Harvesting stormwater runoff is becoming an option in dry climates. Our survey looks at what’s going on.

In search of new sources of water (and with the belated realization that not all applications require drinking-water quality) a variety of municipalities and water districts are experimenting with collecting and reusing stormwater.

The impetus for these harvesting projects varies, from developing alternative sources of water and safeguarding existing supplies to intercepting pollutants before they reach critical receiving waters. The aim is to mimic natural cycles that have been short-circuited by development, particularly the hardscaping of naturally permeable surfaces.

Without any claims for being inclusive but with an eye to demonstrating the range of options being considered, our first article in this two-part mini series focuses primarily on collecting, treating, and utilizing stormwater runoff. The second looks more specifically at rainwater collection, urban runoff’s more glamorous cousin.

In many cases—the Lady Bird Johnson Wildflower Center in Austin, TX; a school playground in Santa Fe, NM; an urban lake in Florida—simplicity is the name of the game. On the other hand, in Santa Monica, CA, where 90,000 residents are surrounded on three sides by urbanization and the city itself is built out, an engineered fix was called for. In some cases the level and type of treatment is a matter of how the water will be used; in others, it’s water-quality regulations. In some projects, stormwater is combined with reclaimed wastewater or even potable water. Many projects consider education and public outreach a critical component—a bike path on the rim of a Tucson flood control basin, cisterns constructed from construction rubble at the Wildflower Center.

As researchers Richard Field and Anthony Tafuri have noted at the EPA’s National Risk Management Research Laboratory, Water Supply and Water Resources Division, in Edison, NJ, total gross water use in the United States currently exceeds the total available freshwater supply, particularly in Florida and the Southwest. To aid the Arizona-based Upper San Pedro Partnership in evaluating stormwater capture opportunities, Bureau of Reclamation Natural Resources Specialist Eve B. Harper undertook a survey of projects that met developed world public standards for health and safety. Harper concludes that while the technology is readily available, the challenge is “competing with cheap water out of the ground.” Heather Kinkade-Levario, Arizona director of planning for ARCADIS and author of Forgotten Rain: Rediscovering Rainwater Harvesting (Granite Press, 2004), notes that it can also be difficult getting skeptical city engineers and citizen committees to think outside the box.

Thinking outside the box has always been a way of life in California, where the Santa Ana River, which flows 100 miles from its source in the San Bernardino Mountains through mostly developed watershed to the coast at Newport Beach, is a critical source of drinking water. In fact the Orange County Water District (OCWD) has been harvesting stormwater from the river to recharge Orange County aquifers since 1949.

Photo: OCWD

Inflatable rubber dams help divert water from the Santa Ana River into 1,000 acres of spreading ponds.

The water receives no engineered treatment but passes through a 450-acre wetlands 30 miles upstream of the coast, primarily to remove nitrates. From there it goes back into the natural riverbed, which in this reach is not armored, allowing for natural percolation. Further downstream water is diverted out of the river using two inflatable rubber dams  “the most high-tech part of the operation,” says Greg Woodside, of OCWD Planning and Watershed Management—and into 1,000 acres of spreading ponds. On average, the district captures and percolates approximately 50,000 acre-feet per year of stormwater flow, providing 10% of annual water demand.

“The difference in depth between the basin’s water surface and underground groundwater basins is anywhere from 5 feet to over 100 feet,” says Woodside. “In some areas water will take 20 years to get to a well. In other areas, it will only be a year or more.” In non-storm periods, the flow into the recharge ponds can be supplemented with potable water purchased from the Metropolitan Water District. Woodside estimates the basin has 1 million acre-feet of usable storage capacity; annual pumping is about 300,000 to 350,000 acre-feet.

Given that much of the river’s base flow comes from wastewater treatment plants in the upper watershed and the river is impacted by both urban and agricultural runoff, monitoring for minerals, nutrients, and selected other constituents occurs monthly. Radioactivity constituents, metals, volatile organics, and semi-volatile organics (e.g., pesticides and herbicides) are monitored quarterly. In addition to surface-water monitoring sites, the district monitors groundwater-quality samples at selected wells where known travel times are less than six months. Recharge samples are collected in coordination with these targeted groundwater samples, which facilitates evaluation of changes in water-quality perimeters such as nitrates during infiltration.

