Dipartimento di Ingegneria Civile - Tesi di Dottorato
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Questa collezione raccoglie le Tesi di Dottorato Dipartimento di Ingegneria Civile dell'Università della Calabria.
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Item A Comprehensive analysis of hydrological benefits of low impact development techniques: experimental investigation and numerical modeling(Università della Calabria, 2020-03-05) Palermo, Stefania Anna; Furgiuele, Franco; Piro, PatriziaUrban floods, recently increasing due to the combine effect of climate change and urbanization, represent a potential risk to human life, economic assets and environment. In this context, the traditional urban drainage techniques seem to be inadequate for the purpose, therefore a transition towards an innovative sustainable and resilient urban stormwater management is a valid solution. One promising strategy is the implementation of decentralized stormwater controls, also known as Low Impact Development (LID) systems that provide several benefits at multiple scales. Despite several studies demonstrated the LIDs’ capability in terms of surface runoff reduction, the transition towards a sustainable urban drainage system, which includes these techniques, seems to be very slow. One of the key scientific limiting factors can be found in the lack of comprehensive analyses able to highlight the hydrological performance and the physical processes involved in LID systems at multiple spatial scale and by considering long-term experimental data. The complexity of the physical processes, involved in each specific LIDs stratigraphy, requires modeling tools able to accurately interpret their hydraulic behaviour, as well as to correlate their hydrologic efficiency with the management of stormwater in the surrounding urban area. For these reasons, so far different empirical, conceptual and mechanistic models have been proposed, however in many of these studies, the hydrological parameters, as well as the physical ones were not properly investigated, limiting the analysis only to specific factors, or by considering literature values for the numerical modeling. Thus, principal aim of this thesis is to present a comprehensive analysis of the hydrological benefits of LID techniques by experimental investigation and numerical modeling. To achieve this goal, several analyses were carried out by considering different: LID systems, spatial scales, weather conditions, modeling investigation, as well as mathematical optimization approaches. Monitored data at the full scale implementation and laboratory measurements were used to support the numerical modeling. More in detail, first a global sensitivity analysis (GSA), based on the Elementary Effect Test (EET) was applied to a PCSWMM hydrodynamic model of the University Campus Innsbruck, which combines traditional drainage infrastructures and low impact development techniques, as Rain Gardens. In this regard, main findings have showed that soil hydraulic parameters considered in the model, (i.e., principally Soil Hydraulic Conductivity and Seepage Rate) were the most sensitive parameters. Therefore, the identification of these properties for LID systems is crucial in order to correctly evaluate their hydraulic performance. Starting from this finding the analysis of the hydrological efficiency of a full-scale extensive green roof, located at University of Calabria in Mediterranean Climate was assessed, by considering field monitored hydrological data, as well as soil hydraulic properties evaluated in lab, and a modeling analysis. Thus, first a field monitoring campaign for one year was carried out, and then hydrological performance indices on an event scale were evaluated. The findings have revealed the optimal behaviour of the specific green roof in Mediterranean climate, which presents an average value of Subsurface Runoff Coefficient of 50.4% for the rainfall events with a precipitation depth more than 8 mm. Later, to evaluate the influence of increasing values of substrate depths (6 cm, 9 cm, 12 cm, 15 cm) on green roof retention capacity, the hydraulic properties of the soil materials were first investigated in Laboratory, by the simplified evaporation method, and then considered for the implementation of the mechanistic model HYDRUS 1D. The results obtained in this phase have showed how the considered substrate depths were able to achieve a runoff volume reduction of 22% to 24%. Thus, as the outflow volume reduction achieved by increasing the soil depth was not significant, the ideal depth for specific soil substrate would be 6 centimetres. Following this study, and based on the findings obtained at building scale, next phase was focused on the analysis of hydrological effectiveness of Low Impact development solutions at largeurban scale in a south Italian case study. This investigation was carried out by considering different LID conversion scenarios by a predictive conceptual model (PCSWMM). In this regards, a specific permeable pavement and green roof, developed and installed at University of Calabria, were considered for the model implementation. Globally, modeling results have confirmed the suitability of these LID solutions to reduce surface runoff even if just a small percentage (30%) of the impervious surfaces is converted. By considering all of the findings, previous achieved by experimental and modelig investigation, it emerged that many aspects related to LIDs design and operation, as well as the choice of the facility and its location can affect the results