Stormwater management in Dauphin Street area, Mobile, Alabama

Transcription

1 Stormwater management in Dauphin Street area, Mobile, Alabama Junyi Li Dept. of Lan scape Architecture and Design, Auburn University Reprinted from "Emerging issues along urban-rural interfaces III: Linking science and society, (Proceedings), David N. Laband, ed., 2010, pg MASGP

2 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.

3 Stormwater Management in Dauphin Street Area, Mobile, Alabama Junyi Li Graduate Student Master of Landscape Architecture Auburn University, Auburn, AL Key Words: Stormwater management, rainwater harvesting, runoff, infiltration Abstract: The purpose of the project is to retain, collect, store and reuse stormwater in Dauphin Street area, Mobile, Alabama. This project seeks to control the quality and quantity of stormwater in the proposed area, in order to reduce surface runoff and urban heat island effect, and reutilize water. Since Dauphin Street was built in 18 th century, and still has impervious surface and old stormwater system. The impervious surface does not allow water to infiltrate into the ground. Most runoff goes directly into the drainage system, and exit into the Mobile Bay. This condition could cause flooding while the system is overwhelmed by the additional flows. Stormwater management is the management of stormwater runoff, often using water retention facility, to provide controlled release into receiving streams (watertechnology.net). Stormwater runoff causes pollution, erosion and flooding problems. These problems occur because we altered the land and changed the way that water moves through the landscape. Also, because this system lacks cleaning function, it cannot eliminate pollution in the water, and thereby pollutes rivers, lakes, and the ocean. pavement. 2) Bioswales to slow, collect, clean rainfall in parking lot, also to provide shade for users. 3) A cistern was used to collect rainwater on the roof, and reuse it. After these installments, it is likely heavy runoff and water pollution would be alleviated for the chosen site. The author proposes the following seventiered approach: 1) The ability of these facilities to slow, collect, and clean stormwater; 2) Longevity of these facilities; 3) Aesthetic value; 4) Utility value; 5) Educational value; 6) Cost-efficient; 7) To promote establishment of regulation about stormwater management. In areas like Mobile, with heavy rainfall and massive evaporation, a solo stormwater management may not comprehensive. A combination of rain cistern, bioswales, and permeable pavement could reduce surface runoff more effectively than a single method. This paper will theoretically point out both successes and failures of this infrastructure. The proposed stormwater management method and permeable design provide a model for future planning. For this project, I used 1) Pervious concrete replaces existing parking impervious Emerging Issues Along Urban/Rural Interfaces III-137

4 Introduction With the urbanization process, human s activity has more and more impact on nature habitat. The concrete surface replaced the natural soil, cut down the connection with rain water and deep soil, which prevent water get into the aquifers, infiltrate and become ground water. Ground water is water located beneath the ground surface in soil pore spaces and in the fractures of lithologic formations. A unit of rock or an unconsolidated deposit is called an aquifer when it can yield a usable quantity of water. What is stormwater? Stormwater is the water come down to the ground during precipitation events. It moves on the ground by gravity and flows into streams, rivers, ponds, lakes and oceans. In the nature environment, when precipitation happens, there are about 40% stormwater go back to the air through evapotranspiration, 25% get into ground through deep infiltration, 25% absorbed by shallow infiltration, and only 10% get away as runoff. In urban area, due to most pavements are impervious. There are about 30% stormwater go back to the air through evapotranspiration, 5% get into ground through deep infiltration, 10% absorbed by shallow infiltration, and there are 55% of stormwater get away as runoff. This runoff usually goes directly into the drainage system What is stormwater management? Managing the quantity and quality of stormwater is termed, Stormwater Management. (Washington State Department of Ecology. Stormwater Management Manual for Western Washington ). Stormwater management is the management of stormwater runoff, often using water retention facility, to provide controlled release into receiving streams (watertechnology.net). Why it s important to management stormwater? About 55% of stormwater goes directly into the drainage system, with dirt, waste, pesticide and fertilizer in urban environment. Stormwater runoff causes pollution, erosion and flooding problems. On the one hand, the runoff greatly increases the burden of the city drainage system while the precipitation is heavy, peak discharges can be as much as two to five times the nature rate; on the other hand, this dirty water gets into the ecosystem without infiltration of soil, that greatly aggravates eutrophication, sediment, bacteria and viruses, oil and grease, metals, organics, pesticides in water. Furthermore, since there is not enough water in urban area for evaporation, heat island effect would become worse. Unmanaged stormwater could also infect the micro environment. If stormwater has not been taken good care, it could cause stream flow at the side walk, path, parking lot, and disturb the people s movement. In some area, accumulation of stormwater could cause a spread of disease, threat people s health. Not only too much precipitation could cause trouble, in drought area, if precipitation hasn t been managed and stored in an appropriate way, it may cause the temperature higher than in the nature environment and make living creature uncomfortable, it will make people use air conditioner more, waste the energy which we could have saved. Mobile, Alabama Mobile is the third most populous city in the Southern U.S. state of Alabama and is the Emerging Issues Along Urban/Rural Interfaces III-138

