ArticlePublisher preview available

Evaluating Retention Capacity of Infiltration Rain Gardens and Their Potential Effect on Urban Stormwater Management in the Sub-Humid Loess Region of China

Authors:
To read the full-text of this research, you can request a copy directly from the authors.

Abstract and Figures

Recognized as an effective low impact development (LID) practice, rain gardens have been widely advocated to be built with urban landscaping for stormwater runoff reduction through the retention and infiltration processes; but the field performance and regional effect of rain gardens have not been thoroughly investigated. In this paper, we presented a four-year monitoring study on the performance of a rain garden on stormwater retention; hydrological models were proposed to predict the potential effect of rain gardens on runoff reduction under different storms and the future urban development scenarios. The experimental rain garden was constructed in a sub-humid loess region in Xi’an, China; it has a contributing area ratio of 20:1 and depth of 15 cm. During the study period, we observed 28 large storm events, but only 5 of them caused overflow from the rain garden. The flow reduction rate for the overflow events ranged from 77 to 94 %. The runoff coefficient from the contributing area (RC) was reduced to less than 0.02 on annual basis, and 0.008 over the four years average. Field observations also showed that infiltration rate remained stable during the operation period. The predictions based on the future landuse and storm variability of the study area showed that by converting a small fraction of the city land area into rain gardens, the negative hydrological effect from expansion of impervious area can be reduced significantly. The challenge, however, lies in how to plan and build rain gardens as an integral part of the urban landscape.
This content is subject to copyright. Terms and conditions apply.
Evaluating Retention Capacity of Infiltration Rain
Gardens and Their Potential Effect on Urban Stormwater
Management in the Sub-Humid Loess Region of China
S. Tang
1
&W. Luo
2
&Z. Jia
2
&W. Liu
3
&S. Li
1
&Y. Wu
1
Received: 29 September 2015 /Accepted: 25 November 2015 /
Published online: 2 December 2015
#Springer Science+Business Media Dordrecht 2015
Abstract Recognized as an effective low impact development (LID) practice, rain gardens
have been widely advocated to be built with urban landscaping for stormwater runoff reduction
through the retention and infiltration processes; but the field performance and regional effect of
rain gardens have not been thoroughly investigated. In this paper, we presented a four-year
monitoring study on the performance of a rain garden on stormwater retention; hydrological
models were proposed to predict the potential effect of rain gardens on runoff reduction under
different storms and the future urban development scenarios. The experimental rain garden
was constructed in a sub-humid loess region in Xian, China; it has a contributing area ratio of
20:1 and depth of 15 cm. During the study period, we observed 28 large storm events, but only
5 of them caused overflow from the rain garden. The flow reduction rate for the overflow
events ranged from 77 to 94 %. The runoff coefficient from the contributing area (RC)was
reduced to less than 0.02 on annual basis, and 0.008 over the four years average. Field
observations also showed that infiltration rate remained stable during the operation period.
The predictions based on the future landuse and storm variability of the study area showed that
by converting a small fraction of the city land area into rain gardens, the negative hydrological
effect from expansion of impervious area can be reduced significantly. The challenge, how-
ever, lies in how to plan and build rain gardens as an integral part of the urban landscape.
Keywords Rain garden .Storm runoff .Design storm .Infiltration .Overflow.LID
Water Resour Manage (2016) 30:9831000
DOI 10.1007/s11269-015-1206-5
*W. Lu o
luowan@yzu.edu.cn
1
State Key Laboratory Base of Eco-Hydraulic Engineering in Arid Area, Xian University of
Technology, Xian, China
2
Department of Agriculture and Water Resources Engineering, Yangzhou University, Yangzhou,
China
3
Department of Biological and Agricultural Engineering, North Carolina State University,
Raleigh, NC 27695-0001, USA
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
... When considering long-term performance of bioretention cells, many design parameters such as soil and vegetative properties have seasonal variations, yet for most models discussed in this paper, these parameters remain constant (Nichols et al., 2021;Tang et al., 2015;Emerson and Traver, 2008). For example, DRAINMOD-Urban accounts for root growth over seasons with monthly rooting depths in the soil profile but this only accounts for seasonal changes, not continuous growth over (2008) a All models are freely available except those denoted with an asterisk which may require a cost to access. ...
