International Low Impact Development Conference 2015: LID: It Works in All Climates and Soils

The state of the practice for hydromodification management for new development is to mimic long-term predevelopment site hydrology. The theory is that if the predevelopment distribution of in-stream flows is maintained, then the baseline capacity to transport sediment, a proxy for the geomorphic condition, will be maintained as well. A popular method of mimicking the predevelopment flow regime is via flow duration control (FDC), which can be achieved by routing postdevelopment runoff through structural stormwater BMPs such that runoff is stored and slowly released to match predevelopment flow rates and durations. Storage requirements for FDC tend to be much larger than for surface water treatment, particularly when the BMPs are small, distributed LID facilities with simple outlet structures. This paper describes a recently invented (patent pending) methodology and programming logic for active stormwater controls to optimize sizing and design of hydromodification control BMPs to achieve FDC (also known as active hydromodification control) and presents one case study to demonstrate benefits. An actively controlled BMP outlet consists of a modulating valve, orifice, or pump in place of a passive stagnant orifice. With the use of active stormwater controls and the methodology described, benefits are three-fold. First, new BMPs can be optimized to be smaller and, thus, more feasible to implement. Second, existing stormwater facilities designed for flood control or other management objectives can be retrofitted to provide hydromodification control. Third, when utilized with real-time flow and water-level monitoring equipment and data, the flow release logic can be adaptively adjusted based on calibrated data without physical retrofit of the BMP's outlet.

In this study, the stormwater management model (SWMM) was utilized to simulate and evaluate the treatment performance of two established treatment systems (i.e., storage-infiltration system and tree box filter) with varying urban land uses based on monitored data. The hydraulic and water quality parameter were optimized through the application of box complex method. The Nash-Sutcliffe model efficiency coefficients for the hydraulic and water quality calibration of both facilities ranged from 0.86 to 0.95 and 0.68 to 0.73, respectively. The storage-infiltration system has maintained a range of 73 to 84% for the volume and particulate reduction with varying land uses. Meanwhile, the tree box filter has a range of 63 to 83% for both volume and particulate reduction.

Low-impact development (LID) has been widely accepted at lot-scale design but less so for watershed-scale cases because of the absence of appropriate assessment tools. The USEPA developed the System for Urban Stormwater Treatment and Analysis Integration Model (SUSTAIN) to evaluate the performance of LID practices at different spatial scales; however, the application of this model has been limited relative to the large number of LID cases. In this study, the SUSTAIN model was applied to a Taiwanese watershed to determine the feasibility of applying the model to international cases. Model calibration and verification were performed, and different types of LID facilities were evaluated. The results showed that infiltration was the dominant contribution to LID performance and that the plant intercept had a minor effect on the treatment. The number of units also influenced the overall performance. Increasing the number of LID units further decreased the pollution. The results of a watershed-scale simulation were used to rank the primary areas for nonpoint-source pollution and to identify effective LID practices.

The Four Major Rivers Restoration Project aimed at rehabilitating the rivers was conducted in Korea as part of efforts to implement comprehensive measures for flood control, reliable water supply, and development of environmentally friendly waterfronts through the effective utilization of water resources. Backed by the enactment of the Special Act on the Utilization of Waterfront Zones, Korea is currently in the process of developing new towns in the waterfront zones that have been rehabilitated by the project. The new waterfront cities were developed with the following three principles in consideration of their geographical locations close to the rivers: first, minimizing the occurrence of extreme flood disasters caused by river overflow; second, minimizing pollutant load and rainfall runoff; and third, harmoniously coexisting with the ecological, historical, cultural, and landscaping values of the rivers. To ensure that all of these development principles can be followed, the formulation of water cycle plans has been made a compulsory part of urban planning. In Korea, LID (low-impact development) technologies have attracted increasing attention as technologies that have the capability to implement plans for developing cities based on the new values of harmony with natural rivers. Currently, however, urban design is being challenged because the introduction of the technologies is still at their early stage. The purpose of this study is to develop modules allowing a cost-effective design of LID technologies that are required for urban planning. The foregoing development will facilitate not only the application of many LID element technologies in urban planning but also the analysis of their effects, enabling the formulation of an optimal design plan through the cost-effectiveness analysis of their alternative scenarios.

In Ontario, underground stormwater detention chamber systems (USDC) are a somewhat new alternative to wet detention ponds for the detention and treatment of urban stormwater runoff. Few tools are available for designers to predict the removal of contaminants from USDC. A conceptual model was developed to fill this void and make USDC a more approachable solution to stormwater management. The model for underground detention sedimentation (MUDS) predicts the removal efficiency of total suspended solids through sedimentation based on the hydraulic properties of USDC. As runoff enters the USDC, waves of particles are released, the pathline of these particles are tracked along vertical and longitudinal axes as they move through the USDC to determine whether a given diameter of particle is removed by sedimentation. Based on the particle size distribution and the density of the particles, the mass removal efficiency is determined. The model was found to adequately predict the hydraulics and treatment efficiency of USDC.