5 county seat of Mobile County. It is located on the Mobile River and the central Gulf Coast of the United States. Mobile located at the junction of the Mobile River and Mobile Bay on the northern Gulf of Mexico, the city is the only seaport in Alabama. Moist and hot for most of the year. Annual average temperature is 67.5 F ; almost 75 days have temperature higher than 90 F. Annual precipitation is 64 inches; in August alone, precipitation as high as 7 inch/month. Average relative humidity is 75%. Mobile is known for having the oldest organized Carnival celebrations in the United States, dating to the 1700s of its early colonial period. Feasibility Analysis Mobile City is beside the Mobile Bay, since precipitation here is very high, flood could be a potential threaten. However, the area I design is in the area of 500-year flood, or areas of 100-year flood with average depth of less than 1 foot. We could almost overlook the factor of flood, and structures I design could ignore the factor of overflow (Figure. 1). Runoff in the site has a pattern to follow. Basically, the highest point on the site is in the middle, rainwater will flow to the surrounding drainage system beside roads. Overall, stream flow from southwest to the northeast, and run into the Mobile Bay. There is not a significant geological burden from doing this project. The Dauphin Street used to be the most popular street in town, but since this area become old, lack of entertainment facilities, it has been desolated especially during the depression. Devices in this area are pretty old which is not sustainable. The system has negative effects for the environment. Some homeless people would sleep and live at the Beniville Square, which could cause safety and sanitary problem. It also could prevent people from enjoy the space. Mobile municipal would like to renew the area to provide a better habitat for residents, also to promote economy here. But the budget is limited, so I have to pay attention to both short term cost and the long term cost. Stormwater Management For this project, I used porous pavement, bioswales, and rain cisterns to reduce and infiltrate runoff on the site. Impervious pervious parking pavement. American own 45% of auto mobiles in the world. While eighty to ninety percent of parking demands in America are met by surface parking, especially in Dauphin Street area I m going to design, almost all the surface parking lot all with impervious paving. Because it will prevent rainfall from infiltrate into soil and supply underground water resource, it has an impact on receiving stream hydrograph as well as water quality. Because of the smooth surface, it also keeps the parking lot wet and slippery while raining. The grey concrete parking lot paving is light colored, with smooth surface will reflect more heat and light, visually, it can result as eyesore and glaring, temperature will be extremely hot in summer days. To address this situation, I would like to replace the paving into a permeable pavement. The paving, from top to the bottom order of porous asphalt, shattered 1 thick concrete, soil, shattered 8 thick concrete, and pipes. Porous asphalt will not produce dust like eroded concrete paving, asphalt could absorb some noise, reduce light reflection. It can easily let rainwater get through it, keep Emerging Issues Along Urban/Rural Interfaces III-139

6 surface dry and clean. Shattered 1 thick concrete could infiltrate roughly; soil could clean and retain some rainwater; concrete shattered into 8 thick can clean runoff for the last time. If there is overflow, those surface waters will get into the bio-swale. Those water left after infiltration of shattered concrete, asphalt paving and soil, will get into the pipes underground and collected in the main cistern. After remove the previous concrete paving, we could shatter them into small rocks with different diameter; they could be used as base of the porous parking lot pavement. Save the money of moving construction waste and purchase new material. Bioswales in the parking lot; Pervious pavement is not enough to solve stormwater problem on the site. The pervious paving is hard to make large amount of water infiltrated and get into the deep ground. Bioswales are landscape elements designed to remove silt and pollution from surface runoff water. Bioswales in the parking lot are intended to slow, collect, clean rainfall in the parking lot. They are several long and narrow planters, with native grass and native deciduous trees. Bioretention swales provide both stormwater treatment and conveyance functions. The swale component provides pre-treatment of stormwater to remove coarse to medium sediments, while the bioretention system removes finer particulates and associated contaminants. Stormwater will be filtered via the following processes: 1) passing through surface vegetation; 2) percolating through prescribed filter media, which provides treatment through fine filtration, extended detention treatment and some biological uptake; 3) disconnecting impervious areas from downstream waterways; and 4) providing protection to natural wetland system from frequent storm events by reducing storm flow velocities when compared to pipe systems (Figure. 2). Plants and soil are key functional elements of all landscaped stormwater facilities. This natural system approach improves the quality of the urban runoff through bioretention processes and helps restore lost hydrologic functions in urbanized areas. Native plants are used because they are more resistance of local environment, easier to manage. Deciduous trees in these bioswales not only will provide shade for users in hot days, but also let sunshine come down in winters. Also, trees in the bioswales could decrease dirt in air, odors, noise, glare and airborne pollutants. Collect and reuse rainwater on the roof. Roof of buildings in this area all covered with concrete or asphalt, drainages connected roof and the ground. Tons of rainwater just pour into the mobile bay without make full use of it. So my idea is to make full use of the rainwater. First, we need to change the drainage system, reorganize the pipes. Then, at the end of each drainage, I put a water sculpture there, to let people notice the rhythm of water dropping, and be able to play with water. After that, water can be over flow out of the sculpture and get to infiltrate into soil. The water can t get further in ground will be collected in pipes, and store in a cistern underground (Figure. 3). The area of the roof in my design area is about ft 2, annual precipitation in Mobile is 64 inches, based the rainwater calculation formula: Emerging Issues Along Urban/Rural Interfaces III-140

