**Steps for GSI Implementation**

1. valuate the site

2. Confirm current requirements 3.Characterizesiterunoff,andhierarchy

Plan

 drainage area,4.Developaconceptualdesign


Once the zone of the city has been selected, the choice of a specific street depends on the availability of space, or in other words, the amount of the right-of-way that is not devoted or assigned for a specific use. A former official and a hydraulic engineer at BES agreed that green streets in Portland tend to be low traffic volume streets [82]. The engineer pointed out that more projects should be located within arterial roads because most pollutants settle there. The former BES official is convinced that GSI can be added to busy streets if they are carefully designed. He points out the advantages that there would be if more stimuli and funds ever become available for retrofitting these roads.

As a current Green Street implementer with a high number of constructed works, the Portland experience serves as an example. Two major elements have been identified as key factors in the fruitful implementation of green streets. The first is the simplification in the exception process for alternative designs, i.e., making it less tedious and risky for officials in terms of professional liability. The second key point is the development of a clear, simple, and standardized procedure for designing (sizing), testing, and constructing green streets. The pilot project process in Portland strongly contributed to developing a straightforward design method. The key was the monitoring and testing of constructed projects, which provided real and accurate information with regards performance. Table 3 shows the performance figures of five green street pilot projects. As a remarkable result, the "sizing factor" arose as the ratio of the facility area over the drainage area. In this way, an estimate of the size of the planter or garden can be easily calculated (e.g., 6% of the drainage area), providing orders of magnitude. Dimensions, materials, types of plants, locations, etc. of different projects were compared to achieve state-of-the-practice in design. Pilot projects were also educational for professionals for different agencies and they helped to explain the possible barriers and difficulties for a large-scale green street program.


**Table 3.** Characteristics and performance of some green street pilot projects in Portland. Source: Kurtz [83].

> The strategy used to overcome the transportation dominance of the ROW was multidisciplinary work according to the former BES official in Portland [84]. In Portland this was possible after years of inter-agency work by, for example, the Sustainable Infrastructure Committee and the Cross-Bureau Task Force. A frank debate among distinct disciplines brought interesting ideas, where green stormwater solutions could have initially emerged. Portland's former official considers that it was fairly easy to break the mono-functional thinking of transportation professionals by using the following logical thinking: 1. Portland

has stormwater problems; 2. there are regulations and the city has to comply with them; 3. we are all in the same city and we were appointed to solve these problems; 4. we need to do this in streets because the city does not own lands. At the end, he stated: "They are engineers . . . they are trained to find solutions to problems" [84].

### *4.3. Philadelphia: A Systemic Approach*

The process in Philadelphia was different. Rather than a formal green street program, green streets are just one of the city's eight strategies to transform the city into a "green machine." The program, known as Green Cities Clean Waters was launched at the very end of the first decade of the 2000s, almost 10 years after the first green street was implemented on the west coast. Its objective is to manage stormwater to solve the CSO situation in the US by means of GSI. The approved Green City Clean Waters plan requires the city to manage the runoff of nearly 40 square kilometers (10,000 acres) of impervious surfaces, at least one-third of the impervious area served by Philadelphia's combined sewer system [85,86]

In 2008, after a decade of approaching CSO problems with palliative actions, the city was required to adopt a strategy to substantially reduce CSOs. After a series of studies, the city decided to manage stormwater through a massive greening program of schools, public facilities, parking lots, parks, industry, business, streets, alleys, and homes. An example of GI implementation in a former parking area is shown in Figure 3. The green stormwater plan is a 25-year program in which the Philadelphia Water Department (PWD) will invest approximately \$2.4 billion (\$1.2 billion in 2009 dollars) [85].

During the first decade of this century, PWD was leading an inter-agency, multidisciplinary process to address water quality problems together with municipalities and counties that share one or more watersheds with the city. Since 1999, Philadelphia has established partnerships with six neighbors (counties and cities) to develop an Integrated Watershed Management Plan, which operates under a three-phase structure: (a) preliminary reconnaissance survey, (b) watershed assessment and planning, and (c) watershed plan implementation [87]. Simultaneously, the city of Philadelphia evaluated five different alternatives including green and gray infrastructure in light of the experiences of other cities, including those using GSI, facing the same problem. According to a former Director at PWD, a systemic decentralized green stormwater alternative with limited additional gray infrastructure to reduce CSO ranked first among the five alternatives [88]. It was determined that the green alternative provides maximum returns of environmental, economic, and social benefits within the most efficient timeframe, making it the best approach for Philadelphia.

