Infiltration Swales Research Articles

Thriving under multiple stressors: Performance of drought-tolerant perennials and their suitability for infiltration swales

Infiltration swales are considered an essential and multifunctional component of water-sensitive urban design. To maintain their functionality, a robust planting is required. However, species selection poses a major challenge due to the extreme site conditions. To identify stress-resistant species, container experiments with 60 perennial species native to Germany were used to investigate their performance and responses to multiple stressors typical for urban swales receiving traffic area runoff. As plant performance is more severely affected if multiple stressors occur rather than single ones, test plants were exposed to de-icing salts, cyclic flooding, and drought. Species were selected primarily for their drought tolerance, as it was assumed that their adaption to drought might also be advantageous for the other stressors. The resistance to drought was examined in a reference group and was approved for 90 % of the experimental species. With a low mortality rate of < 25 %, 72.2 % of the species confirmed as drought tolerant also proved robust to the multiple stressors of an infiltration swale and are therefore recommended for use. Considering all experimental species, significant effects of the multiple stressors compared to the reference group were only found in mortality and a visual vitality score. Data on growth height, chlorophyll fluorescence, and phenology (e.g., flowering time) did not differ significantly between the groups. However, there were large species-specific variations to be considered and investigated in further research. The study serves as a basis for a resilient greening of urban infiltration swales with native species. It is essential to their implementation, as more research is needed to date.

Design of infiltration swales

Conventional designs of infiltration swales either neglect infiltration while the swale is filling or approximate the flow in the swale as being normal instead of gradually varied. The adequacy of these approximations are elucidated, and two common design configurations for infiltration swales are considered. For swales designed to store the water-quality volume behind check dams, the retained volume can be on the order of twice the design water-quality volume depending on the magnitude of the inflow rate normalized by the infiltration rate. In a second configuration, the swale is designed to infiltrate the water-quality flow, where the limiting assumption is that the flow is normal along the infiltration length. The actual required infiltration length can be expressed as a function of the normalized bottom width, and the required infiltration length can be up to 30% longer than derived using the conventional design. Graphical relations are developed that can be used to either quantify the factor of safety of conventional designs or provide credit for in the flood-control function of infiltration swales.

Evaluating the Stormwater Management Model for hydrological simulation of infiltration swales in cold climates

Abstract The Stormwater Management Model (SWMM) is a widely used tool for assessing the hydrological performance of infiltration swales. However, validating the accuracy of SWMM simulation against observed data has been challenging, primarily because well-functioning infiltration swales rarely produce surface runoff, especially over short monitoring periods. This study addresses this challenge by using measured subsurface water storage levels for calibration and validation. The study evaluated three SWMM modules, namely, the snowpack, aquifer, and low-impact development (LID) modules, to simulate subsurface water storage levels of an infiltration swale located in a cold climate region during snow and snow-free periods. Global sensitivity analysis was used to identify influential parameters within these modules. The findings revealed that only a few parameters significantly influenced model outputs. Moreover, the aquifer module outperformed the LID module in simulating subsurface water storage due to limitations in setting the initial saturation of the LID module. Furthermore, simulation accuracy was better during snow-free periods due to challenges in simulating snow dynamics during snow periods with the snowpack module. The calibrated models offer valuable insights into the long-term hydrological performance of infiltration swales, enabling practitioners to identify events that trigger flooding in these systems.

Low-Impact Development (LID) in Coastal Watersheds: Infiltration Swale Pollutant Transfer in Transitional Tropical/Subtropical Climates

The control of runoff pollution is one of the advantages of low-impact development (LID) or sustainable drainage systems (SUDs), such as infiltration swales. Coastal areas may have characteristics that make the implementation of drainage systems difficult, such as sandy soils, shallow aquifers and flat terrains. The presence of contaminants was investigated through sampling and analysis of runoff, soil, and groundwater from a coastal region served by an infiltration swale located in southern Brazil. The swale proved to be very efficient in controlling the site’s urban drainage volumes even under intense tropical rainfall. Contaminants of Cd, Cu, Pb, Zn, Cr, Fe, Mn and Ni were identified at concentrations above the Brazilian regulatory limit (BRL) in both runoff and groundwater. Soil concentrations were low and within the regulatory limits, except for Cd. The soil was predominantly sandy, with neutral pH and low ionic exchange capacity, characteristic of coastal regions and not very suitable for contaminant retention. Thus, this kind of structure requires improvements for its use in similar environments, such as the use of adsorbents in soil swale to increase its retention capacity.

