Temporal and spatial variation of infiltration in urban green infrastructure

Abstract

Infiltration is the primary mechanism in green stormwater infrastructure (GSI) systems to reduce the runoff volume from urbanized areas. Soil hydraulic conductivity is most important in influencing GSI infiltration rates. Saturated hydraulic conductivity (Ksat) is a critical parameter for GSI design and post-construction performance. However, Ksat measurement in the field is problematic due to temporal and spatial variability and measurement errors. This review paper focuses on a comparison of methods for in-situ Ksat measurement and the causes of temporal and spatial variations of Ksat within GSI systems. Automated infiltration testing methods, such as the Modified Philip-Dunne (MPD) and SATURO infiltrometers, show promise for efficient Ksat measurements. Soil Ksat values can change over time and substantially vary throughout a GSI, which can be attributed to multiple factors, including but not limited to temperature changes, soil composition and properties, soil compaction level, plant root morphology and distribution, biological and macrofauna activities in the soil, inflow sediment characteristics, quality of infiltrating water, and measurement errors. There is evidence that infiltration rates in vegetated urban GSI systems are sustained given an appropriate GSI design, reasonable concentration of suspended sediments in the inflow runoff, and routine maintenance procedures.These observations indicate that clogging can be counteracted by processes that tend to increase the soil hydraulic conductivity (e.g., plant root and biological activities). This self-sustainability underlines that infiltration-based GSI systems are a reliable long-term stormwater management solution. Recommendations on how to incorporate the temporal changes of Ksat in GSI design and on obtaining a spatiallyrepresentative Ksat for the GSI design are presented. K E Y W O R D Sgreen infrastructure, hydraulic conductivity, infiltration, infiltrometer, saturated hydraulic conductivity, soil, stormwater, urban areas

Green infrastructure: The future of urban flood risk management?

“…Assessment of the hydrological and/or sedimentological performance of such schemes are not routinely conducted and relatively few studies exist (e.g., Fu et al, 2021). Examples from UK SuDS schemes (Woods‐Ballard et al, 2015); stormwater ponds (Ahilan et al, 2019; Krivtsov et al, 2020); green roofs (Stovin et al, 2013), swales (Allen et al, 2015), bioretention, and integrated stormwater control systems (Ebrahimian et al, 2019; Traver & Ebrahimian, 2017) and a decade of monitoring by the Bureau of Environmental Services (BES) in Portland, Oregon USA (, 2013a; BES, 2010) are available. However, few schemes, to date, have had sufficient long‐term monitoring to provide an evidence base of the effectiveness of GI during a range of flood events and weather conditions.…”

“…Currently, very few monitored schemes exist. Notable examples include extensively monitored green roofs at the University of Sheffield (e.g., Stovin et al, 2013) and over 20 monitored stormwater capture and infiltration/evapotranspiration systems across the Villanova University campus (e.g., Ebrahimian et al, 2019; Traver & Ebrahimian, 2017), including a detention pond, a series of bioretention systems, and vegetated swales which monitor runoff within a functioning urban system and provide insights into the maintenance requirements to allow such systems to continue to fulfill their function.…”

US version of water-wise cities: Low impact development

“…infiltration and evapotranspiration (ET), that affect the performance of LID practices is fundamental to the design process. Temporal variation of infiltration rates over a year has been observed in different LID practices because of the water viscosity changes with temperature (higher infiltration rates in warmer months and lower infiltration rates in colder months) (Emerson & Traver, 2008) and other factors including, but not limited to, soil composition, level of soil compaction, vegetation (plant root) condition, biological activities in the soil, inflow sediment characteristics, and quality of infiltrating water (Ebrahimian et al, 2020). ET is a viable runoff reduction mechanism in vegetated LID practices that is generally greater after a rainfall event than during extended dry periods, but it continues as long as water is available between storm events (Nocco et al, 2016;Wadzuk et al, 2015).…”

It Is Not Easy Being Green: Recognizing Unintended Consequences of Green Stormwater Infrastructure

“…Although every infiltration practice must be considered on an individual basis with pollutant concentrations, runoff volumes, soil properties, and other factors taken into account, research indicates that the soil has the ability to capture many pollutants. Ebrahimian et al [209] provide a detailed analysis of the factors that can affect infiltration rates in GSI and highlight steps that can be taken to improve them. Evidence suggests that hydrocarbons will be degraded by bacteria surrounding plant roots and metals will accumulate on the media, which will eventually need to be treated or excavated.…”