The transformation of natural land cover to urban areas severely alters the hydrologic flow regime of watersheds. The negative impacts include the increase of surface runoff and decrease of infiltration rates, which can result in more frequent and intense flood events and the reduction of groundwater recharge. Low-impact developments (LIDs) are strategies designed to better mimic the natural flow regime by promoting higher infiltration and the treatment of stormwater. Examples of LID structures are bio-gardens, green roofs, bio-swales, and pervious pavements. While the expansion of LIDs in urban catchments would be desirable, retrofitting large urban watersheds with LIDs can be cost prohibitive. This study combines hydrologic simulation with a multiobjective evolutionary algorithm (MOEA) to find solutions in terms of LID design and location in urban catchments that maximize the environmental benefits and characterize the tradeoffs between LID performance indicators and costs. The solutions are evaluated in terms of costs, peak flow, and the hydrologic footprint residence (HFR). The HFR is a new metric designed to quantify the impacts of urbanization in the hydrologic regime by representing the dynamics of inundated areas and residence time of flood waves. The results provide a basis for better stormwater management and planning because tradeoff curves provide a wider spectrum of designs and placement guidelines, improving the sustainability of urban watersheds.

Retrofitting dense urban neighborhoods with green stormwater infrastructure (GSI) requires early and ongoing outreach to the affected public. Add in a combined sewer overflow (CSO) control project that is under a federal consent decree, giving affected neighbors little choice about the upcoming changes to their neighborhood, and a troubled history with large-scale GSI projects in the city, and public outreach takes on greater importance. The King County Wastewater Treatment Division took on its first GSI project for CSO control in two Seattle neighborhoods. Community outreach on the project design began in earnest in 2011. The project, which is nearing the completion of its first construction season, has overcome many challenges and has learned lessons about how to effectively work with the affected community on large-scale urban GSI projects. This paper focuses on the outreach tools and techniques employed during the design phase that built community acceptance of the project and enabled a smooth transition into construction and operation. Examples include taking advantage of creative educational opportunities, building relationships and trust, understanding and speaking to specific concerns about retrofit GSI projects, employing effective outreach techniques (going beyond public meetings), and building neighborhood trust in the construction team. These lessons are applicable to any agency or developer that wants to implement GSI in a dense, heavily used public space where public concerns could slow or stop the project.

Timely, effective, and informative communication with the public is becoming necessary for successful GI projects in the public realm. Outreach goals generally include gaining and preserving public trust and helping to educate ratepayers on the benefits of GI to help facilitate efforts for easier allocation of funds for future GI projects. The San Francisco Public Utilities Commission's Sewer System Improvement Program emphasizes public outreach with well defined goals. The outreach program goals for the Wiggle Neighborhood Green Corridor project included i) gain support and trust from the community for the proposed improvements; ii) provide transparency for the planning and design of the project while balancing key elements of the project; iii) educate the public about what GI is and its available technologies; iv) hear from the community members on their preferences related to different GI technologies, materials, and locations; and, v) demonstrate an integrated approach to planning and design through a collaboration between SFPUC and the San Francisco Municipal Transportation Agency and San Francisco Department of Public Works. As part of the public outreach for the project, the team held three community open houses with more than 274 residents attending. SFPUC also used an online survey tool to gather feedback. Overall, between the open houses and the online tool, more than 1,000 people provided input. Additional specific outreach to property owners and residents who live adjacent to GI features was also part of the public outreach program for this project. In the end, public request for integration of GI and traffic calming measures resulted in bulb-out bioretention GI features planned at many locations along the iconic "Wiggle bicycle route." Online and interactive tools proved to be very effective in reaching people who could not attend the in-person meetings and at the same time delivered much information in an easily understandable format. In addition, the tools allowed the project team to consider public input while finding the right balance of a variety of priorities and preferences for the project.

An undergraduate student team from Norwich University (NU) involved fourth and fifth grade students in the engineering design process (EDP) of a rainwater-harvesting system. They surveyed roof and land areas, measured and calculated various units, and developed models and computer-based designs and drawings of the system. The system is designed to harvest rainwater from a 130 square meter area and yield an average of 890 liters of water per week. The final deliverables included drawings of the proposed system and a preliminary cost estimate. The team utilized the United States Geological Survey (USGS) data to gather average rainfall data in the Burlington, VT area, and used the Texas Manual on Rainwater Harvesting as a basis for its design. An efficiency of 85% is assumed. The school used the NU student design to seek funding and received a grant from Home Depot to install the system starting in summer 2014.

Coconut fiber/husk filters can be appropriate in handling high-turbidity stormwaters without becoming quickly clogged. This low-impact filter can "polish" stormwater removing high turbidity and contaminants. Three filter units were constructed and tested at the University of Trinidad and Tobago for urban runoff recycling and nonpotable supply to improve water sanitation and reduce the risk of flooding.The filter utilized local materials that are both widely available and inexpensive enough to discard after use, thus eliminating back-washing. The accumulated water quality data measured inflow and outflow parameters. The removal of the particulates was measured against local and international water quality standards. Experimental results showed that the coconut fiber/husk filters achieved results equal to conventional sand-gravel media filters. There were no significant differences between the filtration techniques, which showed that the coconut fiber/husk filter can treat stormwaters of high turbidity (usually the case for the southern Caribbean).

