Luca Milanesi

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.

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.

Using web‐based observations to identify thresholds of a person's stability in a flow

Flood risk assessment and mitigation are important tasks that should take advantage of rational vulnerability models to increase their effectiveness. These models are usually identified through a relevant set of laboratory experiments. However, there is growing evidence that these tests are not fully representative of the variety of conditions that characterize real flood hazard situations. This paper suggests a citizen science based and innovative approach to obtain information from web resources for the calibration of peoples vulnerability models. A comprehensive study employing commonly-used web engines allowed the collection of a wide set of documents showing real risk situations for people impacted by flood, classified according to the stability of the involved subjects. A procedure to extrapolate the flow depth and velocity from the video frames is developed and its reliability is verified by comparing the results with observation. The procedure is based on the statistical distribution of the population height employing a direct uncertainty propagation method. The results complement the experimental literature data and conceptual models. The growing availability of online information will progressively increase the sample size of the sample on which the procedure is based and will eventually lead to the identification of a probability surface describing the transition between stability and instability conditions of individuals in a flow. This article is protected by copyright. All rights reserved.

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,

Measuring and Modelling the Nutrients Residual Load from the Combined Sewer of the Eastern Shore of Lake Iseo

The research is motivated by the need to understand the nutrient pollution dynamics in combined sewer overflows (CSOs) contributing to the eutrophication of Lake Iseo, the fifth largest Italian lake in terms of volume. To this end, the effectiveness of the combined sewer system along the lake’s eastern shore is assessed. The sewer’s efficiency is quantified with regard to the residual nutrients load from CSOs, which was originally reckoned at no more than 3% of the overall sewer load. A hydrodynamic model of the sewer system was developed by SWMM and calibrated by a long time series of measurements collected at two selected CSOs. This data allowed to investigate in detail the occurrence of first flush and to estimate the pollutant loads discharged during wet weather periods. The calibrated model then allowed to extrapolate the results of the year-long campaign to a 10-year simulation period providing, for the first time, quantitative information on the total residual loads to the lake. Such loads are at least 5 times larger than the design value. This research provides important insight into the potential impact of CSOs on the other deep lakes of the pre-alpine chain (e.g., lakes Como, Maggiore, and Garda in Italy), that are struggling with growing environmental stressors, opening the way to important technical and management considerations regarding remedial actions.

The Application of the Erosion Potential Method to Alpine Areas: Methodological Improvements and Test Case

The Erosion Potential Method is a valuable instrument for the estimate of the mean annual sediment yield at the basin scale. The goal of this study was to demonstrate its applicability in Alpine basins with relevant presence of areas periodically covered by snow and ice. To this purpose, in order to account for the presence of frozen soil, the application of the model to the thawing periods only may be advisable. A distributed approach for the application of the method was suggested in order to reproduce the features of the original calibration, characterized by field data and experiments at the parcel scale. Finally, the model was tested on two Italian Alpine basins characterized by the presence of glaciers and perennial snow and that are drained by a barrage for hydropower purposes. The results of the model were compared to data of suspended sediment measured at the barrage by the plants manager. The good fit between the measured data and the model outputs shows the reliability of the modified model in Alpine areas.