in terms of hydraulic efficiency. In this regard, a mathematical optimization approach to consider several aspects together could be a suitable tool for designers of LID systems and experts in the field. Therefore, in the last part of the work, new Mathematical Optimization Approaches for LID techniques were evaluated. More in detail, the optimization of rainwater harvesting systems, by using TOPSIS (Technique for Order Preference by Similarity to Ideal Solution) and Rough Set method as Multi-Objective Optimization approaches, was carried out. The results have demonstrated that these approaches could provide an additional tool to identify the ideal system. In conclusion, main findings of this thesis confirm the suitability of LID systems for urban stormwater management providing useful suggestions for their design and tools for assessing their hydrological effectiveness, analysing physical and hydrological parameters that affect their operation, introducing advanced concepts for the optimization of LID systems, therefore providing a significant and innovative contribution for the improvement of scientific research in the field and the spread of these sustainable techniques.Item On the use of mechanistic modeling for the numerical analysis of low impact developments techniques(2017-06-16) Brunetti, Giuseppe; Furgiuele, Franco; Piro, PatriziaThe increasing frequency of flooding events in urban catchments related to an increase in impervious surfaces highlights the inadequacy of traditional urban drainage systems. Low-impact developments (LIDs) techniques have proven to be valuable alternatives for stormwater management and hydrological restoration, by reducing stormwater runoff and increasing the infiltration and evapotranspiration capacity of urban areas. However, the lack of diffusion of adequate modelling tools represents a barrier in designing and constructing such systems. Mechanistic models are reliable and accurate tools for analysis of the hydrologic behaviour of LIDs, yet only a few studies provide a comprehensive numerical analysis of the hydrological processes involved and test their model predictions against field-scale data. Moreover, their widespread use among urban hydrologists suffers from some limitations, namely: complexity, model calibration and computational cost. This suggest that more research is needed to address these issues and examine the applicability of this kind of models. Thus, the main aim of this thesis was to investigate the benefits and the limitations in the use of mechanistic modelling for LIDs analysis. In this view, the mechanistic modelling approach has been used to simulate the hydraulic/hydrologic behaviour of three different LIDs installed at the University of Calabria: an extensive green roof, a permeable pavement and a stormwater filter. Each case study was used to examine a particular modelling aspect. The morphological and hydrological complexity of the green roof required the use of a three-dimensional mechanistic model, which was validated against experimental data with satisfactory results. The measured soil hydraulic properties of the soil substrate highlighted important characteristics, accounted in the simulation. The validated model was used to carry out a hydrological analysis of the green roof and its hydrological performance during the entire simulated period as well as during single precipitation events. Conversely, a one-dimensional mechanistic model was used to simulate the hydraulic behaviour of a permeable pavement, whose parameters were calibrated against experimental data. A Global Sensitivity Analysis (GSA) followed by a Monte Carlo filtering highlighted the influence of the wear layer on the hydraulic behaviour of the pavement and identified the ranges of parameters generating behavioural solutions in the optimization framework. Reduced ranges were then used in the calibration procedure conducted with the metaheuristic Particle swarm optimization (PSO) algorithm for the estimation of hydraulic parameters. The calibrated model was then validated against an independent set of data with good results. Finally, to address the issue of computational cost, the surrogate-based modelling technique has been applied to calibrate a two-dimensional mechanistic model used to simulate the hydraulic behaviour of a stormwater filter. The kriging technique was utilized to approximate the deterministic response of the mechanistic model. The validated kriging model was first used to carry out a Global Sensitivity Analysis of the unknown soil hydraulic parameters of the filter layer. Next, the Particle Swarm Optimization algorithm was used to estimate their values. Finally, the calibrated model was validated against an independent set of measured outflows with optimal results. Results of the present thesis confirmed the reliability of mechanistic models for LIDs analysis, and gave a new contribution towards a much broader diffusion of such modelling tools.Item Multi-level assessment of the environmental benefits of a permeable pavement: numerical analysis and experimental investigations(2018-05-09) Turco, Michele; Furgiuele, Franco; Piro, PatriziaThe increasing frequency of flooding events in urban catchments related to an increase in impervious surfaces highlights the inadequacy of traditional urban drainage systems whose aim is to rapidly collect and convey overland flows to the treatment plants. Recently, scientific community has focused its attention on Low-impact developments (LIDs) techniques that have proven to be valuable alternatives for stormwater