Green Infrastructure: Stormwater Management on Davis Islands in Tampa, FL

Green Infrastructure: Stormwater Management on Davis Islands in Tampa, FL Krisjanna L. Olson Faculty Mentor: Glenn Acomb, FASLA DCP 4290 Sustainability & the Built Environment Capstone Project University of Florida College of Design, Construction and Planning December 7th, 2016

Image Source: http://blog.dupontregistry.com/events/cars-and-coffee-davis-island-71916/ Davis Islands

Table of Contents Part 1: Introduction…………………….…………………………….…………………….…. 3 Purpose of Research……………………….…………………….……………………………… 3 Methodology…………………………………………………….………………………… 3 Background Information- Davis Islands…………………………………………………………4 Problems with Stormwater in Urban Environments…………………….…………………….... 7 Stormwater Management Efforts in Tampa, FL…………………………….…………. 13 Part 2: Literature Review: Green Infrastructure…………………….…………………….. 18 What is Green Infrastructure?………………….…………………………….………………….18 Types of Green Infrastructure and Associated Benefits…………………………………………20 Bioretention Systems …………………………….…………………….………………. 23 Green Roofs…………………………………………….………………………………. 30 Permeable Pavements……………………………………………….…………………...39 Green Infrastructure Barriers…………………………….…………………….………………. 44 Part 3. Conclusions and Recommendations for Davis Islands……………………………... 49 Total Savings with Green Infrastructure………………………………………………….……. 49 Green Infrastructure and Sustainability on Davis Islands…………………………….………...50 Conditions for Green Infrastructure………………………………………………….………... 54 Limitations and Assumptions: Green Infrastructure Implementation………………… 55 Green Infrastructure Recommendations…………………….…………………………….……60 Bioretention Systems…………………………………………………….……………… 60 Green Roofs …………………………….……………………….……………………… 81 Green Infrastructure Example Photos……………………………….……………………103 References…………………………….…………………………….…………………………..107

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Part 1. Introduction Purpose of Research The purpose of this research is to devise potential Green Infrastructure (GI) solutions to address the stormwater runoff issues of flooding and waterway pollution in the small island community of Davis Islands (DI), located in the southern part of metropolitan Tampa, Florida.

The research question is: What types of Green Infrastructure techniques can be used within a community like Davis Islands to reduce flooding and its associated environmental harms?

Methodology This project is qualitative, case study research with some quantitative estimations in the conclusions section of the project. Information was gathered on the composition of soils on Davis Islands, current water infrastructure, and other municipalities already implementing Green Infrastructure and LID strategies. Scholarly articles from University of Florida databases, various federal and local government documents, newspaper articles and current events are some of the tools used for researching Green Infrastructure for the literature review, and to devise a Green Infrastructure plan, and some quantitative benefits within the study area. To come to the conclusions for Davis Islands, metrics from various studies and credible sources were analyzed and applied to Davis Islands, to estimate, retention of runoff, cost reductions compared to gray infrastructure, and pollution reductions. Multiple Green Infrastructure are suggested for Davis Islands based on how suitable the strategy would be in each location, available space in the community, and the natural flow of stormwater based on the current system. The approximate square footage of Green Infrastructure techniques will be calculated to estimate the financial benefits of using alternative stormwater management strategies on Davis Islands.

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This paper will begin with background information on Davis Islands, stormwater issues, and proceed into a review of current literature on Green Infrastructure. The following section will cover implications for Davis Islands and discussion on recommendations for Green Infrastructure techniques that may be implemented throughout various sites on Davis Islands to manage stormwater in an environmentally sensitive way.

Background Information: Davis Islands, Tampa, Florida Composition Davis Islands is a suburban community located in South Tampa, Florida. It is a unique neighborhood compared to the rest in Tampa, since this urban village is an archipelago composed of dredged, fine sand at the mouth of the Hillsborough River, atop what used to be Little Grassy Key and Big Grassy Key in the Hillsborough Bay prior to the 1920s (DICA, 2016).

The climate in Tampa is humid sub-tropical, with yearly precipitation of approximately 46 inches, which is concentrated in the hot and humid summer months, June through September.

The average annual temperature is 74 degrees, with higher summer temperatures in the nineties, and winter temperatures occasionally dipping into the fifties (US Climate Data, 2016). The soil profile on Davis Islands is in the St. Augustine Urban Land Complex, typical of flat marine terraces composed of fine, somewhat poorly drained sand. The depth to the water table is shallow, approximately thirty-six inches (NRCS, 2016). The estuarine environment in Tampa Bay and Hillsborough Bay is home to an abundance of wildlife and biodiverse ecosystems. The dominant ecosystems in the Bays are mangrove forests, seagrass beds, oyster beds, and salt marshes, where seagrass ecosystems suffer the most from urban growth and waterway pollution (TBEP, 2016b).

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Map: Davis Islands in the context of Tampa Bay. The City of Tampa is outlined in red. Davis Islands is located at the mouth of the Hillsborough River in the Hillsborough Bay, part of greater Tampa Bay. The second map below is Davis Islands and South Tampa on a larger scale. Image Sources: Google Maps.

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Community Residents began to move to Davis Islands in 1924, and the community is known as one of the most desirable places to live in Tampa due to the waterfront views of adjacent Downtown Tampa, Harbor Island, and the Hillsborough Bay. Davis Islands is 1.36 square miles, with a population of approximately 5,500 since the 2010 census. The population remains constant relative to the rest of Tampa since there is no opportunity for outward growth on Davis Islands.

New construction of high rise buildings is not part of the Davis Islands Community Plan to preserve the community aesthetic, so developers have had to search elsewhere in Tampa to build sky-scraping condominiums (DICA, 2016)(DI NPTF, 2013). As a result of restricted development, Davis Islands has maintained its small-town character. The community is

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pedestrian and bicycle friendly, with bike lanes and wide sidewalks around the main right-ofway, Davis Boulevard, that provide a safe and enjoyable environment for residents of all ages to enjoy. Points of interest on Davis Islands include a hospital, an airport, a fire station, community centers, a church, a public marina, a yacht club, small parks, a commercial district with locally owned businesses, historic buildings, and institutional buildings. Davis Islands has recreational areas in the form of open waterfront fields used mainly for sports, two dog parks, a 1.3-mile linear pedestrian and cyclist trail, and other recreational facilities for organized sports like baseball, softball and tennis. However, the community is still almost 80% urban-built up, and only 4% of Davis Islands is considered recreational with less than 1% considered to be public open space (DICA, 2016).

Problems with Stormwater in Urban Environments — Tampa Bay Urban Population Growth and Impervious Surfaces Due to rising populations around the world, urban growth is one of the most pressing problems we face as a society. While cities sprawl outward, open spaces are paved over with increasing amounts of impervious surfaces — roads, parking lots, sidewalks, buildings and roofs, driveways, and more, with little regard for the impact it will have on the natural environment. In Hillsborough County, where the city of Tampa is located, the population has increased by almost 170% from 1960 to 2010, and is a part of the most densely populated region of Florida (TBEP, 2016a). This growth is coupled with high rise developments and the creation of more impervious surfaces (Xian et al., 2007). The proximity of Davis Islands to the metropolitan Tampa area results in increased vehicular traffic to and from Davis Islands, adding to the contaminants that will be carried into the Hillsborough River and Hillsborough Bay with runoff from roadways.

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Impervious surfaces pose a threat to the natural hydrological state of any given site, increasing the volume and rate of surface runoff into waterbodies and sewage systems during rain events (Zhang et al., 2015)(US EPA, 2000)(US EPA, 2009)(Xian et al., 2007). When outdated gray infrastructure such as that in South Tampa is overwhelmed, the increased volume and rate of surface runoff due to the alteration of natural hydrology results in flooding, decreased groundwater recharge into aquifers, decreased infiltration, channel erosion, and non-point source pollution of waterways adjacent to impervious lands, which deteriorates ecosystems in streams, rivers, bays and our groundwater (Davis, et al., 2012)(Zellner, 2015)(US EPA, 2009)(US EPA, 2000)(Ahiablame et al., 2012 et al., 2012)(Dhaka, 2016l)(Xian et al., 2007).

Pollution in the Bays Tampa Bay, which encompasses Hillsborough Bay, is a Designated Aquatic Habitat and an Outstanding Florida Water, as well as the largest open water aquifer in the southeast region with an area of approximately four-hundred square miles. However, the bays are assaulted by more than four billion gallons of contaminants each year, including nitrogen from fertilizers, pesticides and heavy metals (Sherwood, 2012). Currently, over half of the nitrogen entering the bay is from stormwater runoff in urban and residential areas, with the amount of nitrogen entering the bay increasing every year (TBEP, 2016a). In addition to non-point source pollution, Tampa Bay has endured decades of point-source pollution from sewage dumping and industry waste, specifically fertilizer industry waste originating from the southern coast of Tampa Bay. In 2011, over seven million gallons of wastewater spilled into the bay due to the deteriorating infrastructure and dumping accidents. Tampa Bay is resilient due to its large size, but rehabilitation is a slow process that is constantly set back by more contaminating incidents

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(Spinner, 2011) (Bay Soundings, 2015). This point-source pollution can only be solved by stricter enforcement of laws related to pollution prevention and industry discharge, but reinvestment in Tampa’s stormwater infrastructure can alleviate the sources of additional nonpoint sources. Due to decades of mistreatment toward our bays, it has become increasingly important to be proactive with pollution control measures. Nitrogen and phosphorus levels in Tampa Bay are the highest in residential and agricultural areas in Hillsborough County, and Davis Islands is one of those residential areas where fertilizers and pesticides from landscape maintenance and other activities contribute to this concentration of chemicals that cause algae blooms in Tampa Bay (Xian, et al., 2007)(Sansalone, 2012).

The Tampa Bay Estuary Program studies the health of seagrass bed ecosystems in Tampa Bay to assess whether nitrogen loads are at manageable levels, or if action needs to be taken to improve the Bays’ water quality. In the last five years, water quality in Tampa Bay has had ups and downs, with instances of higher pollution in the bay correlating with increased rainfall and contaminated runoff. From 2007 to 2011, the Tampa Bay Estuary Program reported that total nitrogen in the bays is increasing slightly each year (Sherwood, 2016) (Bay Soundings, 2015).

Non-point source pollution from vehicular traffic, lawn products, atmospheric deposition, construction, garbage, metallic and galvanized surfaces, and animal waste (Ahiablame et al., 2012 et al. 2012)(Sansalone, 2012), is something that can be addressed on a local level with alternative strategies like Green Infrastructure, to treat contaminated stormwater before it enters the Hillsborough River and Hillsborough Bay.

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The Problems on Davis Islands: Outdated Infrastructure, Flooding, and Pollution Frequent flooding can be a serious issue in dense urban areas, leading to substantial property damage for homeowners and business owners. Flooding on Davis Islands is a threat to public safety, and an inconvenience for residents that may be trapped in their homes by flooded streets (Dhakal, 2016)(Xian et al., 2007). Flooding over impervious areas results in contaminated runoff circumventing the stormwater system, heading straight into the nearest body of water surrounding Davis Islands.

Outdated infrastructure combined with frequent rainfall results in the pooling of bacteria, and chemical-laden water in low lying areas on Davis Islands, sometimes for days, resulting in the perfect breeding grounds for insects that carry diseases. The impervious surfaces on Davis Islands direct polluted runoff into the storm sewer, where storm gravity mains transport runoff directly into the neighborhood’s canals, the Seddon Channel, and Hillsborough Bay that border the archipelago on the east and west sides respectively (City of Tampa, 2016c). Davis Islands is located at the mouth of the Hillsborough River in the northernmost part of Hillsborough Bay, which is part of greater Tampa Bay. Therefore, controlling pollutants in runoff is ever more essential to ensure the health of ecosystems in Tampa Bay, which is the largest estuary in Florida, and one of the largest estuaries in the southeastern United States (Xian et al., 2007).

The need for alternative stormwater solutions on Davis Islands, and the rest of South Tampa, is extremely visible during frequent storm events, including tropical storms and hurricanes during the summer months. Davis Islands’ stormwater system was originally designed in the 1920’s to handle afternoon showers, so even regular thunderstorms can overwhelm the deteriorating, century-old stormwater infrastructure (Brito, 2015). When there is anything close in magnitude to a tropical storm, thousands of sandbags are sold to residents

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waiting in lines, hoping to prevent floodwater from entering their homes. Most of the time, this is all a resident can do (Fox, 2015). During storms that caused record flooding in the summer of 2015, South Tampa residents were urged to remain indoors to avoid dangers associated with flood waters. Meanwhile, manholes bubbled over with water containing effluent as the aging stormwater and wastewater systems gave in (Fox, 2015). Residents became prisoners in their homes, and floodwaters pick up thousands of pollutants as entire neighborhoods are inundated with floodwaters. Homeowners not only must deal with the flooding itself, but the Federal Emergency Management Agency (FEMA) flood insurance rates that increase significantly when a storm causes millions of dollars of damage to homes and businesses (Boatwright, 2015).

