Stormwater is the component of runoff that is generated by human activities, and has gradually become a key issue in achieving sustainability in urban environments. When vegetation and soils are replaced with roads and buildings, less rainwater infiltrates into the ground or is taken up by vegetation, and more becomes surface runoff. A greater area of impervious surfaces leads to increased stormwater runoff volume and velocity, and consequently increases the risk off looding and erosion. Being able to reduce stream flows and pollution of surface flows, green roofs are one technology that may help in alleviating this storm water crisis. This thesis developed a different and effective methodology for quantifying the effects of green roofs on stormwater runoff and calculating the runoff volume and rate for residential housing communities before and after applying green roofs. The method utilizes local climate data like rainfall and evapotranspiration rate, the water use properties of vegetation like crop coefficients of plants, and the areas of impervious surfaces; and then compares the different effects of green roofs in different locations having disparate climatic conditions. It was found that the best way to achieve zero runoff was to green a portion of the total rooftop area and disconnect all impervious surfaces. Implications of this methodology on city planning and site design and for future research are then discussed.

Thesis (M.L.A.) -- University of Texas at Arlington, 2009.

Green roof technology is becoming increasingly more popular in the U.S. as it provides several economical, sociological, and ecological benefits to urban environments. One specific advantage a vegetated rooftop is known to provide is its ability to retain water and release it at reduced rates. However, with increased interest in these systems, concerns regarding their influence on water quality have been raised. Green roofs can be complex systems and the degree to which water quality might be affected may be related to green roof construction and components within. To answer questions regarding green roof influence on metal contaminants in storm water runoff, a field study and a related laboratory study were designed to investigate potential impacts these systems may have on water quality with respect to heavy metals and some micronutrients. Overall, results obtained for Cd, Cr, Cu, Fe, Mn, Ni, Pb, and Zn content observed in leachate collected from the constructs and media treatments from a green roof field study do not indicate that green roofs are a significant source of heavy metal and micronutrient contaminants in urban stormwater runoff and that planted Green Roof BlocksTM release less or the same metal content as planted built-in-place models. Elemental concentrations determined in effluent collected from treatments in the field study were collected for four rain events (June 28, 2007, October 18, 2007, February 4, 2008, and April 11, 2008) and compared to IEPA effluent standards to assess whether or not there were any negative impacts on water quality. Treatments for this portion of the investigation were empty built-in-place models (controls), planted and non-planted Arkalyte media at depths of 5 cm, 10 cm, 15 cm, and 20 cm in built-in place models, planted and non-planted commercial and potential green roof media in Green Roof BlocksTM. With the exception of excess Zn levels in collected effluent from the planted 10 cm treatments in October and the planted 5 cm treatments in February as well as the elevated Fe content in leachate obtained from planted glass media in October, metal concentration in effluent acquired from planted treatments were below effluent standards. Also determined to be above IEPA standards in October were Cu, Fe, and Pb measured in effluent obtained from non-planted glass media. The laboratory portion of this investigation evaluated several commercially-available substrates, bottom ash, lava rock, and composted pine bark to determine the total acid extractable and plant exchangeable content of eight elements (Cd, Cr, Cu, Fe, Mn, Ni, Pb, and Zn). In addition to this, effluent collected from planted and non-planted treatments using these substrates incorporated with 20% composted pine bark were examined over a course of three leaching events. While all elements examined were observed to be within levels normally found in soils, results from the total acid extractable experiments demonstrate large variation in metal concentration with each substrate and composted pine bark. With the exception of total extractable Cd, there were differences in concentrations for the remaining total acid extractable metals between the substrates and amendment tested. An artificial leaching study was conducted in the phytotron at Southern Illinois University Carbondale and consisted of eight repetitions of planted in addition to eight repetitions of non-planted pots containing known volumes of 20 % composted pine bark blended with Arkalyte, Haydite, Lassenite, Axis, bottom ash, Axis + bottom ash, and lava which were subsequently leached over three separate leaching events. Collected effluent was evaluated for Cd, Cr, Cu, Fe, Mn, Ni, Pb, and Zn content as well as volume of water displaced as a function of planting treatment, number of times leached, and substrate type. Metal content in the leachates were typically an order of magnitude lower than values obtained from the batch studies, and the planting, substrate, and leaching interactions varied for each metal with Pb being the most complex. The volume of water displaced upon leachate collection increased across all substrates as a function of leaching event.

Stormwater is the component of runoff that is generated by human activities, and has gradually become a key issue in achieving sustainability in urban environments. When vegetation and soils are replaced with roads and buildings, less rainwater infiltrates into the ground or is taken up by vegetation, and more becomes surface runoff. A greater area of impervious surfaces leads to increased stormwater runoff volume and velocity, and consequently increases the risk off looding and erosion. Being able to reduce stream flows and pollution of surface flows, green roofs are one technology that may help in alleviating this storm water crisis. This thesis developed a different and effective methodology for quantifying the effects of green roofs on stormwater runoff and calculating the runoff volume and rate for residential housing communities before and after applying green roofs. The method utilizes local climate data like rainfall and evapotranspiration rate, the water use properties of vegetation like crop coefficients of plants, and the areas of impervious surfaces; and then compares the different effects of green roofs in different locations having disparate climatic conditions. It was found that the best way to achieve zero runoff was to green a portion of the total rooftop area and disconnect all impervious surfaces. Implications of this methodology on city planning and site design and for future research are then discussed. / Applied Science, Faculty of / Architecture and Landscape Architecture (SALA), School of / Graduate

