Live pole drains for cities (LPD4C) : an easy-to-build nature-based solution (NbS) alternative to conventional sustainable drainage systems (SuDS)

Abstract

Rapid urbanization and the intensification of weather events due to climate change are only some of the drivers altering the water cycle in urban environments. Consequently, the total volume of stormwater runoff rises together with its frequency and severity, placing human life, infrastructure and environment under risks, increasing vulnerability against landslides and floods. Live Pole Drain (LPD), a less known Sustainable Drainage System (SuDS), is a plant-based drainage system deployed to drain the excess of surface water, to regulate the water budget in the soil, and to promote ecological succession and landscape restoration. Even though LPDs have a great potential for cities, they have not yet been explored in urban settings due to a severe lack of evidence on LPD eco-hydrological performance. Therefore, the aim of this thesis is to propose LPD as an original NbS alternative to conventional SuDS for regulating the water budget in the urban environment. In this context, the developed Live Pole Drain for Cities (LPD4C) framework (i) provides information on the main environmental criteria for LPD creation within cities; (ii) delivers guidelines for LPD design and construction; and (iii) delineates the steps to assess the eco-hydrological performance of LPD. Through a combination of eight environmental criteria in a spatial, multi-criteria analysis, results demonstrated that 28% of Glasgow City (Scotland) presents optimal conditions to accommodate LPDs. Among the vacant and derelict land owned by Glasgow’s Local Council Authority, 48% of its surface area have great suitability to receive LPDs. Key findings of the eco-hydrological performance of LPDs observed during a pilot laboratory experiment showed that this Nature-based Solution is effective towards urban flooding mitigation. Particularly to LPDs hydrological performance, this research identified that LPDs, at certain design and environmental conditions, can decrease surface runoff up to 90% and water retention up to 54% when compared to fallow soil, while subsurface flow and percolation are increased up to 170% and 150%, respectively. This research also provided the design for the first LPD within a city. Through a combination of the opportunity sites for LPD creation map with the assessed eco-hydrological performance of LPD, the design showed that the LPD has a great hydrological potential under wetting soil conditions at an urban plot-scale. Interpretation of this analysis suggests that the designed LPD could be implemented to reduce the volume of surface runoff, while acting with functions observed in subsurface flow wetlands (i.e., phytoremediation). Moreover, this study successfully built pioneering evidence on LPDs eco-hydrological performance, which now supports LPDs as a suitable solution to mitigate urban flooding in cities. Within the LPD4C scope, the findings of this research support climate change adaptation in urban environments, especially to address natural hazards such as soil erosion, shallow landslides, and floods. The strategies and recommendations for further LPD adoption throughout cities herein presented can be useful for urban planners, environmental managers, policy makers, decision-makers, and contractors during the planning phase of projects seeking to manage flood hazards whilst enhancing the natural value of the urban environment. Specifically, this study delivered information for implementation of the first ever seen LPD in a city.