... Many field and lab studies have shown effects of vegetation on infiltration through creation of macropores (Tang et al., 2015;Meng et al., 2014;Paus et al., 2014;Jenkins et al., 2010;Emerson and Traver, 2008). Vegetation can lead to infiltration rates several orders of magnitude higher than predicted solely by associated soil properties (Lucas, 2010). ...
Article
Full-text available
Many bioretention models still incorporate simplifications and lumped parameters that do not fully account for fundamental physical processes. This review summarizes the representation of hydrologic pathways, notable features, and applications of bioretention models with the goals of recommending models well suited to bioretention modeling and identifying key research needs. As a result, HYDRUS and GIFMod were identified as the only models that use Richards’ equation for determining infiltration under variably saturated conditions. Secondly, this study identified limited drainage configurations by most models except DRAINMOD-Urban. Thirdly, most models were inadequate for considering vegetation and plant water use, an area for improvement in future research. Finally, more calibration and validation studies are needed to build confidence in model results. This review intends to educate modelers of the processing equations for each water balance component, the input requirements in each model, and other model characteristics that should be considered in model selection.
... As an important part of sponge cities, bioretention is mainly arranged around municipal roads and buildings. At present, research on facilities primarily focuses on runoff reduction, non-point source pollution purification, and facility combination management [4,[11][12][13][14][15][16]. Results show that bioretention facilities can significantly reduce the surface As an important part of sponge cities, bioretention is mainly arranged around municipal roads and buildings. ...
... Results show that bioretention facilities can significantly reduce the surface As an important part of sponge cities, bioretention is mainly arranged around municipal roads and buildings. At present, research on facilities primarily focuses on runoff reduction, non-point source pollution purification, and facility combination management [4,[11][12][13][14][15][16]. Results show that bioretention facilities can significantly reduce the surface runoff, and the regulation effect of facilities on rainfall-runoff is affected by soil matrix conditions, vegetation conditions, rainfall characteristics, and blocking state; additionally, the degree of water purification is affected by vegetation type, flow velocity, adequate water depth, hydraulic retention time, and other factors. ...
Article
Full-text available
It is practical to carry out sponge cities to manage rain and floods in collapsible loess areas where water resources and water disasters are prominent. The infiltration laws of the partial anti-seepage bioretention in collapsible loess fields are helpful to ensure the effectiveness and safety of sponge city, which were learned from the field test and numerical model. The seepage field and displacement field of loess sites with different collapsibility grades were compared during rainwater infiltration of the bioretention with the numerical model; the suitability and optimization suggestions for foundation treatment of this structure in various sites were proposed. It is found that the infiltration characteristics can be divided into three stages, and the infiltration range of bioretention increases with increasing infiltration time under the same site type, and the higher the collapsibility level of the site is, the more significant the rise in infiltration range. The settlement of adjacent roads in class II and III collapsible fields is far greater than that in class I and is greater than the settlement standard. The facilities’ bottom part foundation can be replaced to ensure the functionality of the facilities and the safety of the surrounding roads in the actual project.
... Floods, especially in urban areas, are considered to be one of the most destructive natural disasters, which greatly affect the daily operations of cities and threaten peoples' lives (Cai et al. 2019;Lin et al. 2019;Tariq et al. 2021;Acosta-Coll et al., 2018). With rapid urbanization and climate change, the frequency and severity of floods are increasing rapidly, and the range of urban areas affected by floods has gradually expanded (Tang et al. 2016;Wang et al. 2019;Norallahi and Kaboli 2021). It is predicted that the frequency and intensity of urban flooding will continue to increase in the future (Mahmood et al. 2016;Park and Won 2019;Zheng et al. 2015a). ...