The Philadelphia case is especially important in the green streets design process described in this study because its comprehensive analysis of the situation brought the importance of greening cities beyond pure stormwater management. The specific results of the Stratus Consulting report showed that green solutions provide such a vast and varied set of benefits (social, economic, and environmental) that the green scenario is unbeatable by any other option [89]. For example, the study showed that in a scenario of 50% runoff served by GSI with a large underground storage tunnel handling the remaining 50%, the benefits from GSI surpassed \$2.84 billion from 2009 to 2049 (in 2009 US dollars), while the benefits from the tunnel only reached \$120 million [89]. Surprisingly, the benefits in water quality improvement rank third on the list. Heat stress mortality reduction (accounting for 37%) is in first place followed by improved aesthetics and property value (20%). In third place, accounting for only 12% of the benefits, are increased recreational opportunities and water quality and aquatic habitat enhancement [89]. These results bring the discussion to a tipping point, since the main benefit of green streets in Philadelphia is not stormwater management.

Green streets are a major component of the Green City Clean Waters plan since the city's street network is its most abundant asset for reaching its goal. In Philadelphia, the target (based on models and simulations) is to provide at least some green elements on 50% of the 4465 km (2775 miles) of roads by 2028 [86]. The goal is to manage 25.4 mm (one inch) of runoff onsite, relying on green infrastructure for billions of gallons of required sewage overflow reductions.

What is the local design procedure? The Department of Streets (in the Office of the Deputy Mayor for Transportation and Utilities) and the Water Department worked hard to compile the design standards manual to accommodate green street elements, for street typologies that represent typical conditions in Philadelphia. As background, the Department of Streets issued the Complete Streets Handbook beforehand in 2009. The Complete Streets Handbook is a supplement to existing design codes, and considers the existing design codes and the Bike and Pedestrian Plan. Although the Complete Streets Handbook mentions the stormwater plan and the green streets movement, it does not even consider in its design procedures any functional green infrastructure. It barely mentions that wider ROW, like the planted strips along some of the city's 418 km (260 miles) of state and federal highways, offer opportunities to naturally drain stormwater runoff and incorporate bike lanes [86].

The Green Streets Design Manual defines a complete procedure for the design of green streets with "the primary goal of implementing GSI is stormwater volume reduction." It starts first by presenting a menu of GSI options available to be implemented (types of GSI): street trees, trenches, pump-outs, planters, permeable pavements, green gutter, and drainage wells (all for stormwater infiltration). The so-called sustainability matrix considers the seven types of GSI and the 11 types of street. For each cell of the matrix, the manual suggests whether a certain GSI type is suitable, possible, or not recommended for a given street type. For the most frequent type of streets, with low traffic, local, and residential, all seven types of GSI are suitable.

The manual defines a four-step procedure for designing a green street:


### **5. Green Street Design and Implementation**

Unlike the traditional street design process, green streets require complex, multi-scale, multi-agency, interdisciplinary, stepwise processes. Thus, when speaking of implementing green streets, the word "design" should go hand-in-hand with the word "planning," as long as each GI installed is part of an overall strategy to reach a goal.

Out of the three cases, three main steps were identified for green stormwater infrastructure in rights-of-way: first, a large-scale environmental system analysis; second, a meso-scale assessment to analyze the needs and suitability in different areas within cities; and third, a local-scale street design process (Figure 4). Despite the fact that the three cities have undergone their own independent processes (see Table 4), the same scales proposed by Norton et al. [9] have been evidenced in the case studies presented. In terms of green street planning and design, Portland, Seattle and Philadelphia started with a large-scale (city/basin) systemic analysis. In Seattle, this work was carried out by ecologists and environmentalists who studied the declining environmental condition of the Puget Sound Estuary beginning in the 1980s. In Portland, they used this regional approach to understand both problems and potentials. In Philadelphia, after developing an understanding and diagnosis of the problem at regional level, citywide modeling and simulations were carried out to evaluate the most suitable solutions. The results obtained in the first step are an input for the following steps (meso and local scales) and are required only once.

**Figure 4.** General process for green street planning and design.


**Table 4.** Cross-comparison of many process characteristics.

a Each city has undergone its own process. Differences and similarities are described in the text.

The second meso-scale stage, probably the least well-developed of the three, deals with site selection including both the zone within the city and the specific streets upon which to locate the GSIs. Sewer deficiencies, combined sewer system zones, areas with good soil permeability, and sewer basin backflows due to congested sewer lines were some of the reasons used to explain decisions in these cases.

The third stage includes three separate activities: finding space within the ROW, selecting the GSI typology, and the traditional transportation-landscaping design. Depending on space availability, different GSI typologies can be installed. The decision is a matter of performance, costs, and available space. According to Gallo et al. [90], a simplified design method makes it easy for designers with poor experience in hydraulics to incorporate GSI into streets. Portland is a good example as they created the sizing factor, which has contributed to easy approximation of size by professionals in other disciplines (but not replacing the technical hydraulic design for each facility itself). The construction phase take place following the local scale design.

These previous processes imply complex institutional interactions, a systemic view of the problem, and multidisciplinary work. We found that the planning and design of green streets implicate various federal, regional, and local public entities, besides the DOTs, including the EPA and the local environmental, water, and utility departments. However, the local DOTs still play a paramount role in this complex process.
