A Bit About Our Project:
Green Roofs alleviate many downsides of increased urbanization by mitigating urban stormwater surges, reducing heating and cooling costs, lessening the urban heat island effect, adding much-needed green space in the urban environment, improving water and air quality, and providing habitat for wildlife.
To be able to realize these benefits for Texas’ urban areas, our unique environment must be considered. We believe much can be learned from our native plant-soil systems. These species have evolved to survive in Fort Worth’s climatic regime; the result of thousands of years of trial and error. It is to these systems that we have looked to inform our study. During the summer and fall of 2007, we performed fieldwork studying the vegetation and soils on thin-soiled prairies referred to as “barrens” and “glades”. These thin-soiled ecosystems provided, in our opinion, the closest natural model for a Texas-specific green roof: a few inches of clay soil over thick, lithified bedrock.
Our thesis projects combine the efforts of two Texas Christian University graduate students, David Williams and Jon Kinder, with the oversight and guidance of several faculty and outside advisors. With the knowledge gained from local barrens and glades we have designed an experiment to compare a range of natural and synthetic green roof designs. We have built 14 model roofs, each with an area of sixteen square feet, to serve as our test platforms. Growth media will include current commercial products, transplanted native soil, and experimental designs based on our field observations. All of these media will be planted with a variety of native annual and perennial species which will be routinely monitored to determine how well they adjust to the green roof environment.
Eight of these fourteen boxes will have intensive hydrologic monitoring to track the rate and pathways of precipitation flux in each model roof. A tipping bucket precipitation gauge will monitor site-specific rainfall rates and volumes. In addition, samples of both precipitation and infiltrated water will be analyzed to determine the effects on water quality of passage through our green roof modules.
To supplement our natural rainfall data, we shall use a purpose-built rainfall simulator to simulate storm events. This will provide supplemental irrigation to newly established plants (standard practice for plant transplantation), and allow careful observation and monitoring of individual test boxes with respect to runoff dynamics and water chemistry changes.
Some exciting, tangential goals have emerged during the process of designing this experiment. We may be able to introduce the endangered Dalea reverchonii to our test roofs. If these efforts prove successful, there are interesting implications for green roofs as vessels for conservation. Another product of our research will be a thorough description of the soils and vegetation of the barrens and glades in the Fort Worth prairie, which have not been described in the current scientific literature.
In addition to our experiments with modular systems, we shall continue field work investigating the thin-soiled prairies around Fort Worth to learn as much as possible from these native systems. We will observe responses from our preliminary plant palette and introduce appropriate alternate species as needed. Our experimental modules are designed to last for several years so that as these systems mature, future students can continue this research. We intend for this work to inform the budding green roof industry in Texas so that Texas’ urban centers can maximize the multiple benefits green roofs have to offer.