Low Impact Development for Urban Ecosystem and Habitat Protection

This paper provides a methodology to analyze the hydrologic effects of rain gardens in urban catchments without requiring unsubstantiated assumptions about how small heterogeneities like rain gardens will affect empirical parameters lumped over larger catchment areas. The uses a physically-based, distributed model to simulate overland flows and unsaturated subsurface flows at a resolution finer than the size of the rain gardens. The model was calibrated to simulate observations from rain gardens monitored over a four-year period by the U.S. Geological Survey, providing calibrated topography and soil profiles describing the hydrology of the rain gardens. The model was then calibrated to simulate the runoff observed from a 5.3 hectare urban watershed with 86 residential lots. The calibrated rain gardens were then merged into the calibrated urban watershed model to simulate a variety of scenarios, including random layouts of varying density and size rain gardens. Each scenario was simulated using design storms ranging from 6 month to 100 year recurrence intervals. Results showed significant reduction (compared to the scenario with no rain gardens) in peak discharge and runoff volume and significant increases in time to peak among different scenarios and return period. Reductions for both volume and peak flow ranged from 10 to 50 percent, even for larger storms (10 year to 50 year events).

Municipalities in Michigan are increasingly interested in utilizing rain gardens as a "best management practice" (BMP) for storm water management and a component of sustainable development. However, there exists a need for local technical reference materials and a better understanding of the implications of planting mix design on rain garden performance. This project included conducting a national review or rain garden design criteria, analyzing planting mixture designs in the laboratory, and collaborating results with field infiltration measurements. In the end, the study evaluated numerous design parameters including field capacity, permeability, infiltration, organic content, dry bulk density, porosity, sediment grain size distribution, and field infiltration rate.

Bioretention offers the potential to sustain pre-development water balances while minimizing effects on groundwater quality and providing a landscaped aesthetic. To study cold climate issues including potential trade-offs between groundwater quality and quantity and bioretention system lifespan, a salt and aggregate mixture is being applied to 10 outdoor bioretention columns with soil, mulch and vegetation layers. A detailed methodology and preliminary findings for experimental applications of the salt/sand mixture is presented. Pre testing infiltration rates for bioretention media averaged 24.8 m/day, matching published values. Background Na⁺ and Cl^– levels within the soil matrix averaged 736–1900 mg/L and 95–621 mg/L, respectively. Preliminary mass balance results, demonstrate a consistent response to Na⁺ and Cl^– loading, with increased Na⁺ output mass, and reduced Cl^– mass as compared to input in all columns. The evaluation of the effects of de-icer loading on bioretention systems is essential to the expansion of the functionality of bioretention systems to achieve stormwater management objectives in cold climates.

Low impact development (LID) flow control strategies, such as distributed bioretention facilities, are increasingly used to manage stormwater runoff and mitigate the effects of hydromodification. In evaluating bioretention as part of an overall hydromodification control strategy, continuous simulation is critical in determining appropriate facility sizing factors and evaluating performance. Due to differences in bioretention design standards and complexities in analysis related to soil hydraulics and outlet controls, distinctly different model representations are commonly employed to size and evaluate bioretention performance. Various approaches to simulating bioretention are described herein and compared for a hypothetical design scenario. Selected flow duration and water balance results are presented, illustrating the potential differences between these modeling approaches. Results also highlight issues related to changes in water balance and low flow durations, even with effective controls in place.

This paper presents the elements involved in the design of bioretention systems as an integrated part of an urban retrofit project. This project involved the design of systems to intercept much of the runoff from the first 2.69 inches of rainfall. Diverted flows were conveyed into bioretention systems for treatment. Due to space constraints, the bioretention systems were fingerprinted into areas comprising 2.5% of the contributory drainage areas. The system was modeled using HydroCAD, a design storm (DS) event modeling software. A four-compartment node system is used to model the dynamics of flow through the systems. The resulting response to a series of design storms is then presented.

Seattle Public Utilities (SPU) is implementing a large scale Natural Drainage System (NDS) project in conjunction with the redevelopment of the High Point neighborhood in West Seattle. When developing the design concept for the High Point NDS project, one of the primary challenges SPU faced was modeling the interactions between the various NDS components in order to predict flow attenuation through the entire system. Key inputs to the model were the infiltration rates for the engineered soil layer of the NDS and the underlying native soil. The infiltration rate for the engineered soil layer was assumed to be 2 inches/hour based on results from laboratory testing. Based on geotechnical reports for the project, the infiltration rate for the underlying till soils was assumed to be so low as to be insubstantial.

Increasingly, building owners and city planners are turning to vegetated roofing systems, commonly known as green-roofs, for economic, environmental, and aesthetic benefits. Many studies have shown the potential for green-roofs to mitigate volumetric magnitude and nutrient loadings of rainwater runoff surges immediately following large storms, but further research is needed to help solidify these relationships. Although the insulative capacity of a green-roof has been studied by some researchers, it has yet to be thoroughly tested under a controlled, steady-state environment. Furthermore, a green-roof performance comparison of stormwater runoff has yet to be conducted with controlled rain events and quantifiable antecedent soil-moisture. In this research, rainfall detention and stormwater runoff peak flow attenuation of ten different small-scale green-roof schemes were observed and analyzed in a laboratory environment. Sedum Angelina, Sedum Hispanicum, White Clover, Vinca Major, Ryegrass, and a wildflower blend were grown in separate 2' x 2' trays at separate soil depths of 2" and 6" atop a 1/4" drainage layer to observe how soil depth and root zone development affects stormwater flow-through for each plant type. A constant media mix (porosity=70%) was used consisting of composted paper fiber, leaf compost, pumice, and sand. Antecedent gravimetric soil moisture for each green-roof tray was measured by using initial tray weights and comparing to the residual soil moisture. Water quality levels of temperature, conductivity, and pH were measured on site at Portland State University while nitrate, phosphorus, Total Suspended Solids (TSS), and heavy metals were measured by The Bureau of Environmental Services, Portland, Oregon. This green-roof testing has shown that plant type and antecedent soil moisture have the strongest affect on runoff water quality parameters of pH, nitrate, and selected heavy metal concentrations, while substrate depth primarily dictates runoff conductivity, TSS, and phosphorus concentrations.

To evaluate the viability of green roofs for stormwater management and low impact development (LID) in the Cascadia region, Seattle Public Utilities (SPU) initiated the Green Roof Performance Study (GRPS). The GRPS research project, led by Taylor Associates, Inc., is currently collecting up to three years of continuous hydrologic data at five different buildings with green roofs located throughout Seattle. The data set from each roof will include rainfall, supplemental irrigation, solar radiation, wind speed, air temperature, relative humidity, and runoff. These continuous hydrologic records will be used to calibrate a continuous hydrologic model, which in turn will provide a long term simulation of green roof performance based on a regional 40-year rainfall record. Such long-term monitoring and simulations of green roof performance have not yet been developed in literature or widely used as a basis for zoning, design criteria, or building code incentives. Preliminary results from the GRPS show that green roofs can reduce the volume and peak flow rates of stormwater runoff on an individual storm basis and over the course of a year.

Sustainable stormwater management involves ensuring that site runoff not exceed the pre-development peak flow rate and volume, typically accomplished through the use of water retention, infiltration, and reuse onsite through rainwater harvesting. Certain roofing materials, however, may be a pollutant source, thus, influencing the runoff's potential for harvesting. This project focuses on the first four months of roof life for several traditional roofs and an extensive green roof. Substantial and significant releases of zinc and copper originated from an uncoated galvanized roof and from two treated woods, respectively. Roof runoff concentrations during early life indicated potential toxicity concerns for zinc and copper, plus periodic elevated nutrient concentrations. Additionally, periodic spikes in pollutant concentrations in early life indicated that elevated pollutant levels simply were not a result of washoff from excess preservative remaining on the surface of the material at installation.

The City of Portland, Bureau of Environmental Services (BES) has become increasingly committed to using Green Solutions, also known as Low Impact Development (LID), to manage urban stormwater runoff. Ecoroofs have become a primary option for reducing roof runoff into sewers and streams. Currently, all ecoroofs are considered equal in their ability to manage stormwater. But differences in soil media type, soil media thickness, and irrigation are thought to play a significant role in ecoroof performance. In an effort to ensure ecoroofs provide a reliable benefit, data is being gathered from several ecoroofs to determine which design and maintenance variables are most important to maximize stormwater retention. Monitoring data is available for three Portland ecoroofs (see Figures 1 through 3): 1) the Hamilton Apartments, 2) the Multnomah County Green Roof, and 3) the Portland Building Ecoroof. All are within the downtown Portland area (Figure 4) and have unique designs in terms of soil media, thickness, and maintenance practices.

Green roofs are engineered landscapes designed for the roofs of buildings. The stormwater management benefits of green roofs have frequently been cited as a compelling reason to promulgate the greening of urban rooftops. The most commonly reported stormwater benefits of green roofs are reduction in flow volumes and reduction in peak runoff rates due to flow attenuation. International research has demonstrated the benefits offered by green roofs; however, efforts to quantify and monitor benefits achieved in specific climatic regions of the United States have only begun in recent years. This paper presents field performance data and computer simulations for green roofs in the Pacific Northwest maritime climate. These show that green roof performance varies greatly but all of the evaluated systems reduced peak runoff.

Driven by a contentious regulatory and political environment as well as a simple desire to do better, the District of Columbia's Department of Transportation (DDOT) has begun to transform the way it approaches highway design through embracing the principals of green highways and context sensitive design. Both of these initiatives emphasize innovative stormwater management, including Low Impact Development (LID) and sustainability. This transformation has brought detail and method to delivering innovative stormwater management in roadway improvements and should result in continuous improvement over time. Major factors which drove those changes include: 1) The political environment and Mayoral and City Council priorities, 2) The regulatory environment, 3) Public support, 4) A focused initiative to improve the Anacostia River and the neighborhoods identified with it, and 5) A national effort to reduce or even improve the environmental impact of the transportation system.

The research focuses on the environmental benefits derived from an overall intervention of green envelope types [roofs, façades and streets] in the city core of Vancouver, Canada. To achieve this, it analyzes previous precedents conducted in cities such as Berlin, Germany; Malmö, Sweden; Toronto, Vancouver, Canada; Chicago and Seattle, USA; and applies the data to a particular case study area in Downtown Vancouver. It then applies the Seattle Green Factor to the case study area, and quantifies the contribution of the green envelope interventions in order to ameliorate environmental impacts in terms of reducing stormwater runoff, CO₂ emissions, and energy demand by buildings. Calculated results from the case study area shows that the addition of green roofs, green façades and green streets would reduce stormwater runoff up to 13% (4% by green roofs, 3% by green streets and 6% by green façades), reduce building energy demand by 9%, and CO₂ emissions by 12%. With these findings, the paper proposes a new Vancouver Green Factor for the selected area, which introduces new concepts to these types of green factors, such as the volumetric value of urban surfaces.

A green roof is a multi-layered vegetated roof covering consisting of a root barrier, waterproof membrane, under drainage system, soil, and plants. The hydrologic and hydraulic processes involved are rainfall evapotranspiration, runoff generation, detention, infiltration, and routing. To assess the effectiveness of green roof on mitigating urban stormwater runoff, a Deterministic Lumped Dynamic Model (DLDM) has been developed to simulate these aforesaid processes. This model uses the Green-Ampt equation modified by Mein & Larson (1973) and the infiltration modeling procedure described in Chow et al. (1988) as the basis. However, it further modifies them to describe how infiltration rate changes as the roof substrate wets and dries and their relationship to the Specific Retention of the roof substrate. The runoff module of Storm Water Management Model (SWMM RUNOFF) is adopted by this model for modeling the routing of infiltration through the under drainage system of the green roof. Flow survey data of 5 minutes interval from Hamilton Building in the City of Portland from Year 2001 to 2003 have been used to test the model. We have founded that the simulation results of the peak flow and total volume are matching observation within reasonable range.

Green roofs are an emerging stormwater management tool that have predominantly been analysed with regard to runoff volume reduction and peak flow mitigation. Little research has been completed regarding evapotranspiration (ET). Sedum mexicanum (Mexican Stonecrop) and the NZ native species Disphyma australe (NZ Ice Plant) in a NZ designed, pumice and zeolite based substrate have been analysed to determine daily and hourly ET rates under unstressed and drought conditions. Water loss, and thus storage recharge of the substrate, is greatest in the first 10 days. Transpiration by Sedum mexicanum contributes 47% of the total ET and Disphyma australe (NZ Ice Plant) contributes 44%. After the initial rate of rapid water loss, plants conserve water and ET is not significantly different to evaporation from the unplanted tray. Sedum mexicanum has a greater ability to conserve water and thus has a greater longevity of life than the NZ Ice Plant under harsh drought conditions.

The City of Portland, Bureau of Environmental Services (BES) uses green street facilities, a Low Impact Development technique, to manage stormwater in the urban watershed. Green street facilities have multiple benefits for our urban environments. They are effective in reducing peak flows and flow volume to solve combined sewer overflows and basement sewer backups. Green streets also filter pollutants, replenish groundwater, make attractive streetscapes for neighborhoods, and benefit pedestrian connections throughout our cities. Through design, construction, and monitoring of green street facilities, the City has collected a wide range of design details that have contributed to the success of the facilities. The paper will discuss the variety of constructed facilities in the "Green Street Toolbox" and their appropriate application as well as the range of elements critical to the design of a green street — neighborhood type or adjacent land use, water collection and inlet design, utility conflicts, parking considerations, check dams, lined facility design, traffic volumes, street type and use, pedestrian and bike improvements. Project examples will include built facilities in residential, commercial, and industrial areas of the City.