Article
Full-text available
Urban floods are significantly affected by interactions between the temporal and spatial variability of rainfall and catchment characteristics. However, it is unclear how the influencing factors interact with each other in the form of a factor chain to affect the flood generation in urban areas. This study contributes to discussion of key disaster-inducing factors by proposing an integrated quantitative framework based on a tracer-aided urban flood model. First, a tracer-aided model is adopted to simulate flood process for different design return periods. Then, based on the simulation results, the flood volume contribution of the source area (where flooding is generated) to the flood hazard area (where flooding impacts) was determined. Finally, through the variation partition analysis (VPA) approach and a structural equation model (SEM), the key disaster-inducing factor chains and influence strength that affects the flood volume in the flood source area were quantitatively determined. Longkungou drainage district of Haikou City was selected as the study area, for which the simulations were performed to calculate source area flood volume, and the disaster-inducing factor that caused the urban flooding were quantitatively assessed. The results show that the influencing factors interact with each other in the form of a factor chain and affect the flood volume generation in the flood source area. For the key disaster-inducing factor chains based on SEM, rainfall affects flooding inundation and the influence strength is 0.75, while pipe density is the key factor in mitigating flood volume, and the influence strength is 0.32, which is influenced by the impervious area ratio. In addition, compared to the small return period of rainfall storm events, for scenarios with greater rainfall intensity, the influence strength of the catchment characteristics on the cause of floods is reduced. The framework proposed in this study can be used to find key disaster-causing factor chains, which quantitatively reveals the cause of urban flooding and provides a reference for improving early warning systems.
... and Agave spp.) as shown in Table 1 (Lizárraga-Mendiola et al., 2017). In Xi'an (China), the effect of 28 large storm events on an experimental rain garden has been studied out of which only 5 resulted in an overflow (Tang et al., 2016b). They recorded overflow reduction rates within the range of 77% and 94% and highlighted the ability of rain gardens to significantly reduce the negative hydrological effect of the built environment. ...
Article
Full-text available
Low impact development (LID) practices are able to mitigate the detrimental effects of urbanization and climate change due to their salient design features. LID can restore the hydrology of urban areas to the pre-development functions by using distributed stormwater control and natural hydrological features. LID can help to achieve the goal of sustainable development as it promotes effective urban stormwater management. This review covers a comprehensive list of LID practices, namely bioretention cell, green roof, infiltration trench, permeable pavement, rain barrel or cistern, rooftop disconnection and vegetative swale. For each type of the LID, the recent advances covering the aspects of principles, design, performance, advantages and disadvantages and costs are systematically reviewed. Additionally, although LID has been quite broadly applied and demonstrated success in urban stormwater management in many countries, there are still some main challenges during the implementation such as clogging and water quality. Meanwhile, this review also highlights the great opportunities for further developments for LID practices to realize their wider practical application. Finally, future research directions are provided in order to give critical insights into potential future works to advance this field of research.
... Various comparative and standalone studies carried out through hydrological modeling, such as the soil and water assessment test (SWAT), and field observations emphasize that infiltration facilities have a higher efficiency than storage facilities in reducing runoff volumes [13,14]. These structures primarily mimic natural processes as they behave as a source control and decentralized stormwater absorption system to facilitate the reduction in surface runoff, minimize environmental degradation, and enhance infiltration. ...
Article
Full-text available
The lack of strategic planning in stormwater management has made rapidly urbanizing cities more vulnerable to urban water issues than in the past. Low infiltration rates, increase in peak river discharge, and recurrence of urban floods and waterlogging are clear signs of unplanned rapid urbanization. As with many other low to middle-income countries, India depends on its conventional and centralized stormwater drains for managing stormwater runoff. However, in the absence of a robust stormwater management policy governed by the state, its impact trickles down to a municipal level and the negative outcome can be clearly observed through a failure of the drainage systems. This study examines the role of onsite and decentralized stormwater infiltration facilities, as successfully adopted by some higher income countries, under physical and social variability in the context of the metropolitan city of Lucknow, India. Considering the 2030 Master Plan of Lucknow city, this study investigated the physical viability of the infiltration facilities. Gridded ModClark rainfall-runoff modeling was carried out in Kukrail river basin, an important drainage basin of Lucknow city. The HEC-HMS model, inside the watershed modeling system (WMS), was used to simulate stormwater runoff for multiple scenarios of land use and rainfall intensities. With onsite infiltration facilities as part of land use measures, the peak discharge reduced in the range of 48% to 59%. Correlation analysis and multiple regression were applied to understand the rainfall runoff relationship. Furthermore, the stormwater runoff drastically reduced with decentralized infiltration systems.
... LID facilities mainly include permeable pavement, green roofs, and bioretentions. Previous studies on LID facilities have mainly centered on peak reduction design, non-point source pollution risk reduction, and portfolio management (Ahiablame and Engel, 2012;Tang et al., 2016;Eckart et al., 2017;Ma et al., 2017;Winston et al., 2018;Yekkalar et al., 2018;Chen et al., 2019;Hou et al., 2019a;Sohn et al., 2019). There has been little research to date on risk prevention or rainwater detention control measures in loess area LID facilities. ...
