Massimo Tomirotti

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 This paper reports the main information obtained from the analysis of a vast amount of historical documents regarding the Gleno Dam break to set up a case study useful for validating dam-break models in mountain settings.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.

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.

Dam-break modeling in alpine valleys

Dam-break analysis is of great importance in mountain environment, especially where reservoirs are located upstream of densely populated areas and hydraulic hazard should be assessed for land planning purposes. Accordingly, there is a need to identify suitable operative tools which may differ from the ones used in flat flood-prone areas. This paper shows the results provided by a 1D and a 2D model based on the Shallow Water Equations (SWE) for dam-break wave propagation in alpine regions. The 1D model takes advantage of a topographic toolkit that includes an algorithm for pre-processing the Digital Elevation Model (DEM) and of a novel criterion for the automatic cross-section space refinement. The 2D model is FLO-2D, a commercial software widely used for flood routing in mountain areas. In order to verify the predictive effectiveness of these numerical models, the test case of the Cancano dam-break has been recovered from the historical study of De Marchi (1945), which provides a unique laboratory data set concerning the consequences of the potential collapse of the former Cancano dam (Northern Italy). The measured discharge hydrograph at the dam also provides the data to test a simplified method recently proposed for the characterization of the hydrograph following a sudden dam-break.

Experimental and Numerical Analysis of Side Weir Flows in a Converging Channel

AbstractThis paper investigates the lateral outflow over a short-crested side weir inserted in a converging rectangular channel with linearly decreasing width in the flow direction. This type of ov...

Experimental investigation of reservoir geometry effect on dam-break flow by A. Feizi Khankandi, A. Tahershamsi and S. Soares-Frazão, J. Hydraulic Res. 50(4), 2012, 376-387

The Authors deal with an important topic that deserves continuous experimental, theoretical and numerical efforts to improve the methodologies of hazard reduction. Often sophisticated technologies cannot be used due to the lack of information resulting in simplifications to evaluate the hydrograph following a dam break. The Authors’ study on the effects of reservoir shape on a dam break wave is relevant. The Authors claim that “existing studies consider only the rectangular reservoir shape” and that “practice often requires quick and rough estimates of the peak discharge and maximum water levels”, underlining that the existing methodologies for evaluating this information are based on regression models derived from a limited database, so that the overall confidence on the quality of the results is moderate. However, the work of Pilotti et al. (2010) was overlooked, so that a formula for the peak discharge and a simple approximation to the entire hydrograph are presented. Only the hydrograph at the dam section is considered because its shape downstream of the breach is strongly conditioned by the local bathymetry (Pilotti et al. 2011). The observations are limited to the rectangular, wide reservoir; equations and tables of Pilotti et al. (2010) contain JHE (Journal of Hydraulic Engineering) added to the number. As to the measurement of peak discharge at the gate section, the Authors extrapolated the discharge using the data at location G4–G6, comparing it with that provided by empirical formulae. It is not surprising that there is a wide scatter between the results (up to an order of magnitude) in Table 6. The Authors’ results and these of Pilotti et al. (2010) may explain why empirical formulae may be so inaccurate. Pilotti et al. (2010) computed the hydrograph at the breach section for a partial dam break in a rectilinear, constant slope reservoir of cross-sectional area A = δh, in which h is the water depth and δ and l depend on the cross-sectional shape, ranging from rectangular (l = 1) to parabolic (l = 1.5) and triangular (l = 2). The explored breach ratio a/A0, in which a is the breach area and A0 the initial wetted area at the dam, ranges up to 1, so that the methodology applies also for the full dam break. The comparison is limited to the peak discharge because horizontal bathymetries were not considered. It is interesting to compare Eqs. (12 JHE) and (25 JHE) with the results of Table 6. For the long and 90◦ bend reservoir, Eq. (25 JHE) reduces to Ritter’s (subscript R) equation, providing for peak (subscript p) discharge Qp the value QR = 0.120 m3 s−1 versus the experimental values of 0.123 and 0.125 m3 s−1,

The Microwave Alpine Snow Melting Experiment (MASMEx 2002): a contribution to the ENVISNOW project

A study of the melting cycle of snow was carried out by combining microwave radiometric measurements with conventional micrometeorological data and snow modelling. The experiment took place in the eastern Italian Alps. The high sensitivity of microwave emission at 19 and 37 GHz to the melting refreezing-cycles of snow was confirmed. Moreover, micro-meteorological data provided additional insight on the processes. Simulations obtained with electromagnetic and hydrological models were consistent with experimental data.

Impact of Climatic and Land Use Changes on River Flows in the Southern Alps

River flow time series are far from being stationary and always experienced changes in the past, also dramatic in long time horizons. In recent years it seems that both climatic and anthropogenic factors are accelerating the variability of hydrological processes. It is not clear, however, whether climatic or anthropic factors represent the major forcing to the hydrological cycle. Long-term statistics, lasting over 150 years, of annual runoff for the five major Italian rivers in the Central Alps are presented and compared with precipitation, temperature and land use changes. A homogeneous decreasing trend of annual runoff is observed, and the significance of such a trend at the local and regional scale is tested with Mann-Kendall, Sen-Theil and Sen-Adichie statistical tests. It is shown that for some rivers, the increased agricultural water demand and land use changes are a likely major source of non-stationarity, possibly more relevant than meteorological ones. A natural feedback which is being observed also at the global scale is discussed on the basis of land use in the Adige river basin by comparing cadastral maps of the mid-nineteenth century with recent aerial photographs in four sample areas. Results are consistent with the reduced speed of deforestation observed at the global scale and the natural afforestation observed in Europe occurring over the last decades. This process can play a major role in regulating the hydrological cycle and mitigating flood and drought extremes, but also enhancing evapotranspiration losses and thus reducing runoff volumes.