1,720,973 research outputs found
Impact of urban drainage and sewerage systems on the quality of water bodies and mitigation strategies
No full textPollution due to anthropogenic activities is a significant factor in compromising receiving water quality status. Rural areas accumulate plant protection products and other pollutants which are eventually washed off by irrigation channels or during rainfall events towards nearby water bodies. To assess water quality of rivers and water bodies over time, long-term monitoring activities which usually consist in collecting few samples over the year for laboratory analysis, are done. However, being these activities expensive, time consuming and staff intensive, the frequency of sampling in many cases is limited both in time and space, making the assessment of physical and chemical processes derived from several factors, such as rural activities and urban areas, a challenging task. To overcome limitations related to the possibility of collecting only a certain amount of samples in time and space, models that consider both water quantity and quality aspects, have been developed to interpret data collected, predict future quality status and suggest possible actions to mitigate or eliminate pollution sources.
To manage problems generated as a consequence of the increase of urbanization and of changes in climatic forces, Sustainable Urban Drainage Systems, have being proposed. Among others, permeable pavements can be easily retrofitted in the urban environment and have proved to be highly effective at managing stormwater. However, these systems are subjected to clogging, the accumulation of particles on the porous surface and in the permeable layers. Thus concerns related to the long term performance of this solution as well as the optimal configuration to be adopted to reduce the evolution of clogging in time and allow for effective maintenance have prompted many researchers to test these solutions through both laboratory scale, real scale experiments and modelling.
This research aims at providing insights on the impact of urban areas as well as rural activities on rivers water quality both during normal conditions and rainfall events and at assessing the efficiency of permeable pavements as stormwater control facilities.
For the first research topic, the city of Treviso has been selected as case study. A monitoring system has been designed and developed consisting of 6 stations equipped with radar sensors to obtain discharge data. Results from the analysis of data collected show advantages and limitations of the selected instruments, the evolution in time and space of several water quality parameters and suggest the main sources of pollutants upstream and downstream the downtown. A hydrodynamic model was also developed considering the river-channel network and tested using data collected by the radar sensors. For the second reseach topic, a large scale (6m x 2m) laboratory model of a permeable pavement has been realized. The performances of the newly constructed permeable pavement subjected to different rainfall intensities have been assessed using several sensors (3 piezometers, 6 tensiometers, 4 water content reflectometers and two tipping buckets discharge gauges). Results from the laboratory experiments have proven the efficiency of a newly constructed permeable pavement subjected to very intense rainfall events
Impact of urban areas' drainage system on the quality of water bodies and mitigation strategies
No full textDiffuse urban pollution is a significant factor in compromising receiving water and groundwater standards required by the EU Water Framework Directive. Many studies (e.g., Ashley et al., 2005; McGrane, 2016) show that changes in the built environment and climatic forces contribute to the increase of combined sewer system overflows and of stormwater directly conveyed to nearby water bodies. These discharges are responsible for receiving water contamination, as a result of high concentrations of pathogens, BOD, suspended solids (SS), hydrocarbons, heavy metals and nutrients, thus being a significant source of water bodies’ pollution.
To mitigate/eliminate pathogens and BOD contamination sources, the combined drainage system is usually split into separated sanitary sewer and stormwater systems, although difficulties related to economic and technical feasibility may be relevant. Nevertheless, this solution does not solve completely pollution due to SS, hydrocarbons, heavy metals from urban areas runoff and nutrients from rural drainage.
Sustainable Drainage Systems (SuDS) deal with stormwater at source, helping infiltration and storage of water, increasing groundwater recharge, and reducing peak flood and volume in the drainage system. Moreover, filtration processes through porous media may reduce pollutants driven by first flush, usually controlled by stormwater tanks and sewer system spillways. However, clogging phenomenon limits drainage efficiency in the long-term, making sometimes porous media itself a source of contamination.
In the following, a PhD project focusing on the urban area of Treviso is illustrated. Treviso is crossed by the river Sile, one of the longest (95 km) European wellspring rivers, part of a protected area. The Sile river is polluted by discharges from both the existing combined sewer system and rural drainages.
While responsible agricultural practices will be promoted to mitigate the pollution originating from rural areas, a project aims to separate the combined system, developing a new pipe network for sanitary wastewater. When properly applied in the present drainage system devoted to the stormwater control only, SuDS solutions are able to mitigate pollution coming from wash-off and reduce flood peaks.
