomalies in the data, which are due to several factors such as, for example, the distribution of water particles, low level precipitation and low level evaporation. In addition, much noise may affect radar data, owing to radar calibration, signal attenuation, and electromagnetic signal propagation path. The preprocessing stage may limit the many applications which require a real time estimation of the rainfall field. Furthermore, the MP relationship exploits the radar image at the lowest CAPPI level, while the importance of incorporating the entire vertical profile of Z to improve the estimates of R has been recognised in several works.These considerations raise the following statistical problem: perform a fast multivariate analysis of the Z-R relationship with a view to making real time predictions and filtering the effect of noise and bias and the presence of outliers in the data. The aim of the neural network analysis performed in this work is to stress the differences between the univariate and the multivariate approach to the Z-R relationship and to compare neural networks with the classical MP relationship, in the univariate analysis, and with other flexible non linear statistical methods, in the multivariate analyisis. Performances are evaluated by means of an empirical study.

1999 - Coupled surface runoff and subsurface flow model for catchment simulations [Relazione in Atti di Convegno]
A. C., Bixio; Orlandini, Stefano; C., Paniconi; M., Putti
abstract

A distributed catchment scale numerical model for the simulation of coupled surface runoff and subsurface flow is presented. Starting from rainfall (evaporation) records, the model first determines the infiltration (exfiltration) rates in the soil, by evaluation of the soil field capacity at the specific conditions as calculated 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 are described, and a special algorithm is used for the simulation of pool/lake effects on stormflow response. The importance of including detailed subsurface flow descriptions in catchment simulations is shown in a simple test case characterized by the presence of a central depression.

1999 - On the control volume modelling of near-surface soil drying [Articolo su rivista]
Orlandini, Stefano
abstract

The problem of simulating the topsoil dynamics in response to atmospheric evaporative events is considered in the present paper. It is emphasised how the assumption that soil moisture profiles approximately preserve similarity during simultaneous atmospheric drying and gravity drainage may be required in order to incorporate the effects ofdeeper soils in the near-surface soil control volume hydrologic modelling. The reliability of the proposed formulation is evaluated with rates of evaporation calculated from measurements of the Bowen ratio and soil moisture data obtained from time domain reflectometry measurements for a bare soil field in the Zwalmbeek catchment (Belgium).

1999 - On the impact of flood-control reservoirs on downstream flood characteristics [Capitolo/Saggio]
A., Brath; L., Dall’Agata; Orlandini, Stefano
abstract

A distributed model of catchment dynamics has been used in order to evaluate the impact of flood-control reservoirs on downstream flood characteristics under variable storming conditions. The catchment model calculates local contributions to infiltration excess runoff at each elemental cell of the discretized catchment by means of a time compression approximation water balance model and routes thesecontributions throughout a drainage network extracted from digital elevation model data via a diffusion wave scheme based on the Muskingum-Cunge method with variable parameters. The reservoir is described in terms of elevation-water surface area and elevation-discharge curves. Level pool routing is modeled via a fourth-order Runge-Kutta routine, allowing the dynamic computation of the reservoir outflow during flood events, in response to the inflow hydrograph from the controlled upstream drainage area. The obtained model is applied to the approximately 840-km$^2$ Sievecatchment (Central Italian Apennines), where the $69 \times 10^6$-m$^3$ multipurpose Bilancino reservoir controls an upstream drainage area of about 150 km$^2$. The impact of the reservoir on downstream flood characteristics is evaluated by comparing hydrograph peaks along the mainstream, as simulated by themodel in the natural (without reservoir) and controlled (with reservoir) scenarios. The obtained results indicate that a profound impact may be produced on the scaling properties of peak discharges with upstream drainage area and thus a critical use of such scaling relationships is suggested when dealing with controlled river systems.