The century-old gray infrastructure is a Municipally Separate Storm Sewer System (MS4), which is separate from the also antiquated wastewater system in South Tampa. South Tampa’s water infrastructure is so decrepit, that there were over four-hundred water main breaks in South Tampa in 2015 (Deeson, 2015). During heavy storms, the high volume of water overwhelms the stormwater system, resulting in wastewater effluent infiltrating through broken pipes into stormwater infrastructure. This mixture of runoff and effluent is then directed into surrounding waterbodies, escalating the rate of water pollution. The Tampa Public Works Department attempts to treat flooded areas with lime to neutralize organic matter in waters, but it is not possible to keep up with all areas, therefore tons of untreated sewage seep into the bay (TBEP, 2012)(Brito, 2015). When the American Society of Civil Engineers gave the City of Tampa’s stormwater system a “D” grade, disapproval of the clear infrastructural neglect became painfully perceptible to city officials (Deeson, 2015).

Davis Islands Water Pollution

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The list of pollutants that receiving waterbodies must withstand include sediments, garbage, sewage, feces, bacteria, viruses, raw sewage, vehicle greases and oil, heavy metals, pesticides, and fertilizers, and more. The presence of these substances in our waterways leads to increased rates of water related illnesses, deterioration of drinking water quality, and destruction of ecosystems, especially through algal blooms caused by excess nitrogen in fertilizer runoff (Ahiablame et al., 2012 et al., 2012)(Dhakal, 2016)(Xian et al., 2007). The City of Tampa’s primary drinking water is drawn from the Hillsborough River and treated at the David L. Tippin Water Treatment Facility. When the source of our drinking water is contaminated, it requires more energy resources to treat it, which can result in higher utility costs for Tampa residents (City of Tampa, 2015).

Residents of Tampa and Davis Island enjoy water recreation, but a halt is often put to activities after flooding carries bacteria into recreational waters on Davis Islands. As recent as July 2016, as well as frequently in previous years, a beach advisory was issued for Davis Islands’ recreational Bahia Beach, as the levels of enterococci bacteria at local beaches after a storm were much higher than safe levels recommended by the U.S. Environmental Protection Agency. This unhealthy level of bacteria in recreational waters was determined to be the result of runoff containing fecal matter from nearby parks and residences (Tampa Bay Times, 2016)(FHBP, 2016). Preventing Flooding while also biologically cleansing runoff by alternative means of stormwater management such as Green Infrastructure would alleviate these water quality issues significantly.

Stormwater Management Efforts in Tampa, FL

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Stormwater Utility - More Taxes As thunderstorms, have become more frequent and extreme due to climate change over the past decade, the urgency to upgrade existing gray infrastructure has become apparent in Tampa. In 2003, the City of Tampa passed a stormwater tax amounting to approximately $40 per year for homeowners, but these funds were mainly used for studies identifying flood prone areas and potential improvements, not taking any influential actions. While $6.4 million a year was raised from these taxes, more retention ponds were created around Tampa, and maintenance increased, but the effort was simply a band-aid fix for an issue in need of surgery (Goffard, 2004). As time went on and water problems became worse, the City of Tampa was at risk of being fined for violating federal standards regulating water discharged to rivers and bays (Danielson, 2015).

In November 2015, the Tampa City Council approved a plan that would raise $251.3 million for increased stormwater maintenance, as well as for more culverts, ponds, and culverts to be installed around the city. This plan was rejected because a city-wide tax the fee would potentially burden lower income residents, raising the $40 per year to $180 a year for small homes, and would result in resistance from residents who don't experience flooding in their neighborhoods (Flowers, 2016). Although this plan was rejected, summer storms were still on their way, while a very similar plan was in the works and scheduled for public hearings on September 1st, 2016 (Danielson, 2015).

On September 1st, 2016, ironically during the worst of Hurricane Hermine, the Tampa City Council approved a yearly tax to fund investments in drainage for the entire city. This new stormwater tax is scheduled to start this November 2016 for property owners, and remain in place for thirty years. Homeowners and business owners in flood-prone areas will both pay, with

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the tax starting at $45 annually, eventually increasing to almost $90 annually for small-sized homes. For larger property owners, the tax could be up to $10,000 a year or more because the tax amount is calculated based on the amount of impervious surfaces on each property. Although the tax is controversial, the city wants to make this process as painless as possible through exceptions and assistance programs. Specific areas of Tampa that do not experience issues with flooding are excluded from the tax, and programs will be put in place to help lower income households with the financial burden, assuaging angry residents who opposed the plan in 2015.

In addition, the City of Tampa has developed a mitigation credit to lower or completely waive the tax for residents if efforts are made to control runoff on site (Danielson, 2016)(City of Tampa 2016a). This has huge implications for Green Infrastructure in South Tampa, where owners of larger properties will be eager to lower this tax however they can, and Green Infrastructure is a cost-effective measure that can meet the requirements of the mitigation credit (US EPA, 2000)(City of Tampa, 2016a). When the $251 million tax is divided up into the areas needing most attention, South Tampa has the highest designation of funds, $75 million, to address the aging stormwater infrastructure (Danielson, 2016).

Stormwater Improvement Projects on Davis Islands — Never Part of the Plan The $75 million designated for stormwater retrofits in South Tampa does not specifically include Davis Islands, although Davis Islands is technically part of South Tampa. The reason for this is simply that the policy makers in Tampa do not see any economically feasible opportunities to improve existing stormwater infrastructure on Davis Islands. This is because runoff is discharged off the island and into surrounding waters, in contrast to the rest of mainland South Tampa, where runoff is transported over greater distances into ditches, detention and

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retention ponds (Public Works Staff, 2016)(City of Tampa, 2016c). The fact that Davis Islands is two islands does not help the case for flood prevention measures. In the eyes of the city, there is not much that can be done for stormwater infrastructure in the small community of just over 5,500 residents (Public Works Staff, 2016). In June 2015, a Davis Islands Civic Association Meeting resulted in a letter to the City of Tampa Stormwater Division addressing local issues and possible mitigation activities, but these pleas are usually ignored.

Although the Davis Islands Community Plan adopted in 2007 briefly mentions that “innovative technologies’’ have been employed to reduce flooding and stormwater runoff into the bay and canals, the City of Tampa has not included stormwater retrofits on Davis Island in its capital improvements budget for stormwater investments in the past decade, nor does it plan to over the next five years, shown on project maps in the 2015 Capital Improvements Operating Budget. This was before the 2016 Stormwater Fee passed, and even after the unfolding of this new policy, it is still unclear whether Davis Islands will be included in retrofit projects at all (DICA, 2016)(DI NPTF, 2013)(City of Tampa, 2015)(Hillsborough County Planning Commission, 2015). The only projects conducted by the City of Tampa on Davis Islands regarding stormwater have been part of roadway safety projects. Beginning in 2014 with estimated completion by 2018, efforts by the City of Tampa Transportation and Stormwater Divisions to optimize stormwater runoff flow were started through a $1.3 million pavement resurfacing project on Davis Islands. By 2018, almost all the roads on Davis Islands will be repaved with a mission to increase safety, improve drainage, and reduce ponding in certain areas (DICA, 2016)(City of Tampa, 2016a). Although projects like this have positive intentions, many roads that have already been repaved still experience severe ponding issues, since repaving does not change the overall grading of the site or residential driveways. In many cases, the flooding

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and ponding has worsened. As mentioned previously, solutions such as these still do not address the issues of contaminants in runoff, or reducing the volume, or peak flow of runoff from Davis Islands sites.

Since Davis Islands is intentionally left out of city-wide plans to improve traditional infrastructure, implementing Green Infrastructure as an alternative to gray would be a viable option since the city has not devised any other plans aside from repaving Davis Islands’ roads.

Green Infrastructure is often more cost effective than traditional stormwater infrastructure (US EPA, 2000), and would therefore be more appealing to city officials and policymakers who are concerned with the price tag associated with trying to fix runoff issues in such a unique environment. If cost benefits, as well as pollution and runoff reduction benefits are realized on Davis Islands through Green Infrastructure, Davis Islands will set an example for other Tampa neighborhoods to follow, saving the city millions of dollars. At the same time, we would be preserving the health of local waterways and beautifying our neighborhoods in Tampa, and adding various other amenities to the community, all while contributing to the city’s primary goal of flood mitigation.

Gray Infrastructure — Designed for Floods, Not Pollution Prevention Large expanses of impervious surfaces are only part of the stormwater runoff problem.

Gray infrastructure is engineered to work with impervious surfaces through curb and gutter systems, retention and detention ponds, pipes and drains, pumps, and ditches to manage stormwater. Gray infrastructure is meant to address flooding, collecting stormwater from impervious areas and transporting the water off-site as quickly as possible, which is a peak reduction approach. Unfortunately, the peak reduction approach that most commonly used in

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municipalities does not reduce the volume of runoff, or the pollutants carried with it. Runoff collected through gray infrastructure methods is piped to the closest water body or detention area, readily transporting pollutants into receiving waterbodies, or concentrating them in one location (Ahiablame et al., 2012 et al., 2012). Although gray infrastructure addresses flooding effectively in some places, gray infrastructure is not designed to address environmental issues that are associated with the disruption of natural hydrology (Dhakal, 2016). The large volume of polluted runoff that is transported through gray infrastructure often overwhelms the conventional system in Tampa, and results in more energy resources required to transport and treat this water to the nearest water treatment facility when wastewater infiltration occurs. When flooding occurs in Tampa, stormwater enters the wastewater system, and can result in double or triple the amount of water the Howard F. Curren Advanced Wastewater Treatment Facility must process (Bay Soundings, 2015). If the volume of stormwater can be reduced through means of Green Infrastructure, the energy used and sheer pressure on the treatment facility will be reduced.

Green Infrastructure should be employed all throughout Tampa, and the city will need to shift other mitigation approaches, such as repaving, to work with Green Infrastructure methods to optimize results. Davis Islands is only 1.36 square miles, and would be a realistic pilot project for the implementation of Green Infrastructure in the City of Tampa if traditional retrofits for the community are not part of the stormwater retrofit plans for the community.

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Part 2. Literature Review: Green Infrastructure What is Green Infrastructure?

Green Infrastructure and Low Impact Development

First and foremost, a clarification of the terms Green Infrastructure and Low Impact Development. Green Infrastructure strategies are sometimes referred to as a type of Low Impact Development, but most of the time the terms are used interchangeably. Both Green Infrastructure and Low Impact Development seek to control runoff volume, peak runoff rates, flow frequency, and aim to improve the quality of runoff (US EPA, 2000)(US EPA, 2015).

One of the main distinctions between Low Impact Development and Green Infrastructure is that Low Impact Development usually refers to methods used during the development phase of a site, but both aim to mimic the predevelopment hydrology of the area (Zellner, 2015)(Sansalone, 2012)(US EPA, 2000)(US EPA, 2015). Although Low Impact Development strategies can be implemented as a site retrofit, it is more cost effective to use this best management practice at the beginning of a project, especially when grading the site and installing Low Impact Development measures such as permeable pavements (US EPA, 2000).

Another way to distinguish Low Impact Development from Green Infrastructure is geographic scope. Green Infrastructure not only refers to micro-scale approaches such as bioswales, bio-retention, and green roofs on a single site or in networks that can capture, retain, and treat stormwater, but also more regional methods. This type of Green Infrastructure refers to larger scale stormwater controls such as interconnected green spaces like parks, trails, preserved nature centers, wildlife corridors, and even constructed wetlands in coastal areas, which are not considered Low Impact Development methods since they are on a regional scale (US EPA, 2015)(US EPA, 2000).

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While traditional, gray infrastructure is designed to collect, move, and discharge runoff as quickly as possible (US EPA, 2000), it is not designed to solve problems such as pollutant loading, sedimentation, erosion, decreased percolation, or the high volume and velocity of runoff (Ahiablame et al., 2012 et al, 2012). Green Infrastructure and Low Impact Development methods use passive, natural processes such as infiltration, evapotranspiration, sedimentation, adsorption, and other biological processes in plants and soils to reduce, retain and treat runoff before it reaches existing stormwater infrastructure, and receiving bodies of water (US EPA, 2000)(EPA, 2015)(Portland BES, 2016)(Sansalone, 2012). Green Infrastructure manages the quantity and quality of runoff by managing it where it falls, reducing the need for pipes, curb and gutter systems, that carry water away from the site. Therefore, Green Infrastructure often aims to reduce need for additional gray infrastructure installations (US EPA, 2015)(Portland BES, 2016)(Ahiablame et al., 2012 et al., 2012).

Minor differences set aside, Green Infrastructure and Low Impact Development are relatively new concepts in terms of stormwater management. For decades, traditional gray infrastructure has dominated how we control stormwater runoff in the U.S., which largely depends on impervious surfaces to transport water to treatment facilities (US EPA, 2000). As our urban boundaries and populations expand, impervious surfaces grow, decreasing the opportunities for water to percolate back into the ground, allowing it to carry numerous surface contaminants to its destination (Ahiablame et al., 2012)(Dhakal, 2016)(Xian et al., 2007). As cities around the country experienced the consequences of waterway pollution, the urgency to find an alternative route only heightened. In the 1990s, Prince George’s County in Maryland was in desperate need to address stormwater runoff issues, and became one of the pioneering states in the U.S. to use Green Infrastructure methods, followed later by progressive states like Oregon.