Discharge measurement stations will be realised on the Sile river upstream and downstream the Treviso town, to quantify drainage system outflows of the urban area during rainfall events and in dry conditions. Sampling for qualitative analysis will give a measure of the pollutants’ concentration.
SuDS solutions, e.g. porous pavements, infiltration trenches and vegetated swales, will be tested with laboratory equipment (6×2 m2) capable of considering the runoff and underground drainage in a fully controlled environment subjected to a prescribed rainfall intensity. By this way it will be possible to analyse the main physical processes and assess the SuDS solutions’ efficiency both in the short and long-term, using advanced mathematical models for the interpretation of results.
If the laboratory model will provide satisfactory results, a full-scale test will be developed on an experimental site in Treviso town. The installed qualitative and quantitative monitoring system will allow to determine the effectiveness of the solutions adopted
Monitoring and modeling of rivers crossing urban areas: The case of the Sile River in Treviso (Italy)
No full textA significant factor in compromising receiving water standards required by the EU Water Framework Directive is the use of plant protection products and fertilizers in agriculture and the diffuse urban pollution. Changes in the built environment and climatic forces contribute to the increase of combined sewer system (CSS) overflows and of stormwater directly conveyed to water bodies that, together with rural discharges, are responsible of their contamination.
Here the case of the river Sile, one of the longest European wellspring rivers and part of a protected area located in the Nord-Est of Italy is addressed.
To assess the impact of rural and urban pollution discharges on the quality of the main river and some of its tributaries crossing the city of Treviso (Figure), a monitoring system consisting of 6 discharge measurement stations and 4 sampling systems, together with 3 multiparametric probes, will soon be realized. To identify the most common pollutants and quantify rural and urban area’s drainage system outflows during both rainfall events and dry conditions continuous probe monitoring and lab analysis of automatic water samples will be developed. Monitored discharges and collected quality data will be analysed and used together with the results of a currently under development 1D-2D hydrodynamic model of natural and artificial channel network.
The hydrodynamic model, using as input the data acquired over time, will allow us to determine the nowadays conditions, identify and quantify the main sources of pollution and suggest possible mitigation strategies to improve the current status of the Sile River.
These activities will enable the promotion of responsible agricultural practices and the assessment of the effects of an ongoing project aimed at separating the CSS. Moreover, to solve pollution generating from urban areas runoff, Sustainable Drainage Systems solutions will be tested with a laboratory equipment in a fully controlled environment, to analyse the main physical processes and assess the solutions’ efficiency both in the short and long-term.
If the laboratory model gives satisfactory results, a full-scale test will be developed on an experimental area of the municipality of Treviso, to verify the effectiveness of the solutions adopted through the installed monitoring system
A Monitoring System to Assess the Impact of Anthropogenic Activities on Urban Rivers
No full textMonitoring of rivers is fundamental not only for classifying their status and for identifying the main sources of pollution (Water Framework Directive 2000/60/CE), but, when coupled with numerical modelling, also for defining intervention strategies to improve the water quality status. In the latter case, data must be suitable to evaluate the effects of local actions on a short temporal scale, and to calibrate a numerical model to forecast the effects of actions on a long temporal scale driving the future ones. The water quantity and quality parameters, the choice of sensors, the identification of monitoring locations are just some of the main aspects that must be assessed while planning a monitoring network to obtain useful data with reasonable costs.
In this work, a new water quantity and quality monitoring system developed between 2021 and 2023 to assess the impact of the city of Treviso on the quality status of the Sile River, is presented. The Sile River is one of the longest well-spring rivers of Europe and part of one of the nature protection areas of the European Union (Natura 2000). Although originated from springs, it receives the contribution of discharges from a wide agricultural area, and it is affected by the combined sewer system of the city of Treviso. An ongoing project aims at separating the sewer system: the developed monitoring system has thus been designed and used for quantifying the impact of the urban area during normal condition and rainfall events, identifying pollution sources, and for planning actions for water quality restoration. Moreover, the monitoring system has been designed for the calibration of a numerical model which will be used to forecast the effect of present and future actions.
To this aim, 6 stations each one of them equipped with radar sensors to retrieve continuously water level and discharge data are installed; 3 stations out of 6 are equipped with multiparametric probes and refrigerated samplers. Two additional portable samplers allow quality data to be collected at other locations.
