Ilaria Gnecco

Designing domestic rainwater harvesting systems under different climatic regimes in Italy.

Nowadays domestic rainwater harvesting practices are recognized as effective tools to improve the sustainability of drainage systems within the urban environment, by contributing to limiting the demand for potable water and, at the same time, by mitigating the generation of storm water runoff at the source. The final objective of this paper is to define regression curves to size domestic rainwater harvesting (DRWH) systems in the main Italian climatic regions. For this purpose, the Köppen-Geiger climatic classification is used and, furthermore, suitable precipitation sites are selected for each climatic region. A behavioural model is implemented to assess inflow, outflow and change in storage volume of a rainwater harvesting system according to daily mass balance simulations based on historical rainfall observations. The performance of the DRWH system under various climate and operational conditions is examined as a function of two non-dimensional parameters, namely the demand fraction (d) and the modified storage fraction (sm). This last parameter allowed the evaluation of the effects of the rainfall intra-annual variability on the system performance.

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.

Particle Separation and Hydrologic Control by Cementitious Permeable Pavement

Cementitious permeable pavement (CPP) has the potential to provide in situ particulate, chemistry, and hydrologic control for storm water. The specific aspects of this control that have been the subject of significant interest and discussion are filtration, hydrologic control, and the potential for clogging. This study investigated the behavior of CPP subject to particle loadings for a constant particle size gradation, a sandy silt gradation. Recovered from an I-75 Cincinnati, Ohio, site subject to runoff loadings, these CPP specimens had similar pore size distributions and effective porosities. The total mass removal efficiencies for the particles were significant, ranging from nearly total removal for medium and coarse sands to greater than 60% removal for fine silt-size particles. With an engineered surface matrix, total phosphorus reductions exceeded 80%. The commensurate turbidity reductions were significant, and the turbidity of the effluent was generally reduced from 50% to 90% of the influent values. In situ hydrologic restoration was significant, generating peak flow reductions and storage within the pore space that represented approximately 25% of the CPP volume, and the temporal aspects of the influent hydrograph were attenuated compared with that for conventional impervious pavement. The initial hydraulic conductivity was in the range of 10−2 cm/s and followed a first-order exponential decline, and restoration of this hydraulic conductivity required some form of pavement cleaning approximately once every 6-month period. Cleaning by pavement vacuuming restored more than 95% of the initial hydraulic conductivity.

Control of Highway Stormwater During Event and Interevent Retention in Best Management Practices

Volumetric clarification-type best management practices that provide storage through detention–retention are more frequently incorporating adsorptive filters. This study examines the hydraulic and chemical response of a volumetric clarifying filter (VCF) system to 1,088 m2 concrete-paved watershed loadings in Baton Rouge, Louisiana, for fully captured events. VCF deployment incorporates aluminum oxide–coated media for phosphorus adsorption after it was demonstrated that common media (perlite and sand) were ineffective for adsorption. While event mean head loss is less than 25 mm, instantaneous values are flow dependent, as are filter surface loading rates. Filter ripening head loss is small but evident for the cumulative volume treated for 19 events. During interevent retention, oxidation–reduction drops to anoxic levels after 48 h, continuing a gradual decrease with interevent time. During storage, nitrate decreased (denitrification) and ammonia nitrogen increased (with an increase in NH3), and phosphorus partitioning remained stable. Results indicate that while interevent runoff retention is a common practice, the coupled hydrochemical behavior and fate of runoff chemicals subject to storage must be integrated into such unit operations. Results indicate that best management practices require more frequent maintenance and sludge removal.

Hydrologic influence on stormwater pollution at two urban monitoring sites

The pollutant transport process operated by stormwater runoff on urban paved surfaces and the relationship between the parameters of the wash-off function and the controlling hydrologic variables are investigated in the present work. Data collected during two monitoring campaigns carried out at the plot scale within a residential area and an auto dismantler site are used to this aim. The observed runoff events are classified into different mass delivery processes and the occurrence of the first flush phenomenon is also investigated. The maximum flow discharge obtained as the average value over the time of concentration of the drainage network is proposed as the controlling factor for the total mass of pollutant that is made available for wash-off during each runoff event.