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Green Infrastructure is finally gaining popularity in the U.S., with cities like Chicago, Seattle, Portland, New York, Atlanta, Washington D.C. and more, setting the stage for this environmentally responsible approach to become the new era of stormwater management in our country (US EPA, 2000)(Portland BES, 2016)(Netusil et al., 2014).

Although the definitions of these two stormwater control terms overlap significantly, as do their methods, for the purposes of this project, the term Green Infrastructure will be used to refer to the site-level, stormwater retrofits that will be recommended for areas on Davis Islands, Tampa Florida.

Types Green Infrastructure and Associated Benefits Overall Benefits of Green Infrastructure Green Infrastructure has a variety of benefits, where stormwater management is the most important, as the main function of Green Infrastructure. Traditional gray infrastructure that consists of large pipes, and curb and gutter systems are designed to eliminate flooding on a site, but the increased runoff leaving the site is not taken into consideration. Runoff from sites with a high percentage of impervious surface moves very quickly, and in high volume into the stormwater system, which not only prevents water from percolating back into the ground, but leads to erosion, reduction in water quality and therefore reduced ecosystem health (US EPA, 2000)(US EPA, 2015)(Ahiablame et al., 2012). The more pollutants runoff carries with it, the worse the consequences will be for receiving waters. Green Infrastructure also provides the benefit of pollution prevention through the treatment of runoff, and offers a cost-effective, environmentally sensitive way to retrofit or replace existing stormwater systems. Green Infrastructure addresses all the issues associated with gray infrastructure, and the issues

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associated with the increasing number of impervious surfaces in our cities (US EPA, 2000)(US EPA, 2015)(Portland BES, 2016)(Ahiablame et al., 2012).

Previous studies on Green Infrastructure show that runoff volume and frequency from a site is always reduced across the board of techniques, but the performance is highly dependent on design, climate, soils, and location (Ahiablame et al., 2012)(US EPA, 2009)(US EPA, 2000)(Zhang et al., 2015)(Davis, et al., 2012)(Stovin et al., 2007)(Mentens et al., 2005). While Green Infrastructure retains runoff on site, it treats the “first flush,� of runoff, or the first 1/2 inch of runoff, which contains the highest amount of pollutants during a rain event. Often, Green Infrastructure can control up to the first two inches of runoff during a rain event, treating much more stormwater on site than gray systems. The combination of slowing down and retaining runoff allows the biological processes in vegetation and soils to effectively break down contaminants in runoff, preventing their transport to sensitive ecosystems. (US EPA, 2000)(Ahiablame et al., 2012).

In addition to runoff volume control and reducing pollution, Green Infrastructure is also typically more cost effective than gray infrastructure (US EPA, 2000)(US EPA, 2015)(Portland BES, 2016)(Ahiablame et al., 2012)(Sansalone, 2012)(IFAS Rain Gardens)(Kraus Spafford).

Gray infrastructure usually involves heavy engineering, excavating, large pipes, pumps, cement, and creation of more impervious surfaces that gray stormwater systems rely on to transport runoff far from where it originally hit the ground. Compared to Green Infrastructure where vegetation does most of the hard work, the cost of gray infrastructure can seem unreasonable, especially when the benefits of Green Infrastructure external to runoff control are factored into the equation. In addition to much lower construction costs, long term life cycle and maintenance

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costs are significantly lower than gray methods (US EPA, 2015)(Portland BES, 2016)(US EPA, 2000).

Green Infrastructure not only mimics the natural hydrology of the site, creating a functional hydrological landscape, but the vegetation component in Green Infrastructure has an entire set of benefits external to stormwater control, that no gray infrastructure could ever achieve. The vegetation used in Green Infrastructure creates landscaped areas throughout a site that would not have been there otherwise, increasing green space throughout neighborhoods.

Therefore, Green Infrastructure can be valuable in places where green space is limited and residents lack a connection to nature. To be the most efficient, these functional landscaped areas have a variety of plant species ranging from water loving, to drought tolerant plants that can endure seasonal changes (Krauss & Spafford, 2009 Spafford)(Zhang et al., 2015)(IFAS Rain Gardens). This variety of plants is aesthetically pleasing compared to a curb and gutter, or grassed ditch, so Green Infrastructure therefore contributes to the sense of place, quality of life, and urban aesthetic in an area, where residents can begin to take pride in the unique landscape of their community (Tzoulas et al., 2007). If Green Infrastructure is implemented on a large scale, vegetation can also contribute to urban biodiversity, mitigate air pollution, and has been shown to reduce temperatures in microclimates, reducing the urban heat island effect (Sansalone, 2012)(US EPA, 2015)(Tzoulas et al., 2007).

While the different Green Infrastructure strategies all share the goal of controlling runoff volume, rates, and improving stormwater quality in an environmentally sensitive way, the different strategies are unique in their design and vary in performance of each function (Zellner, 2015), so each is discussed individually.

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Bioretention Basins: Rain Gardens, and Bioswales These terms are often used interchangeably, and that is because they function very similarly in terms of stormwater control, but the term used to describe the Green Infrastructure technique often depends on the site and size of the basin or garden.

Bioretention basins and rain gardens commonly refer to a shallow, low sloped depressional area on a site, planted with vegetation that is designed to attenuate and biologically treat stormwater runoff (Sansalone, 2012)(US EPA, 2000)(US EPA, 2015)(Portland BES, 2016).

Often when the term bioretention basin is used, it is referring to a much larger application of Green Infrastructure, while a rain garden usually refers to a smaller application, such as in a residential lawn or commercial setting near a structure to capture runoff from the building roof.

Bioswales, sometimes called green streets (US EPA, 2000)(Netusil et al., 2014), are a type of open channel bioretention system, but bioswales are linear in application, often used along the right-of-way in an urban environment, on medians, or along the perimeter of parking lots to reduce pollution from automobiles (Ahiablame et al., 2012)(White, 2014)(Acomb & Clark, 2008a). Sometimes these Green Infrastructure strategies can be difficult to distinguish from traditional landscaping, because the functional part of the design takes place in the depressional area. This makes it easy to integrate these systems into just about any environment (US EPA, 2000). Engineered for each site, the growing media restricts the flow of runoff, allowing evapotranspiration to occur, and retaining the water until it infiltrates back into the ground (Davis, et al., 2012)(Acomb & Clark, 2008a)(US EPA, 2000). While the water is retained in the planter or depressional area, it is filtered through engineered soil mixes and plant roots that break down and neutralize contaminants that would otherwise leave the site (Sansalone, 2012)(US EPA, 2000)(US EPA, 2015)(Portland BES, 2016)(Ahiablame et al., 2012). Plant selection in

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these systems is very important, since there must be a combination of xeric and hydric plants to accommodate drought periods, as well as water ponding that will submerge plants in the center of the basin for hours, or sometimes longer (US EPA, 2000)(Acomb & Clark, 2008a).

When bioretention basins, rain gardens, and bioswales are used in settings with highly conductive soils, the retained water slowly percolates back down to the water table. The depressed area will fill up with water when the percolation rate is slower than the rate of runoff entering the system, for example, during a large storm (Davis, et al., 2012). When these strategies are used in settings where soil drainage is poor, a drain can be installed underground at the base of the depression, called an underdrain, which is usually connected to the existing drainage network near the site. This reduces the amount of time water ponds in the basin, and allows the basin to treat a higher volume of runoff than a non-drained system could, and more quickly since the water drains to a destination without restrictions. Therefore, systems with an underdrain would be suitable for climates with more frequent and intense rainfall, such as Davis Islands, Tampa (Davis, et al., 2012)(Acomb & Clark 2008b)(IFAS Rain Gardens).

Bioretention Systems: Runoff Volume Bioretention basins, rain gardens and bioswales can readily capture the entire inflow volume from a rain event, reducing runoff volume and peak flow rate by up to 97% in some cases (Ahiablame et al., 2012). Previous studies have shown that bioretention basin, rain garden and bioswale performance can vary significantly, and this is due to variations in climate, soils, location, design, and size. In North Carolina, a bioretention system only reduced runoff volume by 14% in a larger rain event (Davis, et al., 2012). In Maryland, a 22% reduction was seen in one study (Davis, et al., 2012) while other studies in Maryland showed 61% volume reductions at

24

another site (US EPA, 2000). In Ontario, Canada, 6% to 30% reductions in runoff were seen for roadside bioswales (US EPA, 2000), and 60% reductions in runoff were seen in a Pennsylvania study where runoff quantity and quality was measured for a parking lot bioswale (Davis, et al., 2012). Although research findings vary significantly in terms of volume attenuation performance, bioretention basins and rain gardens are still a viable alternative to gray infrastructure to reduce site runoff, which does not reduce volume or peak flow at all (Ahiablame et al., 2012).

Bioretention Systems: Cost According to research done by the U.S. Environmental Protection Agency, bioretention systems generally require less space and maintenance than large detention ponds and curb and gutter conveyance systems. The cost for bioretention systems can be between $3 and $15 per square foot ($130,000 to $650,000 per acre) on the higher end of the spectrum (US EPA, 2000), or $5,000 to $10,000 per acre in some cases (IFAS Rain Gardens). For bioswales, costs as low as $0.50 per square foot have been seen since these systems are a simple retrofit in most cases (Acomb & Clark 2008b)(US EPA, 2000), and in other cases report $15 to $20 per square foot (US EPA, 2000). Gray infrastructure can be $40 to $50 per square foot, with higher long-term maintenance costs, and less overall benefits. Construction costs have been reported to be 50% to 72% lower for sites that include these Green Infrastructure Strategies in newly constructed developments instead of traditional gray infrastructure (IFAS Rain Gardens)(US EPA, 2000).

Some municipalities, such as Seattle, New Orleans, and Portland, have reported city-wide savings of at least 10% on stormwater management, amounting to millions of dollars saved each year (US EPA, 2000)(US EPA, 2015)(Watkins-Miller, 1997)(Portland BES, 2016).

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Bioretention Systems: Pollution Reduction Bioretention basins, rain gardens and bioswales also reduce contaminants in runoff.

These contaminants include nutrients like nitrogen and phosphorus found in lawn products, bacteria and viruses, heavy metals such as lead, zinc, and copper, sediments, suspended solids, and various other non-point source pollutants. These contaminants are captured and removed from runoff through sedimentation and other biological processes in the soils and plant roots.

The Center for Watershed Protection’s National Pollutant Removal Database covers 166 studies, and reports that bioretention basins, rain gardens and bioswales have a 79% to 86% removal efficiency for heavy metals, 15% to 65% removal efficiencies for nutrients, and up to 89% removal efficiency for total suspended solids (CWP NPRD, 2007a). Research on 17 bioretention sites in the U.S. and other countries show 31% to 99% reductions in heavy metal concentrations, 70% to 99% reductions of bacteria, 47% to 99% reductions in total suspended solids, and 40% to 99% reductions in nutrient concentrations (Ahiablame et al., 2012). In Maryland, heavy metals were reduced by 43 % to 97%, total suspended solids 67%, and nutrients 15% to 67% (US EPA, 2000). In Chicago, phosphorous and nitrogen in runoff were reduced by 79% and 65% respectively, with a reduction of 91% for total suspended solids (US EPA, 2015). In Portland, Oregon, 50% of annual total suspended solids were removed from runoff by bioswales (Portland BES, 2016)(Watkins-Miller, 1997). Studies by the Environmental Protection Agency show total suspended solids being reduced by at least 65% in Florida, Virginia and Maryland (US EPA, 2000). In a parking lot bioswale study in Gainesville, Florida, total nitrogen in runoff was reduced by 90%. Although little research on these Green Infrastructure methods has been done in

26

Florida, results from other studies show that bioretention basins and rain gardens are an effective way to prevent non-point source pollution and improve stormwater quality.

Bioretention Systems: Diagrams Diagrams: The first two images below are diagrams of bioretention basins, or rain gardens, which are bioretention basins on a smaller scale. The last two images are depictions of bioswales, linear applications of bioretention systems.

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28

Image Sources: holemanlanscape.com, landskapsarkitect.tumblr.com, http//bladesandgoven.com/on_the_boards/visualization/low_impact_development/, frantzlandscape.com

Bioretention Systems Benefits Table: The table below summarizes the data researched that translates into benefits of bioretention systems.

Study

Location(s)

Runoff Reduction (%)

Heavy Nutrient/Bacteria Metal/TSS Reduction Reduction (%) (%)

EPA Literature Review on LID 2000

Maryland Florida Virginia Canada

MD: 61%; CAN: 6%30%

Heavy Metals MD: 43%-97% FL: 62%-94% VA: 28%-55% TSS MD: 67%-85% FL: 98% VA: 65%

Nutrients MD:15% - 92% FL: 18% - 48% VA:11-41%

$3 - $20 sq. ft.;

EPA Opportunities for Including GI in Municipal Operations 2015

Maryland Louisiana Washington Illinois Oregon

—

TSS IL: 91% WA: 80%-85%

Nutrients IL: 65%-75% WA: 80%-85%

10% - 15% savings citywide.

