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Copy and Paste This Permanent Link:http://www.stormh2o.com/january-february-2009/rainwater-harvesting-reuse.aspx

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Arid and drought-like conditions affecting different regions across the US are forcing many cities and municipalities to change the way they deal with stormwater management and water reuse. As water scarcity becomes serious, more and more water professionals are recognizing the value of rainwater and stormwater and are beginning to adopt and implement progressive strategies for catchment and retention.

Tucson, AZ
In the arid Southwest, an eight-year drought has significantly drained Colorado River reservoirs, including Lake Mead, the largest reservoir in the nation. In January 2000, Lake Mead had 96% capacity. Two years ago that capacity fell to 51%, and the Senate Energy and Natural Resources Committee has warned that the lake could go dry in 10 years.

In addition to the Colorado River, drought in the Southwest has seriously depleted water resources of many towns and cities, especially in Arizona. Tucson was formerly the largest municipality in the country sustained by groundwater. However, after years of overpumping and less-than-average precipitation, the aquifer has been significantly reduced.

In response, the city has developed and adopted a Water Harvesting Guidance Manual, a tool to help guide residential and commercial developers plan strategies for implementing water harvesting for new developments, including city projects.

“The Water Harvesting Guidance Manual incorporates a long-term view on water sustainability,” says Ann Audrey, environmental projects coordinator for Tucson’s Office of Conservation and Sustainable Development and the manual’s editor. “It is based on the need to reduce our dependence on groundwater, which has been seriously depleted, and on Central Arizona Project water, which is very expensive.”

The primary goals of the manual and Tucson’s water-harvesting program are to reduce water demand, extend water reserves, and best use the opportunities of rainwater. Water harvesting and stormwater retention designs outlined in the manual include microbasins, on-contour and off-contour swales, French drains, gabions, water tanks and cisterns, and the use of mulch. In addition to harvesting water, the designs aim to improve stormwater discharge quality, while at the same time decreasing discharge quantity. The water-harvesting program complements the city’s Xeriscape requirements in the Land Use Code, another external water-use-reduction program that encourages the use of native, drought-tolerant landscaping. Cumulatively, these practices are designed to create a sustainable water model for Tucson and preserve the city’s groundwater supply for the future.

“The basic philosophy in the Southwest for years in terms of stormwater management has been to treat runoff as a waste instead of a resource,” says Frank Sousa, lead hydrologist with Tucson’s Office of Conservation and Sustainable Development. “We’re trying to change that paradigm. Stormwater should absolutely be viewed as something to use and benefit from.”

Photo: Ann Audrey

Large basin collecting runoff water from a parking lot in Sierra Vista, AZ

Photo: Ann Audrey

Microbasin capturing rooftop runoff in Tucson

On average, Tucson receives approximately 11 inches of rain per year. However, rainfall events can be complicated. “In the winter, rainfall in our region is gentle and semi-reliable,” says Sousa. “But our summers are characterized by intensive, localized, and conductive thunderstorms. It’s not unusual during these times to receive an inch and a half of rainfall in 30 minutes. As such, with very infrequent and non-uniform rain supply, it is very important to find ways to slow down runoff, increase retention, and facilitate more uniform groundwater recharge.”

Presently, about 40% of Tucson’s potable water usage is allocated toward landscaping. Taking into account the region’s water scarcity, Audrey says that this usage is a big draw on a limited resource. “The water harvesting program aims to reduce that external water usage. Stormwater that is collected or captured is utilized to supplement irrigation systems for commercial developments,” she says.

The Water Harvesting Guidance Manual outlines a process for evaluating site conditions and developing integrated designs that match the characteristics of the landscape. An efficient design is described as saving resources, while improving the function and sustainability of the site. Effective water harvesting systems reduce water consumption, energy requirements, and landscape maintenance, and are site-adaptive for various developments such as subdivisions, commercial sites, public buildings, and public rights of way. Tucson’s manual was created as a general guide; implementation of specific water harvesting techniques requires site-specific modification, sizing, and engineering.

“There is basically an unlimited amount of different water-harvesting methods with a huge range of associated costs,” says Sousa. “Each site is unique, so it’s very important to find and implement a customized system that is adaptive to the specific onsite conditions. It needs to work with the contours, drainage, and landscape. Cookie-cutter designs can be functional, but they won’t achieve maximum efficiency.”

The manual describes the use of microbasins, which can be effective on gently sloping or nearly flat land areas with low volumes of runoff water. They can also be designed in a series for areas with more concentrated runoff, with offset spillways to create longer flow paths that facilitate more soil infiltration. Microbasins can also be constructed on contour to intercept water running off a ridge, or as localized depressions or lowered soils levels inside curbed areas for rainwater retention.