Analysis of data collected up to now is presented to provide insights on the actual status of the river Sile and to check their suitability for building and calibrating a quantity-quality numerical model. Advantages and limitations of developing and maintaining such monitoring system are also discussed
The impact of anthropic activities on the urban rivers' water quality: insights from the monitoring activities and modeling of the Sile River (Treviso, IT)
No full textUrbanization is a significant factor in altering the hydrologic cycle and compromising receiving water bodies quality status. Indeed, changes in the built environment (e.g. imperviousness), together with climatic forces (e.g. intense rainfall events after long dry periods), contribute to the increase of combined sewer system overflows and of stormwater directly conveyed to water bodies (e.g. Carle et al., 2005; Riechle et al., 2016), responsible for water quality deterioration, as a result of high concentrations of pathogens, BOD, suspended solids, heavy metals, hy-drocarbons and nutrients (e.g. Ji et al., 2022).
In this note, the first results of an ongoing project focusing on monitoring and modeling the Sile River, one of the longest European spring rivers, and some of its main tributaries, to assess the different discharge contributions (springs, sewer and drainage system) and the impact of the urban activities of the city of Treviso, are presented.
A monitoring system consisting of six monitoring stations (3 upstream and 3 downstream the historical center of Treviso) has been developed. Each monitoring station is equipped with two radar sensors, to measure surface ve-locity and water level. Three out of six monitoring stations will be equipped with multiparametric water probes and automatic samplers, to continuously monitor and quantify rural and urban area’s drainage system outflows, and pollutants trend, during both dry conditions and rainfall events.
Data collected from the monitoring stations will be used to calibrate and validate a model of the urban drain-age/sewer system coupled with the 1D hydrodynamic model of the river network crossing the city of Treviso.
Starting from the hypothesis that the quality aspect depends on the quantity aspect (e.g. Depetris, 2021), data col-lected from the radar sensors is here analyzed, assessing possible issues that may occur, to test the hydrodynamic 1D model. A first water balance, during dry conditions, is presented and differences between input and output discharges enables a first estimate of the contribution given by springs and the sewer system.
Results and considerations here presented are fundamental to assess the accuracy of data collected and results obtained from the model, and define the possible contributions given by springs and the sewer system. The ob-tained results set the basis for future analysis to gain an overview of the current status of the Sile River conditions, identifying and quantifying the main sources of pollution, to identify the more suitable mitigation strategies
Permeable Pavement System: Insights on Stormwater Facility Management through a Large-Scale Laboratory Model
No full textThe applicability of green infrastructures (GI) in the urban environment is conditioned by many factors, like hydraulic properties of soils, groundwater table, the specific context in which they are to be developed and construction work and maintenance costs (Salerno et al., 2018), thus requiring technical assessment. Among other GI, permeable pavements (PPs) can be easily retrofitted into the urban environment, although they suffer clogging that reduces their efficiency over time. An unscaled model of a PP section (2 m wide and 6 m long with 1.2% slope), has been realized inside a reinforced concrete box (Lora et al., 2016) to investigate the physical processes controlling runoff vs infiltration along time and the decay of efficiency due to clogging. The surface of the upstream portion (1.85x2 m2) is impermeable to simulate washoff of sediments, while the downstream portion (4.15x2 m2) is realized with Pervious Concrete Paver Blocks (Borgo Veneto _ Micheletto® SaS). The downstream vertical side of the PP is made of permeable bricks and two gutter channels are placed crosswise to separately collect runoff and subsurface discharge. The remaining sides, as well as the bottom of the model, are impermeable. The filter package is laid on top of a 40 cm layer of native sand (silty sand with d50=0.23 mm). From the bottom to the top: a 30 cm sub-base layer (20/40 mm gravel), a 10 cm base layer (8-12 mm gravel) and a 5 cm bedding layer (3-6 mm gravel). A geotextile (200 g/m2) separates the bedding and base layers and a 4m long drainpipe (D=125 mm) was inserted in the sub-base layer in the middle of the PP section. The facility is equipped with probes on both lateral sides: 6 tensiometers (TEROS32 METER Group) in the native sand, and 4 water content reflectometers (CS616 - Campbell Scientific) in the base and sub-base layers, while 3 piezometers (ATM/N STS) will record water table behaviour. Runoff and subsurface discharge are separately conveyed to two tipping bucket rain gauges.