Preprint
The effective and reasonable construction of the low impact development (LID) facilities in loess area depend on the functionality of typical LID facilities and the safety of surrounding structures in areas. A full-scale field test on rainwater concentrated infiltration of bioretentions in a collapsible loess site was conducted in this study. The water content and deformation law of the site were analyzed, and the water movement law of the rainwater-concentrated infiltration at bioretention facilities in the loess site was determined. The site settlements were calculated as per the wetting deformation curve and infiltration depths were calculated on an improved infiltration depth model tailored to the loess area. The rainwater infiltration rules of different bioretention structural forms are different in the collapsible loess field. The diffusion rate of the retaining wall type in loess decreases over time, while that on a sloping type does not. Within the same infiltration time, the retaining wall has a stronger influence on the site than the sloping type. When the water is concentrated in the site, its influence on the subgrade settlement is small (generally less than 1.5 mm) enough to satisfy the relevant engineering requirements. A modified Green-Ampt model based on assumed loess saturated unsaturated stratification can be used to predict the infiltration depth of facility water at the site. The adverse effects of water infiltration related to stagnant bioretentions can be mitigated by adjusting the initial water content and saturated water content at the loess site.
... The use of green stormwater infrastructure (GSI) to mitigate storm sewer overflow, reduce stormwater pollution, and create more livable landscapes for communities is gaining popularity throughout the world (Urbonas 1994;Wang et al. 2019;Bortolini and Zanin 2018;Tang et al. 2015). GSI includes a variety of surface and subsurface soil and plant systems with different dimensions to fit within the land available for stormwater management. ...
Article
Geometric shape can play an important role in modeling and designing green stormwater infrastructure (GSI) systems because of its influence on system infiltration processes. The effects of GSI system geometry were assessed by evaluating the area available for infiltration and pressure head dependency of infiltration. Two common GSI types with different geometries, a bioinfiltration rain garden and an infiltration trench, were continuously simulated using the storage unit (SU) object and low impact development (LID) module in the USEPA Storm Water Management Model (SWMM). The models were calibrated and validated using three years of observed data. The results suggest that the stored water depth in GSI systems has a substantial effect on infiltration in narrow, vertical-walled infiltration trenches, while soil moisture conditions play a relatively more important role for infiltration in shallow rain gardens with gradually sloping walls. As such, when modeling the effect of water depth and soil moisture, the SU object was found to simulate the infiltration trench better than the LID module, while the LID module worked better for the rain garden.
Article
Climate disruption and rapid urbanization present numerous challenges to infrastructure and communities in Chinese cities, from flooding and coastal erosion, to drought and pollution. This review article focuses on the utilization of Blue‐Green Infrastructure (BGI)—a suite of nature‐based strategies combining hydrological functions (blue) with vegetated landscaping (green)—to provide climate resilience and urban multifunctionality in China's large, high‐density cities. Chinese cities are utilizing BGI in new construction, in neighborhood retrofits, and in revival of ancient nature‐based infrastructure. The literature gives most attention to BGI in China's Sponge City Initiative that addresses the pluvial flooding crisis. Quantitative monitoring of BGI shows progress in stormwater‐related functions and to a lesser extent with rainwater utilization to address water scarcity. Other studies document multifunctional aspects of BGI, including cooling and energy‐saving functions of urban trees and green roofs, and green space expansion with parks that serve as retention basins. However, significant challenges and potential remain. China's urban infrastructure, including BGI, needs stronger design to be robust under extreme conditions as climate disruption intensifies. There is potential for BGI to more fully address habitat fragmentation, extreme heat, sea‐level rise and other climate and urbanization hazards. Further research and pilot projects are needed to characterize and quantify the benefits of multifunctional BGI. More integrated planning across city sectors, with greater incorporation of ecological and social functions, will help Chinese cities achieve multiple goals: providing carbon‐neutral and climate‐resilient infrastructure, improving air and water quality, regenerating ecosystems, and enhancing urban quality of life. This article is categorized under: Energy and Urban Design > Climate and Environment Energy and Climate > Systems and Infrastructure Energy and Urban Design > Systems and Infrastructure Blue‐Green Infrastructure (BGI) is a suite of nature‐based strategies combining hydrological functions (blue) with vegetated landscaping (green). BGI works best in integrated networks, providing climate resilience and multiple urban services.
