Blue-green stormwater systems for citywide flood mitigation: Monitoring, conceptualization, modeling, and evaluation

Considering the growth in urbanization, leading to an increase in impervious surfaces, and the changing climate, enhancing the intensity and frequency of rainfall events, existing urban drainage networks—separate or combined sewer systems—are presumed to face substantially elevated hydraulic loads, causing pluvial floods in urban areas.
There are several ways to address these challenges. Cities can invest in replacing existing pipes with new larger pipes to enhance the hydraulic capacity of the drainage network. This solution is considered to be extremely expensive and unsustainable. An alternative solution is to manipulate urban surfaces by constructing blue-green (open) stormwater systems. These systems are built on urban surfaces and include approaches that mimic natural processes, such as infiltration, evaporation, transpiration, pond storage, and slow transport of stormwater through ditches. The implementation of blue-green stormwater systems in dense cities would, to some extent, relieve the overload. However, the method for identifying urban areas in which the implementation of blue-green stormwater systems would have a larger effect hydraulically on the existing sewer network is unestablished.
Thus, general aim of this thesis was to develop a method for studying the interactions between piped drainage networks and blue-green stormwater systems on the city-scale, performed in four steps, which shape the backbone of this thesis:
•An existing blue-green stormwater system—i.e. the Eco-city of Augustenborg in Malmö—was examined to understand how such systems work, locally and regarding the surrounding neighborhoods.
•A simple conceptual model for blue-green stormwater systems was proposed.
•Based on the proposed concept, a fast, easy-to-use, and robust modeling tool was developed, making it possible to simulate the interaction between blue-green stormwater systems and sewer networks.
•The modeling tool was supplemented with a hydroeconomic optimization algorithm and evaluated on the city-scale to identify the most effective site and size for blue-green stormwater systems throughout the catchment of the sewer network.
The developed method and toolchain constitute a new platform for increasing our understanding of complex urban drainage networks. This platform is also a starting point for the development of a more reliable tool for the initial screening of urban catchments to identify urban areas in which it is hydraulically and economically efficient to construct neighborhood-scale blue-green stormwater systems.