7 Collection Area (ft 2 ) x Rainfall (in/yr.) / 12 (in/ft) x 7.43 (Gallons/Cubic Foot) = Gallons/Year So, the amount of rainwater we could collect is: (ft 2 ) x 64 (in/yr) /12 (in/ft) x 7.34 (Gallons/Cubic Foot) = Gallons/Year Over 3 million gallons per year of water could have used in the area. The aesthetic value of the new site would be enhanced a lot comparing to the old space. Green plants bring pleasure to people and relax the eyes. Structures with vivid color also are able to enlighten the space. Deciduous trees and evergreen trees mostly placed in regular pattern but also have some in irregular pattern, this arrangement provided the space order, yet not too rigid. After design, the mixed use parking lot provides spaces for play; have lunch, take a break and opportunity for people to interact with each other. It could attract more people in order to promote consumption. Since there are three elementary schools ( Leinkauf Elementary School; Council Traditional School; and Howard Elementary School), two middle schools ( Calloway- Smith Middle School; and Dunbar Middle School) in the walking distance of the designed area, the space had the potential to become a water-collection procedure display center. Make children to know the importance of water conservation, in order to establish their conscience to protect the environment. For short run, the devices may cost more than usual project in the same size. However, the project could save irrigation water and electricity. And we could reduce a cost by use the materials already existing. Like break up existing concrete paving could be as the foundation of new porous pavement. Use native plants also could effectively cut down the construction and management cost. If this project is successful, it could promote the establishment of regulation about stormwater management. Especially in areas have same environment, they could use the model of rainwater management in this project. Possible Problems The biggest problem of this project is management. Sediment may deposit on the edge of the fountain sculptural, debris could block the curb inlet of bioswales. If there is a large amount of sediment in the designed area, the function of the stormwater management system may have compromised by them. So, it may need to pay more attention on cleaning these areas. Conclusion The Dauphin Street area is a place full with history and glory. But it has not been taken good care of. The old urban planning and construction methods are hard to follow the problems caused by urbanization. It needs to keep updated with new trends. For this project, I used porous pavement, bioswales, and rain cisterns to reduce peak stormwater volume and infiltrate runoff as much as possible on the site. 1) The pervious concrete replaces existing parking impervious pavement. 2) Bioswales are intended to slow, collect, clean rainfall in the parking lot, also to provide shade for users. 3) A cistern was used to collect rainwater on the roof, and reuse it. After these installments, it is likely heavy runoff and water pollution would be alleviated for the chosen site. Emerging Issues Along Urban/Rural Interfaces III-141

8 There are many states have done stormwater project, research, and established stormwater management policy. However, research is still needed in the related field. Especially cross study with wind, noise, and light specialists. Cooperation with experts in different areas could stimulate idea collision and promote to emerge of better resolution. References: Storm, S; Nathan, K; Woland, J. (2009). Site engineering for landscape architects. John Wiley & Sons, Inc. Zimmermann, A. (2009). Constructing landscape-materials, techniques, structural components. Birkhauser Using Smart Growth Techniques as Stormwater best management practices American Society of Landscape Architects; Lady Bird Johnson Wildflower Center at the University of Texas at Austin; United States Botanic Garden (2009) The Sustainable Sites Initiative Guidelines and Performance Benchmarks American Society of Landscape Architects; Lady Bird Johnson Wildflower Center at the University of Texas at Austin; United States Botanic Garden California Stormwater Quality Association (2003) Stormwater BMP Handbook Pollutant Impacts on Water Quality. California Stormwater Quality Association, Stormwater BMP Handbook, (Feb. 2005). Stormwater management manual for western Washington. Washington State Department of Ecology Water Quality Program Christianson, R; Powell, M; Hutchinson, S; Presley, D. (July, 2008). Stormwater best management practice maintenance. Presented by Kansas State University Agricultural Experiment Station and Cooperative Extension Service Gibbons, Jim (1999) Parking Lots. Nonpoint Education For Municipal Officials MA Department of Environmental Protection; MA Office of Coastal Zone Management. (March 1997). Stormwater Management. Volume Two: Stormwater Technical Handbook. MA Department of Environmental Protection Selman, Mindy (2007) Eutrophication: An Overview of Status, Trends, Policies, and Strategies. World Resources Institute. The Importance of Imperviousness. Watershed protection Techniques Clark, Mark; Acomb, Glenn (2008) Florida Field Guide of Low Impact Development. University of Florida. American Society of Landscape Architects (2007) General Design Honoraward NESiskiyou Green Street, Portland, Oregon. American Society of Landscape Architecture. Washington State Department of Ecology Water Quality Program. Emerging Issues Along Urban/Rural Interfaces III-142

9 Appendix: Figure 1. Flood Plan Analysis Figure 2. Design Paving Details Figure 3. Drainage before-after Emerging Issues Along Urban/Rural Interfaces III-143