management and hydrological restoration, by reducing stormwater runoff by reproducing natural hydrological processes in urban areas. However, the lack of diffusion of adequate modelling tools represents a barrier in designing and constructing such systems. In general, Permeable Pavement (PP) represents a good solution to solve stormwater management problems both in quantitative and qualitative way. This thesis focused on assessing the hydraulic behaviour and water quality performance of permeable pavements based on laboratory experiments and developing a modelling approach for the water flow in order to assisting engineers and researchers in the design of these systems. In this way, an adequate hydrological description of water flow in the pavement system relies heavily on the knowledge of the unsaturated hydraulic properties of the construction materials. Although several modelling tools and many laboratory methods already exist in the literature to determine the hydraulic properties of soils, the importance of an accurate description of hydraulic properties of materials used in the permeable pavement, is increasingly recognized in the fields of urban hydrology. Thus, the aim of this study is to propose techniques/procedures on how to interpret water flow through the structural system using the HYDRUS model. The overall analysis includes experimental and mathematical procedures for model calibration and validation to assess the suitability of the HYDRUS-2D model to interpret the hydraulic behaviour of a lab-scale permeable pavement system. The system consists of three porous materials: a wear layer of porous concrete blocks, a bedding layers of fine gravel, and a sub-base layer of coarse gravel. The water regime in this system, i.e. outflow at the bottom and water contents in the middle of the bedding layer, was monitored during ten irrigation events of various durations and intensities. The hydraulic properties of porous concrete blocks and fine gravel described by the van Genuchten functions were measured using the clay tank and the multistep outflow experiments, respectively. Coarse gravel properties were set at literature values. In addition, some of the parameters (Ks of the concrete blocks layer, and α, n and Ks of the bedding layer) were optimized with the HYDRUS-2D model from water fluxes and soil water contents measured during irrigation events. The measured and modelled hydrographs were compared using the Nash-Sutcliffe efficiency (NSE) index (varied between 0.95 and 0.99) while the coefficient of determination R2 was used to assess the measured water content versus the modelled water content in the bedding layer (R2= 0.81÷0.87). The parameters were validated using the remaining sets of measurements resulting in NSE values greater than 0.90 (0.91÷0.99) and R2 between 0.63 and 0.91. Results have confirmed the applicability of HYDRUS-2D to describe correctly the hydraulic behaviour of the lab-scale system. Water quality performance aimed to improve the knowledge of the system to remove heavy metals (Copper and Zinc) from stormwater runoff. It was assessed by using batch and contaminant flow experiments. Batch experiments were conducted on each construction material of the PP and highlighted that, among the pavement materials tested, only concrete blocks had the potential to adsorb the heavy metals investigated. Results shown that the adsorption capacity of the porous concrete is higher in adsorbing Cu (70% ÷ 90%) than Zn (69% ÷ 75%). Flow contaminant experiment were performed under different inflow concentrations. Results show that removal rates of Cu and Zn of the lab-scale pavements range from 85% to 92% and from 65% to 82%, respectivelyItem Soluzioni tecnologiche di idraulica urbana sostenibile per la riduzione di carico inquinante: indagini di laboratorio e installazione sul campo(2012-10-30) Penna, Nadia; Macchione, Francesco; Piro, Patrizia; Sole, Aurelia; Giustolisi, OrazioItem Experimental study and qualitative and quantitative modelling of sustainable urban drainage systems (SUDS)(2013-11-27) Mancuso, Antonello; Macchione, Francesco; Piro, Patrizia; Carbone, :Marco; Laucelli, Daniele BClimate changes have become always more frequent, increasing the interest of researchers in finding the causes and, above all, the structural or non-structural solutions to solve the problem. Economic development together with rapid population growth constantly increase the demand of goods and services. As the same as drought, also precipitation became more intense and frequent, even with more ever short duration. These events for their heavy impact are called ‘extreme rainfall events’. The actual management of urban waters is unsustainable thus, foregoing reasons lead to an imperative need to develop new urban ecosystems, requiring a rethink of traditional development techniques. Traditional urban drainage systems are designed to rapidly collect and convey overland flows to the treatment plants, without taking into account of their qualitative characteristics. In order to reach the aim of the qualitative and quantitative control of stormwater in urban areas, a possible way is the widespread implementation in urban areas of ‘blue-green infrastructure’ that provide an holistic and integrated approach to the problem. They are one step beyond other ‘classic’ sustainable urban drainage measures such as LID (Low Impact Development), SUDS (Sustainable Urban Drainage Systems) or BMPs (Best Management Practices), allowing to emphasize their beneficial effects. Use of BGC as a part of sustainable drainage system