The Green Highways approach to infrastructure planning, design, and construction is a revolutionary approach to resource protection and environmental compliance. The approach is based on providing predictable pathways to streamline the delivery of transportation projects by the use of incentives and recognition for the use of innovate stormwater and environmental designs that are done in the context, or framework, of a watershed approach. Green Highways are transportation corridors which use Low Impact Development (LID) tools, recycled materials, and locally sourced resources in transit right-of-ways to meet regulatory requirements for stormwater management and highway design. The Green Highways approach takes a traditionally viewed "waste product" of development, stormwater runoff, and uses it as a resource to foster desirable end results such aesthetic improvement, habitat linkages, improved air quality and cooler micro-environments. A multi-agency Green Highways Partnership (GHP) has been formed with the goal of creating sustainable transportation corridor solutions which are cost effective and meet multiple objectives, including green infrastructure development.

Infrastructure and roads are essential lifelines for communities and economies. Traditional road design and construction are introducing pollutants into the environment and impacting people's health. Low Impact Development (LID) is an effective tool in improving water quality and mitigating small peak flow events. However, LID's ancillary benefits are now being quantified. Using LID as a tool in a larger systematic approach — one that balances general mobility, habitat, water and community — can dramatically improve our transportation network. This paper uses four projects to demonstrate how designers and stakeholders can redefine Right-of-Way construction and design to create greener, community-enhancing streets.

There are over 7,000 miles of highway in Washington managed by the Washington State Department of Transportation. In non-urban areas, the majority of these roadways drain to unimproved roadside embankments. In order to quantify the stormwater quantity and quality treatment provided by these embankments, monitoring equipment was installed at 4 monitoring sites with edge-of-pavement, 2-meter downslope, and 4-meter downslope runoff collectors. The runoff collectors were installed parallel to the roadway and designed to intercepted overland flow. The data indicate that on average 79% of the runoff from the highway was infiltrated within the first 2 meters of the edge of pavement, while 83% was infiltrated within 4 meters. On average, there was a 72% reduction in peak flow rate between the edge-of-pavement and the 2-meter stations and a 90% reduction in peak flow rate between the edge-of-pavement and the 4-meter stations. Water level observations in the ditch at the bottom of the embankment at two of the sites indicated that runoff seldom emerged at the base of the embankment.

Streets represent a large portion of the impervious area in urban areas, and properly managing runoff from those streets is critical in meeting regulatory requirements in both our sewer and open channel systems. Green Streets have become a huge component of the City of Portland's efforts to manage street runoff. The combination of soil and plants slow down, retain, and clean urban stormwater. There are approximately 500 facilities currently installed, with an expected increase to 1,500 by the year 2013. Green Streets are built by private developers to meet city requirements for new development and redevelopment projects, and by the City to manage sewer capacity and water quality issues. Data from a number of green street facilities has been collected through a combination of continuous flow monitoring and flow simulation tests. The Glencoe Rain Garden has retained 88% of the rainfall runoff from the site over the past four years. Peak flows have remained below the design level for all storm events during that period with no basement sewer backups, with peak flows from the most intense rainfall events reduced by an average of 90%. The SW 12th & Montgomery Street Planters have been flow tested several times using a combined sewer overflow design storm (over 2 inches of simulated rainfall in 6 hours) with volume retention ranging from 50% to 74%. A number of stormwater curb extensions have also been tested and have performed very well. All reduce large peak flows by 70–90%. Volume retention has varied between 61% and 96%. Green Streets in Portland have consistently performed well with only small variations because of location, design configuration, and antecedent conditions. They appear to be a very effective way of reducing peak flows and flow volumes while reducing impervious area, improving aesthetics, and filtering pollutants.

A growing number of U.S. cities and counties are leading the way with policies, regulations and programs that require or incentivize the use of green infrastructure for stormwater management. This report analyzes how a dozen local governments are transforming the management of stormwater runoff at the site level using controls that infiltrate, reuse and evapotranspirate rainwater. The case studies include a broad cross-section of the country geographically, hydrologically, and demographically. These stories provide insight into the barriers and opportunities of many different local policy approaches, including stormwater regulations, economic incentives, retrofit standards and more. Based on outcomes of total build out and retrofits with green infrastructure, this paper provides a menu of policy options that worked for most of these cases and which may be applicable in other jurisdictions looking for ways to improve local stormwater management.

Green infrastructure supports the concept of using natural ecosystems to support a healthy urban environment, specifically to preserve and enhance water, air, cultural and visual resources. Low impact development (LID) is implemented through a set of tools which support the development and enhancement of green infrastructure. Permeable interlocking concrete pavement (PICP) is an LID tool which enables a broad range of opportunities to support integrated green infrastructure goals in new and redeveloped urban environments while meeting regulatory directives and other drivers for implementation. PICP has a variety of design options for stormwater mitigation, increased infiltration, and pollutant control. It is essential for users, and potential users, of this product to fully understand PICP benefits and constraints.

The City of Olympia has completed a roadway reconstruction project using innovative techniques to mitigate the project's stormwater requirements within the existing right-of-way. The reconstructed RW Johnson Boulevard incorporates two pervious concrete bicycle lanes adjacent to two asphalt vehicle lanes. The bicycle lanes treat and infiltrate the stormwater runoff generated by the vehicle travel lanes. The roadway project also includes pervious concrete sidewalks along the length of the roadway. The planter strip between sidewalk and roadway is amended with compost to enhance its infiltration capability. The use of these techniques allows the project to meet its stormwater requirements within the roadway right-of-way. The pervious concrete used for this project is a new material with a surface texture very similar to regular concrete. The concrete has a high fines content (75%) resulting in a smooth finish for the bicycle lanes and sidewalks. This paper details our experience with the design, construction, and costs of pervious concrete bicycle lanes and sidewalks.

Building sidewalks typically triggers stormwater mitigation requirements. Sometimes the cost of creating the stormwater mitigation for a new sidewalk can exceed the cost of constructing the sidewalk. Using permeable pavements is one way to create sidewalks without triggering stormwater mitigation requirements. The City of Olympia, Washington has installed over 9,500 square yards or about three miles of porous concrete sidewalk to date, with more projects planned each year. We have experience with three different types of porous concrete materials over an eight-year period. Materials range from the regular "no-fines" porous concrete to a new form of 100 percent sand "all-fines" concrete. This paper presents the lessons learned and current state of porous sidewalk technology in Olympia. Our experience with different materials, design, construction, and maintenance is provided along with construction and operating costs.

The use of a pervious pavement can be effective as a low impact development stormwater control. The Urban Watershed Management Branch is evaluating interlocking concrete paver systems as a type of porous pavement. Although the pavers are impermeable, the spaces between the pavers are backfilled with washed, graded stone that acts as structural support for the pavers and also allows water to infiltrate. After passing the paving stones, the stormwater moves through several bedding layers where pollutants are removed. Recent literature shows that the concentration of total suspended solids in the exfiltrate is substantially less than in the infiltrate. Other pollutant constituents are subject to removal by microbial communities that develop with time. Concrete paver systems were chosen for this investigation for several reasons. Layers of the system can be removed, examined, and replaced, facilitating long-term system monitoring and maintenance. The overall objective of this ongoing project is to assess the pollutant removal efficiency of a pervious pavement system from parking lot runoff. One bench-scale study (hydraulic study) determined the flow rates and materials necessary for the full-scale experiment. Another bench-scale study (microbial study) will examine the role of microbial colonies in pollutant removal performance of this porous pavement micro-environment. Results from the two bench-scale experiments will be used to refine the full-scale investigation. This paper focuses on the hydraulic bench-scale study.

The City of Olympia has built a demonstration low impact development (LID) roadway that uses traditional pavement materials and infiltrates runoff under the roadway. Our transportation needs prompt extensive amounts of pavement with inadequate right-of-way area for onsite stormwater management. Current roadway designs conflict with the LID goal of dispersing and managing stormwater near its source. The Decatur Street LID Roadway Project is an innovative design that meets LID goals and manages its stormwater within the existing right-of-way. Under-pavement infiltration is advantageous because traditional water quality treatment and pavement construction materials can be used. This accommodates traditional maintenance and life cycle cost expectations for the above-ground roadway features. Utilizing the entire roadway area for infiltration provides designs suitable for poorly drained soils and for use with various roadway widths. This paper presents the design and construction aspects of the Decatur Street LID Roadway Project. The paper describes the three different stormwater management techniques utilized in the project. Roadway structural design is presented, including the use of geogrids for structural stability of the roadway over a subgrade of uncompacted soil. The bid prices, cost comparisons to traditional construction, and lessons learned are provided.

A permeable pavement parking lot in eastern North Carolina consisting of four types of permeable pavement and standard asphalt was monitored from June 2006 to July 2007 for hydrologic differences in pavement surface runoff volumes, total outflow volumes, peak flow rates, and time to peak, and from January 2007 to July 2007 for water quality concentrations. The four permeable sections were pervious concrete (PC), two types of permeable interlocking concrete pavement (PICP) with small-sized aggregate in the joints and having 12.9% (PICP1) and 8.5% (PICP2) open surface area, and concrete grid pavers (CGP) filled with sand. The site was located in poorly drained soils, and all permeable sections were underlain by a crushed stone base layer with a perforated underdrain. All permeable pavements significantly and substantially reduced surface runoff volumes and peak flow rates from those of asphalt (p<0.01). Of the permeable pavements, CGP generated the greatest surface runoff volumes (p<0.01). The PICP1 and CGP cells generated significantly lower outflow volumes than all other sections evaluated (p<0.01), and had the lowest peak flows and the longest time to peak. The response of the PICP1 cell was likely due to an increased base storage volume resulting from an elevated pipe underdrain; whereas, the CGP cell response was attributed to water retention in the sand fill layer. Overall, different permeable pavement sections performed similarly, but were substantially different from asphalt. Subtle differences in the performance of CGP were primarily due to the characteristics of the sand filled media compared to small aggregate typically used in PC and PICP joints and bedding. The pH of permeable pavement subsurface drainage was higher than that of asphalt runoff (p<0.01) with the PC cell having the highest pH values (p<0.01). Permeable pavement subsurface drainage had lower NH₄-N (p<0.01) and TKN concentrations than asphalt runoff and atmospheric deposition. With the exception of the CGP cell, permeable pavements had higher NO_2,3-N concentrations than asphalt (p<0.01), a probable result of nitrification occurring within the permeable pavement profile. The CGP cell had the lowest mean TN concentrations; however, results were not significantly different from those of asphalt runoff. Overall, different permeable pavement sections performed similarly to one another with respect to water quality, but the CGP cell appeared to improve stormwater runoff nitrogen concentrations.

Stormwater management infrastructure and its associated costs are now compulsory in commercial development and increasingly common across a wide array of residential construction. Rainwater and site water harvesting is fast becoming a staple in sustainable developments and green building design and construction, and is a key tool in Low Impact Design. Typical implementations of the two involve simply adding harvesting infrastructure into the drainage profile of the required stormwater management systems for the site, thus imparting the full incremental cost of the harvesting system on the project. However, new, innovative techniques for integrating these systems allow for substantial savings on the combined cost — potentially as much as 50% — due to application of progressive design concepts and use of newly developed control systems to manage the interaction of these systems. The result is no less than a paradigm shift in the way sustainable site water management designs will emerge in the future, where the double benefit of water conservation and stormwater management can be achieved at a minimized cost — often close to the cost of the stormwater infrastructure itself. This paper presents design concepts and techniques for incorporating this integrated approach in site stormwater design, which can result in a new tool for LID practitioners where water conservation is a key objective along with compulsory stormwater management designs.

A spreadsheet model was developed to examine the capacity of rainwater harvesting (RWH) to mitigate the effects of urbanization on the pre-development water balance of a suburban neighbourhood. Simulations showed that RWH in a residential lot or neighbourhood moved the runoff and evapotranspiration components of the area's water balance toward their pre-development proportions. Other rainwater management strategies are needed in conjunction with RWH to manage runoff volumes and maintain pre-development groundwater recharge for the development scenarios considered. The spreadsheet model was useful in determining the extent of RWH implementation desirable on a water balance (or receiving water) basis. It can also provide input to larger, more sophisticated models capable of simulating the linkages between urban areas and receiving streams.

Due to recent concerns over the environmental impact of stormwater runoff and increased water demands, interest in rainwater harvesting systems has developed in humid, well developed regions, such as the southeastern United States. In order to better understand the anticipated usage and reliability of rainwater harvesting systems in the southeastern United States, a monitoring study was conducted at 3 rainwater harvesting systems in North Carolina, measuring cistern water levels and rainfall. Results of the monitoring study showed that the rainwater harvesting systems were typically underutilized. Water usage was most consistent at the location where harvested rainwater was used to flush a toilet; however, the water level within the cistern only dropped below 80% of capacity on one occasion during the 30 month monitoring period. A computer model was developed to simulate the performance of rainwater harvesting systems based upon historical rainfall data and anticipated usage by evaluating a daily or hourly water balance. The rainwater harvesting computer model was used to simulate the performance of a 55-gallon (208 liter) rain barrel commonly used by homeowners in this region to meet household gardening demands. A variety of turfgrass irrigation scenarios were examined, varying the size of the irrigated area and contributing rooftop. Simulation results showed that the rain barrel was not able to adequately meet irrigation demands. The low volume of water the rain barrel was able to supply for irrigation and the large amount of overflow indicated that the rain barrel was not able to effectively utilize the potential water supply coming from the rooftop and provided minimal runoff volume reduction.

