Descriptive Analysis of the Performance of a Vegetated Swale through Long-Term Hydrological Monitoring: A Case Study from Coventry, UK

Abstract

Vegetated swales are a popular sustainable drainage system (SuDS) used in a wide range of environments from urban areas and transport infrastructure, to rural environments, sub-urban and natural catchments. Despite the fact that vegetated swales, also known as grassed swales, have received scientific attention over recent years, especially from a hydrological perspective, there is a need for further research in the field, with long-term monitoring. In addition, vegetated swales introduce further difficulties, such as the biological growth occurring in their surface layer, as well as the biological evolution taking place in them. New developments, such as the implementation of thermal devices within the cross-section of green SuDS for energy saving purposes, require a better understanding of the long-term performance of the surface temperature of swales. This research aims to contribute to a better understanding of these knowledge gaps through a descriptive analysis of a vegetated swale in Ryton, Coventry, UK, under a Cfb Köppen climatic classification and a mixed rural and peri-urban scenario. Precipitation and temperature patterns associated with seasonality effects were identified. Furthermore, a level of biological evolution was described due to the lack of periodical and planned maintenance activities, reporting the presence of both plant species and pollinators. Only one event of flooding was identified during the three hydrological years monitored in this research study, showing a robust performance.

Scientific Evidence behind the Ecosystem Services Provided by Sustainable Urban Drainage Systems

“…Regulation Services: Climate Change and Thermal Control Cfb. Vegetated swales can act as temperature regulators because they can provide a higher surface temperature than air temperature in winter and the opposite in summer, providing a lower temperature than air [114].…”

“…Regulation Services: Climate Change and thermal control: Green swales and permeable pavement can act as temperature regulators [28,114], but other SUDS can emit greenhouse gases due to warmer temperatures [53], the benthic invertebrates metabolism [247], or the use of herbicides to remove aquatic vegetation [210].…”

“…Although vegetated swales [114] and some permeable pavements can act as temperature buffers [28] in temperate climates, other SUDS can increase greenhouse gas emissions: Urban runoff carries a high concentration of nitrogen that, in the processes of nitrification and denitrification in vegetated systems, can be converted into nitrous oxide [53]; the degradation of organic matter washed by the stormwater in small and deep retention ponds without vegetation produces CO2 and CH4, so that, these kind of systems can contribute substantially to climate forcing [210]; the combined treatments (herbicides and harvesting) applied to the conventional stormwater retention basins to remove aquatic vegetation result in poorer water quality and appear to stimulate methane emissions resulting in noticeably higher cumulative fluxes of greenhouse gases from these basins [211]; pollution-tolerant wetland invertebrates have been shown to enhance greenhouse flux CH4 and CO2 [247]; artificial wetlands can sometimes have a water-warming effect in cold climates [158], open water and green areas of artificial wetlands are potential sources of carbon and may even have a net climate warming effect in boreal regions [255].…”

The High-Resolution Calibration of the Topographic Wetness Index Using PAZ Satellite Radar Data to Determine the Optimal Positions for the Placement of Smart Sustainable Drainage Systems (SuDS) in Urban Environments

“…Sustainable drainage systems (SuDS) have been adopted as the main Green Stormwater Infrastructure (GSI) when considering the Nature-based Solutions (NbS) at the core of urban regenerative development [1]. Strategic urban planning is key to incorporating green urban approaches for resilient city designs where GSIs are core [2].…”

Assessment of the thermal properties for the geothermal use of a permeable pavement structure for pedestrian and cycle paths

“…Research have been carried out on the possible effects that the introduction of a surface geothermal system would have on the water quality of the SuDS [12,13]. Investigations have also been carried out on the thermo-hydraulic behaviour of SuDS under real operating conditions [14]. Finally, other studies targeted the asses-sment of the behaviour of permeable pavements with surface geothermal elements under real conditions [15].…”