concept is a winning approach, that allow managing and treatment of stormwater runoff within urban areas, using practices made of green and blue components. Generally green components are represented by any kind of existing vegetation (floral plants, grass, hedges) while the blue one by lakes, ponds, rivers and canals (natural or artificial). Together, these infrastructures allow to create a network between them at regional scale. The real behaviour of these structures is not yet properly modelled. Most of the software currently used in urban hydrology (SWMM by EPA, Music by eWater CRC, etc…) model in a reasonable way the hydraulic behaviour of infiltration practices (such as bioretention cells, infiltration trenches, vegetated filter strips, porous pavement) using a simple mass balance approach. Generation, inflow and transport of pollutants are, instead, determined by the land use assigned to each subcatchments, namely through buildup and washoff laws describing accumulation and washout by either a mass per unit of subcatchment area or per unit of curb length. This approach completely lack of quality algorithms within LID models that take into account of their quality performances as, for instance, reduction of efficiency due to the clogging effect. The clogging phenomenon, described as the decrease in infiltration rate of the soil due to the reduction in soil porosity and hydraulic conductivity, occurs for the majority within infiltration practices such as bioretention cells, infiltration trenches, vegetated swales and permeable pavers. Precisely these latter practices are one of the easiest to implement into urban environment, being aimed to reduce impervious areas and work as ‘link’ within BGCs networks. From these premises the research in the following thesis is developed, whose main objective is to study the implementation of 'blue and green' elements in urban areas and their effect on pollutant loads reduction. Initially, a study of common errors retrieved within a DTM (Digital Terrain Model) has been faced because, if not corrected, they will affect the overland flow network generation and the subsequent hydraulic modelling. DEMs (Digital Elevation Models) can include both terrain elevation data, which commands flow direction of floodwater, and land cover information, which dictates resistance to floodwater distribution. Very often DTMs originate from a variety of ground observations supplemented by various remote sensing techniques (aerial and satellite measurements, total stations, dGPS, aerial LiDAR, terrestrial laser scanning) thus, containing systematic or random errors to individuate and eliminate. A study were carried out to evaluate how DTM resolutions and presence of building affect overland flow network delineation in the Liguori Channel basin, situated in Cosenza (Italy). To achieve this aim, three different DEMs of the study area, generated from different sources, were used: two contour-based DTMs with contour interval respectively of 30 m (DTM 30) and 20 m (DTM 20), and one LiDAR-based DEM, with horizontal resolution of 1 m (LIDAR DTM). Moreover, for a more in depth analysis, LIDAR DTMb (with buildings) cell size has been down sampled from 1 to 5 meters coarse resolution, in order to evaluate also, how cell size affect ponds delineation. Individuation of likely flood areas (ponds) has been carried out using Arc Hydro Tools developed at Centre for Research in Water Resources at University of Texas at Austin. Research highlighted how the correction of DEM generated from LiDAR data and other sources overlapping the buildings (i.e. retrieved from cadas maps) help to diminish the total accumulated water volume into surface ponds, real or spurious, and also that their number does not depend by the raster cell size, but from the accuracy of the source data. Afterwards, a first attempt of best management practices implementation has been carried out within the Liguori Channel situated in Cosenza, Italy. The overland flow network of a highly urbanized sub area has been enhanced through the addition of a certain percentage of green roof and porous pavements. A series of simulations were carried out, using in input the historical annual rainfall series (between 2008 and 2011) and considering a first scenario without LIDs (reference case) and a second scenario with the new practices implemented. Moreover, the same simulation were repeated in continuous, namely considering a single time series composed by 4 years of precipitations (2008-2011) and taking into account, in addition to the two previous cases, of a third scenario where LIDs may deal with clogging phenomenon. In order to perform the EPA SWMM modelling, a ‘residential’ land use has been defined, characterised by build-up and wash off laws for the considered pollutant (Total Suspended Solids – TSS). As regards the green roof and porous pavement simulation parameters, currently these values has been gathered from literature. Within SWMM, the clogging phenomenon is taken into account through a parameter called ‘clogging factor’ that considers the possible decay of LID performance due to the fine material carried by infiltration waters. The empirical formulation is affected by some parameters such as the number of years it takes to fully clog the system (Yclog), the annual rainfall amount over the site (Pa), the pavement's capture ratio CR (area that contributes runoff to the pavement divided by area of the pavement itself), the system's void ratio (VR), the Impervious Surface Fraction (ISF) and the pavement layer thickness (T). The