Article
The effective and reasonable construction of the low impact development (LID) facilities in loess area depends on the functionality of typical LID facilities and the safety of surrounding structures in areas. A full-scale field test on rainwater-concentrated infiltration of bioretentions in a collapsible loess site was conducted in this study. The water content and deformation law of the site were analyzed, and the water movement law of the rainwater-concentrated infiltration at bioretention facilities in the loess site was determined. The site settlements were calculated as per the wetting deformation curve and infiltration depths were calculated on an improved infiltration depth model tailored to the loess area. The rainwater infiltration rules of different bioretention structural forms are different in the collapsible loess field. The diffusion rate of the retaining wall type in loess decreases over time, while that on a sloping type does not. Within the same infiltration time, the retaining wall has a stronger influence on the site than the sloping type. When the water is concentrated in the site, its influence on the subgrade settlement is small (generally less than 1.5 mm) enough to satisfy the relevant engineering requirements. Facilities water infiltration laws in the site can be predicted using the fractional unsaturated infiltration model and a modified Green-Ampt model based on assumed loess saturated–unsaturated stratification. The adverse effects of water infiltration related to stagnant bioretentions can be mitigated by adjusting the initial water content and saturated water content at the loess site.
Article
Full-text available
The transportation and urban infrastructure relies heavily on impervious surfaces. Unmitigated rainfall runoff from impervious surfaces can lead to a myriad of environmental problems in downgradient areas. To address this issue, novel stormwater control measures (SCMs) are being emphasized and implemented widely to mitigate some of the impacts of impervious surface. Bioretention is a soil/media-based SCM that is often used for this purpose, but current design practices are highly empirical. This study compiles work from three research sites in three states to provide some fundamental underpinnings to bioretention design. Although all sites demonstrate different levels of performance, water volumetric performance trends are common to all. These trends are based on the available storage in the bioretention cell, termed herein as the Bioretention Abstraction Volume (BAV). The BAV is directly related to available media porosity and storage in the surface bowl. A finite capacity to completely store all runoff from smaller events is defined by the BAV. Normalization for this storage provides prediction for volumetric performance. Recommendations for bioretention design are provided.
Article
Full-text available
In response to water quality and quantity issues within the Stroubles Creek watershed in Blacksburg, Virginia, a retrofit bioretention cell (BRC) was installed to collect and treat runoff from an existing parking lot. The BRC was completed in July 2007, and 28 precipitation events were monitored between October 2007 and June 2008. For each storm, inflow and outflow flow-weighted composite samples were collected and analyzed for suspended sediment, total nitrogen, and total phosphorus. The inflow and outflow concentrations and loads, as well as total inflow and outflow volumes and peak flow rates, were analyzed to evaluate BRC efficiency. Overall, the BRC successfully reduced flow volumes and peak flow rates leaving the parking lot by 97 and 99%, respectively. Cumulative mass reductions for sediment, total nitrogen, and total phosphorus all exceeded 99% by mass. The findings of this study have significant implications for areas with karst geology: (1)current design recommendations of lining the bottom of BRCs with clay may not be sufficient to prevent large amounts of water from infiltrating into surrounding soils; and (2)in areas with significant elevation changes, designing BRCs deeper than the typical 0.6-1.2m increases the feasibility of retrofits and provides substantial water quality and quantity benefits.
Article
Full-text available
Bioretention systems are increasingly being used to control the adverse effects of urbanization on stormwater quantity and quality. The stormwater capture efficiency of a bioretention system, defined as the fraction of stormwater volume captured by the system, can be used as an important index of its stormwater management performance. In this paper, an analytical probabilistic expression (APE) is derived for estimating the long-term average stormwater capture efficiency of bioretention systems. The derivation is based on the probability distribution functions of the input rainfall event characteristics and the rainfall-runoff-overflow transformations occurring on a bioretention system and its contributing catchment. In the derivation, instead of simply adopting the Howard’s conservative assumption as used in many previous studies, an approximate expected value of the surface depression water contents of a bioretention system at the end of a random rainfall event [denoted as E(S dw )] is derived and used. The accuracy of the resulting APE is verified by comparing its results with those determined from continuous simulations. The use of E(S dw ) is proven to be advantageous than the use of the Howard’s conservative assumption, it demonstrates that similar methods may be developed to analytically evaluate the stormwater management performance of other types of storage facilities for which the Howard’s conservative assumption was employed previously.