A rainfall simulator (Lora et al., 2016) is used to generate quite uniform rainfall distribution (80 - 150 mm/h intensity). A first set of experiments is developed to assess the efficiency of a newly constructed PP and define its maximum in-
infiltration capacity. Then, a second set of experiments will simulate washoff and clogging phenomena to assess the efficiency of PP over time
LABORATORY EXPERIMENTS ON A LARGE SCALE-FULLY MONITORED PERMEABLE PAVEMENT SYSTEM
No full textPermeable pavements (PPs) are one of the so called Sustainable Urban Drainage Systems used to face the consequences deriving from the ever-increasing urbanization and to changing in climatic forces (Burns et al., 2013) that jeopardize the management of stormwater in existing urban drainage networks. Indeed, these solutions have received increasing attention from scientific communities looking for new ways to manage stormwater and restore as much as possible pre-urbanized conditions according to new regulations.
Among other solutions, PPs can be easily retrofitted into the urban environment: roads, parking lots, bike-lanes surfaces which are impermeable, in many cases can be replaced with permeable surfaces without the need of changing the end-of-use of the area, allowing for infiltration and retention of water into the ground during rainfall events. PPs are characterized by a permeable surface layer made of either porous concrete/asphalt or impermeable/pervious paver blocks with joints filled with permeable materials, laid on a filter package usually made of coarse aggregates. The filter package is used to store infiltrated runoff during rainfall events, which in turn is slowly released into the underlying ground or collected by a drain. Consequently, runoff peak discharges as well as the total runoff volume conveyed to the drainage system and to nearby water bodies, is reduced. Moreover, PPs act as filters for trapping particulate matter and pollutants accumulated on the surfaces during dry periods and washed off during rainfall events.
Although PPs seem to be a suitable solution for improving stormwater runoff control and even though there has been a worldwide increase of their use in urban areas, their application remains relatively new and concerns regarding their efficiency over time have rose, prompting researchers at investigating their efficiency over time and at assessing the factors affecting their performance. To this aim, both real-scale and laboratory scale PPs have been monitored, and numerical models have been realized (e.g. Brown & Borst, 2014; Palla et al., 2014, Elliot & Trowsdale., 2007).
Assessing the hydraulic performance of PPs using modelling techniques has been proven to be a complicated task due to several factors: the need of assigning accurate unsaturated hydraulic properties to the aggregate materials and assessing the highly heterogeneous properties of the filter layer package. Thus, to this aim, instrumented laboratory models are fundamental to gain information regarding the unsaturated hydraulic properties of the materials, as well as to provide insights on the physical processes occurring in a PPs. With respect to small scale ones, large scale laboratory models (e.g. VanVuuren et al., 2022), although expensive, allow to reproduce physical processes occurring on PPs near to real scale experiments, for which monitoring is usually very complex. Here we present a new large scale laboratory model of a PP, equipped with several sensors for the continuous monitoring of water level, water content and both runoff and subsurface discharges. The hydraulic performance of the system subjected to rainfall events with different rainfall intensities has been investigated and results are here discussed
Insights on permeable pavement hydraulic performance from large-scale laboratory experiments and physically based modelling
Full text linkAmong other Sustainable Urban Drainage Systems, Permeable Pavements (PPs) are one can be easily retrofitted in the urban environment. However, they suffer of clogging phenomena that reduces their efficiency over time. Laboratory experiments to assess the hydraulic performance of a newly constructed PP subjected to different rainfall intensities have been conducted using a large-scale laboratory model (2x6 m2 with 1.2\% slope). The surface of the upstream portion (1.7x2 m2) is impermeable to simulate runoff generation over impermeable surfaces, while the downstream portion (4.3x2 m2) is realized with PICP. The downstream vertical side of the PP is made of permeable bricks and two gutter channels are placed crosswise to separately collect runoff and subsurface discharge. The remaining sides, as well as the bottom of the model, are impermeable. The filter package below the PICP consists of three layers: 5 cm bedding (3-6 mm gravel), a 10 cm base layer (8-12 mm gravel) and a 30 cm sub-base layer (20/40 mm gravel), which is laid on top of a 40 cm layer of native sand (silty sand with d50=0.23 mm). A geotextile separates the bedding and base layers and a 4m long drainpipe (D=150 mm) was inserted in the sub-base layer. The facility is equipped with probes on both lateral sides: 6 tensiometers in the native sand, 4 water content reflectometers in the base and sub-base layers, and 3 piezometers to record water table evolution throughout the experiments and degree of saturation of the filter layer package. Runoff and subsurface discharge are separately conveyed to two tipping bucket rain gauges. A rainfall simulator is used to generate quite uniform rainfall distribution (80 - 150 mm/h intensity) for 15 minutes or 30 minutes. Moreover, an Integrated Surface-Subsurface Hydrological model (CatHy) has been used to model the permeable pavement, assess and support data collected from the laboratory experiments.