IFAS FL Field Guide to LID: Rain Gardens 2008

—

—

—

—

Cost ($)

50%-72% savings on construction

$3-$15 sq. ft.; $5,000$10,000/acre; Save up to 50%

29

Center for Watershed Protection (NPRD) 2007

166 studies

—

Heavy Metals 79%-86% TSS 59%-85%

Portland BES, 2016

—

—

Sansalone 2012

Florida

—

TSS: 97%

WatkinsMiller, 1997

Oregon

—

TSS 50%

Ahiablame et al., 2012

17 Studies

48% - 97%

Davis, 2012

Maryland North Carolina Pennsylvania

MD: 22% NC: 14% PA: 48%

—

—

—

GRAY

Anywhere

0%

0%

0%

$40-$50/sq.

(US EPA, 2000)

—

Nutrients 5%-65%

—

Nutrients 50% - 94%

—

Heavy Metals 31% - 99% TSS 30% - 99%

Nutrients 14% - 99% Bacteria 70% - 99%

—

Less than curb and gutter.

13%-15% savings; $0.50/sq. ft.

Save $35/sq. ft.

—

Green Roofs Green roofs, also known as ecoroofs, living roofs, or vegetated roofs, are a type of Green Infrastructure used on rooftops to manage stormwater quantity and quality on site, compensating for the replacement of pre-development vegetation with an impervious roof (Berndtsson et al., 2009). Green roofs can cover an entire roof or just a fraction of a roof, and consist of multiple layers. These layers include the vegetation, engineered growing media, a filter fabric, drainage material, root barriers and a waterproofing membrane to protect the roof from root penetration (Ahiablame et al., 2012)(Zhang et al., 2015).

Green roofs can be intensive or extensive. Intensive green roofs are six inches or more in substrate depth. They are more commonly seen on newer buildings, where the additional structural load (50 to 300 lb./sq. ft.) is taken into consideration at the design phase of the project (Dunnett & Kingsbury, 2008). Intensive roofs support larger plant species, including shrubs and small trees, and can also be suitable for growing food crops. The depth and maintenance

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involved with intensive roofs makes them costlier than an extensive roof (US EPA, 2000)(Berndtsson et al., 2009). With the additional structural support in place, intensive green roofs are often accessible to the public or building occupants, providing the additional amenity of green space to the site (Berndtsson et al., 2009).

Extensive roofs have substrate depths of less than six inches, and are usually composed of shorter growing plant species such as sedums, meadow grasses, herbs and small shrubs (Dunnett & Kingsbury, 2008)(US EPA, 2009). Extensive roofs are seen more often in retrofit applications, or applications on large buildings that do not intend to allow public roof access (Stovin et al., 2007). The smaller plant species and shallower media depth result in an additional structural load that most existing buildings can handle (15 to 35 lb./sq. ft.) without additional support (Dunnett & Kingsbury, 2008). Extensive roofs are less expensive than intensive roofs because they are easier to install, and usually don't require as much maintenance as an intensive roof would in terms of irrigation, plant health, and aesthetics. Since extensive roofs are not always meant for public access, they do not always require as much attention (Dunnett & Kingsbury, 2008), while many intensive roofs are meant to look beautiful, as well as retain stormwater.

Green roofs are not only effective in terms of stormwater management, but have also been studied for the various other benefits they have to offer. The addition of a green roof system on a roof has been shown to extend the life of the underlying roof materials, reducing the frequency in which the original roof must be replaced, which saves the building owner money over time. Growing substrate and vegetation also forms an additional layer of insulation on the building roof, which has been shown to reduce heating and cooling costs in many cases. Green roof vegetation can also improve air quality and reduce ambient temperature through

31

evapotranspiration and by raising albedo, reducing the urban heat island effect. Vegetation and other components of the green roof such as branches, logs, and rocks can add biodiversity to a site by providing a habitat for numerous invertebrates and birds that would not have had habitat there otherwise (Dunnett & Kingsbury, 2008)(US EPA, 2000)(Stovin et al., 2007)(Zhang et al., 2015)(US EPA, 2009). Green roofs that are viewable from the ground and other buildings are a public amenity, contributing to green space, sense of place, and increasing biophilia among building occupants (Tzoulas et al., 2007).

Green Roofs: Runoff Volume Reduction Rooftops are one of the largest sources of runoff, accounting for 40% to 50% of impervious surfaces in urban areas (Stovin et al., 2007). Green roofs are a direct way of reducing this runoff by reducing the amount of impervious area on a site, replacing vegetation that was present pre-development. Green roofs slow the runoff from rooftops, and can retain much of runoff in larger rain events, if not all runoff during smaller rain events (US EPA, 2009).

Green roofs are more efficient in high intensity, shorter duration rain events than rain events that are longer in duration, because the growth media in the substrate becomes saturated and retention decreases over time. This is also dependent on the media depth, and roof slope. The steeper the slope of the roof, and the shallower the media depth, the more runoff there will be (Zhang et al., 2015). Once the water retention capacity has been reached, excess water is converted to runoff, but still does not runoff as quickly (Ahiablame et al., 2012)(Berndtsson et al., 2009)(US EPA, 2009)(Zhang et al., 2015).

Green roof runoff retention is dependent on many factors, but various studies have been conducted in many climate types to evaluate the runoff reduction potential a green roof can

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provide for a site. Runoff volume reductions range from 20% to 100% in a study covering 14 green roofs across the globe (Ahiablame et al., 2012). This range is large, but green roofs are extremely effective in temperate climates, reducing annual runoff by at least 50% with substrate depths of three inches (US EPA, 2009)(US EPA, 2000). The U.S. Environmental Protection Agency performed numerous laboratory experiments simulating rainfall scenarios to evaluate the effectiveness of green roofs, and found that at 38% to 54% of runoff volume was attenuated for moderate to heavy rainfall events (US EPA, 2009). Other individual studies reported similar results. A Philadelphia, Pennsylvania green roof study reported a 40% to 48% runoff retention average (US EPA, 2000). A Charleston, North Carolina study reported 60% to 85% runoff retention on a green roof (Stovin et al., 2007), and in Athens, Georgia, 88% of runoff was retained for a smaller rain event, while 48% of runoff was retained for a larger rain event (Zhang et al., 2015). In Portland, Oregon, one of the leaders in the U.S. in terms of implementing green roofs city-wide, over 60% of runoff that hits the city’s green roofs is attenuated (Portland BES, 2016).

A study conducted in Asia shows runoff retention values that would be like those that may be reported in Tampa, Florida. The study took place in Chongqing, China, where runoff retention for a green roof in a humid subtropical climate was evaluated. The results were promising, reducing runoff from smaller events by 100%, and 35-40% for larger rain events (Zhang et al., 2015). Although green roof runoff retention varies with media depth, rainfall intensity, duration, slope, and vegetation, retention values can be used to estimate the potential for flat green roofs in a humid subtropical climate, with media depths of four inches, in Tampa Florida.

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Green Roofs: Cost The cost of installing and maintaining a green roof is perhaps the most limiting factor in the decision to include one as a stormwater management control. Often, green roof construction costs are more expensive than installing a traditional roof, but other benefits that a green roof provides are not usually considered in the cost comparison, leading many developers to dismiss the idea of a green roof all together (US EPA, 2009). When compared to gray infrastructure methods that could be used on a site, the cost range for implementation is about the same in some more expensive retrofit cases, where green roofs can be up to $40 per square foot (US EPA, 2009)(Ahiablame et al., 2012), and gray infrastructure is approximately $40 to $50 per square foot (US EPA, 2000). Then again, the additional benefits of a green roof compared to gray infrastructure are not factored into the cost. Aesthetic benefits, improvement of runoff quality, added biodiversity, and reducing the urban heat island effect can be hard to quantify in terms of dollar value, but extending the life of the roof and reducing energy costs are quantifiable benefits of a green roof that should be considered in the decision-making process.

In Portland, Oregon, where over forty acres of green roofs have been implemented, the cost for retrofit projects ranges from $15 to $25 per square foot, and $10 to $15 per square foot for new roofs (Portland BES, 2016), and some green roof installations with shallower media depths can be as low as $6 per square foot (US EPA, 2009). The cost of implementing a green roof on a site varies, depending on whether the roof is intensive or extensive, the plant selection, the maintenance required for those plants, and whether irrigation is installed.

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Green Roofs: Pollution Reduction Conventional roof runoff usually contains contaminants that were deposited onto the roof surface by wind and atmospheric deposition. This creates a concentrated source of pollution that then washes away into stormwater systems and waterbodies with runoff. Replacing a conventional roof with a green roof eliminates this problem, where vegetation acts as a biological filter to reduce the pollution content of rainfall in addition to preventing roof contaminant build-up (US EPA, 2009).

In highly urbanized regions that experience severe air pollution, acid rain can be an issue for waterbodies that receive unfiltered runoff from storms. Acid rain not only has negative effects on surface waters and aquatic ecosystems, but acidity in runoff can lead to higher concentrations of heavy metals in runoff, exacerbating the pollution problem (US EPA, 2009).

Green roofs have been shown to neutralize acid rain consistently through biological processes in vegetation, making green roofs a valuable tool for places where air pollution leads to acid rain, such as the northeastern U.S. (Berndtsson et al., 2009)(US EPA, 2009)(Zhang et al., 2015)(Portland BES, 2016).

In terms of nutrient and heavy metal reductions, the results are mixed for green roofs.

Research on green roofs in Malmo, Sweden, and Fukuoka Japan, studied the nutrient removal for two green roofs in urban areas. The green roof in Malmo was an intensive roof, and this roof reduced nitrogen in runoff through specific plant species, while the extensive roof had opposite results. Total nitrogen concentrations in runoff from the extensive roof were approximately the same as urban runoff levels due to the growing substrate that was used in the experiment (Berndtsson et al., 2009). Research conducted by the U.S. Environmental Protection Agency show that compared to conventional roofs, green roofs have one-quarter less nitrate per acre

35

from atmospheric deposition (US EPA, 2009). Another green roof study in Chongqing, China, showed promising results, where nitrate level was halved on the green roof compared to a traditional roof, and total suspended solids in runoff were also much lower than the urban runoff values (Zhang et al., 2015). Green roofs can be a sink for nitrogen, if they are designed properly.

Similar results have been seen with phosphorus and heavy metal concentrations in green roof runoff, where higher concentrations of phosphorus and heavy metals are seen when the incorrect substrate is used, such as lava rock, pine bark, Haydite, or Lassenite (Zhang et al., 2015)(Berndtsson et al., 2009)(Ahiablame et al., 2012). The use of fertilizers on green roofs also results in phosphorus leaching, so this should be avoided at all costs (Zhang et al., 2015).

However, when the growing substrate is suitable for the climate and vegetation, green roofs can serve as a sink for phosphorus and heavy metals such as lead, iron, and zinc in rainwater (Berndtsson et al., 2009). Therefore, when constructing a green roof, it is essential to select a suitable growing substrate and vegetation to prevent nutrient and heavy metals leaching from the system. When planning for stormwater management, green roof runoff can be directed to other Green Infrastructure sites to further treat runoff before it reaches waterways (Ahiablame et al., 2012)(Berndtsson et al., 2009)(US EPA, 2009). Studies evaluating the runoff treatment ability of green roofs are limited, but future research can potentially solve these substrate issues to ensure that green roofs do not contribute nutrients or heavy metals to runoff. However, green roofs are still a very effective way to reduce runoff volume from a site.

Green Roofs: Diagrams Diagram: The diagram below is a sectional diagram of the Tremco VR Lite vegetated roofing system. Each component of the layered green roof system is labelled with a letter. This is the system that will be used on Davis Islands

36

Image Source: Tremco VR Lite Specifications Booklet

37

Green Roof Benefits Table: The table below summarizes the data researched that translates into benefits of green roof systems.

Study

Location(s)

US EPA, 2009

Various Lab Experiments

Portland BES, 2016

Oregon

Ahiablame et al., 2012

14 Studies

US EPA 2000

Runoff Reduction (%) 38% - 54%; Annually: 50%

Chongqing, China; CT, NC

Berndtsson et al., 2009

Malmo, Sweden, Fukuoka, Japan

Stovin et al., 2007

Sheffield, UK, Georgia

Mentens et al., 2005 2005 ASPHALT ROOF

Cost ($)

—

—

$6-$40 / sq. ft.

—

—

—

$15-$25 / sq. ft. (retrofits); $10-$15 / sq. ft. (new roofs)

Overall: 20%100%; GA: 39% 90%

—

—

$35-$40 / sq. ft.

—

—

—

Pennsylvania PA: 40% 48%

Zhang 2015

Heavy Metal Nutrient/TSS Reduction Reduction (%) (%)

CHI: 35%100% CT: 51.4% ann.

GA: 48% 88% —

—

Nutrients 64% N; Inc. P (media) TSS Always reduce

Heavy Metals Nutrients Reduced Pb, Reduce N, Fe, Zn, increase P (media)

—

—

UK: 34% 56% NC: 60% 85%

—

—

—

18 Studies

19% - 73% Annual: 45%

—

—

—

Anywhere

3%-5% (if gravel on asphalt) (Zhang et al., 2015)

0%

0%

Green Roof adds additional cost; but reduces roof lifecycle costs and has added. benefits.

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Permeable Pavements Permeable pavement and pavers are an alternative to traditional asphalt and concrete surfaces such as roads, parking lots, driveways, and other impervious surfaces. Both permeable pavements and pavers are designed to reduce the runoff on site, while filtering pollutants through the sub-grade aggregate or sand layers beneath the pavement or pavers (Portland BES, 2016)(US EPA, 2000)(Ahiablame et al., 2012)(US EPA, 2015).