Stormwater management for highly urbanized areas in the tropics: Life cycle assessment of low impact development practices

Within the contemporary view of stormwater management, introduced through integrated urban water management approaches (e.g., low impact development [LID]), there are several strategies that can be used in urban settlements to enhance sustainability. These strategies include the construction of runoff source controls and changes in development patterns. To understand the environmental trade-offs, the comparison of single LID devices using life cycle assessment (LCA) is spreading. However, assessing both LID practices and the urban catchment hydrological response is a less explored field — especially in regions under climate conditions other than the temperate urban areas where LID first emerged. In this context, this paper aims to assess the environmental impacts and the hydrological effects of applying LID practices in a highly urbanized area in the tropics. Using a settlement in Brazil as a case study, three projects were developed and assessed using a hybrid framework based on hydrological modeling and LCA. Even though the projects had different elements, their system function was the same: assure flood protection for rainfall events with a 2-year return period and for a 30-year service life. The business-as-usual scenario, entitled Scen.CONV, used a conventional urbanization and storm-sewer conventional drainage system (CDS), commonly known as gray infrastructure. The alternative scenario, entitled Scen.WELL, used a conventional urbanization and CDS associated with the use of the LID controls to disconnect the lots (infiltration wells). The last scenario, entitled Scen.LID, used LID controls to disconnect both lots and streets (infiltration swales and swale trenches, considered green infrastructure measures) integrated with changes in development patterns. The hydraulic-hydrologic results pointed out Scen.LID as the best alternative for flood protection (100% of runoff source control), followed by Scen.WELL (60% decrease in the peak flow compared to Scen.CONV). The LCA total results indicated Scen.LID as the scenario with lower life cycle impacts, and Scen.WELL as the most impactful. However, this capacity-based approach could not capture the hydrological benefits of Scen.WELL, which were addressed using a performance-based functional unit. Assessing potential impacts per managed stormwater volume, Scen.WELL’s life cycle impacts were 51–65% lower than Scen.CONV, and Scen.LID’s were 74–82% lower than Scen.CONV, both in all life cycle impact categories. This joint approach provides a new perspective to stormwater systems assessment, enhancing their hydrological benefits, without burden shifting.

Urban green infrastructure features influence the type and chemical composition of soil dissolved organic matter

In urban areas, green infrastructure (GI) has been widely developed utilizing different types of engineered soil to enhance ecosystem functions to interact with soil dissolved organic matter (DOM). However, there remains a lack of urban studies that have examined the link between GI features and soil DOM. This study, which was conducted in a typical heavily industrialized and urbanized area (Ningbo City, East China), aimed to characterize the chemical variation and composition of DOM in the engineered soil of four GI types (enhanced tree tips, ETP; street-side infiltration swales, SSIS; vegetated swales, VS; urban forests, UF). The results showed that soil organic carbon varies among the four GI types with significantly lower content in SSIS and ETP compared to VS and UF. Smaller variation was observed in the water-soluble organic carbon (WSOC) content, with UF having significantly higher content than ETP. Three humic-like substances and one protein-like substance were derived using the parallel factor analysis (PARAFAC) model. These fluorescent compositions and their spectral parameters displayed specific distributions among GI features with VS having the highest proportion of humic-like substances (C1) and the lowest proportion of protein-like substances (C4). The distribution of spectral indices indicated terrigenous sources of DOM in these GI engineered soils. Significant positive correlations were found between protein-like substances and the population density and nightlight index, while negative correlations were found between humic-like substances (C1) and these two indices. These results demonstrate significant human disturbance of the chemical composition and characteristics of GI features. Our findings suggest that the overall design and management of GI features have a fundamental influence on soil DOM that is vital for carbon cycling in urban ecosystems.

