The spatial model characterises the urban drainage infrastructure using and abstract representation of the topography, planning rules, demographic and urban characteristics. A coarse-grid is used for the abstraction of the spatial characteristics and the base for the sewer network delineation. The generated drainage infrastructure will be a simplified representation of a real system, with enough information for planning purposes. This method will be used to shape and dimension future configurations of the sewer infrastructure (i.e. alternatives), based on changing spatial characteristics. In comparison with a detailed model, an abstraction of the wastewater drainage infrastructure will reduce the complexity and computational time required for the generation of future alternatives.
The sewer delineation amongst the spatial grid will follow the urban characteristics and the topography assuming a gravity-driven system. Two dimensioning methodologies will be compared to identify which one gets a more accurate representation of the real system in terms of total length of the pipes, diameters frequency distribution, connectivity of the network and required treatment capacity (water consumption). A first approach, will use an adaptation of the Urban Water Infrastructure Model (UWIM) approach proposed by Maurer et al. (2013). UWIM uses the housing density, rain and the catchment area to calculate the length and size distribution of the needed sewer pipes. A second approach, will use an adaptation of the design framework proposed by Duque (2016), using graph theory and dynamic programing to find the cost-optimal hydraulic design of urban drainage systems.
In addition, a descriptive statistical analysis will be done to identify the relevant parameters for dimensioning simplified sewer systems and how do they resemble the real system, regarding the frequency distribution of diameters, number of pipes and network topology. This information will help to describe how the topographic, regulatory, demographic and urban characteristics drive the dimensions of the urban drainage systems.