“We have an extraordinary amount of data on the natural infiltration process,” says Woodside. “Indicator species such as E. coli, Enterococcus, fecal coliform, and total coliform are removed very effectively during recharge. We have monitored the river for the more potent pharmaceuticals like estrogens, which have been at very, very low levels or non-detect. Occasionally we’ll detect very, very low levels of pesticides, again before recharge.” In its effort to preserve the Santa Ana as a primary drinking-water source, the district is currently evaluating fish biomonitoring as a supplement to its program of chemical testing.

Like southern California, South Australia has been caught in the crunch between limited water supplies and an expanding population—which means it’s not surprising that one of the country’s largest stormwater harvesting projects is located in its most populous and capital city, Adelaide, population 1.1 million. Before this innovative public/private partnership got under way, G.H. Michell & Sons, Australia’s largest wool processing facility, used 1,100 million liters of potable water a year to wash its wool. The combined cost of municipal water and sewerage disposal was high enough that management was considering moving its 700 jobs elsewhere. Instead company principals sat down with city officials and, supported by a grant from the Commonwealth Urban Stormwater Initiative and Clean Seas Program, developed a stormwater harvesting facility next door at the Parafield general aviation airport.

A 28-acre, 4,000-acre catchment site drains almost 4,000 acres and is designed to capture one year’s worth of stormwater—800,000 gallons—from an average rainfall of 19 inches a year. The stormwater is diverted via a weir in the main airport drain, and then to a 50-megaliter-capacity, in-stream capture basin. From there the water is pumped to a similar-capacity holding basin from which it gravity-flows to a 2-hectare constructed wetlands. Over the course of seven to 10 days, the wetlands reduce nutrient and pollutant loads by up to 90%. The resulting water meets Australian drinking-water standards and has less than 220 milligrams per liter salinity. The final product is either supplied directly to end users or injected directly into an underground aquifer for storage. The project is expected to eventually harvest 2.43 acre-feet per year. Cost to customers will be half that of potable water.

The Parafield Stormwater Harvesting Facility has also lessened pressure on the River Murray, a major potable water source that had been suffering from lows flows and salinity and helped reduce pollution at Baker’s Inlet, the largest fish breeding nursery in South Australia. The facility is actually part of a larger system of 30 wetlands developed in the mid-’90s. The city maintains its own nursery to supply wetland plants.

In order to apply some structure to considerations of how harvested stormwater might be applied in industry, Field and Tarfuri have adapted New York State’s standards for receiving-water pollution loads to classify grades of stormwater and, from there, suggest treatment trains. They suggest that what they call Class AA stormwater could be used for high-quality applications such as steam-generated boiler feed, Class A for routine industrial process supply that has lower dissolved mineral removal requirements, Class B for industrial cooling as well as recreational water for fishing (although additional nutrient removal may be warranted), and Class C for lawn irrigation, fire protection, and aesthetic ponds.

Field and Tarfuri applied their scheme to a hypothetical case study, evaluating the relative cost of three water use alternatives. Alternative A, which involved using potable water for irrigation, drinking water, cooling makeup, and processes water supply, would amount to an annual cost of just over $13 million. Alternative B, which would use one-third city water and two-thirds treated stormwater, would be just under $4 million. Alternative C, half potable/half stormwater, fell between the others at $6 million or half the cost of the all-potable alternative. The researchers conclude that stormwater is not only technically feasible but also economically attractive for industrial use. 

Dry-weather urban runoff is a challenge throughout arid and semi-arid states. Southern California receives on average 12 to 14 inches of rain a year, but overirrigation generates off-season flows that pick up contaminants as they go. Mandated by regional local water-quality standards for Santa Monica Bay but determined to implement a systemized approach, the environmentally conscious City of Santa Monica established a comprehensive watershed-wide plan to maximize permeability throughout the city and increase runoff infiltration. “Instead of disrupting the water cycle,” says Neal Sharipo, the city’s urban runoff coordinator, “Santa Monica’s approach is to work with nature.”