On-contour swales are described as water-harvesting techniques in small- to moderate-sized watersheds with moderate volumes of shallow, slow-moving stormwater such as open space areas and parks. One example is a large-scale parallel on-contour swale, which is discussed as a retention/detention feature. In the design, a first swale intercepts water and retains it for use. The second swale, in turn, intercepts overflow stormwater from the first swale and can convey excess stormwater offsite, if necessary.

Off-contour swales are recommended for design in moderate-sized watersheds at a slight angle from the contour line and function to convey stormwater slowly downslope in a controlled manner to maximize infiltration, support vegetation, control erosion, reduce stormwater flow velocity, and eventually discharge any excess stormwater in safe locations. Off-contour swale types include pocket swales where a water bar, or gently sloping berm, is installed across a travel surface, extending beyond, and then hooking back to the travel surface, creating an adjacent depression for intercepted stormwater to collect. Other off-contour swale designs include boomerang swales and parking lot berms.

On flat to moderate slopes, French drains are detailed in the manual as effective techniques for intercepting low to moderate-sized flows and encouraging rapid stormwater infiltration through the sides, ends, and bottom of rock-filled trenches. French drains are appropriate for along pathways, for intercepting rooftop runoff, and in vertical gravel columns, which can direct stormwater into the ground around tree roots.

The manual describes the use of gabions in small watercourses, such as narrow and wide streambeds, which function as semi-permeable barriers or grade control structures to slow, but not stop, the flow of stormwater. Gabions also prevent or repair upstream erosion, trap rich detritus, and allow stormwater to infiltrate into the channel sediments and adjacent soils.

Water tanks can be used for collecting and storing rooftop runoff for use at a later time, while mulch is an effective technique for reducing evaporation from soils. Indeed, in comparison to Tucson’s 11 inches of annual rainfall, evaporation of standing water averages around 78 inches per year as solar energy quickly evaporates soil water brought to the surface by capillary rise. Mulch placed over bare soils in water-harvesting depressions can reduce temperatures and thus limit moisture loss from soil. In October 2008, the Tucson City Council passed an ordinance requiring new commercial developments to harvest rainwater for landscaping. The rule, which goes into effect in 2010, says that 50% of water used for landscaping must come from captured rainwater. Tucson is the first city in the US to pass such an ordinance.

New Mexico
In neighboring New Mexico, similar water-harvesting initiatives are being considered, planned, and implemented on various levels. One of the newly instated missions of the city of Santa Fe is to promote the use of stormwater as a clean, valuable, and sustainable natural resource. Traditionally, the city has encouraged active and passive rainwater-harvesting techniques through the city’s terrain management, storm drainage, and landscape ordinances. Developers who implement such strategies can get credits applied for open space requirements.

Credit: City of Santa Fe

At the Santa Fe Railyard Park and Plaza, rainwater from building roofs is stored in underground cisterns and a 35,000-gallon water tower and used for landscape irrigation.

Jim Salazar, division director for the Santa Fe Storm Water Management Division, says that although the city does not yet require water harvesting, there are bills in the works that are being developed to adopt these practices. The measures are being implemented as a response to drought conditions that have affected Santa Fe for a number of years.

“New residential green building codes are slated for adoption that will allow points to be gained towards building permit issuance by using rainwater-harvesting and -infiltration techniques. Additionally, new drainage and stormwater ordinances requiring passive and active rainwater-harvesting techniques for new land developments are being written,” he says. “Typically, stormwater measures have been for the purpose of drainage control, but now they are very important in terms of promoting water conservation.”

Salazar says that although it is not yet required in the city’s codes, the city is asking and encouraging developers to use every opportunity possible for implementing rainwater harvesting and stormwater retention in a beneficial way, mainly for diverting to landscape areas for irrigation purposes.

Photo: City of Santa Fe

Underground cisterns at the Railyard Park and Plaza

Photo: City of Santa Fe

A cistern at a new Santa Fe city library

Passive techniques being implemented by the city, where rainwater is diverted without the use of mechanical systems, include rain barrels placed below a roof drain, curb cuts, and depressed landscape medians. Active techniques include rainwater and stormwater collection systems with a pumping component for landscape irrigation.

