Grantee Research Project Results
Final Report: Floating Island on a Roof for Rainwater Management
EPA Grant Number: SU835712Title: Floating Island on a Roof for Rainwater Management
Investigators: Alford, Celena , Le, Kieu Ngoc , Sulliman, Ahmed , Reynolds, Andray , Mention, Christina , Lee, Clinton , Johnson, Evan , Gayle, Godfrey , Boyd, Jawari , Keefer, Madeline , Reyes, Manuel , Powell, Marquez , Armstrong, Morris , Powell, Robert , Mendoza, Vanessa , Doan, Yen
Institution: North Carolina Agricultural and Technical State University
EPA Project Officer: Hahn, Intaek
Phase: I
Project Period: August 15, 2014 through August 14, 2015
Project Amount: $15,000
RFA: P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity and the Planet (2014) RFA Text | Recipients Lists
Research Category: Pollution Prevention/Sustainable Development , P3 Challenge Area - Sustainable and Healthy Communities , P3 Challenge Area - Safe and Sustainable Water Resources , P3 Awards , Sustainable and Healthy Communities
Objective:
The objectives of our research were: a) to convert a green roof prototype built from P3 and USDA grants into a Floating Island Roof (FIR), b) to show that a floating island roof can be used to significantly reduce stormwater generated from roofs; c) to demonstrate that a biologically diverse ecosystem can be established on a floating island roof; d) to determine what type of structure should be recommended to support a floating island roof; e) to design water table with app sensor system for managing water levels in the floating island roof; f) to install multiple sensors that can monitor plant health, water quality and weather on the FIR, g) to find out based on literature whether a floating island roof can reduce impact of urban heat island; h) to preliminarily see the aquaponics potential of a floating island roof; and i) to observe and infer on recreation/relaxation provided by the floating island roof.
Summary/Accomplishments (Outputs/Outcomes):
Several student teams were involved in carrying out the FIR objectives. The team is composed of undergraduate, high school and graduate students and faculty advisers.
a) Convert a green roof into FIR. Team converted a green roof made of wood built through funding provided by previous P3 and USDA grants. The green roof had three cells, two large outside cells 11.75’ x 6’ and a small middle cell 11.75’ x 2’. The soil was removed from the green roof. We modified the green roof by converting each cell into a pond. We put on top of each cell a floating island foam material to serve as plant growing media. In addition to aerate the FIR for mosquito and odor control, we installed solar powered pumps on each cell. Note the FIR is only elevated about a foot high.
b) Biodiversity: We experimented with 20 species of plants (flowers, vegetables, grasses, and herbs) on a randomized complete block design with ten replications grown on the floating island foam material. Our team measured plant height, mortality and observed the growth for each type of plants from July to December 2014. Plants grew robustly on the floating island. All of the plants survived until the onset of cold weather. Furthermore, the biologically diverse plant system attracted several types of fauna. Butterflies, bees, spiders and other types of insects and also birds which feed on the insects and plants or drank the water from the pond; in addition we observed fauna living in water. We also put common goldfish and it lived very well in the pond under the floating island. FIR can create a biologically diverse ecosystem on a roof. This is better when compared with limited plants that can be grown on typical green roofs; and a lot, lot, lot better when compared to a bare lifeless conventional roof.
c) Storm Water Reduction: The team conducted a hydrologic analysis to determine the dimensions of a floating island roof from a 1000 ft2 house roof as the rainfall catchment area. The rainwater collection surface (1000 ft2, for our purposes) is the area of the roof that is guttered and diverted to the FIR. We chose a design criterion for a 24 hour, 1 year return period rainfall, which is 2.74 inches for Greensboro, NC. We found that for a 12’x14’ floating island roof porch collecting rainfall from a 1000 ft2 roof, the depth of water storage needed in the FIR is about 19 inches. With 3 inches of water added to maintain baseline water depth for plant use, total design depth from a 2.74 inch rainfall will be 22 inches. A floating island roof built 12 ft wide, 14 ft long, and 2 ft deep receiving water from a 1000 ft2 roof will only overflow once a year. FIR can store a significant amount of roof rainwater that will not drain as stormwater. Engineers can adjust the depth, width and length of roof as a function of multiple factors like client preferences, cost, and climate of the area.