The Santa Cruz County Groundwater Recharge Project demonstrates the effectiveness of stormwater LIDs for infiltrating stormwater runoff to recharge groundwater. Although mounting evidence shows that bioretention and infiltration basins (gravel seepage pits) can reduce runoff to overburdened waterways, improve runoff quality, attenuate peak flows, and reduce the potential for hydromodification of receiving waterways, the implementation of bioretention and deep rock gravel seepage pits has yet to be proven an effective method for groundwater recharge. To demonstrate the effectiveness of these LID features, bioretention swales have been installed to pretreat stormwater runoff prior to entering 30-ft deep rock gravel seepage pits at two locations in a county public park. Ongoing groundwater monitoring is being used to evaluate the efficacy of using bioretention and deep rock infiltration methods to recharge local groundwater in areas where aquifer overdrafting, collapse, and saltwater intrusion are occurring.

Rainfall events on urban compacted soils increase the volume and rate of stormwater runoff. A research study was conducted recently in North Carolina to investigate soil amendments to enhance infiltration into compacted soils. Sites were located in the coastal plain, piedmont, and mountain regions, and the sites had sand, sandy clay, and sandy clay loam textured subsoils, respectively. The soil profiles were exhumed into the subsoils and compacted to simulate urban disturbed conditions. Physical treatments/amendments included compacted (control), shallow tillage (15 cm), and deep tillage (30 cm). Fertility amendments included agricultural lime and fertilizer according to soil test results. Triplicate plots were randomized on each of the sites. Fescue grass was seeded, mulched, and covered with jute matting. Steady-state infiltration rate, bulk density, cone penetrometer, grass shoot biomass, and grass root biomass measurements were taken over the study period. Runoff from natural rainfall events was measured for 12 storm events at the two piedmont sites. Tillage greatly increased infiltration rates, and the effect remained after three years. Evidence showed some decline in infiltration rates at the mountain site, but none at the other sites, even though the bulk densities tended to increase over time at all sites. Doubling recommended lime rates, or adding compost, or water-absorbing polyacrylamide usually had no effect on infiltration rates. The initial infiltration rates for compacted soils were usually < 1 cm hr^-1, but the rates improved over several years to up to 10 cm hr^-1. This was somewhat surprising, but the trend was evident at all sites. The tilled soils had infiltration rates of 20 to 35 cm hr^-1 at the end of at least two years. Because this far exceeds the expected rainfall of 3 to 6 cm hr^-1 for 2- to 10-year recurrence storms, the results suggest that treated areas may be able to accept significant amounts of runoff from impervious areas.

Infiltration trenches are a stormwater control measure (SCM) used in urban and ultra-urban areas to provide stormwater runoff volume reduction. Legacy infiltration trenches are difficult if not impossible to maintain and were often built without pretreatment. As runoff with high suspended solid loads enters an infiltration trench, continual buildup of solids clog the infiltrating surface, decreasing the hydraulic conductivity at the soil interface and the performance and longevity of these systems. The present study builds on previous work at Villanova University on an extremely undersized infiltration trench (directly connected impervious drainage area to SCM area of 160:1) to artificially accelerate annual loading to evaluate long-term performance. Ten years and 1,270 cm of rain later, infiltration through the bottom of the trench has nearly ceased and the sides have slowed as well. Recession rates have reached an equilibrium point where they no longer improve or decrease.

Nutrient loading of surface waters has been a growing issue, leading to water body impairment throughout the United States. Current stormwater best management practices (BMPs), such as wet detention ponds, frequently do not reduce nutrient loadings to meet total maximum daily load regulations. This paper presents the implementation of a floating media bed reactor (FMBR) as a form of inter-event stormwater treatment to increase the efficiency in a wet detention pond for reduction of total phosphorus (TP) and total nitrogen (TN) loading to the lower St. John's River (LSJR) in Florida. The FMBR operates on a continuous cycle utilizing green technology solar power and an engineered mixture of sorption media made of natural and recyclable materials. Significant reductions in TP and TN were measured across the FMBR. Pond efficiency improved for TP and TN removal following FMBR implementation. Headloss remained less than 2 cm throughout the study.

Urbanization is altering the composition of landscapes nationwide, with urban areas characterized by a high proportion of impervious surfaces that adversely affects the water cycle of the region. The loss of infiltration of runoff into soil reduces ground water recharge. Increased surface runoff, velocity, and pollution, all byproducts of rainfall on impervious surfaces, impede urban waterways tremendously. Increase in volume of runoff can lead to flooding, with receiving water bodies exhibiting stream bank erosion and channelization. Low-impact development (LID) is a way to mitigate the adverse effects of increasing impervious cover, using decentralized measures to retain stormwater runoff on site, and thereby seeking to mimic the natural predevelopment hydrology of a site. Effectiveness of LID practices in various regions in the United States has been evaluated. However, modeling studies have suggested that the adaptability of LID designs to other regions is problematic, requiring modified solutions to be field tested in every location to confirm how they will perform. Therefore, a great need still exists to evaluate these practices in the field and to collect quantitative data on LID practices' performance, especially in clay soils characterized by low infiltration. This project evaluates urban stormwater best management practices in a typical urban watershed in the Dallas Fort Worth area. The objectives were to design, construct, and demonstrate the effectiveness of permeable pavements and bioretention area at the Texas A&M AgriLife Research and Extension Center in Dallas. Reduction in both volumes and pollutants concentration were recorded for all BMPs.