On basis of a bigger drainage area, the fundamental standard for rainwater harvesting quantity should improve or amend water circle system and eco-environment, with the suitable runoff closed to the natural catchment condition after rainwater harvesting. For rainwater harvesting systems of some smaller watershed the suitable and economical harvesting volume is important. In other special situations integral stormwater management practices with higher efficiency should be adopted to achieve required bigger design return period. When water demand compared with the runoff in a given project is greater, the volume of a rain tank could be determined with a 24h rainfall, and rainfall return period for design should not lager than 0.3 years, and design storm rainfall should not lager than 50mm for all cities in China, or using water quality volume for design storm instead. When runoff in a practical project is sufficient with small daily water consumption, the storage volume could be designed according to water quantity for 5 days water consumption. For those projects with artificial water body with great storage capacity, the storage volume should be confirmed by water balance analysis on the basis of an average year.

Manmade lake facilities have traditionally been considered ornamental and landscape features primarily serving aesthetic purposes in golf courses, parks and residential developments. However, properly design lake system can be applied with innovative design elements to function as primary infrastructure facilities in urban developments, replacing typical stormwater facilities and adding value to the community. These specialized types of manmade lake systems integrate a living ecosystem into an urban environment, which maintains water quality through natural biological processes. Planned lake features integrated into the land plan, particularly in semi-arid areas, offer a combination of many unique advantages for storm water management as well as other benefits that are not available in conventional engineered systems, including: (1) continuous year-round natural treatment process, (2) storm water conveyance and storage, (3) exceptional water quality, (4) flood protection, (5) combined landuse elements, (6) significantly reduced infrastructure costs, (7) dry weather flow treatment, (8) landscape and aesthetic treatment with natural water system, (9) increased surrounding land values, (10) natural ecosystem benefits, (11) recreational design feature, and (12) urban design element for communities.

When urban regions gradually expand due to regional development, centralized sewage collection, treatment, and disposal systems are often unavailable for both geographic and economic reasons. As a consequence, about a quarter of the residences in the United States relied on decentralized treatment of wastewater. Household wastewater contains high concentration of nutrients (mainly nitrogen and phosphorus), disease-causing organisms and viruses, and some toxic chemicals. Nation wide, wastewater effluent from on-site wastewater treatment (OWTS) can represent a large fraction of nutrient loads to groundwater aquifers. Phosphorus and nitrogen compounds are the most frequent measurements to indicate nutrient loadings. Some aquifers may discharge into springs or other surface waters adversely affecting public health. Hence, on-site wastewater effluent disposal has contributed significant adverse impacts to the dynamics of the natural environment. Nowadays, scientists, engineers, and manufacturers in the wastewater treatment industry have developed a wide range of alternative low impact development (LID) technologies designed to handle increasing impact in OWTS. This paper aims to present an innovative design of using a subsurface wetland system with unique growth media and pollution control media to grow three types of plant species that have higher uptake rate of nutrient to polish the effluents from septic tank systems. A control case was prepared for comparison. The pilot plant is up and running at University of Central Florida (UCF).

Gravity-flow compound ecological filter bed was a kind of environmental bioremediation technology, which based on constructed wetlands and was characterized by high hydraulic loading, more effective treatment, lower energy consumption and more economical. For those advantages, gravity-flow compound ecological filter bed technology was applicable to treat polluted urban river in china. In the treatment project of Dasha river in Shenzhen China, gravity-flow compound ecological filter bed technology was adopted, combined with photocatalytic technology and ecological river bank technology. The application results showed that all kinds of pollutants in upstream river water were removed in various degrees by the treatment of gravity-flow compound ecological filter bed system. Under the hydraulic loading of 1.5m⋅d^–1, the removal rate of NH₃-N, TP and CODcr pollutants were above 60%, 55% and 50%, respectively, and river water quality was improved significantly.

Lawrence Technological University is a private university located on a 120-acre campus in highly urbanized Southfield, Michigan (Detroit Metropolitan Area). The campus was primarily developed over the last several decades with limited or no stormwater controls as was customary with regulations of the time. However, an updated campus master plan (2003) and the opening of a student services center in 2005 provided the opportunity for the campus to commit itself to green design and the use of low impact development (LID) techniques. The 40,000 square-foot A. Alfred Taubman Student Services Center (Center) consolidated all student service functions under one roof and provided a unique opportunity to showcase sustainable and energy efficient technologies. As such, the Center provides a living laboratory for Lawrence Tech architecture and engineering students, local municipal officials, community planners, and design engineers to learn about LID techniques and LEED certification. Concurrently, University officials reviewed the existing stormwater system and identified areas for retrofit with innovative stormwater best management practices (BMPs) and LID techniques.

Low Impact Development (LID) is a modern sustainable design approach that is currently being embraced as an efficient stormwater management practice by a wide range of regulatory agencies. By retaining and infiltrating (or filtering) runoff at the source, this approach promises a reduction of peak runoff rates, volumes, and pollutant loads. Although LID is becoming widely accepted, additional research is required to further develop the understanding of its effectiveness as a stormwater management approach. An effective method for enhanced understanding is through the development, observation, and monitoring of case studies where LID is employed as a stormwater management strategy. Such is the case at a remote auxiliary military installation, Pillar Point Air Force Station (PPAFS), located in Half Moon Bay, California. This paper documents an effort by the United States Air Force (Air Force) to implement LID concepts to minimize impacts of a storm water discharge from PPAFS to the Pacific Ocean. The effort was initiated in response to a waste discharge prohibition of the California Ocean Plan (COP) and the fact that the discharge is into a sensitive habitat, designated in California as a Area of Special Biological Significance (ASBS). The project has required an extensive understanding of the regulatory requirements of governmental agencies, environmental concerns of non-governmental organizations, and various interests of local stakeholders. Several engineering alternatives were considered as corrective actions and a thorough selection process was undertaken to engage interested stakeholders and determine a preferred alternative. Although this process is ongoing, the LID concept has been vetted as the primary focus of the preferred alternative. This project will provide a unique opportunity to develop, observe, monitor, and evaluate the effectiveness of a specific LID design. Additionally the COP waste prohibition affects hundreds of discharges along the one third of California Coastline designated as ASBSs; this effort will set a precedent for other dischargers as an efficient and relatively cost effective way to address COP compliance.

Low Impact Development (LID) projects have similar universal goals — maintaining or limiting impacts to the site's original hydrology and reducing water quality impacts — but differences in topography, soils, vegetation, and other project goals may result in projects that appear to be dissimilar, at least on the surface. Two case studies in North Carolina — one in the mountains, and one at the coast, are explored in detail, highlighting how local constraints and project goals shaped the outcome of the projects. Drover's Road Preserve in the North Carolina mountains is a rural large lot residential development on a 186-acre site that draws on conservation planning and source prevention methods for water resource protection. A notable feature of the site is the use of a large conservation easement, placing the highest risk areas of the development into permanent protection. Tonbo Meadow is located in coastal North Carolina in Wilmington, and is a 3.2 acre site with 10 single-family homes. Several variances were sought and granted, allowing the site to reduce its impervious footprint, while the judicious use of innovative stormwater BMPs allowed the site to further reduce hydrologic and water quality impacts.

The District of Columbia storm water management regulations established in 1988 now require mitigation of storm water run off where construction and or 5000 sq/ ft of earth disturbance occurs. As in many municipalities in the Mid-Atlantic seeking to meet requirements of the Clean Water Act (CWA), and the Water Quality Amendment in 1987 to the CWA, the District of Columbia began employing Storm Water Best Management Practices (BMPs) for the treatment of storm water run-off. BMPs have typically been "end of pipe" proprietary devices, underground vaults, modified manholes or filtering practices for water quality treatment and even larger under ground vaults, reinforced concrete, and metal or plastic pipes for storm water quantity control. While the district was a pioneer in the use of underground sand filters for the treatment of storm water in ultra urban settings and continues to approve and install these devices, as well as other subterranean vault and manhole BMP, the city is turning to Low Impact Development (LID) practices which have began to gain more prominence in the development community. This paper investigates publicly financed and implemented LID projects in the District of Columbia and will discuss the types of problems that have occurred and the "lessons learned". Biomass mortality, aesthetics and function, as well as hydraulics and maintenance are blamed for most problems. Two LID retrofits are included in the case study and analysis focusing on a bioretention cell (including cost and monitoring data), as well as a retrofit application of various types of pervious pavers.

This presentation will discuss on-going efforts to coordinate stormwater management approaches with fish and wildlife mitigation strategies to open the door for more natural, cost-effective mitigation approaches in an ultra-urban highway improvement. These approaches can be realized through improved interaction, collaboration, and communication between scientists, engineers, and policy makers. It also relies on more focused technical analyses and effective communication of results to stakeholders. The principles are simple: identify the most cost-effective strategies for stormwater management, water quality improvement, and stream habitat mitigation; recognize the opportunities that regional growth can provide for funding infrastructure improvements; and identify stakeholders who have the potential to directly gain through participation. The effort can result in an integrated resource management strategy, not from a menu of BMPs but custom fit to the specific character and needs of a basin, to protect and restore habit while meeting the stormwater management goals for the basin.

This paper describes the design concepts being developed for the proposed Lincoln Center site in New Castle County, DE. This project consists of a 56 acre parcel which is being developed as a mixed use commercial, office, and residential center. The project is unique in that it will feature a wide range of innovative LID practices as well as some traditional BMPs. This paper focuses on the site analysis and how the site characteristics dictated the selection of the range of BMPs. In addition this paper will describe the interim guidelines that the County is developing to address the stormwater components of the innovative LID practices.

When Wal-Mart selected a site for a new Supercenter in Nashville, North Carolina, initial building plans were rejected by the Army Corps of Engineers and the North Carolina State Division of Water Quality due to adverse wetland and stream impacts. However, project engineers were able to partner with the North Carolina State University Stormwater Team to create a low impact development design that incorporated permeable pavement, bioretention, and stormwater wetlands to lessen the water quality impact of the project and gain approval from the Corps and the Division of Water Quality. The Wal-Mart now has 5,890 square meters (63,400 square feet) of permeable concrete, eight bioretention beds, and two stormwater wetlands. The site will be monitored for water quality impacts for 18 months following completion of construction. This case study will track the evolution of the design and the construction of the BMPs from initial site selection to store opening over the course of 18 months.

Strategies of Low Impact Development (LID) are best known as alternative treatment systems to reduce the impact of storm water runoff on the environment. A more important aspect of LID is the implementation of Environmental Site Design (ESD). ESD is a design process to evaluate the environmental conditions on a parcel of land prior to the creation of a land development project. This process is most important for residential developments. While ESD can work with any land use regulations, the most environmentally sound developments will occur in those communities, whose land use regulations that permit "cluster" or "open space" designs. Trade Winds Farm is a case where the land use regulations and the application ESD created an environmentally sound residential project.

Environmental policies do not normally have widespread use until states require local governments to implement them. Emerging state-level requirements for Low Impact Development (LID) indicate that LID is reaching that stage in the process. Tetra Tech researched LID-related state policies and found requirements that could achieve LID at the local level and others that achieved LID principles but not a true, or holistic, application of LID. Delaware, Maryland, and New Jersey have LID-related requirements, either in place or under development, that can lead to a holistic application of LID. Where state requirements fall short of requiring LID holistically, a number of policy tools are available to local governments for expanding on state requirements. These policy tools are reviewed for use in both complying and expanding upon state LID-related requirements.

In the development of the District of Columbia's Combined Sewer System (CSS) Long Term Control Plan (LTCP) during 1998 – 2002, the use of low impact development (LID) technology became an important consideration. D.C. Water and Sewer Authority (WASA) had established a `Stakeholders' group to seek assistance in developing the CSS LTCP. Some members of the group insisted that rather than the traditional engineered solution, LID should be the way to solve combined sewage overflow (CSO) problem. The debate, the regulatory constraints and the current LID technology drawbacks, the final CSS LTCP, the LTCP related LID plan, difficulties in adhering to the municipal separate storm sewer system (MS4) national pollutant discharge elimination system (NPDES) permit's water quality compliance requirement with LID, etc., reveal serious challenges to the widespread use of LID in wet-weather water pollution control subject to regulatory requirements.