1999 - On the storm flow response of upland Alpine catchments [Articolo su rivista]
Orlandini, Stefano; A., Perotti; G., Sfondrini; A., Bianchi
abstract

Detailed measurements of near-surface soil hydraulic conductivity, Ks, across the Bracciasco catchment(Central Italian Alps) are incorporated into a distributed, digital elevation model-based hydrological model toevaluate the effect of soil heterogeneity on catchment storm flow response. Surface and subsurface storm flowcomponents are simulated for different distributions of Ks, including that obtained directly from measurements,that obtained by averaging measured data and others obtained on the basis of a simple functional parametermodel. The reproduction of the catchment storm flow responses obtained using distributions of Ks based onmeasurements is satisfactory although an adjustment of such distributions is suggested to reproduce thehydrograph peaks owing to rapid surface runoff concentration and to improve the description of recessionlimbs at the same time. Numerical experiments indicate that the simulated storm flow response of the studycatchment is substantially insensitive to near-surface soil heterogeneity in as far as the predominant mechanismof channel storm flow generation is subsurface flow. However, Ks is found to play an important role in thegeneration of overland flow during intense rainfall and, under these circumstances, monitoring of near-surfaceheterogeneity may be important to provide accurate descriptions of both surface and subsurface storm flowcomponents.

1999 - Radar images for rainfall measurements: a neural network analysis [Relazione in Atti di Convegno]
Morlini, Isabella; Orlandini, Stefano
abstract

Motivated by a real world problem, this study develops a neural network approach to identify and evaluate the relationship between atmospheric radar reflectivity and ground level rainfall intensity. Rainfall is one of the most difficult elements of hydrologic cycle to measure and forecast. This is due to the tremendous range of variability it displays over a wide range of scales both in space and time. Weather radar constitutes an attractive possibility for improving the description of rainfall fields as it can provide high resolution images in space and time of the atmospheric reflectivity over large areas. Radars emit short pulses of energy in the radio-frequency portion of the electromagnetic spectrum, which are focused by the antenna into a narrow beam. From the backscattering energy of the hydrometeors that returns to the transmitter it is possible to obtain estimates of the rainfall field. Radar data are displayed on constant altitude plan position indicators (CAPPIs) levels. The empirical Marshall–Palmer (MP) relationship is normally used in operational hydrology to link together the reflectivity factor Z at the lowest CAPPI level and rainfall intensity R at the ground level. The coefficients reflect the dependence of Z from the number and size distribution of meteors present in the volumes scanned by radar beam. The MP relationship needs a careful preprocessing phase to remove known anomalies in the data, which are due to several factors such as, for example, the distribution of water particles, low level precipitation and low level evaporation. In addition, much noise may affect radar data, owing to radar calibration, signal attenuation, and electromagnetic signal propagation path. The preprocessing stage may limit the many applications which require a real time estimation of the rainfall field. Furthermore, the MP relationship exploits the radar image at the lowest CAPPI level, while the importance of incorporating the entire vertical profile of Z to improve the estimates of R has been recognised in several works.These considerations raise the following statistical problem: perform a fast multivariate analysis of the Z-R relationship with a view to making real time predictions and filtering the effect of noise and bias and the presence of outliers in the data. The aim of the neural network analysis performed in this work is to stress the differences between the univariate and the multivariate approach to the Z-R relationship and to compare neural networks with the classical MP relationship, in the univariate analysis, and with other flexible non linear statistical methods, in the multivariate analyisis. Performances are evaluated by means of an empirical study.

1999 - Two-layer model of near-surface soil drying for time-continuous hydrologic simulations [Articolo su rivista]
Orlandini, Stefano
abstract

A two-layer soil water balance model is developed to provide an efficient and robust descriptionof land surface dynamics in response to atmospheric evaporative events. Soil, vegetation, and atmosphere arecoupled dynamically under the assumption that soil moisture profiles approximately preserve similarity duringsimultaneous atmospheric drying and gravity drainage. The exfiltration flux at the land surface in response tothe atmospheric evaporative demand is limited by relating the surface resistance to water vapor transfer in thePenman-Monteith equation to the near-surface soil status. In addition, the control of deeper soils on both exfiltrationand drainage is expressed by performing a time compression approximation water balance over the entiredrying profile and by scaling the obtained exfiltration and drainage fluxes to the near-surface soil layers. Thereliability and robustness of the proposed formulation is evaluated with rates of evaporation calculated frommeasurements of the Bowen ratio and soil moisture data obtained from time domain reflectometry measurementsfor a bare soil field in the Zwalmbeek catchment (Belgium).