Parameters sensitivities for sustainable urban infrastructure

Low-impact development (LID) is an important infrastructure method for improving urban drainage through stormwater best management practices. The parameterisation sensitivities for LID techniques are provided for the current Environmental Protection Agency (EPA) Stormwater Management Model (SWMM). This was completed with the measured LID quantity data from over a 10-year data sample that included pervious pavements and infiltration swales in a commercial area. Critical parameter sensitivities were analysed using the recently released EPA SWMM version 5.1.011. Computational results provide SWMM users a range of acceptable parameter values to simulate these best management practices, to design future LIDs, and other urban green areas to reduce stormwater run-off impacts. This analysis demonstrated sensitivity relationships of key parameters allowing engineers, designers and planners to simulate sustainable urban infrastructure at other locations.

Spatial distribution of zinc in the topsoil of four vegetated infiltration swales treating zinc roof runoff

Since stormwater runoff from zinc roofs is polluted with high concentrations of zinc (Zn), runoff treatment is recommended in order to avoid harmful influences to the ecosystem. For the retention of Zn, vegetated infiltration swales with a topsoil layer are often used as decentralized Sustainable Urban Drainage Systems (SUDS). The aim of this study was to assess the risks of groundwater contamination due to infiltration of stormwater runoff of a Zn roof using infiltration swales. The spatial horizontal and vertical distribution of Zn content in four 15 year old vegetated infiltration swales at a zinc roof was analyzed and evaluated. High Zn contents (up to 27.9 g/kg dry mass) have been measured only for spatially limited areas at the inflow zones of each infiltration swale. Zn content decreased significantly with increasing distance from inflow and with increasing topsoil depth. Because the topsoil is still contaminated in deeper layers and because the soil's sorption potential is locally exceeded, the risk of groundwater contamination was expected to be high. Possible optimization of the hydraulic functioning and regular maintenance of the swales is recommended as well as a regular topsoil exchange of highly polluted areas.

Soil and microbial properties of green infrastructure stormwater management systems

Green infrastructure (GI) refers to environmental design features or engineered systems in an interconnected natural and urban space that provide multifunctional ecosystem services. However, there is great uncertainty and variation in the function of different GI features related to carbon and nitrogen cycling processes that are essential for sustained plant growth and water quality. The objective of this study was to evaluate the effects of GI designs (enhanced tree pits (ETP), street-side infiltration swales (SSIS), and vegetation swales (VS)), including surface area, and watershed area ratio (WAR), on the biogeochemical processes and properties (organic carbon (Corg), total nitrogen (Ntotal), pH, salts, total petroleum hydrocarbons (TPH), Pb, Zn, moisture content (MC), texture, microbial biomass carbon and nitrogen content, potential net nitrogen mineralization and nitrification, microbial respiration, and denitrification potential) of GI engineered soils. Results showed that GI sites did not have significant levels of contamination with metals or TPH and that GI with larger surface area had significantly lower TPH, Pb, and Zn. Microbial biomass and activity were positively correlated with Corg, Ntotal, pH, MC, TPH, and WAR. Denitrification potential was higher in the ETP and SSIS (3 mg N kg−1 h−1) compared to the VS (0.5 mg N kg−1 h−1). Microbial biomass carbon and nitrogen contents were significantly higher in ETP followed by SSIS then VS. These results suggest that relatively young (<10 years) GI sites provide significant levels of microbial biomass and activity that are important for carbon and nitrogen cycling.

Influence of the vegetative cover on the fate of trace metals in retention systems simulating roadside infiltration swales.

Large-scale outdoor mesocosms were designed and co-contaminated with metals (Cd, Pb, Zn) and organic compounds to better understand the complex functioning of urban roadside swale environments. Infiltration systems were planted with macrophytes (P. arundinaceae, J. effusus and I. pseudacorus) or grassed, and natural or spiked target metals were monitored over two years. In the non-spiked mesocosms, atmospheric metal inputs were slightly higher than outputs, leading to low metal accumulation in topsoils and to very low outflow water contamination (<0.7% of the initial metal stock). In the spiked infiltration systems that simulated point pollution through water inflow, transfer of the initial stock of metals to the deeper soil layers was quite low and outflow water contamination was very low (<0.6% of the initial stock). The main metal output from these systems occurred in the first days of their installation because of the high metal solubility in water and insufficient plant cover at that time. The infiltration systems stabilized after a few weeks, probably because of stronger sorption to soil aggregates, and because of plant root development. Mephytoextraction in plant roots was more efficient in mesocosms planted with P. arundinacea and grass. Metal phytoextraction in plant aerial parts was also better for grass and P. arundinacea, when considering metal standing stocks instead of their concentration in plants. J. effusus was a good metal accumulator, but its low aboveground biomass development was less favorable to metal removal through harvesting.