The State of Delaware is currently undergoing the first major revision of its Sediment & Stormwater Regulations since their inception in 1990. It is hoped the proposed revisions will apply the many lessons learned in the interim to better protect our soil and water resources while at the same time improving the regulatory process itself. One of those lessons involved the release of Delaware's "Conservation Design for Stormwater Management" document in 1997. This document provided guidance to land use planners and civil site design consultants in the application of conservation design principles to meet regulatory stormwater management requirements. One of the key components of this approach is the move away from methods that merely detain excess runoff volume and release it at a predevelopment rate to a more holistic approach that attempts to mimic the predevelopment hydrology. The goal of mimicking predevelopment hydrology is certainly laudable. However, Delaware's experience has been that it is difficult to achieve, particularly at the watershed level. While some projects may have the right mix of physical site characteristics to be able to match the predevelopment hydrology, most do not. As a result, attainment of the goal becomes the exception rather than the rule. This is anathema to a regulatory program, often requiring the granting of variances, waivers, or lowering of standards in order to gain compliance. As Delaware's regulatory program shifts from a site-based approach to a watershed-based approach, it is recognized that a more realistic goal must be set so that compliance becomes the norm. The rest of this paper will describe a watershed management optimization approach as currently proposed by the State of Delaware. This approach would mimic watershed processes and employ LID and other non-structural solutions where they are most appropriate in the watershed, rather than relying on a "one-size-fits all" solution.

There is a tendency among low impact development designers to think that any project that uses practices and facilities from the low impact development (LID) toolbag qualifies as a low impact project. But, for over three decades, the literature relating urbanization and stream impacts leads us to believe that this may not always be so. The near total destruction of stream habitat often occurs when a watershed reaches effective impervious surface percentages between 10% and 20%. Moreover, studies suggest that the steepest decline in habitat quality begins with the first few percent of forest converted to effective impervious surface. But, before the first square foot of impervious surface is placed, impacts on streams are observed when a watershed is simply cleared or partially cleared. Moreover, streams are particularly sensitive to clearing in the riparian zone. Thus, in order to qualify development as "low impact" it must preserve the characteristics of a healthy watershed. A standard for low impact development must at minimum include limitations on clearing, impervious area, and buffer disturbance. This paper will focus on a standard for development based on the first two limitations. The standards discussed in this paper are aimed at areas which in the pristine state were forested. Although it is a temptation to say that the same principals would apply to prairies and other landscapes, the data is not at present available to say with certainty.

The path to adoption of Low Impact Development (LID) regulations is often a mine field of competing interests, with very little perceived common ground between the various stakeholders. There is often skepticism on the part of town planners, wetland agents, town engineers and design engineers on how to design and evaluate LID storm water treatment systems. Public Works Departments are greatly concerned about how to maintain LID systems over the short and long term and believe that their municipality will have increased liability if the LID systems fail. Developers and land owners, even those who want to build an environmentally sound project, think twice about using LID systems because it appears to them to be a new and therefore, questionable technology, not proven in the real world. Land use commissioners are hesitant to approve storm water treatment systems that don't have a long track record of working in the real world. But, on the other hand, when knowledgeable people are passionate about their town and LID, good things can happen.

The enthusiasm and demand for stormwater management using "softer" stormwater management techniques has been growing rapidly in Seattle. Seattle Public Utilities' Low Impact Development (LID) program was formed to meet, cultivate and help direct that enthusiasm. Within the last couple years our LID program has implemented numerous new policies and programs to encourage implementation of green stormwater infrastructure by private property developers and owners, as well as allowing the Utility to better evaluate use of Green Infrastructure for solving business area need. This paper provides an overview of the tools in place for new construction and retrofit using the Green Stormwater Infrastructure toolbox.

This paper discusses collaboration for change management of stormwater management in the right-of-way. The cultures of Seattle Public Utilities (SPU) (i.e. stormwater management), Seattle Department of Transportation (SDOT) and Department of Planning and Development (DPD) have historically been very different. The three departments are now key partners in the implementation of Green Stormwater Infrastructure (GSI) such as roadside bioretention systems and permeable pavements. To encourage the implementation of LID throughout Seattle, the City is lowering the barriers through several angles and departments: SPU is updating the stormwater code; SDOT, with SPU input, is updating the Right of Way Improvement Manual; and DPD is implementing new landscaping requirements, tree protections, and a coordinated review process for green building projects. Traditional planning, design, construction and maintenance are all being reinterpreted. In combination, Seattle is innovating a green toolkit via a series of regulations, design details, procedures and policies that simplify building green in the City. This paper focuses on the greening in the right-of-way and associated overlap from private properties; starting from the outside edges of the right-of-way.

Beginning in 1990 the U.S. Environmental Protection Agency (EPA) expanded its National Pollution Elimination System (NPDES) to include certain stormwater flows and require an NPDES permit for such flows. The NDPES program added a permit requirement for additional stormwater systems in 1999. NPDES permits for regulated stormwater systems are subject to the Total Maximum Daily Load (TMDL) requirements of the Clean Water Act. The TMDL requirements place limits on the amount of pollutants of concern that can be approved by NPDES permits if a water segment does not meet its water quality standards. Florida laws for protection of water quality extend stormwater permitting well beyond the threshold required by federal law. Florida implements state water-quality protections through various statutes and rules, including the Environmental Resource Permit (ERP) programs of Florida's water management districts. The ERP programs require many proposed private development projects to secure permits that include review of their proposed stormwater systems. Both the federal permitting and Florida's ERP programs contain stricter regulatory requirements for proposed systems in an area with existing water quality violations.

This paper will highlight key findings of a Water Environment Research Foundation (WERF) research study of the factors that contribute to the success of a BMP beyond its engineered performance. As a foundation for this research, the multi-disciplinary project team, consisting of Tetra Tech, Inc., and Wenk Associates Landscape Architects, convened a panel of experts in stormwater engineering, policy, and landscape architecture to examine some of the issues related to BMP implementation and to identify key factors for success. The team also researched case studies from twelve U.S. cities that demonstrate some of these key factors.

Transdisciplinarity has recently gained favour as an effective strategic approach when dealing with complex environmental issues. The following discussion will show by example how the Urban Stormwater Quality Management (USQM) industry, dealing with a specific aspect of waterway health, has adopted transdisciplinary theory and is moving towards securing a paradigm shift in the way water quality for waterway health is managed. Melbourne Water is seeking to work with local government in a different way from the multidisciplinary relationship that has traditionally divided the public realm. The work is being undertaken as part of the Yarra River Action Plan which has set aside $20 million aimed at water quality improvement throughout Melbourne Water's region of jurisdiction. Melbourne Water's Stormwater Quality Programs work in partnership with thirty eight local governments in and around Melbourne. These programs aim to change the way local governments manage urban stormwater runoff. Each of these thirty eight organisations is at a different stage of change, examples of which will be drawn upon to demonstrate a transdisciplinary process of change towards sustainability in USQM.

This paper describes a strategy that establishes a framework for sustaining ecological functions and processes in high density urban sprawl areas. Traditionally, city planning in China is organized around the placement of construction land. Taking Hefei city in China for example, the non-traditional urban planning strategy developed herein is to prioritize the arrangement of non-construction areas by means of hydrological and ecological processes simulation, and to incorporate factors such as urban flood control, stormwater management, and indicator animals. This research has reached the following main conclusions: (1) Sustaining ecological processes in high density urban sprawl areas should be analyzed and solved using a holistic and multi-objective approach; (2) Urban planning should systematically integrate ecological processes with regulating landscape structure, and prioritize the arrangement of non-construction areas; (3) The approach presented herein makes the best use of local natural resource to solve various ecological problems, effectively maintaining the health of urban and regional natural systems, enhancing the services of natural systems for city and local residents, and reducing construction capitals.

It is widely acknowledged that all land development has impacts on the environment. In the past 10–15 years, the adverse impacts on water quality have become very significant. Many of the water quality impacts are associated with non-point sources of pollution. Many municipal land use commissions now must deal with the changes in various chemical pollutants that occur from the typical development project. In addition, they must evaluate how efficient the storm water treatment system(s) are in the removal of the various pollutants in order to meet treatment goals. The pollutant loading analysis is one tool that can be used for these analyses.

This paper presents the elements involved in the hydraulic and hydrologic analysis of bioretention systems as an integrated part of an urban retrofit project. The system was modeled using HydroCAD, a design storm (DS) event modeling software, as well as SWMM 5.0.013, a continuous simulation (CS) software. The resulting response to a series of design storms was computed by both of these models to provide a comparison between the methods. The resulting SWMM model was then run on the design year rainfall distribution. Even with an infiltration rate of less than half inch per hour, nearly 92% of all runoff was intercepted and infiltrated by the system with a surface area less than 2.5% of its contributory impervious area.

Traditional hydrologic analysis involves simulating a single design storm event for a specific site and using a "peak flow standard" to match the absolute hydrograph peak of pre- and post-development scenarios. Experience with this type of regulatory scheme reveals several problems. Use of a "flow duration standard" and regional-scale detention ponds eliminates many of the known shortcomings while providing better regional planning and protection of aquatic resources. Typically, applications of flow duration standards have involved use of regionally calibrated, HSPF-based hydrologic modeling. Until recently the weakness of this type of application has been the regional calibration. Unfortunately, jurisdictional boundaries typically don't follow watershed boundaries and variations occur due to soil, slope, elevation and others. In addition, the quality of aquatic resources varies spatially as impacts to these resources occur at various time and size scales. The limited financial resources of stormwater management agencies suggest that a more strategic application of funds is required to ensure the most appropriate use of capital. The Flow Duration Design Model allows tailoring model simulations to specific subbasin characteristics. It also incorporates a concept of "target conditions" rather than predevelopment or old-growth-forest conditions. These characteristics allow the model to be tailored to specific community and resource needs depending on constituent goals. In addition, the model incorporates the ability to simulate various low impact development (LID) techniques, such as porous pavement or amended soils. Collectively, these features allow the model to be integrated into and support specific objectives of watershed action plans, even when these action plans differ due to physical watershed differences or jurisdictional goals.

A watershed plan had been prepared by The Conservation Foundation, a non profit environmental group, for the approximately 53,500 hectares (206 square miles) DuPage River suburban watershed near Chicago. The plan needed to be updated to meet USEPA's newer watershed plan guidelines to include information on expected pollutant load reduction, proposed BMPs necessary to meet that load reduction and the estimated cost to implement the selected BMPs. Due to the limited analysis budget, the WinSLAMM program was used to approximate existing and proposed total solids and phosphorus load reductions for two sub-watersheds and the results were then scaled up to the entire watershed. The costs of various BMP combinations were compared to the expected removal efficiencies to help local officials to choose the most cost effective BMPs. Local municipal officials assisted in the selection of BMPs that would be socially and technically acceptable.

Most urban watershed models developed to comply with various regulatory programs can only be used to approximate LID implementation in their existing configuration. These models were developed in order to simulate flow through the thousands of acres that together make up each water pollution control facility (WPCF) service. Consequently, the resolution of the original models is relatively coarse. For example, tens of square blocks are aggregated into single hydrologic units called subcatchments, and only the WPCP's head works, interceptors, major trunk sewers, and large diameter sewer pipes are included in the sewer network. Because of these approximations, and the fact that LID technologies would alter flow patterns and pollutant mobilization rates within the large-scale subcatchments, LID retrofits cannot be directly simulated in many existing urban scale hydrologic and hydraulic models. This paper will present initial work on the development and calibration of a high resolution hydraulic and hydrologic model that is being used to simulate the impact of low impact development retrofits on wet weather flowrates in the combined sewer system of a dense urban watershed. The two-block, Bronx, NY study site was selected due to its location at the hydrologic edge of the sewer service area, and also because of the extent to which its soils, slopes, open space, and building stock and vintage reflected average values for New York City, as confirmed using various statistical analyses. In the model, developed using SWMM 5.0, separate subcatchments are defined for each roof, sidewalk, backyard, and street present in the study area. Realistic routing is also incorporated in the hydrologic representation. Model calibration is accomplished by systematically varying subcatchment properties and comparing time series flowrate predictions at the downstream end of the study area with actual sewer flow observations, using precipitation time series also measured on site. The subcatchment attribute combinations associated with all sets of predictions are recorded, and parameter regions associated with reasonable and unreasonable predictions are identified. Presented are some initial attempts to simulate the effects of green roof retrofits on the outflow hydrograph from the study site. A discussion of how the resolution of subcatchment discretization affects model predictions is also provided.

LID (Low Impact Development) practices, such as, green roofs, bioretention swales, rainwater cisterns, rain gardens, compost amended soil, and permeable pavement can be used to reduce stormwater runoff and return urban creeks to more natural conditions. Continuous simulation computer modeling of LIDs has been achieved by adding the ability to represent these practices in the Western Washington Hydrology Model version 3 (WWHM3), developed for the Washington State Department of Ecology (WSDOE) by Clear Creek Solutions, Inc. WWHM3 uses HSPF continuous simulation hydrology to model LIDs. This paper and presentation focuses on analysis considerations when modeling LID permeable pavement, impervious runoff dispersion, green roof, rain gardens, and bioretention swale practices in Western Washington. Issues related to the Western Washington seasonal rainfall patterns and evapotranspiration, native soil infiltration rates, and the use of underdrains are presented. WWHM3 stormwater modeling results demonstrate the feasibility and limitations of using LIDs to meet Washington state NPDES permit requirements for new land use development.