Article
Bioretention, or variations such as bioinfiltration and rain gardens, has become one of the most frequently used storm-water management tools in urbanized watersheds. Incorporating both filtration and infiltration, initial research into bioretention has shown that these facilities substantially reduce runoff volumes and peak flows. Low impact development, which has a goal of modifying postdevelopment hydrology to more closely mimic that of predevelopment, is a driver for the use of bioretention in many parts of the country. Research over the past decade has shown that bioretention effluent loads are low for suspended solids, nutrients, hydrocarbons, and heavy metals. Pollutant removal mechanisms include filtration, adsorption, and possibly biological treatment. Limited research suggests that bioretention can effectively manage other pollutants, such as pathogenic bacteria and thermal pollution, as well. Reductions in pollutant load result from the combination of concentration reduction and runoff volume attenuation, linking water quality and hydrologic performance. Nonetheless, many design questions persist for this practice, such as maximum pooling bowl depth, minimum fill media depth, fill media composition and configuration, underdrain configuration, pretreatment options, and vegetation selection. Moreover, the exact nature and impact of bioretention maintenance is still evolving, which will dictate long-term performance and life-cycle costs. Bioretention usage will grow as design guidance matures as a result of continued research and application.
Article
Hydraulic conductivity of granular filter media and its evolution over time is a key design parameter for stormwater filtration and infiltration systems that are now widely used in management of polluted urban runoff. In fact, clogging of filter media is recognised as the main limiting factor of these stormwater treatment systems. This paper focuses on the effect of stormwater characteristics on the clogging of stormwater filters. Effect of five different operational regimes has been tested in this study of sediment concentration; pollutant concentrations; stormwater sediment size; loading rate and stormwater loading/dosing regime and compared with the Base case. For each operational condition, five column replicates were tested. Results suggest that sediment concentration in stormwater is a significant parameter affecting hydraulic and treatment performance, eventually affecting longevity of these stormwater treatment systems. Further, the size of sediments (and their relation to the size of filter media grains) in stormwater was found to be an important parameter to be considered in design of coarse filters with high infiltration rates that are used for stormwater treatment. As expected, the addition of metals and nutrients had limited or no contribution to changes in hydraulic or sediment removal performance of the studied stormwater filters. Whilst loading rate was found to be an important parameter affecting the hydraulic and treatment performance of these systems, any variation in the stormwater loading regime had a limited effect on their performance. This study therefore develops an understanding of the effect of catchment characteristics on design of filters and hence their longevity and maintenance needs.
Article
Hydraulic performance of granular filter media and its evolution over time is a key design parameter for stormwater filtration and infiltration systems that are now widely used in management of polluted urban runoff. In fact, clogging of filter media is recognised as the main limiting factor of these stormwater treatment systems. This paper focuses on the effect of physical characteristics of filter media and flow-through rates on the clogging of stormwater filters. Five replicate experimental columns were constructed using zeolite, scoria, riversand and polymeric glass beads, and different flow-through rates were achieved using restricted outlets. The systems were dosed with semi-synthetic stormwater and the evolution of hydraulic performance and sediment removal rate was observed (for four filter media and across four flow rates) to investigate impacts of media type and flow rate. It was found that shape and smoothness of filter media grains had limited effect on clogging and sediment removal rate. All media except scoria clogged after similar volumes of stormwater but scoria-based filters were found to be highly variable in performance, most likely due to breakdown of its particles. Conversely, flow-through rate significantly affected clogging and sediment removal rate. For instance, in the case of zeolite filters, the systems with the lowest flow rate clogged after application of over 30 m of stormwater, while the unrestricted zeolite columns (with 200 times the flow rate) clogged after only 10 m of applied stormwater. At the same time, the zeolite filters with the lowest flow rate had an overall treatment efficiency of 88% compared with the unrestricted design’s efficiency of 59%. Further work is needed to analyse the influence of filter bed design, stormwater inflow characteristics and drying and wetting regimes on clogging and to understand the location of the clogged material in these filters.