Green roofs have become an important urban mitigation technology due to their ability to address multiple environmental issues. One of the most common benefits attributed to green roofs is the reduction in heating and cooling loads in buildings by dissipating heat through evaporation. This study focuses on evaluating the effect that evaporative cooling has on the thermal performance of green roofs. Sponge and floral foam were used as porous media for their ability to retain water inside its body, transport it to the surface, evaporate it at a constant rate and for their different pore sizes. Test trays containing sponge or floral foam saturated with water were tested in a low speed wind tunnel equipped to measure weight, temperature and heat flux. Two types of experiments were conducted: one with evaporation at the surface, and the other with evaporation blocked by an impervious layer. The testing conditions for all tests were kept constant except for the ability of evaporation to happen. Evaporation rate for floral foam was 0.14 kg/m2hr and 0.29 kg/m2hr for sponge. Results of tests with evaporation show a decrease of 45-49% in heat conducted through the roof when compared to the tests without evaporation. For optimal thermal performance of green roofs, a material that enhances water transport and thus evaporation at the surface is necessary with large pores and low field capacity. Surface temperatures on test with evaporation were found to be between 3-7°C lower than those without evaporation. Applying a 2 sample t-test to the data, the relationship between heat flux and evaporation was found to be statistically significant.

This study focuses on how green roof thermal performance is affected by the soil moisture in summer condition. It aims to determine whether moist soil is a better insulator during the summer months than dry soil. A soil model is developed to predict simultaneous conduction, convection, and surface evaporation for a layer of moist soil representing a green roof. It used to analyze evaporation process and its affect on the soil resistance. The model considers only bare soil without vegetation on the roof. The model predicts the soil surface temperature as it is affected by soil moisture content, which can then be used to calculate heat transfer through the soil layer. An experimental dry out test was conducted to measure the soil moisture and soil temperature histories. Comparison of the predicted and measured sol surface temperature shows that the model reasonably captures the actual behavior. The evaporative cooling effectively reduces the soil surface temperature and heat flux in moist soil and can be used as an effective way to insulate the roof.

The urban heat island (UHI) effect is a phenomenon that results in cities being warmer than the surrounding rural areas, due to a large amount of impervious surfaces. The purpose of this study is to evaluate the effectiveness of green roofs to mitigate the effects of solar energy on a building in the southern United States. In order to test the green roofs, temperatures were monitored inside and on top of unconditioned model buildings with green and with traditional roofs. Over the course of the study, the data collected showed that green roofs provided a significant benefit for the buildings by reducing daily high temperatures during summer and daily low temperatures during winter, while also reducing temperature fluctuation. The findings of this study suggest that a green roof will reduce indoor temperature and rooftop temperature, while providing several other benefits for city inhabitants such as reduced air temperature.

This study examines the relationship between environmental sustainability and green schools, seeking to highlight the benefits and determine the Net Present Value (NPV) installing vegetative roofs on all schools in the Atlanta Public Schools District. This study quantifies the costs and benefits of thin-layer, or extensive, green roof systems as they compare to typical flat roofs on Atlanta Public Schools. Quantifiable benefits are detailed and suggestions are made to create the means by which other social benefits may be quantified. The purpose of this thesis is to establish proof to the Atlanta Public Schools District that over a 40 year period there are more benefits associated with installing vegetative roofs on all of their flat roofs than there are costs. While some may argue that greens roof are more costly than traditional roof systems, this study provides evidence that the cumulative benefits over a 40 year life cycle associated with large scale green roof installations, such as on all Atlanta Public Schools, are greater than the initial costs incurred. Factors included in the analysis of benefits were reductions to energy/utility costs, reduced emissions, and avoided best management practices (BMPs). Other considerations include social benefits resulting from the mitigation of storm water runoff, reductions to the urban heat island, productivity level increases (students and teachers), and avoided regulatory fees.

Thesis (M.S.)--Rutgers University, 2008. / "Graduate Program in Geography." Includes bibliographical references (p. 119-124).

Increased urbanization leads to an increasing amount of impervious surfaces and a decrease ofthe natural hydrological function. Urban stormwater does thus risk to create high surface flows which could damage the receiving water bodies (e.g. erosion) or the urban area itself (flooding). Integrating more nature-based systems into the urban area increases the natural hydrological function and the risks for high surface flows are lowered. One way of implementing nature-based systems in the urban environment is to install green roofs. Most of the research and development done on green roofs have been focusing on the conditions of central Europe. Installing green roofs with the same vegetation in the subarctic climate of northern Sweden would expose it to a climate it might not be suited for, and growth would be limited. The vegetation helps increase the retaining and detaining capabilities of the green roofs and therefore the purpose of this thesis was to examine if planting native vegetation would help increase thegreen roofs performance in a subarctic climate. Conventional green roofs vegetated with sedum was hypothesized to have lessened retaining and detaining capabilities when placed in cold climates since the vegetation was exposed to a climate it probably was not suited for. It was examined whether planting more native vegetation could help increase green roofs performance. The vegetation was chosen based on Grime´s “universal adaptive strategy theory”, which describes competitors, stress tolerators and ruderals as three different vegetation groups with different survival strategies. Different species from each strategy were selected and planted on the roofs. There were five roofs per survival strategy and five roofs where all strategies were mixed. Conventional sedum vegetation was planted on five roofs to be able to compare green roofs performance. Five control roofs with substrate only and one reference roof made of steel were installed as well. In total, seven rainfall events were analyzed, and few significant differences could be found between the competitors, stress tolerators, ruderals and the vegetation mix. A conclusion is that stress tolerators may help to increase green roof performance the most, but due to the relatively short study period, continued measurements are recommended to draw further conclusions. The survival strategies did improve retention and detention relatively to using sedum vegetation and substrate only. The extent of vegetation coverage does not affect the retention or detention from the green roofs. The competitors, stress tolerators, ruderals and vegetation mix had larger plant mass than the sedum and the increased plant mass is probably the reason for their improved retention.