Santa Monica’s three-pronged watershed approach includes an ordinance that requires harvesting all runoff from new development, treatment of all dry-weather and some wet-weather urban flow leaving the city (90% travels through two major storm drains), and the Santa Monica Urban Runoff Recycling Facility (SMURRF), which is designed to divert 300,000 gallons a day of dry-weather runoff from the ocean—almost 1 acre-foot a day. The recovered water is used for irrigation in the city’s cemetery and two parks, along the center medium of a busy city boulevard and a section of freeway, and for flushing toilets in dual-plumbed buildings.

The engineered process with which engineers mimicked the action of natural infiltration begins with coarse screening in a continuous deflective separation (CDS) unit that removes large floating debris and trash. The water is then pumped to the SMURRF, where a rotating drum screen removes fine floating particles greater than 0.04 inch, and then to the cyclone-type grit chamber, which removes any grit and sand. The water is then stored in a raw water storage tank to dampen the fluctuations in the influent flows, thereby allowing downstream filtration and disinfection processes to operate at a steady rate. From there the water is pumped to the dissolved air flotation unit where oil and grease are removed, then to microfiltration treatment units, and eventually to ultraviolet disinfection. Monitoring requirements established by local regulators include weekly sampling for coliform and turbidity, monthly sampling for oil and grease, biannual influent sampling for metals and organics, and quarterly sampling for effluent.

The project was designed as a walk-through facility that would help familiarize the public with the city’s water-quality goals. Treatment flow is daylighted in five places, allowing visitors to view the process on their way to the beach. Funds for the $12 million project came from the Cities of Santa Monica and Los Angeles (part of the flow originates in Los Angeles), the State Water Resources Control Board, Metropolitan Water District of Southern California, Los Angeles County proposition funds, and the federal ISTEA grant funds.

Photo: Overland

The Wildflower Center's cisterns and storage tanks have a capacity of 60,000 gallons.

At Overland Partners Architects in San Antonio, TX, less is often more, a mantra it has applied to water harvesting at the Lady Bird Johnson Wildflower Center. “In its original location,” says Overland Partners Principal Bob Shemwell, “the center was doing some water harvesting on a kind of demonstration scale. We took it to a much larger system that became a huge part of the visitor’s education experience. We wanted a straightforward, hey-you-too-can-do-this approach.”

The Wildflower Center’s system collects water off roofs and terraces, runs it through a roof washer (a two-chamber non-mechanical filtering system that removes pollen, leaves, and other large organic matter and results in water that is “very, very” pH neutral), and then into a series of surface cisterns that drain to a central underground cistern located at the lower part of the site. From there the water is pumped back up to a tank farm where it’s stored until it’s needed for irrigation. A filter removes any particles that could foul the irrigation pump; pumping occurs in off-peak hours to reduce electrical costs, and a solar-powered pump is on the agenda.

According to the center’s statistics, the central irrigation rooftop system collects rain from 17,000 square feet of roof, which translates to about 10,200 gallons of water per inch of rain and means that, given an average rainfall of 30 inches per year, the system should collect approximately 300,000 gallons of rainwater annually. A separate Entry Cistern is fed from 1,167 square feet of roof and collects 700 gallons per inch of rain or 21,000 gallons per year. The Little House Cistern collects water from 672 square feet of roof or 12,096 gallons per year. The current storage capacity of the cisterns and storage tanks is 60,000 gallons, and there are plans to add additional storage in the future. The linked system of cisterns and other water features, which were constructed of construction rubble from the site, are an important component of the center’s educational mission. “Cisterns,” says Shemwell, are “incredibly romantic. They draw people in. This is an ancient technology, and the Wildflower Center was one of the first modern applications.”

Romance of another sort was on the mind of planners who developed a western theme for a rest area on Highway 287 in Hedley, TX, a main artery that crosses the Texas Panhandle. Tom Shaw, construction administrator for PSA-Dewberry in Dallas, says the idea was to tap into the local vernacular to help the Texas Department of Transportation persuade travelers to slow down and get out of their cars for a while.