Although rainwater-harvesting systems are designed to capture and use stormwater, use of this practice as a stormwater control measure (SCM) in Colorado is rarely seen as a viable alternative. First, the practice does not typically provide the volume required to capture the water quality capture volume (WQCV) when it rains because the cistern may already be full. Second, western water law dictates that diverting and using rainwater for beneficial use is illegal without a water right. This study pairs rainwater harvesting with cloud-based infrastructure in an effort to increase available volume in the cistern when precipitation is forecast. This type of automated system can be used to address stormwater treatment using a smaller footprint than would be required for conventional methods because it better utilizes the volume of SCMs in series. Additionally, communities with combined sewer overflows (CSOs) can use this type of system to "beat the peak" and reduce the volume of untreated wastewater entering the receiving water. UDFCD is using this data to determine if this type of configuration, utilizing automated controls at the outlet, is an effective tool in managing stormwater, and if this in combination with rainwater harvesting provides a more effective control measure than rainwater harvesting alone. Three years of data have been collected and analyzed.

Stormwater nutrient removal is a major contributor to loadings in natural waterbodies, and any system not protected by the state or less than 10 acres operates without water quality indefinitely. The permits do not require monitoring by private owners, but the effects are considered to be a contributor to the eutrophication of water bodies across the world. Biomanipulation (biological mitigation) with the emerging technology called the floating treatment wetland (FTW) can be used to remove nutrients, while preserving aquatic ecosystem structures with native aquatic plants. However, logistical concerns arise if the mitigation does not achieve an enhanced removal or even negative removals. Two field studies conducted in Orlando, Florida, are used to investigate nitrogen and phosphorus removals when FTWs are deployed and compared to the control counterparts without the FTWs. The first evaluation was performed in Pond 4M at the University of Central Florida (UCF). The data were used to create an estimated 12% nutrient removal credit presented in a report to the Florida Department of Transportation (FDOT).

Between October 2013 and September 2014, DC Water completed construction of 15 bioretention facilities as part of two projects in Washington, DC, stemming from the utility's long-term control plan (LTCP) for combined sewer overflows (CSOs). Many of the facilities, which were designed to drain within a day after rainfall events, exhibited surface ponding several days after rainfall had stopped. The design team conducted a detailed investigation of possible causes and identified the bioretention soil mixture (BSM) as the culprit. DC Water's investigation into BSM permeability included a review of regional bioretention experience (which revealed a lack of pre- and postconstruction permeability testing to validate BSM and facility performance) and more than 400 mesocosm and field permeability tests performed on 25 unique BSM mix designs. The investigation also included particle size analyses, chemical testing, compaction testing, review of the supplier's soil mixing and distribution processes, and installation procedures. This investigation yielded a better understanding of BSM permeability and development of a well draining BSM mix design that will be applied in the utility's proposed large-scale green infrastructure (GI) program.

Green roofs are an effective, yet costly stormwater control measure that reduces runoff volume through ET and can provide other services, such as improved building insulation and reduced urban heat island effect. For green roof systems to be competitive as a low-impact development strategy, they must be designed to maximize ET. Understanding each component's process in a green roof design is the key to designing a green roof to perform optimally. Evapotranspiration (ET) is a primary mechanism for removal of water in a green roof. When adequate water is available, the ET rate is limited by the energy available. However, when the system is water limited then less ET will occur than is climatologically possible, thus causing the green roof to perform suboptimally. One way to retain more water within the green roof is to minimize drainage (outflow) by altering or restricting the drainage layer within a green roof. In the present work, a green roof with a drainage layer is compared with a lysimeter without a drainage layer to determine if hydrologic performance is enhanced or compromised in either system. Preliminary results from the Villanova University green roof systems show that the underdrained system has approximately 65% of rainfall go to ET, while the undrained system showed 77% ET from April through November 2013. However, the system without drainage has seen as high as 88% annually go to ET in drought years. Additionally, the plants appeared healthier during the drought in the undrained system than in the drained system. Delving deeper into quantifying ET and optimizing green roof design, the elements that are related to ET must be better understood. A small-scale study was constructed to isolate the role of solar radiation in observed ET rates for a green roof mesocosm. Preliminary results indicate that, as expected, plants provide shading and decrease temperature fluctuations throughout the day; the next phase will be to understand the impact on ET rates. Overall, this research is part of a longer-term goal to quantitatively understand and properly estimate and accredit ET for widespread green roof implementation as an LID strategy.

Due to slow-draining soils, winter conditions, and hilly terrain, Eastern Washington is considered to be a challenging region for implementation of permeable pavements. Four pervious concrete placements have been installed on the Washington State University campus in Pullman, WA. They have already weathered from two to four winters and are all functioning hydraulically. This paper provides information on the effectiveness of these facilities and their current hydraulic functionality.

The second phase of the University of Toronto's Daniels Faculty of Architecture, Landscape, and Design Green Roof Innovation Testing Laboratory (GRITlab) officially opened in 2014. The GRITlab project is an interdisciplinary research facility that brings together engineering, architecture, and biology researchers. Phase II of GRITlab involved the retrofitting of the Daniels' 106-year old roof to allow the construction of two full-scale integrated green and photovoltaic systems. The completed GRITlab will serve as a research, educational, and demonstration facility for green infrastructure. This paper will present the planning, design, and construction of GRITlab Phase II and discuss the challenges of retrofitting rooftops to support green infrastructure.