This paper presents a methodology to measure the impact of stormwater controls on the receiving stream using a series of discrete events to represent the long-term hydrologic regime as a simpler alternative to continuous simulation. Hydromodification impacts on channel morphology are best evaluated using flow and shear stress duration curves, which typically require continuous simulation. The methodology proposed herein allows the development of these duration curves using discrete events. The methodology was tested in a hypothetical development in the City of Columbia, Missouri. Design assumptions were made for a typical residential development and a typical stream. Various stormwater controls were designed for this site, including conventional detention, a water quality volume and channel protection volume basin, and bioretention. The outflow from each design scenario was analyzed to determine the effectiveness of different levels of stormwater controls. The objective was to compare the effect of each scenario using duration curves to measure its ability of mimic the original hydrology. The study indicates that LID most closely replicates the original regime and that detention provides some benefits when water quality and channel protection are included, although its effect does not reproduce the original hydrology. Detention criteria based on extreme events, such as the 100-year storm event, are ineffective for this purpose.

As part of the 2008 City of Seattle stormwater manual update, a simplified approach was developed for sizing parcel-scale facilities to meet the revised flow control requirements. The simplified, or "pre-sized", approach provides a relatively easy process for designers to select and size flow control facilities for smaller projects without the need for continuous flow modeling. In conjunction with a City-wide emphasis on sustainable designs, the approach prioritizes green stormwater infrastructure over traditional facilities, with an emphasis on retaining existing trees and implementing infiltration to the maximum extent feasible. Green stormwater infrastructure BMPs in the Pre-Sized Approach include retained trees, new trees, permeable pavement, green roofs, dispersion, bioretention facilities, cisterns, and bioretention planters with underdrains. The flow control benefits for each of these BMPs were quantified either as flow control credits (impervious surface reduction credits) or sizing factors (relating the facility size to the impervious area mitigated). Credits and sizing factors were developed for each of the City's flow control standards and typical facility design variations. A Pre-Sized Approach worksheet was developed to guide the designer through the process of selecting and sizing facilities. This worksheet provides guidance for flow control calculations and serves as documentation for project submittal.

North Carolina has an abundance of natural resources and a climate that has helped make it one of the fastest growing states in the nation. With the growth and the jobs, comes the challenge of protecting the environment and quality of life that makes it such a desirable place to live. This is especially true for the 20 coastal counties, where stormwater policies are being updated to protect shellfish habitats and enhance water quality. In theory Low Impact Development (LID) practices are one means to achieve high water quality standards, but until recently guidance for implementing this type of program at any level has been scarce. To that end the North Carolina Coastal Federation (NCCF) with National Oceanic and Atmospheric Administration (NOAA) grant funding and contributions from three jurisdictions: the City of Wilmington, New Hanover County, and Brunswick County, spearheaded the development of LID specific stormwater design manuals and a spreadsheet based modeling tool for each local government. The model was developed to assist engineers and developers with the permitting and approval of LID stormwater management plans as well as act as a tool for the reviewing agencies to use in the approval process. Withers & Ravenel worked with the NCCF and the three local governments to tailor the model to meet specific requirements of each jurisdiction, combining the governmental needs with the calculation requirements of the engineer.

Implementing watershed stormwater Best Management Practice (BMP) aims to mitigate the effects of storm runoff changes attributable to site improvements in a watershed. The BMP itself is an ongoing stochastic process when the BMP devices are installed at various times. In the process, the BMP is treated as a stochastic intervention that can be detected as a long term impact on the watershed drainage system.

Stormwater practices are being installed across the world and studies show they are not being properly inspected and maintained. If not properly maintained, stormwater practices will not perform as intended, but minimal guidance on maintenance procedures is available. In North Carolina, U.S.A., the North Carolina State University Cooperative Extension Service has developed a 1.5 day training and certification program that has certified approximately 500 design, local government, and landscape maintenance professionals and practitioners in stormwater practice inspection and maintenance. To date the response has been very favorable, as several communities now require the certification for anyone who designs and/or maintains stormwater practices. Officials with the state of North Carolina have incorporated designing for inspection and maintenance as part of their stormwater practice review.

To better understand low impact development (LID) implementation under alpine conditions in the Truckee River Watershed, CA, the Truckee River Watershed Council (TRWC) contracted Geosyntec Consultants and Lynell Garfield of Integrated Balance Solutions Consulting to conduct LID workshops. TRWC also requested assistance in the planning and design of two LID demonstration projects in a new residential development. One of the workshops included a field tour of one of the demonstration projects to demonstrate and discuss real world challenges in designing, constructing, and maintaining LID practices in the watershed. This paper discusses: (1) the experience gained designing and conducting the training workshops and field tour, (2) the experience gained assisting the landscape architect and contractor with the demonstration projects, (3) the successes and lessons learned from the workshops and demonstration projects, and (4) recommendations for future LID efforts in the watershed.

This paper describes some innovations, challenges, and success stories with practice of Low impact development in different parts of the world. The paper begins with how LID is defined and used in different countries, the local settings, the types of problems addressed and the development process. The challenges presented are in terms of how to bring LID to prime time as well as in implementation. Background information concerning the uses, ownership and associated costs for LID measures compiled from many countries are also presented. A number of case studies that represent the best examples of projects that use LID concepts for stormwater management in Europe and Australasia are presented. Finally, the paper makes sense from all the available data and discusses the remaining challenges in LID.

Using rain garden to reduce small catchments area stormwater is very effective for runoff volume reducing, peak rate control and pollution control in ultra urban land use such as Beijing. A design method based on water balance and Darcy's law was put forward in this paper. And then a hydrologic evaluation method was illustrated, including the reductions calculation in runoff volume, peak rate and the total pollutants. A typical rain garden was built in Beijing in recent years, under which, the slag and local sand soil as primary material are installed. It mainly treats the stormwater from small catchments area such as roofs and pavements. Taking Beijing urban area for example, the areas of rain garden were calculated when the return periods and effective depths were various. The method and results provide a foundation for the multi-purpose rain garden design.

The Auckland Regional Council (ARC) is piloting a programme that awards Innovative Grants to land developers to include Low Impact Design (LID) into land development. The intention of the grants is to ensure the inclusion of LID early in the design phase, allow the ARC to participate in the design and option selection process, identify issues with implementing LID, and develop demonstration projects and case studies in the Auckland region illustrating how LID can be applied. Case studies will help increase capability in the design and development industry, in turn leading to improvement in LID uptake and improving the understanding of LID by Regional and Territorial Authorities (local governments) staff and developers. Seven grants were awarded with different LID methods applied. Initial outcomes indicate positive results, demonstrating that a LID Innovative Grant programme can succeed in increasing the awareness and uptake of LID within the Auckland region.

The Auckland region is New Zealand's most populous region (1.4 million) and concentrated urban centre, growing at a rate of 63 people per day. The region is confronted with a number of challenges, which can be grouped into five main categories: (1) responding to climate change, (2) doing more with less, (3) capitalising on global economic change, (4) managing population growth and demographic change, and (5) addressing disadvantage. Moreover, within the Auckland region, stormwater is recognised as having the largest impact on the freshwater and marine ecosystems with flow-on adverse impacts on the social, cultural and economic values of the regional community. To respond to these challenges, the Auckland Sustainability Framework (ASF) was developed. Low impact design / low impact urban design and development are stormwater and urban design management approaches that support ASF objectives and improve stormwater outcomes. In this paper, the ASF and low impact design are explained against the backdrop of growth, urbanisation (i.e., land development, re-development and urban intensification) and other pressures faced by the Auckland region.

The Canadian Water Network sponsored a 2-year knowledge translation project to review innovative stormwater management initiatives that are taking place across Canada. Three workshops were held in Vancouver, Calgary and Toronto that featured innovative stormwater practices in the different cities. The results showed that there are considerable differences in the performance of best management practices (BMP) depending on topographic, climatic, and land use conditions. The most important lesson is that no single BMP is sufficient and a wide range of practices need to be considered and integrated within a watershed context. The first step is to focus on rainwater management at the individual property level and then to scale up to the neighbourhood and watershed level. Using a water balance model allows a property owner to determine the amount of rainwater that needs to be collected, reused, detained, and infiltrated on site to prevent surface runoff. There are several on-site management options that can be used in combination, including roofwater collection and indoor/outdoor re-use, green roofs, rainfall interception by trees, minimizing impervious surfaces, developing rain gardens, and requiring at least 30 cm of topsoil on the property. At the neighbourhood and watershed scales the transportation networks should be linked to infiltration systems, swales, detention ponds and wetlands. The main emphasis is to minimize the use of conventional stormwater pipes and not to convey stormwater directly into streams. Infiltration systems have proven to be popular and effective in reducing stormwater peak flows but their effectiveness in detaining non-point source of pollution is still a major issue. This is a particular problem during the winter period and during snowmelt in central and eastern Canada where road salt and pollution from transportation systems cause significant challenges. There are considerable research needs to measure the effectiveness and long term performance of these detention systems in terms of pollution reduction under different climatic conditions.

Stormwater management on Department of Defense (DoD) installations must balance technical requirements for environmental compliance and control against the potential for logistical and other impacts to the Base mission. U.S. military installations in Europe must comply with regulations implemented both at DoD and Host nation level, addressing key elements, such as segregation of runoff from areas with different pollution potential; and protection of drinking water sources and receiving water bodies. Drainage infrastructure commonly in place include combined sewer systems and use of infiltration pits. These older practices do not comply with the newer standards and need retrofitting. Solutions for military installations require low O&M impact, landscape integration, and optimal land use. Sustainable stormwater management solutions, like Low Impact Development (LID), possess such qualities and can be implemented separately or integrated with conventional treatment techniques. Preliminary studies conducted at U.S. installations analyzed the available data and identified critical action areas and feasible solutions. A set of selected pilot projects were designed and implemented. Based on the positive results obtained, Stormwater Management Plans are currently being developed at Installation level. This paper explores the application of LID technology to manage stormwater runoff in a military installation, from the definition of management criteria, to the implementation of specific pilot projects, till the design of the large scale solution.

There are many approaches and tools available for `sustainability assessment'. These share a common foundation in that they take a number of base pillars, invariably including: social, economic and environmental considerations or some variant thereof. The difficulties lie in how these can be combined to make a sustainability assessment (i.e. integrating non-commensurate factors). The current consensus for this is that the information collected in the form of attributes, indicators and criteria, should be used to support discourse amongst the stakeholders in deciding on interventions that are more sustainable. A project is described that is looking at portfolios of interventions in a river corridor with the objective of improving liveability in Sheffield and how the sustainability assessment framework for this has been set up and is being applied.

While the low impact development (LID) community has made tremendous advances in limiting project impacts on site hydrology, there is much more that the LID community can do to incorporate habitat quality measures for fish and other species into their projects. To address the need for broader, ecologically based LID criteria, an organization called Salmon-Safe has developed a series of successful voluntary, market-based certification standards for industry that specifically encourage salmon-friendly design and management practices. Deployment of the Residential Standards indicates a new era for the LID community. Thoughtful development design, conducted in a manner that considers benefits to water quality and quantity as well as habitat quality and quantity, creates opportunities for LID-oriented developers and their development teams to provide new, certified products and market-based services that can set them apart from the competition.

Green infrastructure has emerged as a viable option for urban stormwater management. Combining reductions in runoff volume and pollutant concentrations, green infrastructure has been successfully introduced into separate and combined sewer areas to decrease stormwater pollution and combined sewer overflows. Because green infrastructure uses vegetation, soil, and other innovative materials, these water quality benefits are complemented by additional environmental benefits including improved air quality, reduced urban temperatures, energy savings, aesthetic improvements, and a potential strategy for reducing carbon footprints. The ability of green infrastructure to provide multiple environmental benefits allows municipalities to use limited economic resources more efficiently and provides a framework for sustainable infrastructure management.

Population in Utah is projected to nearly triple in the next 50 years, to more than 6 million people. Although Utah has a small overall population compared to some other states, several regions of the state rank among the fastest growing locations in the country, with the Washington County area in the southwest corner of the state consistently ranked near the top. With massive urban growth projected, the ecological and economic benefits from sustainable development are potentially substantial. Widespread application of low impact development (LID) in Utah has been limited by many factors including lack of knowledge, institutional resistance, and policy restrictions. However, implementation of LID practices is emerging due to public and private interest in sustainable development, installation of demonstration sites, and increased guidance and training provided by local and state entities, and universities. LID is poised to be a key element in the current sustainable development push in Utah. This paper reviews the current status of LID in Utah, describes the limitations and trends, and summarizes constraints and recommendations for future LID expansion. Specific topics include infiltration practices in a large-scale development, Leadership in Energy and Environmental Design (LEED®) driving LID, overview of LID practices in Utah, and the emergence of university-led education programs to produce LID-savvy graduates in planning and engineering design.

Stormwater facility maintenance and costs are key components to the success of any bio-retention or Natural Drainage Systems (NDS) stormwater facility. What are the maintenance requirements for these systems and what are the associated life-cycle costs? On-going communication and information sharing of the lessons learned from these new facilities are vital for continued success. Clear and concise management plans and facility maintenance are necessary for sustaining the benefits of these systems. SPU is finalizing a working operations and maintenance package for Natural Drainage Systems. SPU's total NDS maintenance package includes the following: 1) NDS Maintenance Manual, 2) Workbook Job Costing Access Database, 3) Maintenance Category Checklists, 4) Key Performance Indicators Form. The Maintenance manual articulates different levels of service, based on the goals and requirements of an individual system. A cost database provides cost estimates for achieving the level of service specified for the given system. The maintenance category checklists for both vegetation and swale infrastructure are highlighted in a separate document to allow successful and consistent performance reporting. Checklists are summarized for reporting to management using the Key Performance Indicator forms.

