The Seaholm project is an example of how Austin has promoted rainwater harvesting as part of a multi-faceted water conservation program.
The first part of an unusual $100 million development project opens this year, on 7.8 acres of land in the southwest quadrant of downtown Austin, TX. The historic buildings of Seaholm—the city’s former electric power plant—will form the core of this combined municipal and private project. Seaholm’s main generator building, and three of the four other existing power plant buildings, will be renovated. The completed project will consist of an additional 90,000 square feet, including a two-story office building, shops, and in 2010, a 22-story hotel-condominium tower. An innovative part of the new Seaholm is its raincatchment system.
Water conservation is important in Austin. The city’s Water Conservation Task Force (WCTF), which has been studying best practices for wise water usage, presented its recommendations in early 2007. In May 2007, the Austin City Council unanimously approved a resolution, directing the city manager to implement the recommended measures developed by the WCTF. These measures are powerful enough to save over 32 million gallons of water a day during the peak season.
Any water use reductions by large local entities, such as Seaholm, would not only be noticed by the public and municipal officials, but much appreciated. One such measure is rain harvesting.
“The city of Austin has promoted rainwater harvesting as an integral part of a multi-faceted water conservation program for many years,” says Greg Kiloh, project manager for the city’s Economic Growth and Redevelopment Services Office.
Other raincatching systems in Austin include those at the Zilker Botanical Garden, the Lady Bird Johnson Wildflower Center, the American Botanical Council, Feather and Fur Animal Hospital, The Natural Gardener, Parque Zaragoza Recreation Center, and HEB Grocery. At least three elementary schools—Robert E. Lee, Pickle (named after former US Congressman Jake Pickle), and Summit—and Westwood High School have raincatching systems to help their students learn about water conservation.
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Seaholm is one of the most significant developments in the history of Austin.
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Photos: Austin History Center
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For aesthetic reasons, above-ground tanks were not an option for Seaholm.
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Seaholm has a raincatching system because John Rosato, CEO of Seaholm Power LLC and Southwest Strategies Group, has an interest in sustainable development. Among those meeting with Seaholm’s principals as they planned the development was Dr. Kent Butler, associate dean of the University of Texas at Austin School of Architecture (UTSOA).
Butler recalls that several people in those early meetings mentioned the possibility of including such a system. He pursued the idea and says, “Upon digging more deeply into as-built drawings of the old power plant infrastructure, I discovered old cooling water pipes and tankage, left unused and underground, that could possibly be reused for a modern raincatchment and storage system.”
A rain catchment system would not only lower Seaholm development’s water costs, but also reduce the demand on Austin’s municipal water system. This approach is in line with Austin’s collective effort to conserve water.
Catching rain from the large rooftops at Seaholm would also limit stormwater runoff. This benefit is especially important, because Seaholm’s site overlooks Lady Bird Lake, a source of municipal water. Dealing with runoff is a given at Seaholm, considering the large roof areas, plus extensive swaths of impervious pavement. Collecting rainwater reduces the size and, therefore, the cost of any detention facility needed.
Austin has adopted strict criteria for stormwater control, requiring the first flush of approximately 0.8 inches of runoff to be detained and filtered before being released. Seaholm’s irrigation system will have underground pressure-drip lines that will discharge into the landscape root zone even during wet periods. This design is to provide ample reserve storage capacity to receive stormwater runoff from subsequent rain events.
Seaholm’s Austin location made it very convenient for students and faculty at the University of Texas to become involved with the project. The UTSOA has a Center for Sustainable Development that allows the students to have hands-on learning opportunities, such as this development.
Butler and the researchers—nine graduate students in UTSOA’s Community and Regional Planning Program, who were attending Butler’s research seminar—studied the feasibility of installing a rainwater harvesting system at Seaholm, and then evaluated the advantages and disadvantages of various systems. (Their report is available online at www.radiancetx.org/rainwater/rainwater_harvesting_UT.pdf.) The city of Austin has a commitment to green building and sustainability, but any system they recommended had to be cost-effective.
Median rainfall in Austin over the past 75 years is 24.17 inches. Rainfall data used in the model was calculated monthly for 1930–2005. The amount of average monthly rainfall ranges from March with the lowest, 1.81 inches, to May with the highest, 3.78 inches. In setting up the raincatchment feasibility study on Seaholm, the Center for Sustainable Development assumed that only 90% of the rainwater would be caught by any of the various systems that it proposed.
