Anna Palla

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.

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.

Partitioning of Metals in Urban Drainage from Paved Source Area Catchments

Representation of metal partitioning in urban drainage is required when determining loadings, treatment, maintenance and regulatory compliance. This is particularly the case for paved urban source areas where, if a first-flush exists, the design volumetric capture and treatment will be based on such regulatory requirements. However, such treatment for metals requires partitioning information if metals are to be effectively separated from flows from paved source areas. This study examined partitioning and transport of metals from paved surfaces of four differing land uses: highway, airside and landside within aviation site, commercial/tourism terminals within port area. Equilibrium concentrations of metals and particulate matter (PM) using a non-parametric analysis for a series of six paved surface area catchments were compared. In particular two American highway sites, and four Italian sites located in the Liguria Region (two port terminal sites and two aviation sites) were examined and compared with event based concentrations collected from catchments with similar land uses. The role of hydrology on mass transport and partitioning of aqueous and particulate-bound metal fractions was evaluated. Finally transport of metal phases on an event basis, thus relating hydrology and PM mass delivery impacting metal partitioning were examined. Partitioning, indexed through a partitioning coefficient, Kd (L/kg) accounts for hydrologic transport, PM transport and interactions with and between metals. Kd can vary by orders of magnitude across a runoff event for the source area catchments of this study. Highway sites were more heavily loaded with PM and metals than airport sites. The metals results from the six sites of this study were compared to similar sites around the world. Based on the variability of partitioning, whether intra- or inter-event, results indicate that paved source area treatment requires a combination of sedimentation, filtration and adsorption mechanisms for in-situ unit operations and processes (UOP).

A dimensionless approach for the runoff peak assessment: effects of the rainfall event structure

The present paper proposes a dimensionless analytical framework to investigate the impact of the rainfall event structure on the hydrograph peak. To this end a methodology to describe the rainfall event structure is proposed based on the similarity with the depth–duration– frequency (DDF) curves. The rainfall input consists of a constant hyetograph where all the possible outcomes in the sample space of the rainfall structures can be condensed. Soil abstractions are modelled using the Soil Conservation Service method and the instantaneous unit hydrograph theory is undertaken to determine the dimensionless form of the hydrograph; the two-parameter gamma distribution is selected to test the proposed methodology. The dimensionless approach is introduced in order to implement the analytical framework to any study case (i.e. natural catchment) for which the model assumptions are valid (i.e. linear causative and time-invariant system). A set of analytical expressions are derived in the case of a constant-intensity hyetograph to assess the maximum runoff peak with respect to a given rainfall event structure irrespective of the specific catchment (such as the return period associated with the reference rainfall event). Looking at the results, the curve of the maximum values of the runoff peak reveals a local minimum point corresponding to the design hyetograph derived according to the statistical DDF curve. A specific catchment application is discussed in order to point out the dimensionless procedure implications and to provide some numerical examples of the rainfall structures with respect to observed rainfall events; finally their effects on the hydrograph peak are examined.

Dimensions of shrinkage: Evaluating the socio-economic consequences of population decline in two medium-sized cities in Europe, using the SULD decision support tool

All over Europe, it is a known fact that cities are shrinking. One of the main causes is population decline, but the consequent reduction of urban area is neither immediate nor easy to foresee spatially. Questions arise such as where do cities start to ‘shrink’ first? What are the most fragile areas that face the risk of becoming derelict? What are the most vulnerable social groups? And how does this affect real estate values across the city? Existing models for projecting the effects of shrinkage have been criticized for lacking spatial-explicitness, being excessively data-dependent, and failing to incorporate various socio-economic, urban and environmental aspects in the assessment of attractiveness of urban areas and of decisions by households. In this article, we attempt to overcome this criticism by applying the spatially-explicit Sustainable Urbanizing Landscape Development decision support tool (SULD), based on hedonic pricing theory, in two cities in southern Europe (Aveiro, Portugal and Imperia, Italy). SULD is used to project, assess and compare changes in land-use, household type distribution, real estate values and household densities, in three different scenarios of population decline (−5%, −10% and −15%). Results quantify the amount of contraction of urban area, housing quantity and living space; highlight the most problematic areas; and uncover low income households as the least affected, whereas the relocation of high income households may cause gentrification of medium income households in some areas of the historical city centre.