A BioPave treatment train was retrofitted in an existing parking lot in Fayetteville, North Carolina, USA. The BioPave treatment train comprises a permeable pavement and Filterra devices in series. Additionally, a stand-alone Filterra biofiltration device was installed at the same site to evaluate its performance in treating pollutants of concern in North Carolina and elsewhere. The purpose of this study is to gain insight into the water quality treatment capabilities of a PICP—flow-through filter treatment train and to evaluate the stand-alone device's hydrologic and water quality performance. Automated, flow-proportional water quality samplers were installed to collect samples at multiple locations at each SCM. It was seen that the Filterra stand-alone device had sediment concentration reductions above 95% for both TSS and SSC. For nutrients, the Filterra reduced the percent total phosphorus and total nitrogen concentrations by a median of 62 and 33%, respectively. Overall the system treated the 1-in. design storm before significant overflow occurred and showed a similar watershed characteristics to predeveloped conditions. The BioPave system removed sediment, nitrogen, and phosphorus well despite having some moderate to severe clogging issues throughout the study, resulting in load reductions of 69, 84, and 72% by mass for nitrogen, phosphorus, and sediment, primarily through the mechanism of infiltration into the sandy loam underlying soils beneath the pavers.

This paper discusses challenges associated with green infrastructure implementation in the Lake Tahoe basin and other cold weather climates. Examples of successful green infrastructure elements from several projects in the Lake Tahoe basin are described, along with design and maintenance considerations. To be successful in cold weather climates, these elements must be designed with careful consideration to issues such as freezing temperatures, snow storage, sediment storage, and plant selection. Difficulties and limitations of implementing traditional green infrastructure elements such as rainwater harvesting systems, green roofs, and rain gardens are also discussed.

This paper reports the performance of LID facilities in Shenzhen University Civil Engineering College complex during two extreme storm events on March 31 and May 11 of 2014. The first event was the largest one in March since Shenzhen installed gauge records. The average depth for 24 hours was 195.9 mm, the maximum depth for 24 hours duration was 284.1 mm, and the maximum hourly depth was 116.2 mm. The second event was classified as a 50-year event. The average and maximum depth for 15 hours duration was 223.6 mm and 445.6 mm respectively. During the first event the overflow occurred only at the lower outlet. The facilities were completely drained out within 24 hours. During the second event, overflow occurred at the both lower and higher outlets, but no water accumulated in the designed drainage area compared with the rest of the campus that flooded for 3-6 hours.

Performance monitoring of a three-year old, low-compactibility pervious concrete (hydromedia) parking lot located at the Lake Street Service Centre in St. Catharines, Ontario, Canada, began in July 2014. The parking lot is a zero-exfiltration system. This paper presents preliminary results of just over one month of monitoring of hydrologic and water quality performance. The hydromedia surface shows a high infiltration capacity, capable of infiltrating all stormwater. Reduction of both total stormwater volume and peak discharge were observed. Low concentrations (less than 10 mg/L) of suspended solids were measured in the hydromedia effluent, and pH was greater than 8.5. Additional monitoring was underway at the time this paper was written to gather more hydrologic and water quality performance data.

Road retrofit such as sewer replacement or road reconstruction in existing urbanized area can provide a good opportunity to implement stormwater low-impact development (LID) technologies. In Canada and northern United States, stormwater management should occur not only in summer and fall but also in winter and spring. A stormwater exfiltration system was designed to manage stormwater over four seasons by retrofitting roads with two 200 mm (8 in.) perforated pipes with ends capped below a storm sewer system. The design concept is to direct road runoff up to 13 mm of rainfall to these two perforated pipes with ends capped and fill the void space of the sewer trench for exfiltration to the surrounding soil at all times (i.e., including snowmelt and winter rainfall). Two and a half kilometers of this exfiltration system was constructed in the City of Toronto and found (by monitoring) to be able to control rainfall up to 24 mm without overflowing to the storm sewer above. This paper presents the planning and design criteria, costs, construction and maintenance, and performance evaluation.

The technology of green stormwater strategies has advanced rapidly in the last 20 years so that we can now design or retrofit cities to achieve zero runoff for large storm events. A detailed examination of projects that have achieved zero runoff, full groundwater recharge, or advanced treatment prior to attenuated discharge to surface waters, provides insight into the LID options for cities. Beyond green critical thinking, real multidisciplinary problem solving, and rethinking regulations has led to these new concepts. Yes, stormwater systems can be beautiful, function to a high degree, achieve beyond-green results, and help create dynamic green livable cities.

The City of St. Louis is served by a combined sewer system and faces the problem of combined sewer overflows (CSO). Green infrastructure such as permeable pavement that provides on-site stormwater management for volume reduction and pollutant removal from storm runoff can offer a cost-effective means to address the CSO problem. A pilot study was conducted in St. Louis at three alleys in residential neighborhood, where the existing impermeable pavement at each site was replaced by one of the three different types of permeable pavement (permeable concrete, asphalt, and paver, respectively). The objective of the pilot study was to evaluate the effectiveness of permeable pavement on volume reduction in combined sewers. The flows in the combined sewer at each site were measured for approximately one year during each time period of before and after the change in pavement. To determine the stormwater volume in the measured flows, the base flows (i.e. sewage) were separated from the combined flows. For a given rainfall, the measured flows from the dry days that preceded or followed the rain days were taken as the base flows. The measured flows from the rain days were taken as the combined flows. The difference in flows between the rain and dry days were used to calculate the stormwater volume. To adjust for the difference in rainfalls pre- and postinstallation, the separated stormwater volumes were normalized by the amount of rainfalls before the volume reduction was evaluated. The results showed that permeable pavement resulted in stormwater volume reduction in the combined sewers at each of the three sites. The volume reduction ranged from 46% by permeable paver, 36% by permeable concrete, to 13% by permeable asphalt. The analysis on flow hydrographs from the combined sewers revealed that the application of permeable pavement reduced peak flows as well. The pilot study indicated that the installation of permeable pavement can result in stormwater volume reduction in combined sewers; the effectiveness of reduction differed among different types of pavements. The study recognizes that many factors can affect the flows in sewers and recommends extended flow monitoring over a longer period, so that the long-term performance of permeable pavements can be evaluated.

