Search

Identification and control of the pollutant load in sewer networks (SNs) are among the priorities for utilities to reduce the impact on water bodies and to individuate the presence of pathogens to prevent their further spread, sometimes through interventions on a social scale. This goal can be achieved essentially through the development of a monitoring system. This paper proposes a backtracking methodology for efficiently planning a monitoring system in SNs assuming steady-state conditions during the analysis. The methodology is based on the calculation of the impact coefficient, which is related to the dilution and decay of contaminants and pathogens in the network, to evaluate the impact of each possible contaminated node on a downstream one in terms of concentration. This information supports the identification of candidate monitoring points, i.e., where to place measurement sensors to ensure complete coverage and control of the network. Additional analysis has been performed considering unsteady conditions for comparing the impact coefficient values averaged over 24 h and those of the steady-state methodology. Results show a similar value between steady-state and unsteady conditions, thus justifying the use of steady-state conditions for the proposed methodology, and also for real practical applications, with a significant improvement in terms both of simplicity and computational time saving. [ABSTRACT FROM AUTHOR]

The present work investigates the effect of the flow profile induced by an inlet condition on the roll-wave evolution in turbulent clear-water flows. The study employs theoretical and numerical analyses. Firstly, the influence of the inlet condition on the spatial evolution of a single perturbation in a hypercritical flow is examined through the expansion near a wavefront analysis. The results show that an accelerated unperturbed profile reduces the disturbance spatial growth. A decelerated profile causes an increase. The effect of the flow profile on the spatial evolution of roll-wave trains is then numerically investigated solving the Saint Venant equations with a second-order Runge-Kutta Total Variation Diminishing (TVD) Finite Volume scheme. The numerical simulations comply with the analytical results for the initial and transition phases of the roll-wave development. The unperturbed profile influences even the roll-waves statistical characteristics in the final stage, with a more evident effect in case of accelerated profiles. The influence of the flow profile should be therefore accounted for in the formulation of predictive criteria for roll-waves appearance based on the estimation of the disturbance spatial growth rate.

The paper addresses the prediction of roll-waves occurrence in mud-flows. The spatial growth of a point-wise disturbance is analytically described, based on the linearized flow model of a Herschel and Bulkley fluid, in the neighborhood of an initial uniform base condition. The theoretical achievements allow to generalize to mud-flows the minimum channel criterion commonly used for the prediction of roll-waves in clear-water. The applicability of the criterion is discussed through the comparison with literature laboratory data concerning unstable flows without rollwaves.

Dikes and levees are encountered very often along rivers. They are crucial as defence structures for flow channelization, protecting population and properties from floods as well as against lateral riverbed migration. However, the combination of their aging and increased exposition to extreme hydrological events may cause these structures to breach, and subsequently to fail. Understanding the dynamics of breaching is very important for developing adequate countermeasures, for civil protection initiatives and for land use planning. Recent literature shows many studies concerning, both from experimental and numerical point of views, frontal dike breaching. Based on several evidences, it is well assessed that depth-integrated numerical models can successfully reproduce this kind of phenomenon (e.g. Greco et al., 2012). Recently, Rifai et al. (2017) investigated a different setup in which the embankment is parallel to the main channel flow and thus a lateral breaching occurs. It is worth noting this scheme resembles real-world situation of levees breaching along a river. In present paper, the capability of depth-integrated approaches in reproducing such tests is investigated. Numerical results obtained with different models are compared against experiments from both the qualitative and quantitative point of views. Considerations about the applicability of depth-integrated models in real world situation of lateral breaching of dikes and levees are also drawn.

The paper investigates the influence of the resistance coefficient variability onto the spatial development of roll-waves. Two models, based on time-asymptotic solutions of the linearized St. Venant equations, subject to either impulsive or oscillating perturbation, have been modified by including the dependence of the resistance coefficient on flow conditions, wall roughness, and fluid viscosity. Independently of the perturbation type, it has been shown that the hypothesis of constant resistance coefficient leads to underestimate the disturbance spatial growth. Theoretical predictions are finally compared with results of a fully nonlinear model and with literature experimental data for several combinations of Froude and Reynolds numbers and relative roughness values. The representation of variability of the resistance coefficient fundamentally improves the performance of minimum channel length criteria, whereas its neglect may lead to noncautious channel design. DOI: 10.1061/(ASCE)HY.1943-7900.0000139 CE Database subject headings: Bed roughness: Friction: Open channel flow; Stability; Water waves; Reynolds number; Flow resistance. Author keywords: Bed roughness: Friction; Open channel flow; Stability; Water waves.

In the present technical note, a simple methodology for identifying the source location of an accidental contamination in a water distribution network is formulated. Starting from measured solute concentration data and using the pollution matrix concept, the methodology first selects a group of candidate nodes, which are possible intrusion points. Among all candidate nodes, the source location is then identified, minimizing the differences between simulated and measured concentrations. The source location procedure, which incorporates a hydraulic network simulation model, is formulated as an optimization problem, linearized using the water fraction matrix concept. An example illustrates methodology effectiveness. An uncertainty analysis is performed in order to demonstrate the methodology robustness with respect to uncertainties in some input data, like concentration measurements and water demands. CE Database subject headings: Water distribution systems; Water quality; Water pollution; Uncertainty principles; Water demand.

The 2D shallow water equations are often solved through finite volume (FV) methods in the presence of irregular topography or in non-rectangular channels. The ability of FV schemes to preserve uniform flow conditions under these circumstances is herein analysed as a preliminary condition for more involved applications. The widely used standard Harten-Lax-Van Leer (HLL) and a well-balanced Roe method are considered, along with a scheme from the class of wave propagation methods. The results indicate that, differently from the other solvers, the standard HLL does not preserve the uniform condition. It is therefore suggested to benchmark numerical schemes under this condition to avoid inaccurate hydrodynamic simulations. The analysis of the discretized equations reveals an unbalance of the HLL transversal fluxes in the streamwise momentum equation. Finally, a modification of the HLL scheme, based on the auxiliary variable balance method, is proposed, which strongly improves the scheme performance. [ABSTRACT FROM AUTHOR]