On the efficiency of stormwater detention tanks in pollutant removal

In the design of a stormwater detention tank is important to guarantee a sufficient retention time for the sedimentation of suspended solids, the biological uptake of nutrients and the die-off of bacteria carried in rainwaters. Long retention times increase the capacity of pollutant removal, but also the possibility of spills in downstream receivers and the risk of environmental pollution. In this paper, an analytical probabilistic approach, to estimate the probability distribution function of the average retention time and the efficiency in pollutant removal of stormwater tanks has been proposed. The possibility of water mixing from consecutive runoff events and storage carryover due to successive rainfall events has been considered. The method has been applied to a case study in Milano, Italy

A probabilistic approach to stormwater runoff control through permeable pavements beneath urban trees

: One of the most current and urgent challenges is making cities sustainable and resilient to climate change. From this perspective, Nature-Based Solutions (NBSs) are well-recognized strategies for stormwater control and water cycle restoration. Urban trees are an example of NBS. However, the high degree of soil sealing typically found in urban environments limits natural processes such as infiltration and hinders the water and nutrient supply for proper root development, which weakens tree stability. Permeable pavements at the base of urban trees, on the one hand, facilitate infiltration, which helps runoff control, and on the other hand, improve stormwater retention and soil humidity, which enhance root feeding. This paper proposes an analytical-probabilistic approach to estimate the contribution of permeable pavements to stormwater management. The equations developed in this study relate the runoff probability to the storage volume, the infiltration rate into the underlying soil, and the average values of the hydrological variables in the input. The model allows us to select different runoff thresholds and considers the possibility that residual volume from previous rainfall events prefills the storage capacity. An application to a case study in Sao Paulo (Brazil) has been presented. It investigates the influence of the different parameters used in the model on the results. The comparison of the outcomes obtained using the developed equations with those obtained from the continuous simulation of measured data confirmed the effectiveness of the proposed analytical-probabilistic approach and the suitability of using permeable pavements at the base of urban trees for improving stormwater retention

Uncertainties in Flow Duration Curves in anthropized catchments

Flow Duration Curves (FDC) are a traditional tool in water resources management. Their applications range from environmental protection planning to hydro-systems design. In many problems natural FDC are needed, that is curves referring to river regimes before alterations due to anthropic water uses.Estimation of FDC, as known, is uncertain in ungauged catchments. Also in gauged catchments, however, uncertainty may be relevant if available flow data are few or recorded after the anthropic alterations were set. This uncertainty may be high in mountain rivers, whose regime is typically more irregular and with significant alterations, mostly due to withdrawals for hydropower uses.The scope of this paper is to analyze these uncertainties, using a methodology to link anthropic uses to FDC alterations. Application to a catchment in the southwestern Alps is finally presented

Rainwater Harvesting and Treatment: State of the Art and Perspectives

Rainwater harvesting is an ancient practice currently used for flood and drought risk mitigation. It is a well-known solution with different levels of advanced technology associated with it. This study is aimed at reviewing the state of the art with regards to rainwater harvesting, treatment, and management. It focuses on the environmental and social benefits of rainwater harvesting and links them to the Sustainable Development Goals. The review identifies characteristics of laws and regulations that encourage this practice and their current limitations. It presents methodologies to design a rainwater harvesting system, describes the influence of design variables, and the impact of temporal and spatial scales on the system's performance. The manuscript also analyzes the most advanced technologies for rainwater treatment, providing insights into various processes by discussing diverse physiochemical and biological technology options that are in the early stages of development. Finally, it introduces trends and perspectives which serve to increase rainwater harvesting, water reuse, and effective management

Costs-benefit Analysis for the use of Shallow Groundwater as non-conventional Water Resource

Encouraging the implementation of non-conventional water resources (NCWR) is a fundamental strategy to face the future challenges due to urban population growth and resource scarcity. The implementation of a systematic process of Cost Benefit Analysis (CBA) offers reliable economic indicators to support decision makers in taking actions shifting towards NCWR. While infrastructure costs are directly estimated, while the benefits depend upon the considered stakeholders and require a tough estimation of the achieved ecosystem services. This research provides a framework for CBA analysis adopting NCWR at municipal level. The framework has been then applied to two case studies in Milan focused on the exploitation of shallow groundwater, where the obtained economic indicators has stressed out the importance of considering a complete benefits analysis that could support incentive policies on shifting part of the financial benefits to direct users leading to benefits for the whole community