Evaluation of site-specific factors influencing heavy metal contents in the topsoil of vegetated infiltration swales

Stormwater runoff of traffic areas is usually polluted by organic and inorganic substances and must be treated prior to discharge into groundwater. One widely used treatment method is infiltrating the runoff over the topsoil of vegetated swales. The aim of this study was to evaluate the factors influencing the heavy metal contents in such topsoil layers of vegetated infiltration swales near highways, roads, and parking lots. In total, 262 topsoil samples were taken from 35 sampling sites, which varied in age, traffic volume, road design, driving style, and site-specific conditions. In the evaluation of all soil samples, the median heavy metal values of cadmium, chromium, copper, lead, and zinc were yielding 0.36 (mean: 1.21) mg/kg DM, 37.0 (mean: 44.5) mg/kg DM, 28.0 (mean: 61.5) mg/kg DM, 27.0 (mean: 71.9) mg/kg DM, and 120 (mean: 257) mg/kg DM, respectively. The main purpose was to evaluate the site-specific data (i.e., surrounding land use characteristics, traffic area site data, and operational characteristics). In general, heavy metal contents increased with increasing traffic volumes. However, other factors also had a notable impact. Factors such as road design (e.g., curves, crossings, and roundabouts) and grade of congestion significantly influenced the heavy metal contents. High heavy metal contents were detected for stop-and-go areas, roundabouts, crossings, and sites with traffic lights, signs, and guardrails. Findings of this study can be used to identify highly polluted traffic areas and to verify or improve standards regarding the treatment of runoff from traffic areas.

Behaviour of chromium(VI) in stormwater soil infiltration systems

The ability of stormwater infiltration systems to retain Cr(VI) was tested by applying a synthetic stormwater runoff solution with a neutral pH and high Cr(VI) concentrations to four intact soil columns excavated from two roadside infiltration swales in Germany. Inlet flow rates mimicked normal (10mm in 2h) and extreme (100mm in 3h) rain events. The objectives were to understand the behaviour of the anionic and toxic Cr(VI) in soil at neutral pH and to asses treatment efficiency towards Cr(VI). During normal rain events Cr(VI) was largely retained (more than 50%), even though pH was neutral, while under extreme rain events approximately 20% of Cr(VI) was retained. In both cases effluent concentrations of Cr(VI) would exceed the threshold value of 3.4μg/L if the infiltrated water were introduced to freshwater environments. More knowledge on the composition of the stormwater runoff, and especially the occurrence of Cr(VI), is needed.

Performance of infiltration swales with regard to operation in winter times in an Alpine region

In cold climate regions winter conditions significantly influence the performance of stormwater infiltration devices. Frozen soil and water storage by snow changes their operation. In this paper winter operation of a grassed infiltration swale was investigated using on-site and laboratory measurements. The field investigation of a grassed swale at a parking place in an Alpine region showed that the swale fulfilled its function properly. Although the top layer was frozen for some time, the storage capacity of the swale was sufficient to store the precipitation until the conditions improved. The soil attenuated the air temperature, at 20 cm below ground surface the soil was only frozen for one week. winter maintenance proved to be a problem, together with the snow from the parking place a lot of gravel and fine particles were deposited at one end of the swale. This decreased the hydraulic conductivity at that point significantly. The laboratory tests with soil columns showed an increase of flow time through the soil column with decreasing soil moisture content. For soil temperatures below 0 degrees C the hydraulic conductivity was reduced for increasing initial soil moisture contents. All in all the hydraulic conductivity was best around 0 degrees C for all soil water contents. However, also at minus 5 degrees C the coefficient of hydraulic conductivity was always at least above 10(-6) m/s, thus within the range of tolerated hydraulic conductivity specified in the national guidelines. Nevertheless, the handling of the soil was found to have high influence on the results. The results indicate that in the Alpine region infiltration swales operate sufficiently under winter conditions although with decreased performance.