The scope and expectations of Stormwater Management have changed dramatically in the last few years, moving away from a purely flood control perspective toward a green infrastructure approach protecting the sustainability of our rivers and watersheds (PaDEP 2006). The first transition occurred when we as a profession realized that we could start to address water quality issues in our flood control based detention facilities, by creating naturalized basins or stormwater wetlands. Our next advance has been to integrate Low Impact Development concepts, such as pervious pavements, green roofs and bioretention, into the landscape to minimize the adverse effects of land form change and to address stormwater volume. As our profession becomes more confident in the performance and longevity of our BMP tools, we are again progressing, moving toward a "No Net Impact", or better stated, "No Adverse Impact" design goal.

To identify new LID opportunities within San Francisco's ultra-urban setting while addressing the distinct interests of its residents, the San Francisco Public Utilities Commission (SFPUC) hosted two LID charrettes that brought together local stakeholders and helped shaped the future of green stormwater management in San Francisco. The charrettes were designed as a game involving a unique hands-on watershed planning exercise that helped participants visualize and quickly quantify the impact of specific LID projects. Charrette participants were divided into teams and given the necessary data about LID types and drainage basin conditions to assess the impacts of implementing potential LID projects. The teams worked together to identify the most promising LID projects in their assigned basin and estimate the projects' costs and benefits. These candidate projects are now undergoing more detailed engineering analysis to assess their feasibility and prioritize them for implementation. This unique charrette process provided insight into the public's preferences while capturing valuable local knowledge and identifying neighborhood LID opportunities. The charrette also encouraged inter-agency cooperation and generated enthusiasm and acceptance of LID. The tools and approach were developed such that the game could be easily applied to build awareness and identify LID opportunity areas in communities nationwide.

This paper explores an expanded definition for watersheds that, in addition to undeveloped and less developed areas outside of cities, includes private and public spaces located in urban areas. Innovative stormwater strategies that improve water use in a range of urban and non-urban environments are discussed, in addition to the techniques and challenges involved in employing a watershed-based approach to low impact development (LID). Through pointed design layout and element recommendations, a watershed-based planning approach empowers regulatory agencies to provide (and communities to demand) versatile, pedestrian-oriented, appropriate open spaces and improved ecological function and performance. San Francisco, in particular, offers a tremendous opportunity to serve as a model in approaching integrated infrastructure and ecology in an urban context. This paper aims to present, through various watershed scales, a critical path for large and small, urban and non-urban communities seeking similar infrastructural and ecologically-restorative solutions.

Although it has been established that thermal pollution from urban stormwater can negatively impact the aquatic ecosystem, there are few mechanisms available to reduce the temperature or urban stormwater runoff. A monitoring study was conducted at 4 bioretention areas in western North Carolina, located along the southeastern extent of United States trout populations, to examine the effect these systems have on runoff temperature and identify any design criteria pertinent to temperature reduction. Median runoff temperatures leaving the pavement surfaces, based on storm events, exceeded the 21°C upper avoidance temperature of trout at all sites during the months of June through September. Of the bioretention areas studied, the two systems that covered an area smaller than 10% of their contributing watershed were able to significantly (p<0.01) reduce both maximum and median storm temperatures between the inlet and outlet. At the two bioretention areas that were larger than 10% of their contributing watershed area, maximum effluent temperatures were significantly (p<0.01) cooler than influent temperatures; however, there was no significant (p<0.05) difference between median influent and effluent temperatures. Despite reductions in temperature, effluent temperatures were not significantly (p<0.05) cooler than the upper avoidance temperature for trout at any of the monitoring locations. There was evidence that substantial reductions in runoff volume occurred at all bioretention areas, especially the systems that were larger than 10% of their contributing watershed. Overall, monitoring results indicated that bioretention areas served as effective treatment mechanisms for reducing, but not eliminating, the thermal impacts associated with urban stormwater runoff.

Retrofitting existing sites to remove stormwater from the sewer systems and reintroduce stormwater to vegetation and soils is critical to the restoration and revitalization of our urban watersheds. It is a goal of the City of Portland's Bureau of Environmental Services to integrate Low Impact Development (LID) concepts into existing urban development to realize broad based goals for watershed health and community livability. Beyond just being an alternative to piped solutions, LID projects realize multiple benefits such as neighborhood beautification, removal of impervious surfaces, restoration of the tree canopy, heat island reduction, groundwater recharge, safe pedestrian crossings, and traffic calming.

The Little Stringybark Creek restoration project is the first of its kind, focusing on reducing stormwater runoff using LID strategies across an entire sub-watershed. Urban streams around the globe demonstrate common characteristics associated with the increased imperviousness of their watersheds, including a flashy hydrograph, elevated concentrations of pollutants, altered channel morphology, and increased dominance of pollution tolerant species. Urban streams cannot be restored to pre-disturbance stream health conditions without addressing the combined water quality and hydrologic disturbance (increased volume and frequency of polluted stormwater runoff) from impervious areas delivered by drainage infrastructure in developed watersheds. This poses a great challenge for stream restoration, since it is much easier to implement local or reach scale in-stream or riparian projects than to reduce the stormwater impacts of impervious areas in a catchment. One of the key needs for the protection or restoration of streams in urban or urbanizing catchments is, therefore, a better understanding of specific and practical stormwater management objectives at the catchment and site scale aimed at addressing hydrologic characteristics that affect streams.

In this paper, reflect on the issue of building China's urban landscape, reference LID's ideas and experience, established a evaluation index system which look the two major themes (runoff pollution control and landscaping) as the core content, including three levels and 16 sub-indicators. The evaluation system evaluate the ecological functions and standards of landscape construction from multi-angle, such as promoting rainwater infiltration, maintain water, alleviate runoff pollution, releve oxygen and absorb carbon, absorb and stop dust, improve the micro-climate, and adopt a new evaluation method for the evaluate of ecological functions which made use of a landscape-level analysis. We try to use this system to the assessment of landscape ecological function of a place of Wuhan, preliminary verification of the method is reasonable, applicability; Proposed scientific ideas and operational evaluation methods to the current large-scale urban development in China, the ecological civilization, the concept of eco-the first and promote the building of the ecological landscape run through urban development.

Soils on residential developments typically have lower stormwater infiltration rates than the soils they replace. This is due to reduced topsoil depth and increased subsoil compaction as land is reshaped and worked with heavy equipment during development. Loss of infiltration leads to increased stormwater runoff and associated downstream problems of flooding, pollutant transport, and warming stream temperatures. This paper explores improvements to stormwater infiltration rates by amending soils on residential developments with tillage methods and compost application rates. Field studies to measure how tillage and compost soil amendments perform under actual conditions and the practical aspects of using them are being performed.

Increasing impervious surfaces in the urban landscape has created a need for stormwater management practices that control both volume and peak flow rate. Infiltration systems are preferred because they address both issues. However, the potential for groundwater contamination is a concern when siting an infiltration practice. In addition, soil is not homogeneous and its variety of layers provides a heterogeneous environment for pollutant removal. This study, started in November 2007 and to be completed by October 2008, is using undisturbed natural soil columns of a Wharton silt loam and Leetonia loamy sand to treat stormwater runoff from roofing, parking lots and sidewalk. This research is a temporal study of runoff treatment and soil accumulation as a function of soil horizon and resultant soil chemistry. Early water results show leaching of total nitrogen and removal of total phosphorus by all soil horizons of both soil types. Potassium and sulfate removal has been seen in the AB/A1A2 and OAB/OA1A2 soil horizon columns of both soils but may only be temporary. The lower horizons and the entire profile are able to retain the leaching potassium and sulfate from the organic horizon. All soil horizons of both soil types have lowered the pH of influent stormwater and increased conductivity, turbidity, color, and hardness.

The first tool in the Low Impact Development toolbox should be preserving existing soil and vegetation where possible, and then restoring minimum soil function on areas that are disturbed during construction by reducing compaction and reusing high quality topsoil or amending site soils with compost. Science and practice demonstrate that these "soil BMPs" not only enhance stormwater infiltration and water quality, they also reduce long-term needs for irrigation water, fertilizer, and pesticides, promote healthier landscape establishment, and create more attractive, marketable projects. In Washington, a collaborative effort by State stormwater regulators, local governments, the compost industry, and the design and building industries is bringing these soil BMPs to construction sites throughout western Washington. This project is being used as a model for soil standards around the U.S.

The City of Portland's Bureau of Environmental Services (BES) investigated the benefits of ecoroofs and concluded that they work well for stormwater management. To date, over 1,000,000 square feet (SF) of ecoroofs or roof gardens have been built in Portland, with more planned in the near future. As part of an effort to understand the implications of widespread installation of ecoroofs throughout the City, this evaluation studied the range of costs and benefits associated with ecoroofs. The analysis compared the performance of an ecoroof with that of a traditional roof on a new five-story commercial building with a roof area of 40,000 SF in downtown Portland. The categories of economic impacts include capital and O&M costs of stormwater management, energy consumption, building construction and O&M costs, amenity values, impacts on climate including carbon reduction, and habitat values. The results of the cost-benefit analysis provide insights into the net economic benefits of ecoroofs and the relative magnitude of private vs. public costs and benefits over time.

Sustainability and more extensive applications of LID in different parts of the world depends, to a large extent, on the understanding and ability of the professionals who plan, design and manage civil infrastructure systems. Thus, UNESCO-IHE Institute for water education in Delft, the Netherlands has developed a unique approach to transfer and internalize LID concept and technology with international groups of engineers who plan, design and manage urban infrastructure. This paper presents the approach, the ideas behind it, the current achievements and challenges and lessons learnt so far as well as the European experiences used as case studies.

Prince George's County and their partners (U.S. EPA, City of Laurel, Prince George's County Public Schools, Maryland National Capital Park and Planning Commission, Lowe's Home Improvement Center, and Patuxent River 4-H Center) have been collaborating on a comprehensive storm water management plan using Low Impact Development (LID) for urban retrofit and decentralized wastewater treatment system. The Demonstration Project was funded by a Congressional Earmark Grant of Total Project amount of $1,324,667 the Federal Grant portion is $993,500 (75%) and match portion is $331,167 (25%). LID is a concept that began in Prince George's County, Maryland in 1990 as an alternative to traditional storm water Best Management Practices (BMP's) installed at construction projects. The LID project components are an integrated storm water management approach using LID techniques to retrofit a mixed use, high density area and a decentralized wastewater treatment system. LID techniques can be simple, but cost effective instead of depending on expensive, and complicated collection, conveyance, storage and treatment systems. The LID techniques used in this project are bioretention cells, grass swales, rain barrels/cisterns, green roofs, Bayscaping, and permeable pavements. LID techniques can also play an important role in Smart Growth, Green Infrastructure, and Land Use Planning. The implementation of these techniques will reduce water consumption, run-off, and non-point sources.

One of the most exciting new trends in water quality management today is the movement by many cities, counties, states, and private-sector developers toward the increased use of Low Impact Development (LID) to help protect and restore water quality. However, while the increase in application of these practices is growing rapidly, data regarding both the effectiveness of these practices and their costs remain limited. This presentation will focus on the latter issue and will show that LID approaches and practices can provide significant cost savings and reductions compared to conventional development techniques. The U.S. Environmental Protection Agency (EPA) has published a new document, "Reducing Stormwater Costs through LID Strategies and Practices" that provides information that will assist communities and practitioners in their efforts to promote and implement LID. This 30-page publication summarizes 17 case studies from the United States and Canada and directly compares the costs of LID to traditional approaches in the context of new developments, including 8 subdivisions, a corporate campus, an apartment building, streets, and other common modes of development.

Seattle Public Utilities (SPU) has implemented a Stormwater Facility Credit Program (SFCP) to encourage customers to install stormwater management facilities that treat and detain stormwater runoff on site. These onsite stormwater management facilities, or best management practices (BMPs), reduce the amount of stormwater runoff and associated pollutants from private properties that would otherwise enter the City's storm drainage network. The SFCP offers stormwater facility credits, applied as a percentage discount off a customer's annual drainage bill (up to a maximum 50 percent discount), for eligible BMPs that have been properly installed and maintained. Eligible BMPs include rainwater cisterns, vegetated roofs, bioswales, permeable pavement, rain gardens, stormwater vaults, and oil-water separators, among many other types of facilities. The SFCP is intended to increase environmental stewardship among Seattle residents, reduce stormwater runoff and pollutant loadings to the City's storm drainage network, and improve the equity of annual drainage charges.

This project comprised of designing and equipping two bioretention cells on the campus of Lawrence Technological University in Southfield, Michigan to quantify the effectiveness of these structural stormwater best management practices (BMP's). Each of the cells was equipped with soil moisture and temperature sensors, water quality samplers, and flow meters. The purpose of this project is to analyze varying soil compositions and quantify the effectiveness of bioretention cells in storing and treating stormwater runoff through analyzing rain, temperature, soil moisture data, and underdrain discharge for multiple natural and simulated storm events. This paper will present results from collecting natural rainfall data as well as outline future tests that will enable the comparison of soil mixture compositions for efficient and effective water quality and quantity goals. An example of simulated events is also included.

