A model for the assessment of the water footprint of gardens that include sustainable urban drainage systems (suds)

Abstract

The limitations presented by traditional urban water cycle systems, which are linearly designed systems, highlight the need to develop new technologies in a new circular strategic approach. In order to quantify the improvements, new methodologies are needed that integrate indicators that assess direct and indirect water consumption, as well as the origin of the water consumed and the incorporation of grey and rainwater. The methodology proposed provides quantitative data in terms of water to calculate the payback period of the new circular systems, comparing the conventional ones with new installations of Sustainable Urban Drainage Systems (SUDS), which are proposed as alternatives to optimize the urban metabolism by improving the water infiltration. The water footprint indicator (WF) is adapted to the construction sector, it allows to quantify the direct and indirect consumption. The first approximation is made to evaluate the impact of the urban water cycle systems. To this end, three possible scenarios are modelled, one of which is a conventional system and another two with SUDS, but different gardens, one of them with autochthonous vegetation and the second one with ornamental vegetation, with greater water requirements. Through this quantification, the amortization period is analyzed in terms of water, considering; the reduction of direct water consumption achieved with the SUDS as compared to the conventional systems; and the consumption of indirect water embedded in the materials necessary for the execution of the systems. The SUDS implementation works require approximately twice as much indirect water as conventional systems, due to the necessary improvements in the terrain for the proper functioning of these eco-efficient systems. This study, together with the technical and economic evaluation, allows us to analyze the viability of the SUDS and contribute with quantitative data in the decision-making phase for the future incorporation of this type of eco-efficient systems into the urban networks. The results of the impact of an urban space renovation project applying water-sensitive urban design techniques are shown by evaluating the nature of the materials to be incorporated in the work, the hydrological design of the project, its suitability for the urban environment and its capacity to adapt to future scenarios, evaluating both direct and indirect water. Likewise, the calculation of the WF developed by Hoekstra and Chapagain, generally applied to the agricultural sector, is also adapted to the estimation of the water balance of urban systems with the presence of green areas. The methodology incorporates local biophysical, climatic and temporal data, together with the specific data of the project to calculate the water consumption in the urban area derived from the re-naturalization of urban areas, which has been little explored until now, and to have a measurable indicator to quantify economic and environmental impacts, applicable to the construction sector. In the analysis of the results, it is worth highlighting how the scenarios in which water-sensitive urban design technologies are incorporated presents higher WF values (increased by 1.7 times), referring to the materials and execution of the works than a project in which these design technologies are not applied. The saving of water resources during the use and maintenance phases is 82% per year. The balance means that, at the end of the life cycle, 66% less WF is accumulated and the amortization in terms of water of the infrastructures occurs in year 4. © 2021, The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.