A rainwater coefficient of 0.9 gallons of water per square foot of roof area for every inch of rainfall was used for calculating the total rainwater that could be collected. Using that coefficient ensured that such factors as losses from roof surface evaporation and roof washing were taken into account.
The same rooftops were considered in all possible plans, but they were utilized differently in each plan. The roof on Seaholm’s existing main generator building is approximately 35,000 square feet. The proposed office building’s roof will measure approximately 30,500 square feet. The goal of collecting rain from the two rooftops and storing it was to provide non-potable water for use on the Seaholm site. This water would be needed for irrigation of the extensive landscaping and possibly to supply fountains.
Butler explains that the underlying goal for each of the four plans was “to meet as much of the total demand as possible with rainwater without acquiring large surplus or a deficit of water storage at the end of the year.”
Since most of the cost of a commercial rainwater collection system is for its storage facilities, adding too much storage capacity can be costly, both in the short term and in the long term. The short-term cost is, of course, for the construction. The long-term cost, for maintenance, could more than offset any savings realized from lower municipal water bills.
Tanks were sized so that minimal water was spilled, and the amount of rainwater to be collected, plus the amount to be used were noted for each month of the year. Although the amount of storage fluctuated heavily at the end of each month, due to higher irrigation needs and less rain collected in the hot, dry months, the system’s storage level at the end of the year was approximately even with minimal net gain or loss. Existing water storage, in front of the main power plant building, holds approximately 57,000 gallons. Whatever plan was chosen; more storage tanks would need to be installed. Depending on the amount of rainfall, the storage capacity required would vary from 30,000 to 100,000 gallons.
For aesthetic reasons, above-ground tanks were not an option at Seaholm. Existing tanks are, fortunately, underground. The majority of the cost of a commercial rainwater collection system is spent on storage facilities. More storage area provides makes more water available for use, thereby increasing the benefit of the system.
“However, from an economic perspective, storage should only be increased to a volume that can be reliably filled and consumed by the collection and utilization system,” explains Butler. “Otherwise, the potential created through the cost of additional storage cannot be obtained.”
Additional costs for the assorted options include piping to send water from various collection, storage, and usage points, plus pumping and filtration equipment. Pumping configuration “will depend on specific storage elevation and site data, and on irrigation equipment pressure requirements,” he adds.
The researchers considered maintenance costs and the costs of replacing equipment for each system. Simple maintenance could be done by Seaholm employees at no extra charge, but an additional $50 per month was included to account “for minor system repairs, for adjustments, and for testing,” says Butler. “In the economic analysis, the cost of the rainwater system measured the cost avoided [through collection of rainwater] of the volume of water, which would have been supplied by the water utility.”
At the time of analysis, Austin municipal water rates for commercial customers, such as Seaholm, were $3.62 per 1,000 gallons during the peak season (July 1–October 31). Off-peak season rates (November 1–June 30) were $3.38 per 1,000 gallons. In calculating costs, the researchers used $3.50 per 1,000 gallons as the cost of water saved. All replacement and maintenance costs were adjusted for inflation, assuming an increase of 2% annually. Water rates were “studied by increasing increments of inflation above the model’s 2% rate by 1% increments,” reads the researchers’ 100-page report.
The researchers’ economic analysis “looks at the relation of the estimated total future water cost savings to the estimated total installation and maintenance costs of the rainwater collection system on a yearly basis” for each possible plan.
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Photo: Austin History Center
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When visitors tour the site, they will be told about the raincatching system.
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Accounting for inflation of water prices from every conceivable reason indicated that all of the systems considered would pay for themselves within the 50-year analysis period. From the point of economics only, researchers concluded that almost any scale of rainwater harvesting system at Seaholm would be a viable project.
As plans were developed for the raincatching system, both outdoor and indoor water usage were considered. Outdoor water would be required to irrigate more than 65,000 square feet of landscape and fill decorative fountains that are approximately 12,800 square feet.
The planners assumed that different sections of the landscaping would need different amounts of water. They guessed that 70% of the landscaping would use a medium amount of water, 20% would be high demand, and 10% would require only a minimum amount of water.