With the growing concern about bacterial impairment of recreational waters associated with stormwater runoff, extensive laboratory and field studies were conducted by Filterra®, division of Americast, Inc., to determine an optimum blend for bacteria removal. The Filterra® bioretention BMP blend is currently designed to utilize physical, chemical and biological pollutant mechanisms to remove typical stormwater pollutants such as TSS, phosphorus, nitrogen and heavy metals. Filterra® has developed a specialized treatment media to remove fecal coliform and other pathogens from urban stormwater runoff. This new media blend has been trade marked Bacterra. This study showed that high bacteria removal rates of over 90% were achieved at extremely high flow rates at 100 inches per hour. This study does not support conventional thinking that slow flow rates and long contact times are needed to effectively remove bacteria from stormwater runoff using bioretention media. This paper summarizes the research effort and findings of Filterra® in the development of their Bacterra^TM high flow bioretention media treatment technology.

Recommendations for rain garden media design typically specify high sand content and low organic matter content to promote infiltration and avoid excessive ponding. This design is effective at infiltrating stormwater and removing solids, heavy metals, phosphorus, and some species of nitrogen; however, the aerobic and low carbon conditions inhibit denitrification, the microbial reduction of nitrate to nitrogen gas which is released to the atmosphere. As a result, rain gardens typically release nitrate in effluent. In this study, media enhancements that promote denitrification are tested for hydraulic properties in bench- and full-scale experiments. At the bench scale, media, with one and two layers of shredded, unprinted newspaper added as a carbon source for denitrification, will be tested for drainage properties. If drainage properties are acceptable, then full-scale, outdoor mesocosms containing three experimental treatments, high versus low organic matter content (as newspaper), presence versus absence of a saturated zone at depth, and large versus small mesocosm size, will also be tested for hydraulic properties. Infiltration rates and timing, flow rate, and volume of effluent will be measured following stormwater additions timed to coincide with high or low antecedent moisture conditions. Results will be used to design future nutrient removal studies.

Bioretention is a principal low impact development (LID) practice. A study underway in North Carolina is examining the performance of bioretention cells with respect to hydrology and water quality under varying vegetative covers and media depths in the sandy in-situ soils of the upper coastal plain. Two types of cells are being monitored in both Rocky Mount and Nashville. In Rocky Mount, the cells were designed with 0.9 m deep media depth and a 0.6 m deep internal water storage layer (IWS). The IWS is intended to create anaerobic conditions to increase the rate of nitrate and total nitrogen reduction. Current data shows the IWS having a strong effect on flow reduction. Out of 37 events that were monitored since September 2007, outflow was generated in the grassed cell and mulch/shrub cell two and one time, respectively. Grab samples have been collected from the underdrains after an event to quantify treatment. Preliminary data from ten events show concentration reductions of total nitrogen, total phosphorus, and total suspended solids of 80, 72, and 92%, respectively. In Nashville, two sets of cells were designed without IWS and with media depths of 0.6 and 0.9 m. Preliminary data shows the deeper media depths meet a LID hydrology goal of volume reduction more frequently. Data collected from these four sets of cells will be used to compare performance of bioretention in the sandy in-situ soils of the upper coastal plain to those sited in clayey soils from past studies in the Piedmont region.

In moving towards a water balance approach to stormwater management and the modelling tools that can support such an approach, it is clear that there are substantial gaps in our knowledge of groundwater recharge and evapotranspiration (ET) in urban areas. At a microscale, weighing lysimeters can be used to estimate ET and may also be designed to also allow drainage (groundwater recharge) to be quantified. A weighing lysimeter has been designed, constructed and tested and will be used to quantify ET and groundwater recharge from a bioretention area. Results at this scale will vary with urban surroundings, but will nevertheless contribute to the scant information available. Installation of similar systems in various urban micro-meteorological conditions will help to build a database of urban ET and recharge. Other approaches, such as the eddy correlation approach for ET, are also needed to complement microscale measurements.

The capacity to infiltrate stormwater is an important aspect of many low impact development practices. Quantitative evaluation of infiltration capacity has typically been performed by monitoring the inflow and outflow of various storms, and determining the infiltration through a mass balance. Monitoring programs, however, are typically of long duration (i.e. one or more field seasons), require intensive effort, and frequently do not yield useful data for individual LID practices. We propose a new approach for assessment of stormwater LID practices that includes controlled testing as a key component in a Four Level assessment program. In increasing order of effort, the four levels are: (1) visual inspection, (2) infiltration capacity testing, (3) synthetic runoff testing, and (4) monitoring.

This study measured removal of total phosphorus (TP) and total suspended solids (TSS) by both conventional and LID stormwater BMPs installed to treat stormwater runoff from a bus transit station and carpool parking lot in King County, Washington. Significant and high removals of TP and TSS loadings were measured, and overall downstream loadings were minimized by the sequential nature through which stormwater flowed through multiple BMPs on the site. Removal of TP (74 percent on average) fell just short of municipal guidelines specifying 80 percent reduction. Removal of TSS (97 percent on average) exceeded the 80 percent reduction municipal target. The data presented in this study is comparable to similar studies elsewhere in the United States.

A grass swale is a Low Impact Development (LID) technology useful in managing complex stormwater management challenges, especially in linear applications such as highways. In this study, the addition of vegetative check dams on swale performance is evaluated. Check dams will reduce runoff velocity, increase the retention time and therefore allow more time for water quality improvement processes to occur. Two full-scale grass swales in the median of a four-lane highway on Maryland Route 32 have been monitored for 24 storm events. Each swale includes two vegetated check dams and one swale has a pretreatment grass filter strip adjacent to the swale. The project was designed as an input/output comparison between the hydrologic and water quality characteristics, specifically Total Suspended Solids (TSS). Results suggest that grass swales improve the water quality of the runoff and help to reduce the runoff peak. The swales manage to reduce the average peak runoff from 45 to 18 (MDE-CD) and 20 L/s/ha (SHA-CD). MDE-CD performs slightly better due to the ability of the pre-treatment area to increase the infiltration time. Furthermore, the swales managed to reach the TSS research goal of 30 mg/L for 85% (SHA-CD) and 72% of the storm events (MDE-CD). Without those swales, only 28% of the storm events met the research goal. Compared to a previous study, however, addition of check dams shows no improvement for TSS removal.

Traditional construction practices lead to degradation of watershed hydrology through increased flow in pipe networks, increased flow volumes, decreased groundwater recharge, and increased peak flows. Recent regulations in North Carolina have led to the use of level spreaders in combination with a vegetated buffer as an end-of-pipe method to reduce erosion and decrease stresses on riparian buffers. However, little research has been done to evaluate their effectiveness. A total of four level spreaders were studied at two sites, Apex and Louisburg, NC. At each site, stormwater from small, impervious watersheds (0.4 ha or less) was conveyed proportionally to two level spreaders. Flow was released along the length of the level spreaders and into two vegetated buffers. This study evaluated the hydrologic and water quality impacts of level spreaders (combined with vegetated buffers) as an LID practice. The idea is to disperse flow across the length of the buffer, in order to improve infiltration capacity of the buffer. Varying buffer widths and buffer vegetation were studied. Preliminary findings show that substantial reduction in peak flow rate and flow volume can be expected when this LID practice is implemented. This system was also studied for its impacts on nitrogen, phosphorous, suspended solids, and runoff temperature. Further data collection and analysis should provide design engineers guidance on the functionality of this system.

The object of Low Impact Development (LID) is to mimic the hydrologic cycle, to handle and infiltrate stormwater on-site and to minimize the impact of development. A good way to accomplish this is through infiltration practices. This paper discusses seven sites located in Massachusetts where infiltration practices, including bioretention cells, raingardens, and porous pavements, have been designed and installed and provides design information and performance monitoring/infiltration results and challenges for each site. The results indicate that when properly designed, constructed, and maintained, infiltration practices can be a practical and effective method of stormwater management.

National trends for greener construction and comprehensive stormwater management are resulting in changes in the design and requirements for stormwater Best Management Practices (BMPs). Practices such as porous pavement/pavers, bioretention areas, and rainwater recovery are becoming more common at sites across the country, with the engineering designs and specifications evolving as the demand increases. Situations occur where regulations and LID site design requirements are being put in place before the existing site condition information that is necessary to determine the requirements for LID designs, construction/installation, and maintenance needs have been collected. This paper discusses how site conditions drove stormwater LID designs and implementation on three different project sites. The projects include: a suburban/rural mixed use project on a green-field site, a dense residential development built on a former gravel pit site; and an urban mixed-use redevelopment on a highly impacted City of Boston site. While local review processes often required specific LID practices for stormwater management, site conditions resulted in either modifications or elimination of certain LID practices, especially those relying on recharge. Additionally, the need for detailed site condition information very early in the planning stage was required. For each site, modifications to the details/designs/specifications and operation and maintenance plans for specific LID BMPs based on site conditions were required. No standardized details were applicable for all sites.

The Port of Bremerton is proposing the construction of a business park for clean energy technology and sustainable design companies. The project, called SEED (Sustainable Energy and Economic Development), includes the redevelopment of an existing brownfield site and full integration of LID techniques. The project will adhere to a Full Dispersion BMP, codified in the 2005 Washington State Department of Ecology Stormwater Management Manual for Western Washington standards for achieving "zero impact" or "full dispersion" of stormwater runoff. To achieve compliance, the site will have 65% minimum maintained or reforested area, 10% maximum impervious area, and 0% effective impervious area. To meet this goal, Kitsap SEED will use bio-infiltration swales, bio-infiltration cells, a variety of permeable pavements, restored forest and meadows, and green roofs. This combination will remove over 95% of the stormwater runoff from the regional detention facility system.

Research conducted at the North Carolina State University and elsewhere has determined that bioretention practices are very effective in reducing polluted stormwater runoff from urban areas. Smaller residential bioretention areas, also known as rain gardens, have proven to be an effective means of removing metals, nutrients, sediment and fecal coliform provided that they have been designed, sited, constructed and maintained properly. The university, local and state governments have been promoting the installation of rain gardens and other stormwater practices in Phase I and II communities for many years; however, very few homeowners and commercial landscape contractors have a working knowledge of the benefits of rain gardens, their installation or their maintenance requirements. To help promote rain gardens and address these needs, the North Carolina Backyard Rain Garden Program was implemented during the summer of 2006 in a six-county pilot area. Funded as an EPA 319(h) project, the program (1) developed an education program by conducting homeowner workshops in each county, (2) installed more than 40 residential demonstration rain gardens, and (3) developed educational and reference materials making them available at the following website: www.bae.ncsu.edu/topic/rain_garden. More recently, an assessment was performed to determine: 1) How many rain gardens continued to function properly, 2) What, if any maintenance had been performed, 3) Common traits among the cooperators with successful rain gardens. 4) Education needs for homeowners and installers.

The grounds surrounding the Core Sound Waterfowl Museum and the Cape Lookout National Seashore Visitor Center provide little stormwater runoff treatment as they are currently configured. Because both facilities are immediately adjacent to Core Sound and Back Sound, any pollutants that fall on the grounds, particularly on impermeable surfaces, can easily migrate to sensitive waters. Also, as thousands of visitors pass through the National Park Service property each year, there is a tremendous opportunity to demonstrate low impact development practices to reduce the amount of runoff, and its associated pollutants, entering the sounds. Faculty and students from the Department of Biological and Agricultural Engineering Department at NC State University evaluated the site for potential best management practices. They identified 13 potential retrofits for the Core Sound Waterfowl Museum and the Cape Lookout Visitor Center including water harvesting, rain gardens, and permeable pavement. Design elements including a cost estimate for each potential BMP has been developed for future use by the visitor center and the museum. Detailed designs were completed for five of the identified BMP's including two rain gardens, a water harvesting system, and permeable pavement. Three of the BMP's were installed: one at the Cape Fear Visitor Center and two at the Core Sound Waterfowl Museum. An 7.5 m² (80 ft²) rain garden was constructed that treats the runoff from a rooftop at the museum. A 5,678 L (1,500 gal) cistern was installed that captures runoff from 70 m² (750 ft²) of rooftop at the museum. The harvested water will be used to irrigate the landscaping at the museum. Runoff from the rooftop at the Cape Lookout Visitor Center will be treated in a rain garden located near the entrance. Each of the practices will improve the quality of the stormwater leaving the site while serving to educate the public about using low impact development to treat stormwater runoff.

Many coastal waters are designated under the federal Clean Water Act to be used for swimming and shellfishing. While Congress has established a legal obligation to protect and restore these "existing" uses of coastal waters, conventional stormwater management measures fail to adequately treat and remove bacteria from urban stormwater runoff. This means that as development occurs these existing uses of coastal waters are frequently prohibited to protect public health. This presentation examines the potential of Low-Impact Development (LID) practices to successfully prevent and reverse this persistent and widespread form of water quality degradation in urbanizing coastal areas. The legal water-quality protection imperatives that LID must satisfy are identified, technical challenges unique to coastal areas discussed, and real life experiences with LID use and performance along the coast on North Carolina reviewed. The conclusion is that LID has the potential to protect and restore coastal water quality as long as it successfully replicates natural hydrology, and LID strategies should become the cornerstone of watershed management strategies including Total Maximum Daily Load implementation plans.