Better insight into the benefits of LID/GI practices can be gained from a continuous distributed physics-based model that allows us to scale up from the individual practice to watershed response within a single modeling framework. The conservation laws of rainfall runoff are used to formulate watershed response for prior conditions and postconstruction of LID/GI. Weather radar, when properly quality controlled and enhanced for accuracy, accounts for the local/regional weather affecting the natural, urbanized, and/or modified hydrology of the watershed. By using continuous rainfall data, the modeling and our understanding of how practices affect the hydrologic response is extended beyond single frequency-based approaches. Commonly used synthetic hyetographs, such as the SCS Type I, II, or III temporal distributions, are based on the 25-yr storm frequency depths. With actual rainfall time series, understanding can be gained as to performance given realistic mean inter-event arrival, depth, duration, and intensity from the historic record. Continuous simulation for a typical year or multiple years reveals how these practices will perform under realistic inputs and with physics-based model assumptions. When sizing LID/GI practices and infrastructure, and in particular, detention volume using synthetic hyetographs as model input rather than using continuous actual rainstorms can result in oversizing of outlet works and reduced settling times, while underestimation of storage volume can result if successive storms are not taken into account.

Low-impact development (LID) and green infrastructure are both conceptual and practical strategies that can upgrade urban landscapes to manage urban water, including surface water and ground water recharge. Landscapes in cities and towns are a limited resource, and they must be "multitasking" to optimize functions and benefits. Communities and infrastructure professionals are increasingly interested in the cobenefits that are possible if LID installations incorporate multiple purposes. Nearby nature and urban ecosystems within cities and towns include all ecological, cultural, and engineered green spaces, such as (but not limited to) parks, open spaces, community gardens, and the urban forest. These spaces, in addition to private properties, are potential LID sites. Environmental services are important yet nearly 40 years of research across social disciplines demonstrates a broad array of human health and wellness benefits associated with the human experience of metro nature. A health-oriented cobenefits approach in LID planning and design can promote expanded community support for LID and potential collaborations with diverse partners, such as urban planners, social services providers, and public health professionals.

Media filter drains (MFDs), which are also known as ecology embankments, are linear best management practices used by many state departments of transportation (DOTs) for highway runoff treatment. Initial studies on MFDs indicated that their life spans were at least 10 years. Recent studies indicate that for dissolved zinc and copper metal removal, the life span may exceed 20 years. This study extended the life further in laboratory tests for media from existing MFDs, indicating that the life might be many decades. Zinc and copper are particularly of concern for various aquatic species, and the removal rates were extremely high.

GIS software was used to identify the geographic overlap of spatial datasets and then prioritize potential opportunities based on factors considered conducive to LID implementation. The resulting areas were presented in a series of LID bioretention opportunity maps for urban sub-watersheds within the Monterey Bay region. These maps identify potential areas for the implementation of bioretention features to achieve an increase in stormwater infiltration in urban areas overlying permeable soils with opportunities for groundwater recharge. Mapped areas are within Watershed Management Zone (WMZ) 1 or 4 (as defined by the California Central Coast Regional Water Quality Control Board), overlie a mapped groundwater aquifer, and drain to a stormwater collection system. Selected areas are prioritized into very high, high, moderately high, and moderate infiltration and recharge potential based on nine characteristics such as soil type, surface slope, and opportunity to recharge over drafted water supply aquifers. For nine catchments within five of the urban areas, infiltration potential was estimated based on average annual runoff and runoff during a design storm. The product of this analysis, the maps, GIS shapefiles, and a GIS modeling tool were made available for partner agencies to use in their planning and implementation projects. The maps were subsequently used to identify, survey, and ultimately design LID retrofits on suitable parcels.

This study discusses the innovative design of the gravel infiltration retention system for the underground parking garage of the phases 5 and 6 of Project of the Hills in Panyu District, Guangzhou City. The runoff from this project site is mainly managed by an innovative subsurface detention gravel system that provides stormwater storage during storm event and irrigation reuse during the dry season. This gravel infiltration retention system is generally provided by a 20-cm layer of coarse gravel placed over the garage under the landscaping soil surrounding the buildings. The areas not treated by the gravel infiltration retention system will be treated by a bioswale and a rain garden designed to remove nutrients. The synthetic 133-mm 4-hour storm event with 10-year return period was used to design the gravel infiltration retention system, rain garden, bioswale, and other pipeline conveyance. The 24-hour historical rainfall of 389 mm was used to evaluate these low-impact development facilities responses to an extreme event. The simulation results show that the gravel infiltration retention system have very large flood control performance.