Each of the three categories is for the amount of irrigation required in comparison to the amount of water that is evaporated. The water demand for the fountains was based on similar evaporation, or “pan evaporation rate.” An additional evapotranspiration factor of 1.2 was used to account for additional loss of water because of spraying fountains. The researchers thought that the greater surface area of the fountains and the wind would result in greater evaporation than the standard pan evaporation rate. They assumed that the fountains would be filled with 25,000 gallons of municipal water at the beginning.
The researchers considered indoor water needs, but only for non-potable (non-drinking) uses, such as flushing toilets in the main power plant building and the new office building. To calculate water requirements, the projected number of visitors and employees in each of the buildings per day was tallied. Considering typical water demands of office employees and retail visitors in the Austin area added to the accuracy of the research team’s projections.
Each possible scenario had advantages and disadvantages. The first scenario provided for irrigation using only the power plant’s roof. It required the least amount of equipment and maintenance. Only 30,000 to 35,000 gallons of additional storage tanks would be needed. Using the power plant roof alone could meet more than 50% of the irrigation needs, but not 100%. Existing storage was inadequate because the large roof area spilled a huge amount of water during the months of heaviest rainfall. Due to increased demand and decreased supply in summer, the stored water level fluctuated heavily. Additional municipal water would be required if this scenario were selected.
The second scenario was for irrigation with runoff from both roofs and 60,000 gallons of added storage. It would require additional equipment and maintenance than did the first scenario. A new gutter system and piping from the office building would be necessary. This scenario would provide enough water to irrigate all of the landscaping. However, the rainwater collected exceeded the water demand, and, consequently, the tanks spilled approximately 40,000 gallons between February and May.
The third scenario supplied enough water for irrigation and the fountains, with 100,000 gallons of added storage. It would require about the same amounts of additional equipment and maintenance, as would the second scenario. Additional maintenance would be needed to fill the fountains and filter and test the water in them, because they would be accessible by the public. This system could supply about 81% of the total outdoor water demands. The demands exceeded the water available from storage during July through November, thus requiring additional use of municipal water.
The fourth scenario yielded enough water for irrigation, fountains, and the toilets, with 100,000 gallons of added storage. It would require the most additional equipment and maintenance. Using rainwater for indoor service requires a lot more plumbing, plus additional parts and labor. This scenario was deemed the most inefficient. Trying to supply enough water for flushing the toilets, plus the outdoor landscaping and fountains, was beyond the capacity of the rooftops.
The second and third scenarios “were able to implement effectively the most amount of water in terms of what was collected,” the report says. Both had the additional catchment area of the new office building. They would use “almost the entirety of what was collected due to the lower demands and increased storage than” would the fourth scenario. The researchers calculated that the second scenario would have the shortest payback period, but that the third scenario would be the most cost-effective. In the report, they recommended that when cost of a raincatchment system is considered, it was best to design the system “to serve as few purposes as completely as possible.”
Butler describes Seaholm’s rain harvesting system as, “a banner example of Austin’s initiatives to promote rainwater catchment systems.” As part of a joint public-private interests development, the system provides “an opportunity for the city to participate and showcase the potential of such systems if they become widespread,” he adds.
Austin’s officials are “especially interested in conserving summertime, peak water demand that stems principally from outdoor irrigation,” acknowledges Butler. “This system will operate expressly to address that challenge.”
Because Seaholm is one of the most significant developments in the entire history of Austin, many thousands of local residents and tourists spend time on its grounds. As they walk through the site, they will hear about its raincatching system. When Seaholm’s visitors see the verdant landscape flourishing and the fountains splashing playfully, they are bound to appreciate the value of rain harvesting. Achieving this sense of water abundance, despite adhering to the strict water conservation measures Austin has enacted, is an achievement worth emulating.
Butler believes that he and other professionals in landscape design and water management have “a special challenge to educate our clients of the importance and the opportunity to engage in aggressively sustainable design.”
While acknowledging, “projects like the Seaholm rainwater system are not ‘solutions’ in and of themselves,” Butler mentions the “need to integrate ways of designing the buildings themselves, in concert with their surroundings landscapes, with full consideration of their ongoing operability, and with an eye to adaptability and change over time.”
Demands for water increase as does need to conserve it and use it wisely. Butler suggests, “We need to prove with ever better examples, that there are wonderful aesthetic as well as practical benefits in the ‘less is more’ approaches to facility and site design and construction.”