Can Greenwalls Contribute to Stormwater Management? A Study of Cistern Storage Greenwall First Flush Capture

Abstract

The authors set out to study the stormwater management viability of greenwalls in a simulated retention of roof runoff, using a cistern for simulated runoff to irrigate the greenwalls. By experimenting with two greenwalls of different exposures (one southeast and one northwest), this study demonstrated that the southeast facing greenwall and the northwest facing greenwall retained comparably favorable amounts to greenroof stormwater retention systems. With more and more competition for limited horizontal surface area in urbanized and urbanizing areas, the use of vertical surfaces for stormwater mitigation and evapotranspiration has attractive potential. This article presents the background, project, methods, findings, and conclusions of the study.

Field evaluation of precipitation interception potential of green façades

“…This observed delay in precipitation reaching the ground surface is broadly speaking, in line with a previous observation for a green roof, which concluded that nearly two thirds of all the precipitation events resulted in runoff delays of a minimum of 30-minutes (Czemiel Berndtsson, 2010). However, given the faster flow under gravity in a vertical green façade, its delay should be lower than in a green roof (Kew et al, 2014). Retention of a proportion of precipitation in this manner, and its eventual evaporation and transpiration, and the delay associated with flow through the system, can potentially reduce the peak flows and the consequential overwhelming of urban drainage infrastructure (Czemiel Berndtsson, 2010;Loh, 2008).…”

“…This can be attributed to the tall, thin, vertical nature of the façade which creates a dense canopy, capable of holding quite a lot of water. In general, the findings corroborate previous studies suggesting the proportion of precipitation interception is directly proportional to the vegetation cover (Czemiel Berndtsson, 2010;Kew et al, 2014;Natarajan et al, 2015). The vegetation cover is linked to the extent to which the building façade is enveloped, and dictates its ability to retain and prevent precipitation from entering drainage infrastructure.…”

“…Conventional urban drainage systems are often overwhelmed during adverse hydrological events, as they mainly rely on collection in a singular or a networks of sewer systems (Kew et al, 2014;Nickel et al, 2014). In recent years, the combined use of vertical greening structures and green roofs has been increasingly adopted as "bioclimatic" design to complement (or partially replace) urban grey drainage infrastructure systems (Nickel et al, 2014;Pérez-Urrestarazu et al, 2015).…”

“…In recent years, the combined use of vertical greening structures and green roofs has been increasingly adopted as "bioclimatic" design to complement (or partially replace) urban grey drainage infrastructure systems (Nickel et al, 2014;Pérez-Urrestarazu et al, 2015). As almost 80% of the existing housing stock in Europe is still expected to be in use in 2050 (Sandberg et al, 2016), building surfaces could be effectively utilised for implementing green infrastructure (GI) stormwater management solutions (Francis and Lorimer, 2011;Kew et al, 2014). Specifically, urban fabric provide a plethora of vertical surfaces such as embankment walls, corridors next to rail and road tracks, building walls, bridges, fences etc.…”

“…To date there is little empirical evidence on the potential role of vertical greening systems of different density in building-scale stormwater management under real-world conditions. Previous studies have focused on specific issues: for example, assessing the ability of vertical greening solutions to moderate urban hydrological regimes (Loh, 2008) or simulated retention of roof runoff using a cistern to irrigate the greenwalls (Kew et al, 2014). There is also ambiguity in the extent to which implemented schemes can be deemed sustainable, mainly in terms of the installation of the 'living materials' and the regular maintenance, nutrient and water requirements that are necessary for optimal performance over its lifetime (Perini et al, 2011).…”