Patrizia Piro

A distributed real-time approach for mitigating CSO and flooding in urban drainage systems

In an urban environment, sewer flooding and combined sewer overflows (CSOs) are a potential risk to human life, economic assets and the environment. To mitigate such phenomena, real time control systems represent a valid and cost-effective solution. This paper proposes an urban drainage network equipped by sensors and a series of electronically movable gates controlled by a decentralized real-time system based on a gossip-based algorithm which exhibits good performance and fault tolerance properties. The proposal aims to exploit effectively the storage capacity of the urban drainage network so as to reduce flooding and CSO. The approach is validated by considering the urban drainage system of the city of Cosenza (Italy) and a set of extreme rainfall events as a testbed. Experiments are conducted by using a customized version of the SWMM simulation software and show that the CSO and local flooding volumes are significantly reduced. HighlightsWe propose a distributed real-time control of urban drainage system.A gossip-based algorithm is exploited together with local PID controllers.The case study confirms the approach reduces effectively local flooding and overflow.

Influence of stratigraphy and slope on the drainage capacity of permeable pavements: laboratory results

A small size laboratory test-bed was realized at the University of Genoa in order to evaluate the drainage capacity of permeable pavements by monitoring inflow, runoff and sub-surface outflow. The laboratory test programme was designed to investigate the influence of rainfall intensity and pavement slope on the hydrologic response of permeable pavements. Four permeable pavement systems combining two paving types (concrete cell and pervious brick) with two filter layers made of recycled glass aggregate and a mix of gravel and coarse sand are tested. The hydrologic response of permeable pavements is analysed by using a dimensionless volume index (discharge coefficient) and a timing index. Laboratory results reveal that the hydrologic performance is fairly consistent for all the investigated permeable pavements. The recycled glass aggregate turns out to be a valid solution. No surface runoff occurs even at 98 mm/h rainfall intensity.

A Cumulative Rainfall Function for Subhourly Design Storm in Mediterranean Urban Areas

Design storms are very useful in many hydrological and hydraulic practices and are obtained from statistical analysis of precipitation records. However considering design storms, which are often quite unlike the natural rainstorms, may result in designing oversized or undersized drainage facilities. For these reasons, in this study, a two-parameter double exponential function is proposed to parameterize historical storm events. The proposed function has been assessed against the storms selected from 5-year rainfall time series with a 1-minute resolution, measured by three meteorological stations located in Calabria, Italy. In particular, a nonlinear least square optimization has been used to identify parameters. In previous studies, several evaluation methods to measure the goodness of fit have been used with excellent performances. One parameter is related to the centroid of the rain distribution; the second one is related to high values of the standard deviation of the kurtosis for the selected events. Finally, considering the similarity between the proposed function and the Gumbel function, the two parameters have been computed with the method of moments; in this case, the correlation values were lower than those computed with nonlinear least squares optimization but sufficiently accurate for designing purposes.

A Cyber-Physical System for Distributed Real-Time Control of Urban Drainage Networks in Smart Cities

This paper focuses on a distributed real time control approach applied to drainage networks. The increasing of urbanization and climate change heightens the challenge for new technologies to be developed for drainage networks. Higher runoff volume, produced by the increase in impervious surfaces and intense rain events, overwhelms the existing urban drainage systems. Recent technical improvements have enabled the exploitation of real-time control on drainage networks. The novelty in this paper regards the use of a totally decentralized approach based on a proper combination of a Gossip-based algorithm, which ensures a global correct behaviour even if local faults occur, and a classic controlling technique (PID) used for local actuations.

Green Roofs in the Mediterranean Area: Interaction between Native Plant Species and Sub-Surface Runoff

Green roofs (GRs) may represent a solution for minimizing the impact of urbanization on the hydrological cycle and for sustainably managing water resources in urban environment. Several studies have shown that GRs effectively control the surface runoff conveyed into the combined sewer systems, by reducing overall volumes and peak flow rates. The hydrological/hydraulic performance of a GR is strongly dependent upon vegetation species used. In this study the influence of plants on the sub-surface runoff is investigated by monitoring two experimental GRs in wet weather conditions. It is hypothesized that although plants reduce sub-surface runoff, they may also boost the formation of preferential flow paths. The results showed that the sub-surface runoff is strongly influenced by vegetation. While for smaller storm events the GR highly retains stormwater due to the plant interception, for larger storm events the GR’s performance decreases due to the increase of sub-surface runoff. This may be due to the presence of the plant root which produces preferential macropores flow through the substrate.

