GREEN WALLS: Utilizing and promoting green infrastructure to control stormwater in Mobile, Alabama

Transcription

1 GREEN WALLS: Utilizing and promoting green infrastructure to control stormwater in Mobile, Alabama Van Webb, Graduate Student, Master of Landscape Architecture, Auburn University Reprinted from "Emerging issues along urban-rural interfaces III: Linking science and society, (Proceedings), David N. Laband, ed., 2010, p MASGP

2 GREEN WALLS: Utilizing & Promoting Green Infrastructure to Control Stormwater in Mobile, Alabama Van Webb Graduate Student Master of Landscape Architecture Auburn University Auburn, AL cell: (256) KEYWORDS Stormwater, green infrastructure, green walls Abstract Due to Mobile, Alabama s coastal geographic location, there are many storms that make their way through the Gulf of Mexico and travel north into the city of Mobile. These storms create a great amount of stormwater runoff throughout the city leading to flooding of streets, water qualities are degraded by trash and other pollutants, stagnant water-creates breeding grounds for mosquitoes, and many other issues. Urbanization and population growth has led to greater impervious surfaces throughout the city which in turn increases stormwater quantity and velocity. Retrofitting green infrastructure into the existing urban form of Mobile is an excellent method towards stormwater management while also utilizing vacant lots throughout the city to create a network of natural systems. In this paper, I will discuss how utilizing green walls within the built city will provide aesthetic improvements, reduce energy consumption, help control stormwater, and promote green infrastructure. Introduction Stormwater has been a growing problem for many cities across the United States. Many organizations have been searching for ways to reduce sewer system overflows and stormwater runoff. According to the most recent U.S. Annual Rainfall Report, Mobile, AL. topped the list at 67 /year and averaged 59 rainy days. Stormwater not only affects the livability within the city but it also affects the aquatic life of the Mobile River and Mobile Bay areas. For example, with the great amount of impervious surface in the Mobile area, stormwater runoff sheet flows across hot surface, warms up, and empties into the larger bodies of water nearby. Consequences include: killing off many invertebrates, degradation of various aquatic systems, and surface pollutants intruding on one of the most biodiverse bodies of water in the world. A paper by Celina Bochis and Robert Pitt studied the relationship of impervious surfaces and aquatic systems. Their findings showed that aquatic systems are directly related to watersheds of impervious surfaces. Reporting on stormwater has dramatically emerged in the news over the years. There are many reasons why stormwater can be detrimental, however beneficial uses of stormwater are beginning to come into practice. Robert Pitt quotes Dreiseitl (1998), stormwater is a valuable resource and opportunity to provide an aesthetic experience for the city dweller while Emerging Issues Along Urban/Rural Interfaces III-130

3 furthering environmental awareness and citizen interest and involvement. Stormwater is a valuable resource and when combined with green infrastructure can be very helpful in reducing runoff discharge within the urban environment while also providing aesthetically pleasing environments and promoting environmental awareness and citizen involvement. Some recent efforts by The City of Mobile, The Mobile Area Chamber of Commerce, and The Downtown Mobile Alliance have introduced coastal sustainability and a green streets initiative plan. My studio class and I participated in a charrette that took place in Mobile on August 29, 2009 sponsored by The Mississippi-Alabama Sea Grant Consortium. The goal of the charrette was to develop ideas and suggestions that focused on a four block segment along Dauphin Street in Downtown Mobile. The ideas were to focus on enhancing the city aesthetically, economically, and culturally while also promoting the city s sustainable vision and progressive development practices. The day consisted of a site visit, group brainstorming, graphical analysis and concept diagramming, and a final presentation and discussion. During the discussion, the idea of green roofs was pondered, but input by a city engineer brought up concerns of the buildings capabilities to hold such significant gardens atop. When my class got back to Auburn, we continued to develop our own individual concept ideas of implementing green infrastructure techniques into our designs to mitigate stormwater, enhance urban livability, and aesthetically improving the Dauphin Street area. Benjamin Grumbles, a water assistant administrator for the U.S. Environmental Protection Agency talks of green infrastructure writing, Green infrastructure approaches essentially infiltrate, evapotranspirate or reuse stormwater, with significant utilization of soils and vegetation rather than traditional hardscape collection, conveyance and storage structures. Retrofitting green infrastructure into the urban environment of Mobile will reduce stormwater discharges, improve water and air qualities, reduce the urban heat island effect, reduce energy consumption, promote community awareness, and restore the urban environment. Since a large percentage of the Dauphin Street area s land use is made up of buildings, I chose to focus my designs and research around rooftop stormwater management by proposing green walls on existing structures throughout the city. Greenwall Description Green walls are not a new form of design. They have been around since the Babylonian period. It wasn t until the 1920 s that British and North Americans began integrating the house and garden with planted structures. There are two types of vertical green structures. The first is a green façade. A green façade consists of climbing plants or aggressive groundcovers that are trained to cover a specifically designed structure and are planted either in the ground or in planters. The second is a green wall. Green walls are living systems. According to Green Roofs for Healthy Cities, living wall systems are composed of pre-vegetated panels, vertical modules or planted blankets that are fixed vertically to a structural wall or frame. A green walls plant variety far exceeds that of a green façade including: groundcovers, ferns, low shrubs, perennial flowers, vegetables, and herbs. Green walls are moderately low in maintenance requiring only simple fertilization, watering, and pruning. According to Randy Sharp, green walls provide many benefits including: Emerging Issues Along Urban/Rural Interfaces III-131