Pervious pavement is composed of asphalt or concrete containing large stone aggregates that create pore spaces for runoff to percolate through. After percolating through the pavement, runoff is retained for a short period in a layer of crushed aggregate beneath the pavement. The concrete and asphalt used in permeable pavements is very like traditional concrete and asphalt, but designed with more pore space, so when applied, the result looks slightly thicker than traditional pavement (Portland BES, 2016)(US EPA, 2000).

Permeable pavers, or unit pavers, are composed of brick, stone, concrete or cobble stones, and typically form interlocking patterns. On sites where infiltration is limited, an underdrain can also be used, but this method is less efficient since permeable pavers are best used where infiltration can occur easily. With permeable pavers, runoff infiltrates through gaps or pores in the pavers and into an underlying sand bed, allowing water to infiltrate into the subsoil.

Permeable pavers are often used in residential settings on a small scale, as well as for crosswalks, sidewalks, bike lanes, alleys, and parking spaces (Portland BES, 2016)(US EPA, 2015)(US EPA, 2000).

These types of alternative pavements have some limitations. Pervious alternatives should be used in areas where soils drain moderately well, and where the sediment load is not too high.

Sediment in runoff can result in clogging of the pore spaces that allow infiltration through the

39

pavement, so in some cases using permeable pavements as a secondary stormwater control in combination bioretention basins or bioswales is a preventative maintenance approach. Permeable alternatives to pavement can only be used in areas where hazardous materials are not present to prevent contaminants from easily percolating through to the water table (Portland BES, 2016)(US EPA, 2015).

Permeable Pavements: Runoff Volume Reduction Permeable pavements have shown to be very effective at recharging groundwater and reducing runoff from leaving a site, especially in areas where the slope is flat and subsoils on site drain well (US EPA, 2000)(Portland BES, 2016)(CWP, 2007b). Permeable pavements may not have vegetation to absorb and treat runoff, but sand and aggregates filter water, and when used strategically as a complement to other types of Green Infrastructure, the results are significant enough to potentially replace traditional gray infrastructure entirely on a site (US EPA, 2000)(Sansalone, 2012). Permeable pavements can absorb all the runoff from smaller rain events, and almost always retain the first flush in larger rain events, even in soils that drain only moderately well (Ahiablame et al., 2012). A study done at the Florida Aquarium parking lot, in Tampa Florida, evaluated the runoff volume and quality from areas where permeable pavement and bioswales were implemented together. This method of combining both types of Green Infrastructure resulted in runoff reductions of 80% to 90% (US EPA, 2000). In research covering ten studies of permeable pavements in various locations, runoff reduction varied from 50% in Florida, to 93% in Georgia, USA (Ahiablame et al., 2012).

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Permeable Pavements: Cost Permeable pavements and pavers used as an alternative to asphalt or concrete can cost the same as these traditional pavements (Sansalone, 2012), but sometimes are costlier, especially when all benefits are not taken into consideration. Per research done on permeable alternatives by the US EPA, costs can range from $2.00 to $4.00 per square foot (US EPA, 2000). In Portland, Oregon, permeable pavements have been reported to costs as much as $11.00 per square foot for pavements, and $5.00 per square foot for permeable pavers, including the cost of the base rock (Portland BES, 2016). The cost for this type of Green Infrastructure can seem high compared to the low cost of asphalt and concrete, which ranges from $0.50 to $2.00 per square foot (US EPA, 2000). However, in addition to reducing or eliminating the need for additional stormwater infrastructure on a site, pervious pavements have lower long term maintenance costs, requiring fewer repairs compared to traditional pavements, which further reduces the overall cost of this method. In colder climates where roads often freeze, permeable pavements are less prone to cracking, reducing associated repair costs in these climates (Portland BES, 2016).

Permeable Pavements: Pollution Mitigation Permeable pavements and pavers are an effective means for pollution mitigation on a site, especially since these alternative pavements are often implemented in parking lots and roads, or other places where automobiles are used or parked. Automobiles are a source of many contaminants found in runoff, so controlling these contaminants at the source is a proactive way to control runoff quantity and quality on sites that would otherwise be completely impervious.

In the study done in Tampa, Florida, pervious pavements combined with small scale bioretention systems reduced heavy metals by 75% to 91%, total suspended solids and reduced

41

nutrients by 42% (US EPA, 2000). A study in Gainesville, Florida showed nutrient reductions of up to 80% (Sansalone, 2012). In research covering ten studies of permeable pavements, heavy metal reduction ranged from 20% to 99%, total suspended solid reduction ranged from 0% to 94%, nutrient reduction 10% to 85%, and bacteria in runoff was reduced by 98%-99% in the permeable pavements (Ahiablame et al., 2012).

Permeable pavements also have been shown to break down grease and oils from automobiles due to microbial activities in the sand and aggregate layers beneath the pavement, preventing these substances from entering waterways (Ahiablame et al., 2012). Traditional asphalt also leaches harmful contaminants from binders in the pavement into runoff, which adds to pollutant concentration on top of contaminants that are deposited on the surface of the pavement. Permeable pavements eliminate this issue, and some types of pervious concretes even neutralize the acidity of runoff infiltrated through the system. In addition, permeable pavements and pavers also reduce thermal pollution on a site, because these pavements do not absorb and emit thermal radiation as traditional asphalt would (Sansalone, 2012)(Ahiablame et al., 2012).

Permeable Pavements: Diagrams Diagram: The image below is a sectional diagram of a permeable pavers system. Permeable pavements are very similar, except they look more like traditional concrete on the top layer.

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Image Source: http-//farleypavers.com/permeable-paver-installation/

Permeable Pavements Benefits Table: Study

Location(s)

Runoff Reduction (%)

Heavy Metal/TSS Reduction (%)

Nutrient/ Bacteria Reduction (%)

EPA Literature Review on LID 2000

Tampa, FL

80%-90%

Heavy Metals: 75%92% TSS: 91%

Nutrients: 42%

Ahiablame et al., 2012 2012

10 Studies

50%-93%, in some cases 100%

TSS: 0%94% Heavy Metals: 20%-99%

Bacteria:98%99% Nutrients: 10% - 85%

Sansalone 2012

Gainesville, FL

—

—

Portland BES, 2016

Portland, OR

—

—

—

$11/ sq. ft. (pavement) $ 5/ sq. ft. (pavers)

ASPHALT

Anywhere

0%

0%

0%

$0.50 - $1.00 sq. ft.

(EPALID)

Nutrients: 80%

Cost ($)

$2.00 - $4.00 sq. ft.

—

Same as conventional

**PPs reduce LT maintenance costs.

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Green Infrastructure Barriers Site Development Limitations The ability to use Green Infrastructure is not only dependent on the spatial limitations of a site, but also depends on site conditions such as soil type and drainage, slope, and depth to the water table (US EPA, 2000). To use Green Infrastructure techniques that function independently of the existing stormwater infrastructure, or without an underdrain, the soils must drain well enough to allow runoff to percolate into the ground in a timely manner. In soils that have low conductivity, underdrains can be used to reduce the ponding time in bioretention systems, while also allowing a larger volume of water to be treated, since the percolation rate is not entirely dependent on the natural drainage of soils on site (IFAS Rain Gardens)(Krauss & Spafford, 2009 Spafford).

When Green Infrastructure plans are included from the very beginning stages of a project, it is easier to implement and often less expensive. However, in a retrofit project such as Davis Islands where Green Infrastructure is implemented on a site that has already been developed, the design and implementation process can face some challenges. Some of these challenges include compacted soils, potential utility conflicts in places where most utilities are located underground, and space constraints (US EPA, 2015). For example, installing bioswales along a busy right of way is more difficult than installing the bioswales during the construction phase of a new road that is not open yet.

In addition to the physical conditions on a site, Green Infrastructure practices are limited by municipalities through zoning regulations or codes and ordinances related to stormwater management (Ahiablame et al., 2012). These sets of rules determine how stormwater management practices can be used and where they can be used on a site, whether it is on a public

44

or private development. Some communities have development regulations that favor gray infrastructure, so there could be rules in place that prevent practices that would reduce the amount of impervious cover on a site, to ensure that the existing stormwater infrastructure designed to convey runoff off-site remains in-tact. These regulations can be the greatest obstacle to Green Infrastructure in communities, as they are difficult to overcome and change to include new, environmentally sensitive techniques (US EPA, 2000)(CWP, 2007b). Municipalities like Tampa have technical manuals about stormwater management practices for public and private development, most of which do not include innovative, alternative stormwater management techniques such as Green Infrastructure (City of Tampa, 1996ab).

Governance Ordinances and development regulations are part of the site development limitations to green infrastructure, but also part of limitations associated with governance over stormwater management in municipalities. As mentioned before, development regulations in private and public settings can be difficult, if not impossible to overcome, because Green Infrastructure is usually not addressed at all in such regulations, if it is not clearly stated that Green Infrastructure is not an accepted practice (Ahiablame et al., 2012). For example, in the City of Tampa, technical manuals and city codes related to stormwater management do not specifically address Green Infrastructure, nor are these practices banned. In places like Tampa, Green Infrastructure guidelines could be factored into policies without having to change what is already there, because Green Infrastructure is simply a practice the municipality hasn't explored (City of Tampa, 1996ab).

45

City governments are also reluctant to use Green Infrastructure as an alternative stormwater management method because the scientific research behind Green Infrastructure has not shown that cost benefits are substantial enough to shift toward a practice that seems much more costly than traditional, and very well-integrated gray methods (US EPA, 2015)(Dhakal, 2016). Runoff reduction benefits alone from Green Infrastructure are not enough to convince municipalities that Green Infrastructure is a more cost effective method (US EPA, 2009), so future research should aim to quantify construction cost reductions, water and air pollution reduction, added biodiversity and habitat, flood reduction, aesthetic and social benefits, new job generation, and lower life cycle costs of Green Infrastructure methods.

Green Infrastructure can also be more difficult to govern in general, because these strategies are often on private property. The typical approach a municipality has towards stormwater management does not include property owners or non-governmental organizations, as Green Infrastructure often does, because traditional stormwater management has a top-down approach, where the city controls every aspect of gray infrastructure independent of residents (Dhakal, 2016). It can be challenging for municipalities to make a shift toward a distributed management approach, which involves stakeholders, like residents, throughout the process of design and implementation. In addition, Green Infrastructure has many benefits that are not related to controlling runoff, so it has a greater chance of receiving funding from organizations concerned with beautifying neighborhoods, public health, improving air and water quality, increasing habitats and biodiversity in urban areas, and environmental education for children (US EPA, 2015). This means municipalities must work with new organizations as opposed to traditional sources of funding, which can be challenging, but would also help cover perceived high costs.

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Maintenance and Public Perception Green Infrastructure requires a completely different type of maintenance than gray infrastructure, since the productivity of the system is based on plant and soil health, as opposed to large pipes and curb and gutter systems. Municipalities have engineers and other technocrats that are trained and very experienced with the design, implementation and maintenance traditional stormwater infrastructure, not Green Infrastructure. This can lead to reluctance from the municipalities’ perspective (Dhakal, 2016). As a newer stormwater management technique, municipalities would have to adjust current methods of training and policymaking to include Green Infrastructure as an integral part of development in their communities. Although it is challenging to do this, the outcome would be entirely positive, as new jobs would most likely be created in addition to factoring Green Infrastructure into existing city development codes and future development.

Other issues associated with the maintenance of Green infrastructure include resident’s perception of maintenance responsibilities, and change in the community aesthetic. In bioretention systems such as bioswales that are in front of residents’ homes between the street and sidewalk, issues can arise when residents are held partially responsible for the maintenance of Green Infrastructure. Although the city may purchase an access easement to permit the implementation of a new stormwater management technique, the residents will need to be involved in the design and plant selection if the municipality wants to avoid conflicts with unhappy residents who complain to the city, because part of their yard no longer looks as they would like it to. Residents who may be trying to improve the way their yard’s bioswale looks may apply fertilizers or pesticides to Green Infrastructure systems, not realizing those are the

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types of chemicals Green Infrastructure aims to remove from runoff (White, 2014). Education on the city’s part is a vital aspect of ensuring proper maintenance of Green Infrastructure in private developments such as bioswales that would be implemented on Davis Island. Ideally, a department within the city’s stormwater division would be responsible for the regular maintenance of publicly owned, and possibly privately owned bioretention systems, which again, would create new employment opportunities. When municipalities and organizations that support Green Infrastructure promote this alternative through financial incentives and educational outreach programs linking the many stakeholders involved, Green Infrastructure will begin to take hold in a community (Dhakal, 2016). However, much research still needs to be done on how to efficiently link municipalities, homeowners, developers, contractors, planners, and engineers to address the lack of awareness, and how to incorporate Green Infrastructure into their field and community (Ahiablame et al., 2012).