Assessing the socio-economic impacts of green/blue space, urban residential and road infrastructure projects in the Confluence (Lyon): a hedonic pricing simulation approach

Urban green/blue spaces are put under pressure as urban areas grow, develop and evolve. It is increasingly recognized, however, that green/blue spaces provide important ecosystem services, stimulate higher real estate prices and prevent flooding problems. This paper aims to assess and compare the socio-economic impacts of potential green/blue space, urban residential and road infrastructure development scenarios in the Lyon Confluence project area (France), using the Sustainable Urbanizing Landscape Development (SULD) hedonic pricing simulation model. Results show four major tendencies regarding the value-added of green/blue spaces in urban landscapes: (1) cities become more compact; (2) population densities increase; (3) real estate values rise; and (4) demographic distribution patterns change. The magnitude of these impacts depends, however, on the quality and size of the intervention, the social classes attracted to the intervention area and on the location of the intervention relative to existing residential areas, urban centres, road infrastructure and environmental amenities.

A green roof experimental site in the Mediterranean climate: the storm water quality issue.

Since 2007, the University of Genoa has been carrying out a monitoring programme to investigate the hydrologic response of green roofs in the Mediterranean climate by installing a green roof experimental site. In order to assess the influence of green roofs on the storm water runoff quality, water chemistry data have been included in the monitoring programme since 2010, providing rainfall and outflow data. For atmospheric source, the bulk deposition is collected to evaluate the role of the overall atmospheric deposition in storm water runoff quality. For subsurface outflow, a maximum of 24 composite samples are taken on an event basis, thus aiming at a full characterization of the outflow hydrograph. Water chemistry data reveal that the pollutant loads associated with green roof outflow is low; in particular, solids and metal concentrations are lower than values generally observed in storm water runoff from traditional rooftops. The concentration values of chemical oxygen demand, total dissolved solids, Fe, Ca and K measured in the subsurface outflow are significantly higher than those observed in the bulk deposition (p < 0.05). With respect to the atmospheric deposition, the green roof behaviour as a sink/source of pollutants is investigated based on both concentration and mass.

An Integrated GIS Approach to Assess the Mini Hydropower Potential

An analytical approach to assess the mini hydropower potential is proposed on a GIS platform. The mini hydropower potential is defined in terms of a synthetic index that measures the investment feasibility of a given hydropower plant. The investigation of the mini hydropower potential is performed at the catchment scale by integrating: catchment morphometric analysis; setting criteria for locating the weirs and powerhouses; hydrological modelling; engineering analysis; economic analysis and mapping. The integrated approach has been tested on the Arroscia catchment (Italy) where 27 weir sections have been examined thus resulting into 640 evaluated mini hydropower plant alternatives. Hydropower potential results indicate that in 14 over 27 sub-catchments it is possible to select at least a specific powerhouse location where the investment is affordable. The determination of MHP indexes in a simplified framework overcomes the typical problem due to the single prediction of hydropower potential for a specific plant configuration. The comprehensive MHP analysis allows to supports the energy management strategies while ensuring the sustainable water resource management at the catchment scale.

Enhancing the Retention Performance of a Small Urban Catchment by Green Roofs

In existing urban areas the drainage systems can be retrofitted in order to address flooding and water quality problems. In this study, the installation of green roofs is assumed as hypothetic retrofitting scenario according to a sustainable storm water mitigation strategy for a selected urban catchment. The modelling is undertaken using EPA SWMM; the simulations are performed over a continuous simulation of 26-years of rainfall records. The modelling results point out that the retrofitting scenario contributes to the storm water runoff mitigation mainly in terms of volume and peak reduction.

Green Roofs to Improve Water Management

Abstract Green roofs are increasingly used as a sustainable urban drainage system due to their positive impact on the storm water management. The mitigation consists in reducing the total outflow volume, while delaying the initial time of runoff and distributing the outflow over a longer time period. The retention, detention, and infiltration processes promote the occurrence of adsorption and dissolution mechanisms throughout the green roof components generally limiting the total pollutant mass delivered on an event basis. An overview of the green roofs hydrologic performance metrics as well as experimental data to provide a quantitatively assessment is presented. Similarly the impact of a green roof in altering storm water quality is examined based on the observed pollutant loads reported in the literature. Finally, the needs for future research and suggestions for green roofs integration in urban water mitigation strategies are discussed.