4 Public Benefits Noise reduction- plants and planting medium act as an insulator for reducing sound reflection. Improved exterior air quailtycaptures airborne pollutants and atmospheric deposition on leaf surfaces while filtering noxious gases and particulate matter. Reduce urban heat island effect- vegetation cools exterior surface of buildings and reduces amount of reflected heat. Green walls can create microclimates which will help in reducing the city temperature as a whole. Aesthetic improvementstudies have shown that the presence of plants can improve human health and mental well being. Promoting of green infrastructure- green walls are considered as green infrastructure. Elaborate green walls can show a city s concern for the environment, therefore promoting green infrastructure techniques. Private Benefits Improve energy efficiencygreen walls improve thermal insulation capacity by providing a thick layer of vegetation between the building structure and external temperatures. For example, a green wall in Beijing reduced the peakcooling load transfer to the building s interior on a clear summer day by 28 percent. (Di 1999). Mitigate stormwaterabsorbing 45-75% of rainfall, act as a natural water filter and water temperature moderator. Building structure protectiongreen walls protect exterior finishes from UV radiation, stormwater, and temperature fluctuations that wear down materials. Green walls contribute towards several LEED credits when used in combination with other sustainable building practices. Objective The objective of this research is to show how innovative planning and design techniques such as green walls can help mitigate stormwater, aesthetically improve the urban environment, reduce energy consumption, and promote green infrastructure. In order to utilize green walls in an urban environment, certain measures and investigations must be taken in order for the wall to succeed. Picking a suitable site for green wall application is the number one objective when analyzing an urban environment. In this study, one demonstration site of green wall techniques will be discussed along with the steps I took towards completing the analysis and research of the project. I will also discuss the steps I took towards development of several other potential sites. I will graphically show how green walls can create a dramatic visual design element. Emerging Issues Along Urban/Rural Interfaces III-132

5 Methodology The first step in this research was a site visit. Creating aerial maps before the initial site visit was very beneficial in recording important field data. Mobile gets a large amount of rain every year and existing gutters drain rooftop stormwater into the storm drain system causing them to back up, overflow, and eventually flood. Our class was given G.I.S. data by the city of Mobile, which helped inform site selection and design decisions. I began by creating an existing conditions map depicting the topography, manholes, sewer lines, drainage points, fire hydrants, utility poles, and the paved edge of the street system throughout the study area {figure 1}. This allowed me to make accurate design decisions. Further site locating details involved the creation of an existing land use map using G.I.S. {figure 2}. This map allowed me to establish building priorities. It shows the different commercial, civic, industrial, residential, and mixed use building usage in the downtown Mobile area. During the site development stage, these maps were very beneficial by providing critical analysis on site specific detail. I chose my site location because of its relationship to Dauphin Street, which is located in the core of the social entertainment district of the downtown area which gives it many great opportunities for public awareness and involvement. Another reason I chose this site is because of its direct relationship to the surrounding buildings in the area and also because it has two vertical walls where I am proposing green walls to be installed. The next step towards site development involved the creation of a master plan scenario {figure 3}. This plan shows my design intentions for the green wall demonstration site. {Photo 1} shows the existing vacant site where I am proposing the green wall systems. I further qualified my design intentions by using a section of my site as a design test {figure 4aexisting; 4b-proposed}. The green wall system in this section would be composed of a freestanding modular trellis panel system. The proposed site is in a prime location for promoting green infrastructure. The vacant lot is surrounded by three large walls creating a perfect site for green wall installation. I then calculated the rooftop square footage of the block area and calculated the amount of rain that could be infiltrated through the green walls seen below: +Total Block Area= 55,000 sq.f. +Total Rooftop Area= 48,925 sq.f. +Amount of rooftop water with one inch rain= 30,498 gallons/1 rain +Mobile Averages 67 per year. 67 x 30,498 gallons= 2,043,366 gallons/year +Green walls can absorb 45-75% of stormwater. I chose the median at 60%. +60% of 2,043,366 gallons/year= 1,226,020 gallons infiltrated by green wall. From there I found myself constricted to this one area and wanted to find a way to link other green spaces within the city to my site. I went back to the drawing board and came up with a rough concept plan {figure 5}. This plan reveals the idea of linking multiple green spaces together by a connection of green walls acting as visual cues throughout the city. Finding the appropriate sites for the other green walls was a bit more challenging. I began by analyzing the maps I had previously created and tried associating building characteristics with building importance. I wanted to propose the new green walls in places of interest to draw city dwellers towards them. The next step in my research was the creation of a building heights analysis map {figure 6}. I Emerging Issues Along Urban/Rural Interfaces III-133