d) Structure to Support Floating Island Roof: The structure to support the FIR will be subjected to a variety of loads from the material to build the roof, stored water, the people on the roof, the animals on the roof, the plants growing on the roof, snow and wind. Based on a common design approach known to structural engineers as the Load Resistance Factor Design, the team concluded that the best and safe support for FIR will be steel columns to provide sufficient compressive strength. Steel beams with a concrete decking on top will be used to take on lateral loading and tension causing loads. Steel is one of the strongest materials in tension used in structures. Also, depending on the soil load bearing value of the location of implementation, concrete footings of a specific size will have to be used as well. FIR can be safely supported steel columns.
e) Water table sensor: Team of electrical engineers started canvassing and looking for hardware for wireless monitoring of water table in the FIR. They purchased the Monnit water table sensor. As of this time, they have not yet completed installation of the water table sensor. The team also intends to develop an App for wireless reading of the water level of the floating island roof. This will enable the homeowner to manage rainwater harvested FIR. Homeowner can drain FIR when rain is coming and store water if no rain is forecasted for various water uses.
f) Multiple sensors for monitoring plant health, weather and water quality. As of this writing the team has purchased and was prevented (unusual snow weather at Greensboro last February) from installing and testing several sensors with apps for monitoring plant health, water quality and weather. Team will demonstrate success and limitations of these sensors to monitor FIR environment during the P3 competition.
g) Urban Heat Island: An urban heat island occurs when cities are generating an excessive amount of heat because of increase in impervious surfaces and also little vegetation. According to the Environmental Protection Agency, cities that are considered urban heat islands can be 10°F warmer than their surrounding areas. The hot temperatures causes people in these communities to turn on air conditioning more often which keeps the power plants that run these units running, emitting more greenhouse gases into the air. Reducing heat in urban areas can also help with the life expectancy rate of these communities. In the U.S., heat typically kills more people each year than tornadoes, hurricanes, floods, and lightning put together (NOAA). Our design provided a means to grow a biologically diverse flora and fauna system roof porch. Increasing vegetation on roofs of buildings and houses in cities will reduce temperatures, if funded the design team will model reductions in urban heat as the number of houses and business establishments adopt the FIR.
h) Aquaponics: It is possible to grow fish below the floating island. Team released common goldfish in the FIR and the fish survived until the beginning of winter. The team also put floating island roof foam on top of a six ft wide by one ft length and one ft height aquarium. Tropical fish was released in the aquarium. Tropical aquarium fishes were more sensitive than common gold fish with a number of them dying whenever the team transplanted new plants on the floating island. Water quality was regularly measured in the aquarium with some of the fish deaths accounted due to a rapid change in some water quality parameters when new plants were transplanted on the floating island roof. It is possible to grow fish in FIR, if funded the team will continue monitoring fish growth in FIR, probably testing tilapia. In addition, team will study roots and growth of various plant species grown on a floating island on top of an aquarium.
i) Recreation: The team observed students at N.C. A&T look at the floating island roof. Many are convinced that it is a more relaxing system compared to a typical lifeless roof. We also designed scenarios wherein the floating island roof is an open porch for sitting and relaxation and on the bottom is the covered porch.
Conclusions:
Implementation of the floating island on a roof design will allow for effective management of stormwater runoff contributed by roofs. Water can be saved in FIR for irrigation and other gray water needs during periods of low rainfall; and water can be slowly drained from FIR to a permeable surface for increase stormwater storage during winter or before occurrence of an intense rainfall. FIR can be a biologically diverse food producing mini-ecosystem on a roof. Herbs, vegetables, flowers, grasses and several other endemic species can be grown in FIR. These plants can provide food and habitat for several kinds of animals. Fish can also be cultured in FIR. FIR can be supported by reinforced concrete and is expected to mitigate urban heat island. Lastly, FIR can be an excellent environment for recreation because it replaces a typical lifeless roof with a food producing and mini-biologically diverse terrestrial and aquatic ecosystem.
Journal Articles:
No journal articles submitted with this report: View all 2 publications for this projectSupplemental Keywords:
storm water management, urban biodiversity, water quality, urban heat island, green roofRelevant Websites:
- FIR is a type of natuculture. Natuculture website Exit
- Floating Island Roof photos Exit
- Living porch presentation of partial results of this study Exit
- Southern High School of Energy and Sustainability Presentation
The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.