1999 - Using neural networks to identify the relationship between radar reflectivity and rainfall intensity [Relazione in Atti di Convegno]
Morlini, Isabella; Orlandini, Stefano
abstract

Motivated by a real world problem, this study develops a neural network approach to identify and evaluate the relationship between atmospheric radar reflectivity and ground level rainfall intensity. Rainfall is one of the most difficult elements of hydrologic cycle to measure and forecast. This is due to the tremendous range of variability it displays over a wide range of scales both in space and time. Weather radar constitutes an attractive possibility for improving the description of rainfall fields as it can provide high resolution images in space and time of the atmospheric reflectivity over large areas

1998 - Parameterization of stream channel geometry in the distributed modeling of catchment dynamics [Articolo su rivista]
Orlandini, Stefano; R., Rosso
abstract

A simple and efficient procedure for incorporating the effects of streamchannel geometry in the distributed modeling of catchment dynamics is developed. At-astationand downstream fluvial relationships are combined and the obtained laws ofvariability in space and time for water-surface width and wetted perimeter areincorporated into a diffusion wave routing model based on the Muskingum-Cunge methodwith variable parameters. The parameterization obtained is applied to the approximately840-km2 Sieve catchment (Central Italian Apennines) to test the possibility of estimatingchannel geometry parameters from cross-section surveys and to assess the impact ofdynamic variations in the channel geometry on catchment dynamics. The use of theestimated channel geometry in surface runoff routing produces a significant improvementin the flood hydrograph description at the catchment outlet with respect to less detailednetwork parameterizations. In addition, the results obtained from a “downstream” analysisof the velocity field indicate that the stream characteristics related to the locally varyingcross-section shape may have a strong control on flow velocities, and thus they should bemonitored and synthesized for a comprehensive description of the distributed catchmentdynamics.

1997 - Closure to discussion to "Diffusion wave modelling of distributed catchment dynamics" by V. M. Ponce [Articolo su rivista]
Orlandini, Stefano; R., Rosso
abstract

There is no abstract in this kind of contribution.

1997 - Il telerilevamento nel controllo dei fenomeni idrologici [Capitolo/Saggio]
Orlandini, Stefano
abstract

Lo sviluppo di modelli idrologici alle diverse scale spazio-temporali risulta notevolmente complicato dalla forte eterogeneità dei sistemi naturali. Data l'onerosità delle campagne di misura a terra, il telerilevamento può produrre un notevole impatto sulla descrizione dei processi idrologici. La minore precisione delle misure telerilevate rispetto a quelle tradizionali può infatti essere compensata dalla possibilità del terilevamento di fornire informazioni su estesi scenari in modo relativamente veloce ed economico. Tuttavia, sia i modelli idrologici distribuiti sia le tecniche di telerilevamento presentano aspetti non completamente risolti e, pertanto, lo sviluppo di sistemi integrati deve essere condotto con molta cautela. L'introduzione acritica di notevoli quantità di dati telerilevati nei modelli idrologici distribuiti può risultare non solo inefficace ma addirittura controproducente. Solo sulla base della conoscenza esatta dei limiti dei modelli idrologici, da un lato, e delle tecniche di rilevamento, dall'altro, può risultare possibile un efficace utilizzo dei dati telerilevati per il controllo dei fenomeni idrologici sul territorio.Per il corretto sviluppo della modellistica idrologica e del telerilevamento è necessario condurre validazioni separate, per confronto con poche misure affidabili piuttosto che con enormi masse di dati di incertezza non ben definita. Questi concetti vengono illustrati nel presente lavoro attraverso la descrizione delle attuali tendenze di sviluppo dei modelli idrologici distribuiti e delle possibili applicazioni del telerilevamento all'idrologia. Vengono inoltre riportati i principali risultati di un'applicazione del radar ad apertura sintetica per il telerilevamento dell'umidità del suolo.