6 then built a 3d model using Google SketchUp in order to create a shadow study {figures 7a-c}. By analyzing the building heights and shadow study, I was able to quantify suitable green wall sites. An ideal building for green walls consisted of a building height greater than twenty-five feet and a northeast or southwest facing façade. I further qualified the new green wall sites with a section drawing as my design test {figure 8a-existing; 8b-proposed}. The section is taken across Jackson Street looking east down Dauphin Street. This section exemplifies the aesthetic value green walls can add to an urban environment. Green walls that size would create dramatic visual gardens throughout the city, showing citizens and tourists that Mobile is taking positive steps towards becoming more sustainable and eco-friendly. Waters of Alabama Related Work There are many rivers and streams located in Alabama which all form different watersheds. Within these watersheds, many plant and animal habitats exist. A watershed is the surrounding land area that drains into a particular body of water. Land use within a particular watershed, not only contributes pollutants to their local streams and rivers, but those pollutants are also carried downstream damaging numerous wildlife and vegetative habitats. There are seven major rivers in Alabama consisting of: the Black Warrior, Tombigbee, Cahaba, Coosa, Tallapoosa, Alabama, and the Mobile. The Mobile-Tensaw Delta is a geographic barrier between urban environments and Alabama s water systems, making it the 2 nd largest delta in the United States. It is not a typical delta; it is more elongated than most other deltas. The size of the Mobile-Tensaw Delta is estimated to be ten miles wide and forty miles long, covering a total acreage of 185,000 acres. Twenty percent of the U.S. waters flow through the Mobile-Tensaw Delta down into the Mobile Bay. The Delta is habitat to many endangered species including the red bellied turtle, which lives nowhere else in the world. There are more than 250 bird species. The plant species exceed 500 different types including: willows, sweet bays, sycamores, pond pines, gums, gulf cypress, red cypress, and many others. The estuaries are habitat to many different types of marsh grasses. Estuaries are considered environmentally and economically important because of their exceptional biological diversity and productivity. Alabama s numerous watersheds are very important to the water qualities and plant and animal habitats within the Mobile-Tensaw Delta and Mobile Bay areas. Green walls can help mitigate stormwater runoff and also act as a water temperature moderator, therefore lowering ground surface temperature in order to keep aquatic systems thriving. (Doug Phillips) Conclusion The ideas of green infrastructure are beginning to sink in and become more pervasive throughout the United States. I have learned that by critically analyzing an urban space accurately using graphic analysis and data, green infrastructure can be innovative and site specific. Mobile, Alabama is one of the most beautiful coastal cities in the United States and stormwater runoff has been an ongoing problem in the Dauphin Street area. Rooftop stormwater can be utilized in the creation of on-site infiltration systems. The site I chose would provide as a green wall demonstration site and also provide as a stormwater reduction system. Green walls can improve the urban environment by mitigating stormwater while Emerging Issues Along Urban/Rural Interfaces III-134

7 also creating healthier and aesthetically pleasing living environments, reducing energy consumption, and also promote green infrastructure to the public through extensive vertical gardening. Appendix FIGURE 1 References Pitt, Robert. (1987). Small Storm Urban Flow and Particulate Washoff Contributions to Outfall Discharges. A Thesis submitted for the degree of Doctor of Philosophy (Civil and Environmental Engineering). FIGURE 2 Pitt, Robert. (1999). The Beneficial Uses of Stormwater in Urban Areas and the Need for Change in Urban Water Management. Section 2 of the Guidance Manual for Integrated Wet Weather Collection and Treatment Systems for Newly Urbanized Areas. Bochis, Celina and Pitt, Robert. (2005). Impervious Surfaces in Urban Watersheds. This paper was presented at the 78 th Annual Water Environment Federation Technical Exposition and Conference in Washington D.C. FIGURE 3 Loh, Susan. (2008). Living Walls-A way to green the built environment. BEDP Environment Design Guide. Sharp, Randy; Sable, James; Bertram, Flavia and Mohan, Eva; Peck, Steven. (2008). Introduction to Green Walls Technology, Benefits and Design. Developed by Green Roofs for Healthy Cities. PHOTO 1 Phillips, Doug. Mobile-Tensaw Delta. Discovering Alabama Video Series. Emerging Issues Along Urban/Rural Interfaces III-135

8 FIGURE 4a FIGURE 7b 12:15 p.m. FIGURE 4b FIGURE 7c 4:15 p.m. FIGURE 5 FIGURE 8a FIGURE 6 FIGURE 8b FIGURE 7a 8:15 a.m. Emerging Issues Along Urban/Rural Interfaces III-136

9 Mississippi-Alabama Sea Grant Consortium Project Number: R/MG/CSP-10 Program Year: 2010 Grant Number: NA07OAR The U.S. Department of Commerce s National Oceanic and Atmospheric Administration under NOAA Award NA07OAR , the NOAA Gulf of Mexico Coastal Storms Program and the Mississippi- Alabama Sea Grant Consortium (Project number R/MG/CSP-10) supported this work. The views expressed herein do not necessarily reflect the views of any of those organizations.