Over the last couple of years, several new Santa Fe projects have incorporated rainwater-harvesting methods. Santa Fe’s new Civic Center, which has a roof surface area of 75,000 square feet, includes a catchment system and roof rainwater cisterns capable of storing 45,000 gallons. Another city project, the 12.5-acre Santa Fe Railyard Park and Plaza, includes water-harvesting systems that capture rainwater from nearby building roofs and store it in 75,000-gallon cisterns buried below the newly built park and in a 35,000-gallon water tower. The rainwater stored in the cisterns and the water tower will be used for landscape irrigation at the park. Additionally, the new city library features a rooftop harvesting system and a 26,000-gallon storage tank. “For every new city project, we are looking at ways to utilize impervious surface and find opportunities to harness stormwater in a beneficial way,” says Salazar.

Other water conservation incentives being offered by the city include a rain barrel credit program. Residents who buy rain barrels receive a one-time $30 credit toward their water bill. “The city is also promoting low-water-use appliances and plumbing appurtenances as well as looking into ways that rooftop runoff can be diverted for flushing toilets,” says Salazar.

Salazar says the city’s Storm Water Management Division is also promoting a stormwater infiltration program, which includes the use of infiltration technologies such as bioretention and low-impact development (LID) techniques. “We are in the process of changing the way we approach land development,” says Salazar. “We are heading in a direction that encourages more use of LID technologies for site design.” This initiative also includes a pilot program for the use of porous pavement systems. “We are being very proactive and using every opportunity we can to promote the infiltration of stormwater back into the ground,” says Salazar. “Our overall philosophy toward stormwater management is definitely heading in this direction.”

Some of the different infiltration systems the city is using include bioswales, such as roadside collection ditches that are used for smaller-scale developments, bioretention ponds, permeable pavements, rain gardens, and other techniques that facilitate stormwater infiltration and aquifer recharge.

Santa Fe County has implemented similar water harvesting measures because of ongoing and sustained drought. The Santa Fe County Water Conservation Program includes stormwater and water-harvesting requirements to ensure that residential and commercial development is sustainable and built in a way to conserve water resources. “The Water Conservation Program was created as a way to conserve water that is drawn from our domestic wells,” says Wayne Dalton, permits and enforcements manager for Santa Fe County.

According to the guidelines, all residential development is required to collect roof drainage from a minimum of 85% of roof area for reuse in landscape irrigation. Residences that have 2,500 square feet of heated area or less must use rain barrels, cisterns, or other catchment basins. Residences over 2,500 square feet must install active rainwater catchment systems comprising of cisterns. For commercial development, all roof drainage is required to collect in cisterns for reuse in landscape irrigation.

Santa Fe County land-use regulations also require retention ponds to be used for capturing stormwater from rooftops and hard surfaces to facilitate onsite ponding and allow proper drainage. “Generally, a good practice is to have landscaping located in proximity to the retention ponds,” says Dalton. “However, the best use of collected rainwater that I have seen for watering landscapes is through drip irrigation. These systems operate with timers and apply water directly to the soil where it is needed. They are highly efficient.”

In addition to the water harvesting requirements, the county has implemented an ordinance requiring that all new residential and commercial development install hot-water-recirculation systems, which work to instantly activate hot water. “Cumulatively, it is estimated that up to 17,000 gallons per year can be saved with these systems,” says Dalton.

Atlanta, GA
In Georgia, a severe and prolonged drought has affected the northern third of the state, causing severe water shortages. Buford Dam, the primary water supply for metro Atlanta, has fallen to 38% capacity, and Georgia Governor Sonny Perdue released an executive order declaring a state of emergency in 85 counties across the state because of exceptional drought and the subsequent threats to the water supply in those areas. The executive order stated that numerous lakes and reservoirs have experienced record-breaking low water levels, putting the availability of drinking water for over 4 million citizens at great risk. Georgia residents, businesses, and industries are required to be extremely vigilant in exercising aggressive water conservation methods.

“In 2007, the region’s precipitation levels came very close to 1954 levels—the driest year on record,” says Sally Mills, deputy commissioner with Atlanta’s Bureau of Watershed Protection. “In the upper state of Georgia, a level 4 drought stage as been declared. It is very serious and very severe.”

In addition to his executive order, Governor Perdue directed the Georgia Environmental Protection Division to require a 10% reduction in drinking water systems for 61 drought-stricken counties. “These are the highest levels of water restrictions, which include a broad prohibition of water usage,” says Mills. “The state is working with industries, providing audits, initiating public education, conducting inspections, and issuing fines for uses that violates the restrictions.”

At the local level, a residential initiative has been implemented involving a policy on water reuse. Citizens are being encouraged to use less water and also to install cisterns or catch basins—anything that can be bought from a retail store like Home Depot and used to retain or capture water. Such measures extend as far as taking buckets into the shower and using excess water as landscape irrigation. Atlanta is also considering more use of Xeriscape and landscaping that incorporates more native plants and drought-tolerant species.