Management of combined sewer overflows based on observations from the urbanized Liguori catchment of Cosenza, Italy

This paper examines an urbanized catchment in Cosenza, Italy where an off-line basin intercepting CSOs was studied to illustrate reduction in CSO discharges to the Crati River. While the hydrologic transport of pollutant mass is never known a-priori and can be flow-limited, the volumetric requirements of the basin were modeled based on the classic assumption that wet weather flows transport urban and sewer loads in a mass-limited (first-flush) delivery. The volumetric capacity of the basin was varied from 10 to 50 m(3)/ha. Operational basin control was simulated with historical datasets from the Liguori catchment, event-based loading data, and continuous simulation modelling with SWMM. Utilizing data from the catchment, the SWMM simulations were conducted considering the storage basin with or without sedimentation treatment. Results illustrate the potential benefits of the off-line operation for the system with respect to the volume and mass reduction of CSOs into the Crati River. Results demonstrate the importance of particle size distribution (PSD) as an index of basin efficiency, coupled with analysis of the hydrodynamic response of the basin. The basin model attenuated influent PSDs, separating the coarser fraction of the PSD, and reduced the load of influent particulate matter (PM).

Experimental Testing for Evaluating the Influence of Substrate Thickness on the Sub-Surface Runoff of a Green Roof

Green roofs (GRs) represent one of the most widespread Low Impact Development (LID) techniques, although the lack of adequate modeling tools is a limiting factor in the diffusion of such practices. GRs may represent a solution for minimizing the impact of urbanization on the hydrological cycle and for sustainably managing water resources in urban environment. Several studies have shown that GRs effectively control surface runoff in urban drainage system reducing overall volumes and peak flow rates. The performance of a GR is strongly dependent upon substrate soil depth. The understanding of infiltration phenomena in soil medium is one of the most important factors in the LID’s hydrological behavior analysis. In this study the hydrologic/hydraulic behavior of a GR for varying substrate thicknesses and constant rainfall intensities, ranging from 45 to 130 mm/h is tested. The results show that sub-surface runoff is linearly influenced by substrate thickness.

Sampling, testing and modeling particle size distribution in urban catch basins

The study analyzed the particle size distribution of particulate matter (PM) retained in two catch basins located, respectively, near a parking lot and a traffic intersection with common high levels of traffic activity. Also, the treatment performance of a filter medium was evaluated by laboratory testing. The experimental treatment results and the field data were then used as inputs to a numerical model which described on a qualitative basis the hydrological response of the two catchments draining into each catch basin, respectively, and the quality of treatment provided by the filter during the measured rainfall. The results show that PM concentrations were on average around 300 mg/L (parking lot site) and 400 mg/L (road site) for the 10 rainfall-runoff events observed. PM with a particle diameter of <45 μm represented 40-50% of the total PM mass. The numerical model showed that a catch basin with a filter unit can remove 30 to 40% of the PM load depending on the storm characteristics.

Proposal of a Conceptual Model as Tool for the Hydraulic Design of Vegetated Roof

Vegetated roof technique is becoming increasingly popular, particularly in highly urbanized areas, among the Sustainable Urban Drainage Systems (SUDS) for urban stormwater management. Several studies [1,2] have shown that vegetated roofs may significantly reducing the runoff volume and hydrograph peaks, as well as slowing the contribution to the urban drainage network.This study proposes a conceptual model to predict the hydraulic behavior of a full-scale physical model of a vegetated roof. The model idealizes the vegetated roof as a system consisting of three individual components in series. A mass balance equation is applied to each block, taking into account the specific physical phenomena occurring in each module [3]. The model is validated using dataset observed from the monitoring campaign carried out on the prototype of a full-scale vegetated roof.This study aims to provide quantitative information about the hydraulic performance of vegetated roofs, and identify the most sensitive parameters for describing the hydraulic behavior. The results show a good ability of the model to fit the measured data.

On the use of global sensitivity analysis for the numerical analysis of permeable pavements

Abstract The aim of this study is to investigate the use of different global sensitivity analysis techniques in conjunction with a mechanistic model in the numerical analysis of a permeable pavement installed at the University of Calabria. The Morris method and the variance-based E-FAST procedure are applied to investigate the influence of soil hydraulic parameters on the pavement’s behavior. The analysis reveals that the Morris method represents a reliable computationally cheap alternative to variance-based procedures for screening important factors and provides the first inspection of the model. The study is completed by a combined GSA-GLUE uncertainty analysis used to evaluate the model accuracy.