Article
Flows into and out of two bioretention facilities constructed on the University of Maryland campus were monitored for nearly 2 years, covering 49 runoff events. The two parallel cells capture and treat stormwater runoff from a 0.24 ha section of an asphalt surface parking lot. The primary objective of this work was to quantify the reduction of hydrologic volume and flow peaks and delay in peak timing via bioretention. Overall, results indicate that bioretention can be effective for minimizing hydrologic impacts of development on surrounding water resources. Eighteen percent of the monitored events were small enough so that the bioretention media captured the entire inflow volume and no outflow was observed. Underdrain flow continued for many hours at very low flow rates. Mean peak reductions of 49 and 58% were noted for the two cells. Flow peaks were significantly delayed as well, usually by a factor of 2 or more. Using simple parameters to compare volume, peak flow, and peak delay to values expected for undeveloped lands, it was found that probabilities for bioretention Cell A to meet or exceed volume, peak flow, and peak delay hydrologic performance criteria were 55, 30, and 38%, respectively. The probabilities were 62, 42, and 31%, respectively, for Cell B.
Article
Three bioretention field sites in North Carolina were examined for pollutant removal abilities and hydrologic performance. The cells varied by fill media type or drainage configuration. The field studies confirmed high annual total nitrogen mass removal rates at two conventionally drained bioretention cells 40% reduction each. Nitrate-nitrogen mass removal rates varied between 75 and 13%, and calculated annual mass removal of zinc, copper, and lead from one Greensboro cell were 98, 99, and 81%, respectively. All high mass removal rates were due to a substantial decrease in outflow volume. The ratio of volume of water leaving the bioretention cell versus that which entered the cell varied from 0.07 summer to 0.54 winter. There was a significant p0.05 change in the ratio of outflow volume to inflow volume when comparing warm seasons to winter. Cells using a fill soil media with a lower phosphorus index P-index, Chapel Hill cell C1 and Greensboro cell G1, had much higher phosphorus removal than Greensboro cell G2, which used a high P-index fill media. Fill media selection is critical for total phosphorus removal, as fill media with a low P-index and relatively high CEC appear to remove phosphorus much more readily.
Article
Urban stormwater has negative environmental and ecological effects. Bioretention systems are starting to be used in efforts to mitigate these effects. A bioretention system receiving water from a light industrial catchment and a busy road was designed, built and monitored for changes in soil physics as well as hydrological and hydrochemical efficiency. The soils in the bioretention system were designed to have high metal removal potential and high permeability to compensate for undersized bioretention volume. The inflow hydrograph was a series of sharp peaks with little baseflow, typical of runoff from impervious surfaces. The bioretention system smoothed the hydrograph by reducing peak flow and volume for all 12 events monitored in detail. Overflow occurred in 10 events indicating the increased permeability did not fully compensate for the undersized volume. Runoff was heavily polluted with sediment and heavy metals, in particular zinc. The majority of the zinc, lead and Total Suspended Sediments were removed from the stormwater that flowed through the bioretention system, with TSS and total zinc concentrations reducing by orders of magnitude. Despite high removal efficiency, median concentrations of zinc exiting the bioretention system still exceeded ecosystem health guidelines and the bioretention system was both a source and sink of copper.
Article
Storm water control measures (SCMs), also known as best management practices (BMPs), such as rain gardens, are designed to infiltrate storm-water runoff and reduce pollutant transport to surface waters. The life span of these SCMs may be limited depending on the composition of sediments in runoff water. Settling of fine sediments may clog soil pore spaces, reducing the infiltration capacity of the soil and reducing the potential benefits of this SCM. A study was conducted on a Villanova campus rain garden that accepts runoff from an adjacent parking lot to determine if there was a relationship between the accumulation of fine sediments over time and the infiltration capacity. The soil textural profile within the rain garden was characterized prior to SCM installation (2001), after installation, after five years, and after seven years of receiving storm-water runoff. Infiltration data were collected by the single-ring infiltrometer method in 2006 and 2009. Differences in soil texture were found between locations within the infiltration basin, and accumulation of fines smaller than 0.1 mm was observed at both locations sampled in 2009. Infiltration rates were significantly different between the two locations measured within the rain garden, but infiltration rates did not change significantly over time within those regions. This SCM was designed at a 10:1 watershed to SCM area ratio, which is twice what is recommended by the PA DEP BMP Manual. The data collected over the seven years since installation indicate that while fines have accumulated in the SCM there has been no significant change in infiltration potential.