The facility was built on both sides of the highway and was designed to be green. It features restrooms with waterless urinals along with other water-saving devices and a stormwater harvesting system. To collect sheetflow, 8- to 10-inch-thick terra cotta gravel arroyos were constructed adjacent to the rest area buildings using Gravelpave2 from Invisible Structures. The idea was to expand the capture area for the belowground Rainstore3 units, also from Invisible Structures, which are located directly beneath the arroyos. Water off the building’s roofs is routed through a downspout in catch basins, each equipped with filter screens, and then directly into the ground. The underground Rainstore3 stackable cells are wrapped in filter fabric. Shaw says the system collects enough stormwater to meet all of the water demand for the rest area. The system can store 10,000 gallons.

Florida is projected to add another 4 million people by 2030, increasing the strain on already strapped water supplies, especially in south Florida where combined water and agricultural demand in coastal regions is expected to increase by approximately 25% over 1995 usage. In this kind of milieu the goal is twofold: Protect current supplies while investigating new sources. The City of Winter Park aimed to do its part on both issues and ended up saving $4,000 on its annual irrigation bill in the bargain.

“It’s flat in Florida,” says the city’s David Zusi, explaining the origin of the project. “So lakes tend to be where all the stormwater ends up. A lot of these lakes are landlocked, so without some sort of flood control they would typically overflow. Drain wells solve the problem. When the wells were first built, nobody cared about the water quality, even though in some cases there was potential for the well water to reach an aquifer that was a source of potable water. That situation has changed.”

Photo: Overland

A cross-section of a cistern at the Lady Bird Johnson Wildflower Center.

To capture, treat, and reuse stormwater that collected in a small lake located in the city’s civic center—and thus reduce the amount of untreated stormwater that flows into the lake from residential and commercial development—Winter Park undertook a demonstration project with the University of Central Florida. A berm and weir system was constructed to isolate approximately 0.7 acre of the lake as a surface reservoir for irrigation water. Accumulated sediments and invasive exotic vegetation were removed as part of the project, and the littoral zone was revegetated with native aquatic species. After less than a year, a mass balance study indicated an average irrigation rate of approximately 1.07 inches per week, which accounts for 55% of the incoming runoff and an annual reduction in the lake’s pollution load of 80%. The $143,000 project was paid for by funds from the state Pollution Recovery Trust Fund and the City of Winter Park. The University of Central Florida provided $64,000 in money and in-kind services.

At the University of Florida IFAS Extension, Sanjay Shukla thinks there are answers to Florida’s coming water crisis in the state’s citrus fields, specifically in agricultural stormwater impoundments. If they’re managed correctly, says Shukla, these runoff ponds could provide a local alternative to using potable supplies to water fruit trees.

Almost 70% of south Florida’s rainfall occurs from May to September, which means storage is necessary. Shukla established, however, that without any kind of intervention, volume in the impoundment he selected to study fell below the minimum volume for reuse within the first week of the dry season. (The mean ground elevation in the grove was 30.74; in the impoundment, it was 28.8. The outflow weir was 29.53 feet. Water was pumped into the impoundment with a “throw-out” or drainage pump).

If, on the other hand, the entire 18-million-gallon impoundment was lined with a 6-inch-thick compacted bentonite clay liner, it provided enough water to irrigate almost 550 acres of citrus for a total of 13 weeks. Lining the embankment and distribution ditch with a 12-inch clay liner showed a higher volume and retention time than a 6-inch liner and allowed the impoundment to provide enough water for four weeks of irrigation. Since lateral seepage losses were identified as a problem, a third strategy was implemented—pumping water that seeped out into the borrow ditches (which collect grove drainage) back into the impoundment, a strategy that maintained the reservoir at full capacity.

“Using this type of recycled water to irrigate crops would reduce the farmer’s reliance on groundwater,” says Shukla. “It could help increase the profitability of farms and keep the land in agriculture, facilitating groundwater recharge, reduced runoff, and increased hydration of wetlands and wildlife habitat.”

After 50 years of abnormally high rainfall, Santa Fe, NM, is in the middle of a prolonged water shortage, to the point that some observers are calling it climate change. So when the Salazar Elementary School was rebuilt in 2002 and nonprofit Partners in Education proposed a plan to build a playground and the Norma Green Family Foundation contributed $100,000 toward the effort, the plan was for a water-harvesting system to landscape the school grounds and a public garden.

