Water demand management in the expanding urban areas of south Attica

Modern decentralized water-aware technologies (including for example grey water recycling and rainwater harvesting) enable water reuse at the scale of household or neighbourhood. Such options reduce the pressure on the infrastructure and alleviate the need for upgrading the centralized infrastructure, hence reducing the cost of urban growth. To study the benefits of the water-aware technologies on expanding urban areas, an urban water cycle and a land use model were coupled. The former, UWOT, is a bottom-up urban water model that simulates the generation, aggregation and routing of demand signals (potable water demand, runoff discharge demand, and wastewater discharge demand). The latter, SLEUTH, is a cellular automaton model of urban land use change (see project GIGALOPOLIS). The coupling of UWOT and SLEUTH was tested in South Attica. Cellular automaton models use a group of discrete units to simulate the land use evolution of the studied area. For this reason, classes of land uses should be formed based on a set of predefined criteria. The criteria of the classification of the South Attica were the population per cell, the total built area per cell and the population per building. SLEUTH was calibrated using the 2001-2011 census data. Then, SLEUTH was used to simulate the urban expansion and intensification. The simulation period spanned from 2011 to 2031. Afterwards, the results of SLEUTH were fed into UWOT, which simulated the conventional network of this area to estimate the evolution of the water demand, the runoff and the wastewater generation. Finally, a sequence of simulations were performed assuming that the network of all new buildings (those built between 2011 and 2031) incorporated water-saving schemes and that water-saving schemes were being installed in the existing buildings (those built before 2011) with a constant penetration rate. The only difference among the simulations of this sequence was the time of the initiation of the water-saving schemes installation. This provided a nomograph with a group of lines corresponding to potable water demand for different intervention timings and various penetration rates. This nomograph could be used in supporting either the planning of the expansion of the water services to newly urbanized areas and/or the decisions regarding the maintenance and capacity increase of the existing infrastructure.