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Giovanni MORETTI

Professore Associato
Dipartimento di Ingegneria "Enzo Ferrari"

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Pubblicazioni

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 - 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 - 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 - 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 - 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 - 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.

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 [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 - 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).

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.

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).

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.

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 - 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).