Educational opportunities for residents on the benefits of green infrastructure are essential to the acceptance of new stormwater management techniques in a community, especially one where curb appeal taken very seriously by residents. Many homeowners like the way wide streets lined by manicured turf grass looks, and the way the manicured, resource intensive turf grass looks covering most the area of their lawns. Some residents may view Green Infrastructure as a safety impediment compared to low-lying turf grass bordering streets (US EPA, 2000). However, if residents become aware of the environmental and social benefits of Green Infrastructure, change will be more accepted. People are used to gray infrastructure and how the city is entirely responsible for how runoff is discharged from their properties, without paying direct costs for the maintenance and implementation of traditional systems. Although Green Infrastructure results in lower long term costs (US EPA, 2015), when implementation

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costs are even partially the responsibility of the resident, it can seem less appealing because residents are used to the “out-of-sight, out-of-mind� approach of gray infrastructure, where monthly or yearly stormwater taxes are paid by everyone, because the municipality is responsible for maintenance and capital costs (US EPA, 2015)(Dhakal, 2016).

On Davis Islands, residents will be paying a yearly stormwater tax based on the amount of impervious surfaces on their property, because the community is considered a flood-prone area. Although the City of Tampa does not have plans for stormwater retrofits on Davis Islands, residents will still be paying this tax, unfairly. This situation would hopefully lead to residents willfully involving themselves in the implementation of Green Infrastructure on their properties to avoid being taxed, while also improving water quality and reducing flooding on Davis Islands.

Part 3. Conclusions and Recommendations for Davis Islands, Tampa, FL Total Savings Using Green infrastructure South Tampa, the lower peninsula of the City of Tampa, does not include Davis Islands physically, but Davis Islands is considered part of South Tampa. As mentioned in the introduction section in regards to the funds allocated from the 2016 Stormwater Fee, South Tampa is designated $75 million of the $251.3 million. The lower South Tampa peninsula is approximately six times larger than Davis Islands, so if we assume the cost of investments on Davis Islands based on area, we can estimate that $12.5 million would be necessary to upgrade the traditional stormwater system. Green Infrastructure on Davis Islands would not only cost a fraction of $12.5 million, but add a multitude of benefits to the community that gray infrastructure simply could not provide.

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Green Infrastructure recommendations on Davis Islands total approximately 942,000 sq. ft. of bioretention systems, and approximately 1,001,000 sq. ft. of green roofs, totaling 44 acres of added Green Infrastructure methods. The total approximate cost of bioretention systems on Davis Islands would be $2.5 million, and by incentivizing 20% of over 1 million square feet of green roofs, approximately $5 million could be spent by the city on green roofs on Davis Islands.

The total cost to the city of green infrastructure is approximately $7.5 million dollars, which is 40% less than the assumed cost of gray infrastructure retrofits. This even includes the city funding 20% of the cost of 23 acres of green roofs, an ambitious but doable goal. If the City of Tampa were to employ Green Infrastructure methods in the rest of mainland Tampa, millions more could be saved of the $251.3 million to be raised by taxes, saving taxpayers money and giving residents and the environment much more desirable outcome.

Green Infrastructure and Sustainability on Davis Islands Environmental Sustainability Green Infrastructure on Davis Islands is a sustainable alternative to traditional stormwater management because all Green Infrastructure methods are environmentally sensitive by design.

Using plants and natural processes to treat stormwater mimics the nature hydrology of the land that we develop on. Green Infrastructure allows water to percolate back into the ground table in site, as well as cleansing runoff before it enters our waterways, preventing contamination of surface water and drinking water, and preventing damage to vulnerable aquatic ecosystems.

Tampa Bay is the largest open water estuary in the Southeast, and home to a variety of ecologically important wildlife and ecosystems. If municipalities throughout the Tampa Bay area

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were to implement Green Infrastructure programs, it is extremely likely that the amount of nonpoint source pollutants would significantly decrease in Tampa Bay in the following years.

In addition to water quality benefits, Green Infrastructure contributes to urban environmental sustainability by reducing the urban heat island effect and improving air quality with vegetation creating additional, functional green space. In addition, when Green Infrastructure plantings are native or adapted selections, the vegetation contributes to habitat and biodiversity in urban areas. Green roofs can provide habitat for bird species and invertebrates on roofs, as well as potentially reduce energy consumption in the building that the green roof is installed on. On Davis Islands, there is hardly any natural habitat left for native wildlife to find sanctuary in. The same can be said for the rest of Tampa, a very urbanized and growing metropolitan area.

Community Sustainability Adopting Green Infrastructure on Davis Islands and Tampa is an opportunity to raise awareness about the water quality issues that Tampa Bay suffers from, as well as an opportunity to raise awareness about sustainability initiatives in general. Tampa is lagging behind the progressive cities that are taking on the responsibility of preventing pollution in surface waters.

A movement toward Green Infrastructure practices throughout Tampa would help residents understand water quality issues in the bay, and how these water quality issues arise. Many residents do not understand the implications of having a highly treated lawn on our drinking and surface water systems. If Tampa residents were exposed to a new type of stormwater management that directly involves their input, these connections will be made and Tampa can

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more successfully gravitate toward a sustainability minded policies, as residents and policy makers become more open minded, once the benefits of Green Infrastructure are observed.

Educating children is another way that Green Infrastructure will contribute to community or social sustainability on Davis Islands and Tampa. Growing up in a very urban or suburban environment can take a toll on children that do not get regular exposure to natural ecosystems.

Currently, Davis Islands, and the rest of Tampa, is a very highly developed environment where most of what you see is completely unnatural. Creating spaces within an urban environment like Tampa that mimic natural ecosystems is a way to bring environmental education to children who are never exposed to it. This can be said of children in any neighborhood in Tampa, unfortunately Tampa is simply lacking in the environmental preservation department.

A few ways Green Infrastructure can help open the minds of children (or all residents) include: placing educational placards about vegetation, functions, and wildlife throughout locations of Green Infrastructure, allowing local schools to view new green roofs throughout the city, placing kiosks at bike share locations in Tampa to guide users through Green Infrastructure corridors, and hosting educational programs for local children to educate them on the function and importance of Green Infrastructure they will soon see throughout their hometown.

Finally, Green Infrastructure creates a new urban aesthetic that ultimately contributes to, and creates a sense of place throughout a community. The locations on Davis Island where Green Infrastructure is recommended are all currently vegetated with turf grass. Not only is this vegetation ordinary and uninteresting, but it requires mowing, fertilizers, and pesticides.

Replacing these areas with interesting, beautifully designed, and functional Green Infrastructure will turn ordinary spaces into points of interest, especially places such as the South Davis Boulevard trail bioswales that would border a very busy pedestrian trail, as well as the

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uncommon proposal for bioretention at the airport. Davis Islands is already unique in many ways, but Green Infrastructure would create a sense of biophilia that would bring residents closer to the place they call home, increasing community pride and sense of place in Davis Islands, and hopefully the rest of Tampa.

Economic Sustainability Green Infrastructure is much less expensive than traditional stormwater management methods, and as mentioned in the conclusions. The first and foremost economic benefit of Green Infrastructure is the 40% savings the city could see in an area like Davis Islands just by supplementing the existing system with Green Infrastructure. If the City of Tampa implemented Green Infrastructure throughout the rest of mainland Tampa, millions and millions more can be saved.

In addition to direct savings, Green Infrastructure’s main benefits of improving water quality before it enters surface waters is usually not given a monetary value, although preventing pollution results in fewer efforts to reverse pollution, which is typically extremely expensive. In addition, when the volume of runoff is decreased before it enters the stormwater system, flooding is less likely to occur, preventing costs associated with flood damage.

Green Infrastructure would be a new endeavor in the City of Tampa, and new endeavors result in the creation of new jobs. The demand for environmental planners, landscape architects, and other sustainability professionals would rise in Tampa, a city that does not employ enough sustainability minded professionals to create worthwhile sustainability initiatives. Maintenance workers would need to be trained in regards to the specific type of maintenance that Green Infrastructure requires, creating new jobs in this sector, as well as creating new opportunities in

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the private sector for the maintenance of home rain gardens, green roofs, and bioswales on private property that may not be maintained by the city. The opportunities for economic growth are endless with Green Infrastructure. The table below illustrates some of the benefit of Green Infrastructure compared to tradition gray methods.

Conditions for Green Infrastructure on Davis Island The areas chosen as potential Green Infrastructure sites on Davis Islands are based on the available space in the community, site suitability, and existing drainage patterns based on the City of Tampa’s Storm Gravity Mains map. Davis Islands is only 1.36 square miles, with 80% of available land classified as urban/built-up, with less than 1% of land designated as public open space (DICA, 2016). These open spaces are parks such as the Seaplane Basin Park at the south end of the community, and the Robert Ferlita Trail on South Davis Boulevard, considered a

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linear park, and other small parks less than five acres in size that are part of facilities such as the little league baseball complex, airport, dog parks, and tennis courts.

Davis Islands is composed of two islands connected by small bridges, with canals that feed into the archipelago. Davis Islands is five to ten feet above sea level, and the depth to the water table is approximately three feet. The soils that form that composition of the archipelago are part of the St. Augustine Urban Land Complex, composed of fine, somewhat poorly draining sand, typical of dredged marine terraces (NRCS WSS).

Limitations and Assumptions: Green Infrastructure Implementation Bioswales and Bioretention Soils The soil profile on Davis Islands indicates that Green Infrastructure is limited not only by space constraints, but also soils. The assumption is made that Green Infrastructure techniques can be used in areas with poorly draining soils, as long as underdrains are part of the design for bioretention facilities, as this has been done in other municipalities. Underdrains for bioretention facilities would be connected to the existing stormwater infrastructure, allowing the cleansed runoff to slowly enter the stormwater system, and then into the Hillsborough Bay and Seddon Channel.

Water Table Depth The depth to the water table is also a limiting factor in terms of how the Green Infrastructure is designed for Davis Islands. Per the City of Tampa’s Stormwater Public and Private Development Technical Manuals, stormwater management techniques such as grassed

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ditches, the most similar technique in the manuals to bioretention facilities, should be at least one foot above the water table (City of Tampa, 1996). The assumption is made that the locations of bioretention facilities (no deeper than one to two feet) would not allow encroachment into the water table in this island environment.

Access Easements The City of Tampa will need to be granted access easements to construct bioswales along the right of ways on East and West Davis Boulevard, because these bioswales will be in front of residential properties. The assumption is made that the city will work with residents on the design and implementation of bioretention systems to gain public support in the initiative to manage stormwater. On South Davis Boulevard, the parcels proposed for Green Infrastructure are owned by the city, and no access easements would need to be granted.

Design Bioswales situated along roads will range from six to twenty feet in width, as the grass buffers around Davis Island vary in size depending on the width of the sidewalks. As mentioned before, these bioswales will be no deeper than two feet, and will all be designed with an underdrain that connects into the main storm drains. The bioswales will be planted with Florida native vegetation and other adapted varieties to ensure proper plant establishment and to contribute to biodiversity, while also eliminating the need for irrigation and pesticides or fertilizers that have been necessary for existing vegetation.

Bioretention Basins

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Various large bioretention facilities are proposed for traffic islands and expanses of open space that are currently lawns, both with turf grass as the main vegetation type. These bioretention basins will turn these traffic islands and open spaces into a functional landscape that can retain runoff in locations that otherwise have no function in terms of runoff attenuation.

These basins will also need to be equipped with an underdrain to prevent excessive ponding and overflow into surrounding roadways. The assumption is made that bioretention facilities can be connected to bioswales to retain overflow during heavy rain events.

Cost The bioswales and bioretention facilities will be shallow, one to two feet deep, and be equipped with an underdrain. Bioretention facilities that are simple in design and do not require much piping are less costly than those equipped with underdrains. The assumption is made that the approximate cost of roadside bioswales would be $10 per square foot, and the cost for bioretention basins would be approximately $10,000 per acre. These cost approximations are representative of costlier bioretention systems (IFAS Rain Gardens)(US EPA, 2000).

Green Roofs Public vs. Private Buildings The green roofs proposed for buildings on Davis Island are located on privately owned, as well as publicly owned buildings. The assumption is made that the city would implement green roofs on publicly owned buildings such as recreational facilities, the fire station, historic buildings, and contribute to the implementation of the largest green roof proposed, Tampa General Hospital. For privately owned buildings where green roofs are proposed, such as the

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thirty-eight apartment buildings, we can assume that building owners would be inclined to install green roofs to obtain the mitigation credit offered by the city to waive the new stormwater tax everyone in the community will be paying. The assumption is also made that the city would offer additional financial assistance to private building owners wishing to install green roofs, as various other municipalities have done in the past.

Development Codes The assumption is made that green roofs will be a method which is allowed by city codes in the future. Florida municipalities have faced challenges when it comes to green roofs due to the high winds Florida can experience from hurricanes, which can lead to wind uplift on green roofs, potentially damaging the system. As more research on green roofs and severe weather has been conducted, stronger materials in manufacturing has allowed green roofs to be used in environments with high wind speeds.

Cost The cost of green roofs is the most challenging aspect of convincing a building owner to install a green roof. The assumption is made that the cost for installing a modular green roof on an existing building would be approximately $25 per square foot, because existing building retrofits can be more complicated than installations on new buildings (Portland BES, 2016). We can assume the city of Tampa and building owners will recognize the many benefits green roofs can bring to a community aside from runoff reduction, to alleviate the perception that green roofs are not a cost-effective strategy compared to traditional gray infrastructure.