1996 - Diffusion wave modeling of distributed catchment dynamics [Articolo su rivista]
Orlandini, Stefano; R., Rosso
abstract

A diffusion wave model of distributed catchment dynamics is presented. The effects of catchment topography and river network structure on storm-flow response are incorporated by routing surface runoff in cascade throughout a digital elevation model (DEM) based conceptual transport network, where the Muskingum-Cunge scheme with variable parameters is used to describe surface runoff dynamics. Dynamic scaling of hydraulic geometry is also incorporated in the model by using the 1953 “at-a-station” and “downstream” relationships by Leopold and Maddock. Numerical experiments indicate that the model is more than 98% mass conservative for possible slope and roughness configurations, which may occur for hillslopes in a natural catchment. Fluctuations in the simulated discharge may occur in response to discontinuities in rainfall excess representation if Courant number Cu during the simulation exceeds a threshold of about 3. Catchment scale simulations with different temporal resolution show that the model response is independent of structural parameters (model consistency). Also, the overall accuracy is preserved for computationally inexpensive space-time discretizations (for which Cu > 3) because fluctuations that may occur at the local scale are dampened when propagating downstream. Comparison of model results with observed outlet hydrographs of the Rio Missiaga experimental catchment (Eastern Italian Alps) show this approach to be capable of describing both overland and channel phases of surface runoff in mountainous catchments.

1996 - Local contributions to infiltration excess runoff for a conceptual catchment scale model [Articolo su rivista]
Orlandini, Stefano; M., Mancini; C., Paniconi; R., Rosso
abstract

The response of a conceptual soil water balance model to storm events iscompared to a detailed finite element solution of the one-dimensional Richards equationin order to test the capabilities of the former in calculating the local contributions toinfiltration excess runoff in a distributed catchment scale model. Local infiltration excessrunoff is computed from ground level precipitation using the time compressionapproximation and a Philip infiltration capacity curve with Brooks-Corey constitutiveequations. The validity of applying the conceptual model for local runoff and soil waterbalance calculations is investigated by performing numerical experiments over a range ofsoil types, control volume depths, and initial soil moisture conditions. We find that a goodagreement between the conceptual and detailed models is obtained when the gravitationalinfiltration rate in Philip’s formula is set to the saturated hydraulic conductivity, and whenpercolation from the control volume is updated as a function of the soil moisture contentin a stepwise fashion. The comparison between these two models suggests that the simpler(and much less computer-intensive) conceptual water balance technique could beincorporated into distributed models for large scale complex terrains as an efficient meansof retaining consideration of spatial variability effects in catchment scale hydrologicsimulations. This is illustrated in an application to the Rio Missiaga catchment in theeastern Italian Alps, where the local contributions to surface and subsurface runoff arerouted onto a digital elevation model–based conceptual transport network via a simplenumerical scheme based on the Muskingum-Cunge method.

1996 - Sull’onda di piena diffusiva nei reticoli di drenaggio naturali [Relazione in Atti di Convegno]
Orlandini, Stefano; R., Rosso
abstract

Un modello distribuito dell'onda di piena diffusiva viene applicato alla rete idrografica del bacino della Sieve (840~km$^2$) per analizzare gli effetti della descrizione dinamica del deflusso superficiale sulla risposta idrologica di piena. L'onda di piena viene propagata in cascata sulla rete idraulica identificata a partire dal modello digitale delle quote del bacino secondo il metodo Muskingum-Cunge a parametri variabili. La geometria idraulica del reticolo è rappresentata mediante sezioni rettangolari con base che varia dinamicamente, in accordo con le relazioni di autosomiglianza di Leopold e Maddock. Gli idrogrammi simulati mostrano come la descrizione dinamica del reticolo idrografico causi il rallentamento e l'attenuazione dell'onda di piena rispetto al caso di reticolo a geometria costante nel tempo, consentendo una migliore riproduzione della risposta del bacino. Le velocità ottenute dall'analisi "lagrangiana" del fenomeno di piena risultano in accordo con gli studi sperimentali riportati in letteratura per quanto riguarda la loro variabilità spaziale e rivelano una sensibile dinamica del campo di moto nelle diverse fasi dell'evento di piena.

1995 - Su un modello idrologico distribuito dei fenomeni dipiena con aggiornamento continuo dello stato di imbibimento del suolo e della copertura vegetale [Articolo su rivista]
M., Mancini; Orlandini, Stefano; R., Rosso
abstract

Viene descritto un modello idrologico distribuito. Tale modello riproduce il bilancio idrologico nel sistema suolo-vegetazione-atmosfera nella sua continuità temporale. I contributi locali al deflusso superficiale sono accumulati lungo una rete di drenaggio estratta automaticamente dal modello digitale del terreno.