This study addresses the innovative design of the low-impact development (LID) facilities of the Congdu Ecological Grange in Conghua District, Guangzhou, China. The stormwater in the project area was treated with innovative LID facilities such as raingarden, bioretention swales and terrace trenches, and the treated stormwater was diverted to the landscaping lakes for irrigating the entire project during the dry season. To maintain the lake water levels and water quantity for irrigation, the polluted Yangmeikeng River water is pumped into the raingarden on the southwest corner, from which treated water enters the upper west lake. The synthetic 133-mm 4-hour storm event with 10-year return period was used to design the LID facilities and other pipeline conveyance. The 24-hour historical rainfall of 389 mm was used to evaluate the LID facilities responses to an extreme event. The simulation results show that the LID facilities have very large flood control performance.

Phase I project of the Beijing CITIC Complex was completed in 2010. Its pipeline drainage system was built to convey a 1-year storm event. But the new regulation heightened the design standard to three years for any new development. Phases II and III projects upstream of Phase I project site are under planning, and their conveyance systems connect to the drainage system built for Phase I project. Therefore the bottleneck is how to convey the runoff of a 3-year storm event without causing downstream flooding. This paper discusses various solutions including construction of underground detention tanks and low-impact development (LID) facilities. The performances of various combinations of LID facilities and detention facilities were evaluated by SWMM model. The total cost including construction, operation, and maintenance for each combination is also calculated. The optimal schemes were finally decided in favor of the LID facility deployment without underground detention tank based on the performance and cost. The types of LID facilities and the configurations are also identified.

The Denver High Line Canal is a 130-year-old irrigation channel that follows a 106 km (66 mi) serpentine path through the Denver urbanized region. While it once served to bring 200 km² (500 mi²) of semi-arid, high plains prairie into agricultural production, nearly all of that land has now urbanized, rendering much of the canal obsolete. With urbanization, the canal has become a treasured recreational trail, due in part to the impressive gallery of giant cottonwoods that have grown up along its banks over the past 90 years, providing a full canopy of shade in many areas. The canal is extremely inefficient at delivering water due to seepage, infiltration, evaporation, and evapotranspiration via the thirsty cottonwoods. Reasonably, these same things that make it bad for water delivery should make it good for stormwater pollutant reduction and runoff reduction. In 2014, the Urban Drainage and Flood Control District, Denver Water, and four local governments completed a feasibility study that confirmed the practicability of retrofitting the High Line Canal to provide stormwater quality enhancement and runoff reduction. Specific project outcomes included characterization of all watersheds that cross the canal; determination of the canal's treatment capacity; determination of infrastructure needed; estimation of the annual stormwater volume available for infiltration and evapotranspiration; estimation of capital, operational, and maintenance costs; evaluation of a framework for operating within the Colorado water rights administration system; conceptual design of a pilot project to further confirm the project feasibility; and identification of future steps for project implementation. Construction of two pilot projects is proposed to begin in 2015 and 2016.

The Parks Reserve Forces Training Area, also referred to as Camp Parks, is an active Army Reserve training installation located in Dublin, California. The cantonment area, located in the southern portion of the installation, will be redeveloped. The proposed redevelopment includes new facilities that will result in a more dense spacing of buildings than currently exists. These redevelopment activities will affect the surface hydrology and water quality. This paper discusses the site-specific hydrologic analysis conducted to evaluate the additional stormwater runoff from proposed redevelopment activities and to provide preliminary recommendations for green infrastructure and low-impact development (LID) to retain stormwater runoff volume and replicate predevelopment hydrology. LID controls considered in the hydrologic analysis for Camp Parks redevelopment areas included cisterns, permeable pavements, bioretention areas, vegetated swales, and green roofs. These LID controls were modeled in PCSWMM to calculate the runoff volume reduction at the sub-catchment level. The total runoff volume increase resulting from the proposed redevelopment was approximately 12 MG. After adding LID controls, the total runoff volume was 5.8 MG, which equates to a runoff volume reduction of more than 50% if LID controls are implemented. The assumptions made in this analysis for modeling LID were conservative. Additional runoff volume retention could be attained by adding more LID controls to these sub-catchments and refining the modeling parameters with more detail and site-specific infiltration data.

Spring Lake Park is located in South Omaha on the bluffs of the Missouri River. It consists of native upland forest on loess soils surrounding a valley rich with several seeps, wetlands, and waterways with a contributing drainage area of 79 hectares. An antiquated and leaky combined sewer line flows through the center of the park, short-circuiting natural drainage patterns and lowering ground water levels. The forested park, named for a spring-fed lake that has since silted in, has been somewhat neglected and underutilized in past years. As part of sewer separation and park retrofit efforts, seepage water and surface runoff will be retained, filtered, and infiltrated through several LID practices located throughout the park. The design aims to reengage the community with the park by utilizing constructed LID practices as multifunctional facilities and reintroducing a 0.8-hectare fishing lake. The restoration of the naturally dynamic drainage system infused energy into the design process and allowed robust design objectives to be achieved. Three design themes emerged: ecological sensitivity, integration, and innovation. The park design sought ecological sensitivity through preserving seep and wetland areas, significantly reducing sediment loads near the source, and including an aggressive planting plan with all native plants. The design integrated passive recreation, education, and aesthetics and included community input as part of the design process. Finally, the design utilized several innovative practices including several diversion structures, off-line systems, and a zero-discharge basin. The presentation will further describe several design elements that support the three aforementioned design themes.