yearly simulation performed show how the percentage reduction of volumes into the network is around 35% on average each year, the mass of Total Suspended Solids is around 30% on average while the relative concentration undergoes an increment around 15%. The latter result can be explained looking at the SWMM runoff quality algorithm. In fact, currently SWMM takes into account of the reduction of pollutants only in terms of reduction of overland flow, due to the lacking of quality algorithms for LIDs simulation. Consequently, the presence of BMPs increases the amount of stormwater that infiltrates, decreasing runoff, therefore the mass of pollutants reaching the sewer outlet. The lower is the volumes of water reaching the sewer, keeping constant the total mass of pollutant over the catchment, the higher is the average outlet concentrations. The results of the continuous simulation are, also, very interesting. While during the annual simulations the trend of volumes for the scenario ‘LIDs with clogging’ ranges always between the other two cases, without and with LIDs, when the continuous simulation is considered, the volumes of the clogged LID are even higher than the volumes occurring without any BMP implemented. The efficiency tends to decrease during time, from 50% when simulation starts to almost 0% at the end of the second year, continuing then to swing around zero per cent for the remaining part of the simulation. In this case, in fact, during the first two simulated years the trend is similar to what it has been found during the annual simulation, while starting from the third year (January 2010), volumes generated for the case ‘LIDs with clogging’ are equal or even higher than those ones generated when no LIDs are used. Although EPA SWMM results are interesting and indicative of LID operation, they are not very accurate, especially concerning the qualitative simulation of the stormwater management practices. For this reason, later, the research has been focused on improving the qualitative simulation algorithms, with particular attention to porous pavements. Data collected into an experimental laboratory rig of three different and widely used permeable pavement types has been analysed. The investigated systems were: monolithic porous asphalt (PA), modular Hydrapave (HP), and monolithic Permapave (PP). The rig, made of three vertical compartments in which the three porous pavers stratigraphies has been rebuilt, has been subjected to a semi-synthetic hyetograph, made of five different rain intensities (wetting regime) plus several drying periods. From the frequency curve typical of Brisbane (AU), in correspondence of different percentile ranges four flow rates has been chosen (A, B, C, D). In addition, a 1 in 5 year storm of 5 min duration was selected; this represents the typical design storm where the porous pavers are likely to be developed. The accelerated laboratory test allowed to simulate 26 years of operation under Melbourne climate. About the water quality monitoring, an intense sampling regime has been conducted in which samples were collected from inflow and outflow and analysed for Total Suspended Solids (TSS), Total Phosphorus (TP) and Total Nitrogen (TN). Afterwards, a correlation analysis has been performed in order to individuate the key variables affecting the porous pavement functioning. According to these results, the key variables identified to affect the pollutant concentration values were: the cumulative flow every 6, 12 and 24 hours before the sampling time, the cumulative inflow volume in each time step and the cumulative trapped mass. Initially, it has been tried to analyse the phenomenon through the ‘k-C* model’, that is a conceptual model used to simulate the pollutant behaviour through the system, based on a first-order kinetic decay equation. Notwithstanding the wide popularity and tested applicability on various other treatment practices such as sand filters, wetlands, ponds, infiltration systems and vegetated swales, the model did not show satisfying results when applied to porous pavements, especially about heavy metal and total nitrogen modelling. The predictive power of the model has been assessed through the calculation of the Nash–Sutcliffe model efficiency coefficient, widely adopted in the Anglo-Saxon world to evaluate behaviour and performance of the hydrologic models. Nash-Sutcliffe coefficient is an indicator of the model’s ability to predict about the 1:1 line between observed and simulated data. NSE ranges between −∞ and 1.0 (1 inclusive), with NSE = 1 being the optimal value. Values between 0.0 and 1.0 are generally viewed as acceptable levels of performance, whereas values < 0.0 indicates that the mean observed value is a better predictor than the simulated value, which indicates unacceptable performance. Considering this, the concentration data collected has been processed, also taking into account of the correlation analysis previously carried out, which allowed to estimate the concentrations of the main pollutants such as TSS (Total Suspended Solids), TP (Total Phosphorous) and TN (Total Nitrogen) to the output section of the porous pavements. The reliability of the new proposed formulas has been demonstrated both by high values of the Nash- Sutcliffe coefficients, always positive, and also by very low errors (between 10% and 25%) among modelled and measured concentrationsItem Caratterizzazione delle acque di una rete di drenaggio di tipo misto come supporto alla scelta di sistemi di trattamento(2014-04-11) Carbone, Marco; Piro, Patrizia; Veltri, Paolo