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The assumption is made that the City of Tampa would incentivize green roofs further with a per square foot incentive of 20%, as other successful municipalities have done, such as New York City and Portland, Oregon, as mentioned previously.

The largest green roofs are proposed for Tampa General Hospital, the Village Shoppes, and the various apartment buildings in the area. These green roofs will be the most expensive due to their size, but entities owning these buildings will also be paying the highest stormwater fees to the city due to large amounts of impervious surfaces on site. The assumption is made that these building owners would not be as hesitant to spend the money on a green roof to reduce their taxes, compared to a homeowner, because these large properties don't have space available for other stormwater management techniques to reduce runoff due to parking lots.

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Green Infrastructure Recommendations for Davis Islands Bioretention System Recommendations 1. East Davis Boulevard & Intersecting Streets Bioswales

Location(s): East Davis Boulevard, Cayuga Ave, Chippewa Ave, Biscayne Ave, Bosphorus Ave, Barbados Ave. Length of Site/Road: 0.94 miles, plus ~0.6 miles of intersecting avenues.

Number of Bioswales: 78+ Total Square Feet of Bioswales: ~92,676 sq. ft. (2.12 acres) Approximate Cost: $926,000 Surrounding Structures: Commercial district, multi-family residential, single-family residential Description: East Davis Boulevard is where Davis Boulevard splits into East and West after driving approximately 0.5 miles down Davis Boulevard, where most of the proposed green roofs are located. The parcels of land that will be used are grass buffers that separate the sidewalk from the right of way. The grass buffers are composed of turf grass and mature trees that may or may not be incorporated into bioswales, depending on their size. The bioswales proposed in the

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commercial district will replace small islands of landscaping that form the crosswalks at the three intersections dividing the commercial district.

After traveling down East Davis Boulevard past the commercial district, runoff from sites on East Davis Boulevard is directed off site by the curb and gutter system currently in place, and routes the runoff down intersecting streets that direct runoff into the Seddon Channel through inlets at the eastern seawall. These streets are Biscayne Ave, Barbados Ave, Chesapeake Ave, Chippewa Ave, and Cayuga Ave. These streets terminate on the east side of the island at Channel Drive where runoff exits the island. When turf grass buffers are converted to depressed bioswales, runoff will be cleansed and reduced before entering the channel, preventing various contaminants from the commercial district and nearby homes from entering waterways.

Photos: Below are aerial images from Google Earth showing the locations of roadside bioswales along East Davis Boulevard and the four streets that intersect East Davis, carrying runoff into the Seddon Channel shown on the right side of the first image below.

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Site Photos: The images below are how sites on East Davis Boulevard and side streets currently look. Image Source: Krisjanna Olson

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2. South Davis Blvd. Trail and Peter O’ Knight Airport Bioretention

Location(s): South Davis Boulevard, Severn Ave Length of Site/Road: 1.22 miles Number of Bioswales: 15 large bioswales Bioretention Facilities: 4 Total Square Feet of Bioswales: ~ 85, 486 sq. ft. bioswales, ~ 459,560 sq. ft. bioretention basins. (12.46 acres) Approximate Cost: $960,000 Surrounding Structures: Peter O’Knight Airport, single family residential.

Description: East Davis Boulevard turns into South Davis Boulevard upon approaching the Peter O’Knight Airport on the south side of Davis Islands. This section is two lanes, with the Robert J. Ferlita 1.3-mile-long pedestrian trail following South Davis Blvd. along the perimeter of the airport.

The parcels of land that will be used for bioswales are grass buffers that separate the sixfoot wide pedestrian trail from the right of way. The grass buffers are composed of turf grass, shrubs, and young and mature trees that may be incorporated into bioswales, depending on their

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size. The width of bioswales will range from ten to twenty feet on this section of Davis Boulevard.

South Davis Boulevard runoff is directed by curb and gutter systems, east and south down South Davis Blvd. The runoff enters storm drains, which carry the runoff straight into the Hillsborough Bay. The bioswales on South Davis Boulevard would capture and treat a majority of the runoff from South Davis and adjacent properties before it enters the storm system.

Large bioretention facilities are located at each end of South Davis Boulevard, as well as in a northern section of the airport to serve as overflow basins for bioswales on South Davis.

Two bioretention facilities are proposed for the traffic islands at Hudson Avenue and Severn Avenue. Both traffic islands are across South Davis Boulevard from proposed bioswales, so underground piping would need to be installed.

The other two bioretention facilities are located on the Peter O’Knight Airport property.

The largest bioretention facility proposed is here, and would capture any overflow from bioswales in the pedestrian trail. This bioretention facility would be at an extremely low slope with minimal vegetation to follow safety guidelines for aircraft runways. The second bioretention facility on the airport property is located at the eastern end of the airport, retaining runoff overflow for the east end of the South Davis Boulevard bioswales. All the property where bioretention systems are proposed is owned by the City of Tampa, making this site proposal one of the most feasible applications of Green infrastructure.

Aerial Images: The aerial image below from Google Earth shows the locations of bioswales and bioretention facilities along South Davis Boulevard. The locations of bioswales were chosen based on the amount of available and unobstructed parcels bordering the right of way.

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Site Photos: The pictures below show how South Davis Boulevard looks currently. Image Source: Krissy Olson

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3. West Davis Boulevard Bioswales

Location(s): West Davis Boulevard Length of Site/Road: 1.5 miles Number of Bioswales: 40+ large bioswales Total Square Feet of Bioswales: ~ 63,300 sq. ft. (1.45 acres) Approximate Cost: $633,000 Surrounding Structures: Single-family residential Description: West Davis is the section of Davis Boulevard that travels up the west side of Davis Islands before turning back into Davis Boulevard. This section ranges from two to four lanes in some places, and has new bike lanes on both side of the road.

The parcels of land that will be used are grass buffers that separate the sidewalk from the right of way on this entirely residential section of Davis Boulevard. The grass buffers are composed of turf grass and mature trees that may or may not be incorporated into bioswales,

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depending on their size. The width of bioswales will range from ten to twenty feet on this section of Davis Boulevard.

West Davis Boulevard runoff is directed by curb and gutter systems down intersecting streets that carry the runoff west toward storm drains streets, which carry the runoff straight into the Hillsborough Bay through three canals that meander through the archipelago. The bioswales on West Davis Boulevard would capture and treat a majority of the runoff from properties on West Davis Boulevard before it enters the storm system, and then receiving waterbodies.

Aerial Images: The aerial images below from Google Earth shows the locations of bioswales along West Davis Boulevard. The locations of bioswales were chosen based on the amount of available and unobstructed parcels bordering the right of way.

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Site Photos: The following photos are how sites on West Davis look currently. Image Source: Krisjanna Olson, Google Maps

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4. Columbia Drive Bioretention Basins

Location(s): Columbia Dr.: Davis Islands Marina, Davis Islands Garden Club lawns, DI Tennis Courts lawn, HCC Administration building roundabout.

Number of Bioretention Systems: 7 Total Square Feet: 130,000 sq. ft. (2.98 acres) Approximate Cost: $30,000 Surrounding Structures: multi-family residential, single-family residential, recreational facilities, community building, institutional buildings.

Description: The bioretention basins proposed for Columbia Drive are adjacent to the Seddon Channel on the northeast side of Davis Islands. Runoff from these four properties is conveyed directly into the channel via storm inlets on site. The bioretention basins proposed would replace two large traffic islands at the DI Garden Club and HCC Administration Building, and the other

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basins would be in larger expanses of open space on the DI Marina lawn and DI Garden Club lawn. These properties are owned by the city except for the HCC property, making this area more feasible to retrofit with Green Infrastructure.

Aerial Images:

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Site Photos: The following photos are how some the Columbia Drive Sites look currently. 1.

Davis Islands Garden Club Lawn, 2. Davis Islands Marina, 3. Tennis Courts, 4. HCC traffic island. Images Source: Krisjanna Olson

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5. Bahia Beach and Dog Parks Bioretention

Location(s): Severn Avenue Number of Bioretention Basins: 8 Total Square Feet of Bioretention Basins: 111,000 sq. ft. 2.52 acres Approximate Cost: $25,200 Surrounding Structures: Peter O’ Knight Airport, Davis Islands Yacht Club.

Description: The Bahia Beach and Davis Islands dog parks are at the southernmost point of the island at the seaplane basin. This area is only a few feet above sea level, and therefore no stormwater system exists at the southern point. Bahia Beach waters suffer from bacterial contamination from the adjacent dog parks and boat ramp area. Several beach advisories have been issued for Bahia Beach warning residents to stay out of the water due to high levels of enterococci bacteria. The greened areas in the image above are proposed bioretention basins for the parking lot of the dog parks and boat ramp. On the left side of the image above is a dog park beach, and on the right, is the dry dog park. The runoff from these areas must be captured by bioretention basins to prevent contaminated runoff from entering the Hillsborough Bay and 78

Bahia Beach recreational area. This land is all owned by the city, making this Green Infrastructure proposal one of the most feasible.

Aerial Images:

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Site Photos: The photo below is how the Bahia Beach and Davis Islands Dog Park area sites currently look. Image Sources: Google Earth, TampaBay.com.

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Green Roof Recommendations Green Roof Sites on Davis Islands

All the green roofs on Davis Islands will be retrofits to existing buildings. Therefore, it would be best to use a lightweight system that is easier to install on large, existing roofs. The largest concentration of green roofs will be on the north side of Davis Islands, where numerous institutional, and large residential buildings are located. This coincides with more automobile traffic on the north side of Davis Islands, so controlling runoff in this area is essential to the health of the Hillsborough Bay, as most of these buildings are adjacent to the Bay and channel.

The total approximate square footage for proposed green roofs in this plan is 1,001,000 sq. ft.

The manufacturer selected for use is Tremco, a company that manufactures multiple types of roofing systems, including vegetated roof systems. Tremco offers a variety of media depths and vegetation types to provide a vegetated option for almost any roof.

The Tremco VR Lite Meadow system is a built-in-place system that results in a planted roof. The vegetation can be composed of sedums plants, short grasses, perennials and wildflower blends. For Davis Islands, the grass, wildflower and perennial blend would be used due to the humid, subtropical climate where sedums would not thrive as well. The Tremco VR Lite Meadow system has a 4-inch media depth, and has a maximum stormwater retention capacity of 2.2 gallons per square foot. These metrics will be used in retention calculations for the green roofs proposed on Davis Islands.

Calculations Explanation

Green Roofs are a type of Green Infrastructure that can more difficult to convince building owners to use, because the benefits are often hard to quantify. Approximate runoff calculations are used to demonstrate runoff reduction benefits that could translate to tax dollar savings for property owners that must pay the new monthly stormwater utility tax.

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A runoff amount for an asphalt roof will be calculated using the highest and lowest monthly precipitation averages in Tampa. During the summer months of June, July, and August, Tampa receives the most precipitation, with a summer average of about 7.5 inches. This number will be used to demonstrate approximate runoff from the asphalt roof, and the percentage of runoff the green roof could retain in the wettest months.

During the dryer months, the monthly precipitation averages range from one inch to just over three inches of precipitation, so three inches is used in the calculations to determine the amount of runoff from the asphalt roof, and the percent of runoff that green roofs can retain during the dry months in Tampa, or just during shorter rainfall events. Shown below is a climate graph for Tampa, Florida showing where the 7.5-inch and 3-inch baselines are from, for the summer and winter months.

For 7.5-inch rain events, the roofs will be able to retain approximately 47% of runoff.

During 3-inch rain events, the roofs should be able to retain 100% of runoff.

Asphalt Roof Runoff Calculations Explanation: Convert the building’s roof square footage into square inches by multiplying by 144. Multiply square inches by the inches of rainfall (7.5 in. max, 3 in. min) = cubic inches of runoff. Divide cubic inches by 231 to equal gallons of runoff for each rain event.

(Roof square feet) x 144 = (Roof square inches) x inches rainfall (7.5’’ and 3’’) = (cubic inches runoff) / 231 = gallons of runoff during rain event.

Green Roof Retention Calculations Explanation: Multiply the roof square feet by the retention capacity, 2.2 gal/sq. ft. (from Tremco). This equals the roofs total retention capacity. Then divide this number by the asphalt roof runoff total from each rain event, this will result in the percentage of runoff that can be retained by the green roof.

(Roof square feet) x (2.2 gal/sq. ft.) = (total gallons that can be retained) / [asphalt runoff from first calc. (3’’ and 7.5’’)] = % runoff retained during rain event.

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Tampa’s Monthly Average Precipitation and Temperature Graph:

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1. Tampa General Hospital & Parking Garage Green Roof

Location: 1 Tampa General Circle, Tampa, Fl. 33606 Buildings: 15+ connected structures, various stories, including the top level of the 173,000-sq. ft. parking structure.

Roof(s) Total Sq. ft.: ~440,695 square feet Runoff before Green Roof: 2,060,392 gallons (7.5’’); 824,155 gallons (3’’).

Runoff Retained (%) 7.5” rain event: 47% Runoff Retained (%) 3’’ rain event: 100% Description: This site is the largest green roof of the recommendations for Davis Islands. This green roof proposal includes all the largest buildings on the TGH campus with a flat roof and minimal obstructions. The proposed roofs are at various levels, allowing the newly greened roofs to be visible from many wings of the hospital, including patient wings and doctors’ offices.