Results from the laboratory experiments performed have proven the efficiency of a newly constructed permeable pavement to very intense rainfall events. The monitoring with spatially distributed sensors allowed to assess the evolution in time of the water table as well the “recovery” phase to pre-event conditions after the event. This is useful to assess the effect of repeated rainfall events at short distance in time. For each experiment performed, a rapid increase of subsurface discharges was recorded by the tipping bucket, whereas surface runoff occurred only for short and intense rainfall events (approximately 150 mm/h for 15 min). The system did not reach saturated conditions in any of the performed experiments due to the high permeability of the filter layer package. The monitoring with spatially distributed sensors also allowed to assess the heterogeneities of the physical processes (synthetic rainfall events, infiltration processes) as well as of the filter layer package.
Future laboratory experiments simulating clogging phenomena will be performed and compared to the results obtained from the developed experiments up to now and of the ISSH model
Calibration of a Physics-Based Hydrological Model of a Permeable Pavement using Data from a Laboratory Unscaled Physical Model
No full textIn the last two decades, green infrastructures have gradually been introduced in urban areas as a countermeasure for street flooding and pollutants wash-off to nearby water bodies. Among other solutions, permeable pavements (PP) are one of the most implemented one since they limit changes to the end of use of the urban space. However, due to the knowledge gap regarding the performance of the installed solutions and the efficiency over time of PPs, their adoption is often prevented.
To overcome this problem, several modelling tools have been used to describe the hydraulic behaviour of PPs both at the short- and long-time scale. To accurately describe the physical processes occurring on the PPs surface, in the layers below and between PPs and nearby impermeable surfaces, the interaction between surface and subsurface flows must be considered. To this aim, Integrated Surface Subsurface Hydrological (ISSH) model (Camporese et al., 2010) can be fruitfully used to investigate the runoff vs infiltration processes along time in PPs.
Here, the ISSH model reproduces an unscaled physical model of a section of permeable parking lot 6 m long, 2 m wide and with height varying between 0.9 and 1 m (surface slope of about 1.2%) realized inside a 6×2 m2 concrete box facility in the Laboratory of Hydraulics and Hydraulic construction of the University of Padova (Lora et al., 2016; Mazzarotto et al., 2024). No-flow boundary conditions are imposed on the bottom of the ISSH model as well as on the lateral sides, to reproduce the concrete walls surrounding the PP, except for the downstream side where a seepage face boundary condition is assumed to reproduce the porous wall built in the physical model that allows subsurface discharge quantification.
A first set of experiments was performed on the physical model using a rainfall simulator. Data collected by the installed sensors is used to calibrate the parameters of the ISSH model, in particular the hydraulic characteristics of the blocks and of the aggregate materials, and reproduce the unsaturated hydraulic behaviour of the PP (e.g. Turco et al., 2017).
The calibration results of the ISSH model based on a first set of experiments developed on the unscaled PP model are shown highlighting the major difficulties related in the assessment of parameters
HYDRAULIC PERFORMANCE OF A PERMEABLE PAVEMENT: LABORATORY EXPERIMENTS
Full text linkIn the last two decades, green infrastructures have gradually been introduced in urban areas as a countermeasure for street flooding and pollutants wash-off to nearby water bodies. Among other solutions, permeable pavements (PP) are one of the most implemented ones. However, due to the knowledge gap regarding the performance and the efficiency over time of PPs, their adoption is often prevented. A large scale fully monitored PP system is here presented and used to assess the physical processes occurring on the PP system when subjected to heavy rainfall events
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