While low-impact development (LID) has become a well known best practice guidance in developed countries, the awareness and techniques are still far behind in developing countries such as China. With its GDP growth and strong demand in urban expansion, Chinese municipalities often face ever-complicated runoff management and surface water quality degradation. This problem is particularly agonizing when there is simply no time to act, and the standard engineered drainage does more harm than help. In these circumstances, the landscape architect is in a position to bridge the gaps and advocate urban drainage alternatives, which apply not only in the integration of low-impact development concepts, but also in the synchronization of the planning and design processes within rapidly growing urban areas. This paper explores the possibilities of LID in large-scale new-town projects and how it redefines the urban open spaces. Three fastest-growing second-tier cities in the lower Yangtze River Delta region were chosen to showcase typical development site challenges and possibilities: 1) Wusong Riverfront Pilot Project: Funded by a regional "Clean Water Act," a riverfront park treatment prototype is targeted to mitigate storm runoff before discharging to the river. Test results from 2013 show a nearly 80% reduction in BOD and other parameters. 2) Ningbo Eco-corridor: A disconnected canal network is retrofitted to be an urban filter for mitigating runoff from its 1,000-hectare urban watershed. As a large-scale regional park, it also provides ancillary benefits such as recreational amenities and wildlife habitat. 3) Hefei Raycom City Green Spine: With careful drainage grading and collaboration with local civil engineers, a series of rain gardens replace 1 km-long storm pipes and become the green infrastructure of a new 45-hectare public-private joint venture residential development. Although these case studies are from China, for its extreme circumstances, the strategies and techniques are universally applicable in developing countries' socioeconomical context. Lessons learned include budgeting for low-cost solutions, targeting appropriate interventions, collaborating with stakeholders and academia, involving local communities, and reimagining/redefining open space and green infrastructure.

Unusually heavy rains occurred in the spring and summer of 2007 and caused significant flooding across Oklahoma. One area, known as Babcock Basin—a 180-acre drainage basin in southwest Stillwater, Oklahoma—experienced flooding, and residents became very aware of the need for proper stormwater management. The city obtained funding through FEMA's Hazard Mitigation Grant Program (HMGP) to design a regional retrofit of the stormwater system to reduce flood risks. However, a condition of the grant was to use low-impact development (LID) techniques to the extent feasible, an approach that is atypical for Oklahoma. The area was nearly fully developed, primarily residential on quarter-acre lots with some institutional (church) property. Buying existing homes was not an option, therefore, the design team had to be creative in adapting LID elements to occupy a smaller footprint and serve a hybrid function of providing water quality benefits in frequent events and managing the runoff such that no structures would be inundated in a 1% annual chance (the so-called 100-year) event. In addition to the design challenges, there was a significant component of community outreach and education and the need to work with the property owners to gain acceptance of the project. This paper provides an overview of the design and addresses some of the inherent benefits, challenges, and other details associated with the project.

The Cape Fear region in North Carolina has long been recognized for its scenic location, clear ocean waters, and productive tidal creeks. Like many coastal communities, an increase in the popularity of this region has resulted in a rush of traditional development over the last four decades. Impervious roads, parking lots, roofs, and sidewalks have replaced pine forests and sandy dunes, and stormwater volumes entering the local tidal creeks have increased dramatically. By the 1980s, water quality in local tidal creeks was in decline. As the decades passed, the local creeks experienced progressive shellfishing closures that have since become typical for the region. By 2010 a vast majority of the waters previously open to shellfishing had been closed permanently, with additional areas open only conditionally and outside of predetermined rain events.

A new guidebook, Watershed Stewardship for the Edwards Aquifer Region: A Low Impact Development Manual, sets a framework for water quality protection and recharge for the Edwards Aquifer. The book is intended for use by design practitioners, land developers, land conservancies, and local and state officials charged with balancing the demands of aquifer protection with rapid land development. The guidebook concentrates on methods for sustainable development across one of the most sensitive aquifer regions in the United States, the Edwards Aquifer region of south central Texas. The guidebook begins with a contextual discussion of aquifer functioning, land use, and regulation, and concludes with recommendations for a set of LID tools specific to the requirements of this region.

Sustainable urban drainage systems (SUDS) are increasingly prominent as a solution to many of the performance and environmental problems associated with traditional drainage systems. Questions remain regarding the values of maintenance costs and environmental benefits delivered throughout the useful lives of SUDS. Using the Dunfermline East Expansion area in Scotland as a case study, this study represents a novel approach in that it collects actual maintenance data, assesses ecosystem services, and carries out whole life cost analyses. Findings suggest that SUDS may be accounted as a net asset, although assumptions inherent to ecosystem services assessment methodologies produce a wide range of uncertainty.

This study discusses the low-impact development (LID) facility planning of Phase 1 project of the Guangzhou Educational Town in China. The project site will deploy LID facilities to reduce the flood risk and nonpoint pollution and to utilize the rainwater for landscaping and irrigation. In addition to traditional LID facilities, two newly developed LID features such as gravel infiltration retention system and depressive green field are used for the first time in the project. The low- and high-density LID configurations were deployed. SWMM model was used to stimulate runoffs with and without LID facility deployment. The simulation results show that deploying low- and high-density LID configurations can improve the drainage system from handling five-year design storm events to 10- and 20-year storm events, respectively. The high-density LID configuration was recommended as the implementing scheme.