Marco Pilotti

Reconstruction of Clastic Porous Media

In this paper we present a refinement of an algorithm (Pilotti, 1998) to generate three-dimensional granular media by deposition of spherical grains in a viscous fluid. The proposed improvements allow the construction of clastic porous media made up of irregular grains, with controlled level of angularity, sorting and porosity. On the basis of visual comparison with prototypal cross sections and of computed two points correlation functions, we argue that the intergranular void spaces resulting from this procedure provide a satisfactory reproduction of the micro-geometry of several clean consolidated sandstones and can be used to explore the effect of void topology on the flow field properties.

1923 Gleno Dam Break: Case Study and Numerical Modeling

On the morning of December 1, 1923, the Gleno Dam (located in the Central Italian Alps) suddenly collapsed a few days after the first complete reservoir filling. Nearly 4: 5×1 0 6 m 3 of water was released. The consequent inundation caused significant destruction along the downstream valley and a death toll of at least 356 lives. This failure is the only historical case of dam break caused by structural deficiencies that has occurred in Italy. As a result, it has deeply influenced the evolution of Italian regulations regarding dam design and hydraulic risk evaluation. However, in spite of its relevance, this event has never been characterized from a hydraulic standpoint. This paper reports the main information obtained from the analysis of a vast amount of historical documents regarding the Gleno Dam break to set up a case study useful for validating dam-break models in mountain settings. Moreover, it presents the main results of one-dimensional (1D) modeling of the dam break wave propagation accomplished with a first-order finite volume numerical scheme recently proposed in the literature for field applications. The overall effectiveness and reliability of the model are evaluated for this case characterized by very irregular topography. Finally, the practical relevance of several choices that the numerical reconstruction of this kind of event demands is tested. DOI: 10.1061/(ASCE)HY.1943-7900.0000327.

Generation of Realistic Porous Media by Grains Sedimentation

In a recent paper, Tacher and co‐workers proposed an interesting numerical technique to generate granular porous media. In this contribution, we present a similar procedure based on a sedimentation algorithm, that is able to overcome some of the difficulties present in the former technique. These are: (a) the impossibility to choose a priori a grading curve for the generated medium while retaining a realistic stacking where each grain is connected to at least three of its neighbours, and, (b) he random pattern of the grains in the porous medium, arising from their location inside the remaining void space of a box according to an arbitrary space filling criterion. We propose to generate three‐dimensional granular media by simulating the deposition of spherical grains in a viscous fluid. We argue that the resulting chaotic grain pattern, by reflecting the actual generation process of sedimentary aggregates more closely, provides a better image of the complex topology of natural granular porous media. Although the generated medium is made up of spheres, it can be transformed, by changing the geometry of the grains through suitable domain mappings. The resulting three‐dimensional porous media provide a realistic boundary for the numerical solution of linearized Navier–Stokes equations.

Beginning of sediment transport of incoherent grains in shallow shear flows

In this paper the main results of an experimental investigation on the beginning of sediment transport of incoherent granular materials in shallow viscous flows are presented. The experiments, performed in a laboratory flume in both laminar and smooth turbulent flow conditions, complement the data already available in literature, and confirm that the hyperbolic trend shown by the Shields curve when the grain Reynolds number X decreases to zero is not supported by experimental evidence. In addition, they confirm the Yalin and Karahan (1979) hypothesis on the existence of a distinct curve for the inception of sediment transport in viscous dominated flows. On the basis of the observed phenomenology, we propose to interpret the process as a function of the probability distribution of the repose angle of the grains of the erodible bed. Accordingly, a simple mechanical relation is derived that explains the pattern exhibited by the experimental data.

Flooding Hazard Mapping in Floodplain Areas Affected by Piping Breaches in the Po River, Italy

AbstractIn recent years, flood-related risk has been increasing worldwide, being inundations among the natural disasters which induce the maximum damage in terms of economic losses. In the research reported in this paper, a methodology to map the flooding residual hazard due to levee failure events induced by piping in embankments protecting flood-prone areas is proposed. Ensemble simulations are used to account for uncertainties in location, geometry, and time-evolution of the levee breaches. Probabilistic flooding-hazard maps are generated combining the results of 192 inundation scenarios, simulated by using one-dimensional (1D) and two-dimensional (2D) hydrodynamic models. The methodology is applied considering 96 different locations and sizes of breaches occurred along a 23-km reach protected by the right levee of the Po River, the right levee of the Taro River, and the left levee of the Parma River, which delimit a 100-km2 study area. The influence of obstacles to the flood propagation and consequent...