The parking garage for Tampa General Hospital is six stories, and adjacent to the hospital. The top level of the parking garage is seldom full, so a green roof has also been proposed for the structure. The lack of additional parking could be solved by encouraging the

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local bus system to include Davis Islands as a stop as it was in the past. Davis Islands was removed from public transit routes years ago, as the stop was not receiving enough passengers.

Tampa General Hospital is at the northernmost point on Davis Islands, forming the apex that divides the opening of the Hillsborough River into the Hillsborough Bay, from the Seddon Channel on the eastern coast of the archipelago.

Runoff Calculations Highest Rainfall Average (Summer) Runoff: (440,695 sq. ft.) x (144) = (63,460,000 sq. in.) x 7.5 in = (475,950,600 cubic in.) / 231 = 2,060,392 gallons runoff.

Lowest Rainfall Average (Winter) Runoff: (440,695 sq. ft.) x (144) = (63,460,000 sq. in.) x 3 in = (190,380,000 cubic in.) / 231 = 824,155 gallons runoff.

Green Roof Retention Calculations 7.5-inch rain event: (440,695 sq. ft.) x (2.2 gal/sq. ft.) = (969,529 gallons retained) / (2,060,392gal runoff) = 47% runoff retained.

3-inch rain event: (440,695 sq. ft.) x (2.2 gal./sq. ft.) = (969,529 gallons retained) / (824,155-gal runoff) = 100% runoff retained.

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Context Map:

Aerial Image: Tampa General Hospital. Image Source: emeraldmap.com

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2. Davis Boulevard Medical Buildings Green Roofs

Location: 1 Davis Blvd, 17 Davis Blvd, and 6 Columbia Dr., across the street from TGH. Buildings: Three total. One Davis Medical Building, USF Pediatrics Building and associated office building.

Roof(s) Total Sq. ft.: 6,900 sq. ft. + 14,160 sq. ft. + 13,300 sq. ft. = 34,360 sq. ft.

Runoff before Green Roof: 160,644 gallons (7.5’’); 64,258 gallons (3’’) Runoff Retained (%) 7.5’’ rain event: 47% Runoff Retained (%) 3’’ rain event: 100% Description: This green roof site is composed of three medical buildings adjacent to the Tampa General Hospital. The One Davis Medical Building is the northernmost building in the aerial image above, and the University of South Florida Pediatrics Building and offices are the two buildings just below. You can see in the aerial image above that Tampa General Hospital is just across the street.

Runoff Calculations Highest Rainfall Average (Summer) Runoff: (34,360 sq. ft.) x (144) = (4, 947,840 sq. in.) x 7.5 in = (37,108,800 cubic in.) / 231 = 160,644 87

gallons runoff.

Lowest Rainfall Average (Winter) Runoff: (34,360 sq. ft.) x (144) = (4, 947,840 sq. in.) x 3 in = (14,843,520 cubic in.) / 231 = 64,258 gallons runoff.

Green Roof Retention Calculations 7.5-inch rain event: (34,360 sq. ft.) x (2.2 gal/sq. ft.) = (75,592 gallons retained) / (160,644-gal runoff) = 47% runoff retained!

3-inch rain event: (34,360) x (2.2 gal./sq. ft.) = (75,592 gallons retained) / (64,258-gal runoff) = 100% runoff retained!

Context Map: Davis Boulevard Medical Buildings

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Site Photos: Davis Medical Building currently. Image Source: tampaniatampa.blogspot.com

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3. Adalia Bayfront Condominiums Green Roof

Location: 2 Adalia Avenue, Tampa, FL. 33606 Buildings: 1 Roof(s) Total Sq. ft.: 19,489 sq. ft.

Runoff before Green Roof: 91,117 gallons (7.5’’); 36,447 gallons (3’’) Runoff Retained (%) 7.5’’ rain event: 47% Runoff Retained (%) 3’’ rain event: 100% Description: The Adalia Bay Front Condominiums are located on the Hillsborough Bay, the northwest side of Davis Islands just as the Hillsborough river opens into the Bay after passing through downtown Tampa. Adalia Bay Front condominiums are just across Davis Boulevard from the Davis Medical Buildings, USF Pediatrics, and Tampa General Hospital, shown in the aerial image and context map.

Runoff Calculations Highest Rainfall Average (Summer) Runoff: (19,489 sq. ft.) x (144) = (2,806,416 sq. in.) x 7.5 in = (21,048,120 cubic in.) / 231 = 91,117 gallons runoff.

Lowest Rainfall Average (Winter) Runoff:

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(19,489 sq. ft.) x (144) = (2,806,416 sq. in.) x 3 in = (8,419,248 cubic in.) / 231 = 36,447 gallons runoff.

Green Roof Retention Calculations 7.5-inch rain event: (19,489 sq. ft.) x (2.2 gal/sq. ft.) = (42,876 gallons retained) / (91,117-gal runoff) = 47% runoff retained.

3-inch rain event: (19,489 sq. ft.) x (2.2 gal./sq. ft.) = (42,876 gallons retained) / (36,447-gal runoff) = 100% runoff retained.

Context Maps: Adalia Bay Front Condominiums

Site Photo: Adalia Bay Front Condominiums currently. Image Source: highrises.com

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4. Hillsborough Community College Administration Building Green Roof

Location: 39 Columbia Dr., Tampa, FL. 33606 Buildings: 1, 8 stories.

Roof(s) Total Sq. ft.: 10,800 sq. ft.

Runoff before Green Roof: 50,493 gallons (7.5’’); 20,197 gallons (3’’) Runoff Retained (%) 7.5’’ rain event: 47% Runoff Retained (%) 3’’ rain event: 100% Description: The Hillsborough Community College Administration Building is located on the Seddon Channel near the Tampa General Hospital Parking Garage, the northeast side of Davis Islands. This site also has a large grassed roundabout where a bioretention facility is proposed.

Since the HCC building is a higher education building with Soil and Water Science offices and facilities located here as well, a green roof is the perfect opportunity to expand research opportunities within the college.

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Runoff Calculations Highest Rainfall Average (Summer) Runoff: (10,800 sq. ft.) x (144) = (1,555,200 sq. in.) x 7.5 in = (11,664,000 cubic in.) / 231 = 50,493 gallons runoff.

Lowest Rainfall Average (Winter) Runoff: (10,800 sq. ft.) x (144) = (1,555,200 sq. in.) x 3 in = (4,665,600 cubic in.) / 231 = 20, 197 gallons runoff.

Green Roof Retention Calculations 7.5-inch rain event: (10,800 sq. ft.) x (2.2 gal/sq. ft.) = (23,760 gallons retained) / (50,493-gal runoff) = 47% runoff retained.

3-inch rain event: (10,800 sq. ft.) x (2.2 gal./sq. ft.) = (23,760 gallons retained) / (20,197-gal runoff) = 100% runoff retained.

Context Map:

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Site Photo: HCC Building. Image Source:hccfl.edu

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5. The Historic Mirasol Apartments Green Roofs

Location: 84 Davis Blvd, Tampa, FL. 33606 Buildings: 1, multiple levels.

Roof(s) Total Sq. ft.: 7,500 sq. ft.

Runoff before Green Roof: 35,064 gallons (7.5’’); 14,025 gallons (3’’) Runoff Retained (%) 7.5’’ rain event: 47% Runoff Retained (%) 3’’ rain event: 100% Description: The Mirasol apartment building is one of the oldest buildings on Davis Islands, used in the past as a luxury hotel in the 1920s. The location is on the east side of Davis Boulevard, with waterfront views of the Hillsborough Bay. The roof of the Mirasol is many different levels, but a green roof would still be feasible on the flat areas of the roof where the Mediterranean-style shingles are not used.

Runoff Calculations Highest Rainfall Average (Summer) Runoff: (7,500 sq. ft.) x (144) = (1,080,000 sq. in.) x 7.5 in = (8,100,00 cubic in.) / 231 = 35,064 gallons runoff.

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Lowest Rainfall Average (Winter) Runoff: (7,500 sq. ft.) x (144) = (1,080,000 sq. in.) x 3 in = (3,240,000 cubic in.) / 231 = 14,025 gallons runoff.

Green Roof Retention Calculations 7.5-inch rain event: (7,500 sq. ft.) x (2.2 gal/sq. ft.) = (16,500 gallons retained) / (35,064-gal runoff) = 47% runoff retained.

3-inch rain event: (7,500 sq. ft.) x (2.2 gal./sq. ft.) = (16,500 gallons retained) / (14,025-gal runoff) = 100% runoff retained.

Context Map:

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6. - 44. Davis Islands Apartment Buildings Green Roofs

Location: East Davis Boulevard, Danube Ave, Como Street, Columbia Drive.

Buildings: 38, 1-5story, flat roof buildings.

Roof(s) Total Sq. ft.: 236,625 sq. ft.

Runoff before Green Roof: 1,106,299 gallons (7.5’’); 442,519 gallons (3’’) Runoff Retained (%) 7.5’’ rain event: 47% Runoff Retained (%) 3’’ rain event: 100% Description: Davis Islands has many apartment buildings located on East Davis Boulevard and parallel streets, concentrated at the north end of the archipelago and commercial district. Thirtyeight apartment buildings were selected for green roofs due to their location on the main road, proximity to one another, and for their flat roofs, which most apartments on Davis Island have.

The buildings range from single story duplexes, to three story multi-family apartment buildings.

On the aerial map below, the smaller greened roofs are the various apartment buildings.

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Runoff Calculations Highest Rainfall Average (Summer) Runoff: (236,625 sq. ft.) x (144) = (34,074,000 sq. in.) x 7.5 in = (255,555,000 cubic in.) / 231 = 1,106,299 gallons runoff.

Lowest Rainfall Average (Winter) Runoff: (236,625 sq. ft.) x (144) = (34,074,000 sq. in.) x 3 in = (102,222,000 cubic in.) / 231 = 442,519 gallons runoff.

Green Roof Retention Calculations 7.5-inch rain event: (236,625 sq. ft.) x (2.2 gal/sq. ft.) = (520,575 gallons retained) / (1,106,299gal runoff) = 47% runoff retained.

3-inch rain event: (236,625 sq. ft.) x (2.2 gal./sq. ft.) = (520,575 gallons retained) / (442,519-gal runoff) = 100% runoff retained.

Aerial Image: Davis Islands Apartments near the commercial district.

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Site Photos: Examples of Davis Island Apartment buildings. Image source: apartments.com

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45-53. Davis Islands Commercial District Green Roofs

Location: East Davis Boulevard Buildings: 9 Roof(s) Total Sq. ft.: 79,239 sq. ft.

Runoff before Green Roof: 370,468 gallons (7.5’’); 148,187 gallons (3’’) Runoff Retained (%) 7.5’’ rain event: 47% Runoff Retained (%) 3’’ rain event: 100% Description: The commercial district on Davis Islands is called the Village Shops, and consists of multiple buildings within walking distance of the many apartment buildings which will also be potential green roof sites. This area of Davis Island has the most vehicular traffic on Davis Islands, so reducing runoff in this area will reduce the amount of contaminants from leaving the site. This area is also prone to flooding, especially in parking areas, so green roofs and bioswales will benefit this area greatly. The Village shopping center buildings all have flat roofs. The two main buildings that house the most businesses are composed of separate businesses, but connected structures, all owned by one entity. The establishments in the Village Shops include

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restaurants, bars, retail stores, two banks, office buildings, two convenient stores, a fire station, and an automobile repair shop.

Runoff Calculations Highest Rainfall Average (Summer) Runoff: (79,239 sq. ft.) x (144) = (11,410,416 sq. in.) x 7.5 in = (85,578,120 cubic in.) / 231 = 370,468 gallons runoff.

Lowest Rainfall Average (Winter) Runoff: (79,239 sq. ft.) x (144) = (11,410,416 sq. in.) x 3 in = (34,231,248 cubic in.) / 231 = 148,187 gallons runoff.

Green Roof Retention Calculations 7.5-inch rain event: (79,239 sq. ft.) x (2.2 gal/sq. ft.) = (174,325 gallons retained) / (370,468-gal runoff) = 47% runoff retained.

3-inch rain event: (79,239 sq. ft.) x (2.2 gal./sq. ft.) = (174,325 gallons retained) / (148,187-gal runoff) = 100% runoff retained.

Aerial Image: Davis Islands Village Shops green roofs. Unlabeled areas are DI Apartments.

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Context Map: Tebella Tea Company is in the heart of the commercial district, the Village Shops.

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Green Infrastructure Example Photos

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Image Sources: http-//www.svrdesign.com/high-point- Seattle; fernhilllandscapes.com; svrdesign.com; unknown source; urbanwatercyclesolutions.com, www.svrdesign.com/high-point-redevelopment/8ezq5k11tdb6yokh6gvx94cg9qs1km.jpeg; SFbetterstreets.org; http-//www.svrdesign.com/high-point-redevelopment/8ezq5k11tdb6yokh6gvx94cg9qs1kmSeattle2.jpeg; nacto.org; sf.streetblog.org, http://cookjenshel.com/green-roofs/#!prettyPhoto%5BGallery%5D/12/ Stuggart, Germany Green Roofs, http///cookjenshel.com/green-roofs/ Chicago Green Roof

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