As the environment comes under increasing stresses, typical low impact development goals are no longer suitably ambitious targets. Standard stormwater management focuses on mitigating peak discharges or runoff volumes resulting from storms with specific recurrence intervals. More appropriate designs mimic natural processes such that post-construction water balances and annual hydrographs closely approximate their pre-construction states. Sonoma Mountain Village, a 200-acre planned residential and commercial community 40 miles north of San Francisco, seeks to minimize the impact it will have on the hydrologic cycle through its adherence to a thorough site baseline monitoring program which informs innovative engineering design.

The concept of "artful rainwater design" is based on the premise that new stormwater management techniques focusing on non-point source pollution, water balance, and small storm hydrology can also be used to create new site amenities. These designs can result in greater user satisfaction and perceived value—i.e. design that not only addresses stormwater management in better ways, but also transforms these management systems into site design assets. These new stormwater requirements present significant amenity design opportunities that deserve to be recognized and exploited. This paper presents specific design techniques, grounded in case study of 21 selected projects across the U.S., to transform stormwater management into experientially rich artful rainwater design.

Advanced design concepts such as Low Impact Development (LID) and Green Solutions (or upland runoff control techniques) are currently being encouraged by the U.S.EPA (EPA) as a management practice to contain and control stormwater at the lot or upland residential parcel level. These controls have shown that when implemented and maintained properly, they can increase retention at the runoff source — decreasing the runoff volume entering the drainage system and the demand on a drainage system. Both developed storm and combined sewersheds can benefit from the added storage from areas retrofitted with bioretention cells or rain gardens and other management, e.g., catchbasin retrofits or curb-cuts with tree planting. This paper documents an effort by the U.S. EPA to demonstrate the efficacy of implementing integrated, green infrastructure-based solutions to wet- weather flow pollution problems in and urban core neighborhood within a combined sewer system. The project involves local and regional efforts to provide the basis for success of the implementation of green infrastructure and stormwater management at the neighborhood, watershed, and regional levels. Specifically, the project will demonstrate the strategy and methodology for where and how attainment of Green Solutions will be implemented, including model support, within Kansas City, Missouri.

The Enhanced Green Build-out Model is a planning tool that quantifies the cumulative stormwater management benefits of various green infrastructure practices intensively applied across the District of Columbia. The Enhanced Green Build-out Model calculates potential reductions in stormwater runoff within the municipal separate storm sewer system (MS4) and the combined sewer system (CSS) that contribute to water quality impairment in the Nation's capital. The green infrastructure component of the Enhanced Green Build-out Model was added to an existing hydrologic and hydraulic model of the District called Mike Urban. Mike Urban was developed and applied by the DC Water and Sewer Authority (WASA) to support development of the Long Term Control Plan for the CSS. The MS4 areas were added to the model so that all of the municipal sewer systems were included in one planning tool. In its original application, the Green Build-out Model was designed to simulate tree canopy expansion and green roof conversion and progression (Casey Trees and LimnoTech, 2007). The Enhanced Green Build-out Model includes the green roof and tree coverage from the original model and builds upon them by quantifying wet weather flow reductions for a new set of practices including rain barrels, roof leader disconnection to rain gardens, sidewalk bioretention planters, curb bump-out bioretention planters, and permeable pavement. Green infrastructure was integrated into the model by utilizing detailed GIS coverages and mimicking the hydrologic processes inherent with each green infrastructure practice. The model was run with average annual rainfall conditions. Reductions in runoff volume and CSO discharge volume and frequency were calculated for both the CSS and MS4 areas and for the Anacostia, Potomac, and Rock Creek watersheds within the District.

The Philadelphia Water Department is committed to a balanced land-water-infrastructure approach to achieve watershed management and combined sewer overflow (CSO) control goals. This method includes infrastructure-based approaches where appropriate, but also includes a range of land-based stormwater management techniques and physical rehabilitation of aquatic habitats. The goal is to restore the water environment in the City of Philadelphia and the surrounding areas, while achieving regulatory compliance in a cost-effective manner. This paper explains the hydrologic and hydraulic modeling used to design the approach and quantifies potential benefits of stormwater management and green infrastructure in one of the three highly urbanized drainage districts in Philadelphia. The results indicate that a significant reduction in stormwater volume can be achieved by requiring stormwater controls for redevelopment and through implementation on public lands.

This paper will describe ongoing efforts to improve LIDRA, a previously developed model for rapidly assessing the cost-effectiveness of investments in low impact development (LID) for reducing combined sewer overflows (CSOs) in urban watersheds. The efforts discussed in this paper involve the application of risk analysis. LIDRA can be used to simulate the cost-effectiveness of reducing CSOs through incremental installation of LID technologies across urban watersheds, when they are introduced alone, or in combination with conventional CSO abatement technologies. The potential reduction in CSOs resulting from various levels of LID adoption is simulated using a simple power function. A life-cycle cost analysis is used to compare LID with other alternatives. Given that LID implementation on private property leads to reduced CSOs, a cost sharing scheme is presented that divides the total LID cost into a private cost fraction (born by the property owner) and a public cost fraction (provided by a public agency). The model improvements described in this paper use risk analysis to establish ranges and probability distributions for the key variables. These ranges and distributions are specific to each type of land surface and BMP and include: (a) Existing runoff coefficient; (b) BMP runoff coefficient; (c) Percent of surface area replaced with suitable BMP; (d) Number of years until suitable BMPs reach maximum coverage; (e) Installation costs; and, (f) Maintenance costs. Some sample results are presented.

The literature indicates the value of Low Impact Development (LID) practices in reducing stormwater impacts in moderately densely developed urban and suburban settings. Almost exclusively, case histories show the techniques constructed in parking lot locations, new subdivisions, and similar developments where available land and existing infrastructure are conducive to LID. These installations usually are associated with new development on previously undeveloped sites. However, descriptions of LID deployment in previously developed ultra urban settings and urban redevelopment sites are extremely difficult to locate. The key features of a program to implement LID in a well established ultra urban setting are described. Considerations that are addressed include policy and planning, geology/soils, education and cultural change. A discussion of these considerations is presented as they relate to a moderate sized Puget Sound city's efforts to implement LID in its downtown and near downtown environs.

Low impact development (LID) is emerging as the latest generation in strategies to manage stormwater. The LID approach has moved beyond the acceptance stage and implementation is encouraged at a much wider scale. The current challenge for stormwater managers is how to integrate newer practices with traditional stormwater management methods, both in terms of meeting regulatory standards and existing stormwater infrastructure. Due to limiting glacial soils commonly found in the Puget Sound region, LID techniques alone often cannot eliminate the use of traditional detention. These challenges require a more layered approach to implement LID where practicable to complement the existing infrastructure or application of traditional methods. In this paper, the efforts of two established Puget Sound communities to integrate LID with existing stormwater standards will be reviewed. The City of Bellevue has developed a Natural Drainage Practices (NDP) Manual to provide methods for evaluating site conditions, selecting and sizing appropriate practices, and calculating credits toward meeting the City's stormwater management requirements. In the City of Burien, an LID Implementation Plan is being developed to identify regulatory gaps for adopting LID, create a toolbox for implementing practices, and educate the public on LID. The Burien toolbox will include updated standard details of natural drainage practices, alternative LID road standards, and checklists for siting and designing small-scale practices.

Burnt Mill Creek is on the EPA's 303(d) list for impairment due to urban stormwater runoff. Located within downtown Wilmington, NC the urban nature of the watershed presents challenges for restoration because of the varying land uses including single and multi-family residential areas, recreational parks, and commercial and industrial areas. Restoration efforts are multiplying in Burnt Mill Creek as a result of passionate involvement from local community leaders and partnerships with state organizations. Watershed Education for Communities and Local Officials (WECO) of NC State University (NCSU) coordinated a partnership with NCSU Department of Biological and Agricultural Engineering (BAE), the City of Wilmington, as well as several other key state and local organizations and citizens groups, to obtain an EPA 319 grant that addresses stormwater management in the watershed. Collaboration with community leaders has led to several retrofit opportunities and successful partnerships.

San Diego County, with a population of over 3 million, is one of the fastest-growing regions in the United States. With a population of over 1.3 million, the City of San Diego is approximately ninety-five percent developed. This has resulted in substantially less open space for naturally-occurring hydrologic function. There are also fewer opportunities to implement low-impact development in new projects, as most future development in San Diego will be infill or other redevelopment. As the San Diego County LID Handbook notes, the intermittent and ephemeral nature of many streams in the county (and Southern California generally) contributes to their increased sensitivity to urban runoff. Finally, institutional and psychological barriers have until recently hindered the acceptance and growth of LID as a viable alternative to stormwater management. These circumstances have all contributed to the uniquely complicated and arduous task of minimizing the effects of urban runoff in the region.

The U.S. Environmental Protection Agency, Office of Research and Development, Sustainable Environments Branch (EPA) is implementing a field research study of low impact development in a suburban watershed. Under contract to EPA, Tetra Tech has installed Best Management Practices (BMPs) on single-family residential lots across the 2 square-kilometer watershed in Cincinnati, Ohio. The project is studying public attitudes about these practices, the cost and feasibility of watershed-scale dispersed BMP programs, and effects on stream health and water quality.

In 2007, Oregon Health and Science University (OHSU) developed a Comprehensive Stormwater Management Plan for their main campus located in Portland, Oregon. The plan strategy employed a unique and unconventional approach for improving the health of campus watersheds. Low Impact Development (LID) techniques such as ecoroofs, bioretention facilities, and rainwater harvesting were utilized to reduce the runoff from impervious areas including rooftops, parking lots, patios, sidewalks, and roadways. Minimizing the stormwater flows from impervious surfaces and the potential pollutant load associated with the runoff will both improve the health of the watershed and provide relief for the City of Portland's already taxed combined sewer system. Through full implementation of this plan, OHSU could realize up to a 21 percent reduction in impervious area, significantly reducing stormwater runoff leaving the campus. The plan included detailed descriptions of each CIP with a project summary, example photographs, ranking criteria scores and a preliminary cost estimate on a single sheet for quick reference and comparison. LID techniques recommended by this plan are meant to compliment the vision of OHSU and its desire to advance to the forefront of sustainability and green design. This project provides an alternative to traditional methods of managing stormwater on campus facilities through the creative implementation of LID, and is a model for other campuses and cities to follow for diverging from conventional stormwater management practices.

The City of Portland, Oregon Bureau of Environmental Services (BES) recently completed a pre-design project that saved the City nearly $60 million, thanks in part to low impact development facilities. The centerpiece of the original solution BES recommended in 2000 that addressed sewer capacity and structural problems in the Taggart D combined sewer basin was a new, parallel, separated stormwater collection system. However, in 2004, a number of factors prompted BES to revisit the recommendation of the 2000 pre-design. Following nearly three years of work, the Integrated Taggart D Pre-design solved these same problems with a heavy reliance on low impact development facilities, along with new combined sewer pipes. These stormwater facilities not only provide sewer capacity but also watershed health benefits such as groundwater recharge and added vegetation that improves urban habitat conditions. The cost estimate of the 2007 watershed-based solution is $81 million, compared to the $144 million investment needed to construct the original 2000 solution. The 2007 integrated pre-design approach enabled BES to address multiple goals through one pre-design. The project recommendation included elements to resolve sewer backups, to address pipe rehabilitation needs, to improve watershed health, and to assist in combined sewer overflow control. It produced 35 projects ready for final design within BES' capital improvement program. Construction of the first two projects, together includes approximately 75 low impact development facilities, is anticipated in spring 2009. These capital projects complement other parallel programs BES recently initiated that collectively advances watershed health conditions in this basin: street tree plantings, community outreach, and revegetation of areas containing invasive species.

The City of Santa Monica promotes the use of low impact design in construction projects for the specific purpose of harvesting most stormwater urban runoff for use, infiltration or treatment, reducing the amount of runoff flow and pollution that leaves the City and enters the Santa Monica Bay. Programs incorporate sustainability and Low Impact Development (LID) principles during the design of construction projects and requires post-construction Best Management Practices (BMPs) to harvest runoff. Moreover, these programs shift from a paradigm of runoff as a waste product to be discarded and of paving over permeable surfaces to a new paradigm of viewing runoff as a local natural resource for use. The City has an urban runoff mitigation ordinance, requiring that runoff from newly constructed or redeveloped buildings be reduced through the installation of post-construction BMPs. This strategy accomplishes two goals: harvests a local water supply for future extraction and prevents a water pollution problem from entering the Bay. This paper describes different types of BMPs used in private and public construction projects. Moreover, the City hopes that other municipalities will learn from the City's experiences and follow in this sustainable path.

School sites are major local sources of runoff, with the potential to create sewer capacity problems and to have a negative impact on the health of rivers and streams. They also provide some of the best opportunities for stormwater retrofitting as far as layout and available space. Given the overall imperviousness of many school yards, planters and swales can do more than just meet stormwater management goals; they can provide visual amenities and improve the overall environment at schools. The stormwater project at Mt. Tabor Middle School, completed in 2007, is a valuable example of the opportunities and challenges associated with retrofitting schools with stormwater facilities, particularly vegetated facilities. The project added a range of facility types to the school grounds, with numerous "firsts" in integrating attractive open-air facilities with existing infrastructure and site uses. The facilities include a 186 m² "rain garden", a large swale, six planters, three drywells, and a stormwater curb extension in the street next to the school. The rain garden received a 2007 design award from the American Society of Landscape Architects. Lessons learned range from the complexity of developing plan sets for custom vegetated facilities to specific geotechnical and construction issues.