Distributed evaluation of the contribution of soil erosion to the sediment yield from a watershed

The correct determination of the sediment yield from a basin is of paramount importance in several hydraulic and environmental applications, such as the evaluation of the storage reduction of artificial reservoirs. However, due to the highly episodic nature of sediment supply and transport in many environments and to the extreme complexity of the processes involved, the evaluation of the sediment load in a river is still highly uncertain. When the time scale of interest i s sufficiently long, and when the primary sediment source comes from distributed erosion in the watershed, the problem can be tackled in an indirect fashion, by computing the contribution to the annual suspended sediment yield from soil erosion. In order to accomplish this task, we propose a distributed application of the widely used USLE formula. The formula is automatically applied along drainage networks derived from a digital elevation model and properly modified to take into account the presence of deposition zones in the watershed.  1997 John Wiley & Sons, Ltd. Earth surf. process. landforms, 22, 1239–1251 (1997) No. of figures: 5 No. of tables: 2 No. of refs: 24

IDENTIFICATION AND ANALYSIS OF NATURAL CHANNEL NETWORKS FROM DIGITAL ELEVATION MODELS

The identification and analysis of natural channel networks from digital elevation models are discussed from the point of view of their environmental applications. An interactive, graphical software package that implements some of the most widely used techniques for the automatic recognition of channel networks and for the computation of some useful geomorphologic indices and functions is presented.

A conceptual model of people's vulnerability to floods

Hydraulic risk maps provide the baseline for land use and emergency planning. Accordingly, they should convey clear information on the potential physical implications of the different hazards to the stakeholders. This paper presents a vulnerability criterion focused on human stability in a flow specifically devised for rapidly evolving floods where life, before than economic values, might be threatened. The human body is conceptualized as a set of cylinders and its stability to slipping and toppling is assessed by forces and moments equilibrium. Moreover, a depth threshold to consider drowning is assumed. In order to widen its scope of application, the model takes the destabilizing effect of local slope (so far disregarded in the literature) and fluid density into account. The resulting vulnerability classification could be naturally subdivided in three levels (low, medium, and high) that are limited by two stability curves for children and adults, respectively. In comparison with the most advanced literature conceptual approaches, the proposed model is weakly parameterized and the computed thresholds fit better the available experimental data sets. A code that implements the proposed algorithm is provided.

Simplified Method for the Characterization of the Hydrograph following a Sudden Partial Dam Break

This paper presents a simplified approach to the characterization of the hydrograph following the partial collapse of concrete gravity dams. The proposed approach uses a simplified representation of the reservoir geometry and is based on the numerical solution of shallow water equations to study the two-dimensional evolution of the water surface within the reservoir. The numerical results are made dimensionless and reorganized so as to compute the peak discharge, the duration and the recession limb of the dam break hydrograph. The proposed practical approach provides a quite satisfactory reproduction of the computed hydrograph for a wide set of realistic situations that have been simulated in detail.

A simple approach to the evaluation of the actual water renewal time of natural stratified lakes

In natural lakes, where thermal stratification hinders complete mixing, the theoretical value T0 of the water renewal time provides a low-order approximation to the time T37 when 37% of the original water is still present within the lake; this time could be operatively regarded as the actual value of the water renewal time. In this paper, we present a simple nonparametric model to estimate the age distribution of water within stratified natural lakes, taking into account fundamental aspects of its mass exchange and thermal evolution. This distribution provides a straightforward way to compute T37. The model is presented as a system of ordinary differential equations along with a MATLAB script for its numerical solution, so that it can be easily applied to lakes where a minimum of limnological data are available, without the need of extensive meteorological data set and modeling expertise that an hydrodynamic model would require to the same purpose. The case of a deep oligomictic Italian prealpine lake (Lake Iseo) is considered: after a positive comparison with the results obtained using a 1-D lake hydrodynamic model, the reiterated application to the available time series allows to approximate the water age probability distribution. This distribution is used to compute the actual value of the water renewal time, that resulted T37 = 1.6T0.