However, Mills says that although water retention strategies are possible in small individual kinds of ways, the city is not initiating any large-scale municipal stormwater collection or redistribution policies, because, practically speaking, the region is in such a drought that stormwater retention is not feasible. “There is literally no accumulation or ponding,” says Mills. “From a surface water management perspective, we have no stormwater delivery options.”

Additionally, the district’s overall watershed plan does not necessarily include reuse. “The city of Atlanta does not have large expanses of landscaped areas that could benefit from supplemental irrigation, which would be one of the most practical uses of retained stormwater,” says Mills. “The existing policies are centered on returning flows to the region’s rivers and tributaries, which is consistent with the district’s strategy for managing the basin. In this way, the flows can be better quantified in a hydrologic model.”

Another drawback is that a major reuse system would require a large capital investment and the building of parallel infrastructure. “The construction of this secondary system could have adverse impacts on neighboring streams and tributaries,” says Mills.

Looking ahead, Mills sees every indicator pointing toward continued dryness and unusually warm conditions. The governor has also created a Drought Response Unified Command and a Drought Response Working Group, which are coordinating more objectives and strategies for better responding to the drought emergency.

Forgotten Rain
One Phoenix, AZ–based company is advocating rainwater harvesting by acting as a consultant to large-scale property owners and developers, advising on various techniques and strategies for obtaining certification from the US Green Building Council’s Leadership in Energy and Environmental Design (LEED) rating system. Forgotten Rain LLC is a company dedicated to rainwater harvesting, stormwater reuse, and rain garden design for private and city projects.

“By incorporating sustainable designs and meeting LEED guideline requirements, property owners and developers can obtain benefits such as tax breaks and other financial incentives,” says Heather Kinkade-Levario, president of Forgotten Rain. “In addition to those incentives, property owners who implement rainwater harvesting and other techniques can have self-sufficient systems and full control over water quality and supply.”

Kinkade-Levario says her efforts in consulting are a different and more effective approach than the direction she was previously taking with her company. “I used to spend a considerable amount of my time promoting stormwater retention and rainwater harvesting to cities, helping them become more aware and understand how to implement various techniques,” she says. “However, I found governments were too slow to react. I wasn’t seeing the type of results I had envisioned. Now that I have taken a corporate direction and a top-down approach working directly with property owners, I’m seeing much more progress. As an advocate, this is a much better way to push my goals.”

Kinkade-Levario has served as president of the American Rainwater Catchment System Association (ARCSA), where she led an effort to instate an accreditation for rainwater professionals. Currently, ARCSA is advocating for legislation that would standardize different types of systems, in addition to developing rainwater harvesting and stormwater reuse goals for cities to adopt. “Most county and city development guidelines include codes for plumbing, roofing, and gutter systems, but not necessarily for rainwater harvesting,” she says. “Engineers and architects also need to become more updated on implanting these techniques into development plans and designs.”

As the severity of drought and water supply escalates, Kinkade-Levario is finding that more cities and municipalities are recognizing the importance of rainwater harvesting for reuse. “Tucson, for instance, has really embraced a number of strategies because of their water scarcity situation,” she says. “However, in Phoenix, the level of commitment is much less. Phoenix currently has more water supply options, such as a canal that conveys Colorado River water and dams that collect rainwater. They are not nearly as progressive as Tucson because they perceive their situation as less dire. They are starting to consider rainwater harvesting, but nothing is being required at this point.”

With urban sprawl and horizontal development characterizing growth in Phoenix, a considerable amount of opportunities exist for implementing rainwater-harvesting systems. Large-scale slabs of impervious surfaces, such as car dealerships that can take up as much as 800,000 square feet, are ideal areas for installation of catchment systems. “There is no reason why, especially in drought-prone regions, these spaces shouldn’t be utilized to catch and retain rainwater and stormwater,” says Kinkade-Levario. Because rain events in the Southwest can be sudden and intensive, harvesting systems should be planned with capacity in mind. “A sudden burst of 1-inch of rainwater over 100,000 square feet is a considerable amount of water volume,” says Kinkade-Levario. “These rain events only come twice a year in our area, so it is critical that rainwater and stormwater retention systems are able to convey flood-like waters by including large storage areas.”

Kinkade-Levario says there are many more strategies and accessible techniques for harvesting water. “Cooling towers are a great example of an alternative water source,” she notes. “These units contain lots of available water for reuse that is otherwise just going into the sewer. Two buildings in Phoenix and one in Kingman, AZ, are currently utilizing cooling blowdown water to irrigate their total site. Anything that is not blackwater should be reused.”