Local infiltration devices at parking sites – Experimental assessment of temporal changes in hydraulic and contaminant removal capacity

On site infiltration of stormwater is a common practice in order to avoid hydraulic overload of the urban drainage system. If hydrological conditions allow on-site infiltration--this is even mandatory from a legal point of view. Focus in this work is on surface infiltration of stormwater from parking lots. Proper operation of those devices is assumed to be appr. 15 years, as permits granted are limited to this time. Questions are raised whether this considered life expectancy is feasible. One apprehension is a possible clogging effect reducing the hydraulic capacity of the swale. The second aim was to identify magnitudes of accumulated pollutant loads with respect to limitations onto lifetime. The experimental investigation covered infiltration swales of different ages from eleven supermarket parking lots in Tyrol. Hydraulic permeabilities were assessed as well as chemical conditions of the soil material regarding hydrocarbon index (HI) and heavy metals (Cu, Zn, Pb and Cd). Further mass balance of contaminants has been performed in order to assess the operational life time based on pollutant load consideration. Calculations were based on load estimations using literature based minima and maxima concentrations from surface flows. Testing the correlation of hydraulic and pollutant measurements against site specific parameters (age, traffic load) revealed no distinct relation. In general all measured pollutants were found under limit concentrations. Mass balance calculations showed that limit concentrations are not exceeded either for worst case loading and considering 15 years of operation.

Best Management Practice: A Sustainable Urban Drainage System Management Case Study

The Glasgow Sustainable Urban Drainage System (SUDS) Management Project satisfies the first of three phases of the Glasgow Surface Water Management Project. This is Glasgow City Council's contribution to the Transformation of Rural and Urban Spatial Structure (TRUST) project, one of the European Union's (EU) inter-regional (INTERREG IIIB) funded research projects. The contribution of SUDS to the overall catchment dynamics of cities such as Glasgow was studied. Fifty-seven sites within 46 areas of Glasgow were identified for initial investigation, including a preliminary SUDS feasibility assessment and a desk study relating to historical planning issues that may be relevant for subsequent future development and regeneration options. The methodologies for a SUDS Option Decision Support Key and a corresponding SUDS Option Decision Support Matrix that are adaptable to different cities and countries have been outlined. The key should be used during a preliminary site investigation and can help to classify potential SUDS sites. Corresponding findings should be compared with the conditions listed in the matrix, which will inform the planner about potentially-suitable SUDS techniques for a particular site. Detailed design guidelines were then drafted for seven selected representative SUDS demonstration areas including the Pollok Centre area. This case study, for example, is representative for a class of 24 areas and sites. Combinations of infiltration trenches or swales with ponds or underground storage were the most likely SUDS options for the majority of the demonstration areas.

Stormwater resources development and management in Glasgow: two case studies

The ‘Glasgow Surface Water Management Project’ is Glasgow City Council’s contribution to the Transformation of Rural and Urban Spatial Structure (TRUST) project, one of the European Union’s (EU) inter‐regional (INTERREG IIIB) funded research projects. This project assesses how sustainable urban drainage systems (SUDS) can contribute to relieving stress on the current predominantly combined sewer system. Fifty‐seven sites within Glasgow were assessed with a novel SUDS feasibility tool that can be used for stormwater resources assessment, development, planning and management in developed and developing countries. Two environmental desk studies incorporating historical planning issues that are relevant for regeneration were undertaken. A combination of infiltration trenches or swales with ponds or underground storage were the most likely SUDS options for the majority of the areas studied. The drainage of the Lillyburn Place area should be dominated by infiltration trenches draining into a nearby burn during extreme rainfall events. The drainage of the Ruchill Hospital and Park area should be dominated by a single network of swales conveying water either into underground storage tanks or retention ponds. The runoff will ultimately drain into a sewer or canal. The Ruchill Hospital and Park area was selected as being the prime choice for the TRUST demonstration project.