Richard Jennings of Santa Fe–based Earthrights Design designed the system using a modified Vortechs 2000 hydrodynamic separator from Contech Stormwater Solutions to accommodate the combined flow of the roof and playground, and then distribute it through drip irrigation. “Typically,” says Jennings, “stormwater enters a hydrodynamic separator, flows through the system, and leaves through an outlet. In this case, we worked with Contech to redesign their system and add a pump that will move the stormwater uphill 600 feet laterally and 20 feet vertically.

“Generally when you’re harvesting water, you’ve got the floaters and the sinkers. I expected a little bit more sediment than normal because the water was coming off the playground and an unfinished landscape upslope, and I wanted to clean the water as much as possible before I pumped it back up the hill to the irrigation system. In this kind of separator any floaters will be caught in the front stream while the first chamber settles sediment. Since I’m not concerned with oil and grease, I took out one of the baffles, which allowed me to turn the back chamber into a pump chamber.”

Photo: Pima Valley Flood Control

This flood facility, located just 4 miles southeast of downtown Tucson, was restored in 2003.

For storage Jennings designed a system that uses a custom, fish-safe bladder from Colorado Lining inside a concrete culvert. “This is the least expensive way to store lots of water underground and get it out again, and it’s easy to fix and clean.” Once completed the system will store 80,000 gallons. 
“It was just a wild idea,” says Paul Bennett about Pima County, AZ’s project to restore a 1966 Army Corps of Engineers flood control facility 4 miles southeast of downtown Tucson. Bennett is deputy director of planning and engineering for the Pima County Wastewater Management Department, which helps explain how stormwater got combined with effluent to establish newly configured native vegetation onsite and irrigate nearby Kino Sports Complex, the spring training grounds for the 2005 World Champion Chicago White Sox and Arizona Diamondbacks pro baseball team.

The Ed Kino Environmental Restoration Project was undertaken under Section 1135 of the 1986 Water Resources Development Act, which authorizes the corps to identify opportunities to improve the environment through modification of flood control facilities. The site, which is owned by the Pima County Flood Control District, was originally designed to capture floodwaters from a 17.6-square-mile drainage basin, the object being to reduce a 100-year, 24-hour storm event from 11,397 cubic feet per second to 5,134 cubic feet per second (cfs). The redesigned project has the same inflow, but outflow has been reduced to 5,021 cfs). In event there isn’t sufficient stormwater to maintain the plants in the basin plus provide irrigation for the sports complex, the harvested stormwater is supplemented with reclaimed water through an already existing reclaimed line located close to the site.

Photo: Pima Valley Flood Control

The Pima County, AZ, project harvested 200 to 300 feet of water in 2005.

The 141-acre project includes 5.6 acres of holding ponds and 28 acres of riparian habitat. Three streams flow from the northern side of the basin toward the 50-foot-deep, 30-million-gallon impoundment called Deep Pond in the southeast corner, where water is stored for delivery to various points in the project. In addition to Deep Pond, Small Pond, and Irrigation Pond (designed primarily for offsite irrigation), the project has a series of in-line ponds primarily designed to accept sheet flow runoff from the area east of the project and to provide an opportunity for sediment to settle. The in-line ponds have the potential to harvest 162 acre-feet of storm runoff per storm event. When the ponds reach capacity, excess runoff drains into a flood control channel.

A debris removal system removes sediment and larger objects and debris as the stormwater enters the basin, but otherwise the captured stormwater is not treated. To minimize stagnation in Deep Pond, an aeration system has been designed to improve the dissolved oxygen levels at the bottom of the pond. “If we have good rains in July and August, we can fill up and use the water until about January,” says Bennett. “Then we have to augment with reclaimed water. Usually we get a little rain in January and February, which helps top it off. When we get toward the end of the cycle in April-May-June, we might also have to use reclaimed.”

Bennett estimates the $7 million project harvested 200 to 300 feet of water in 2005. Original estimates were that it would take 574 acre-feet of water to irrigate the revegetated habitat and the Kino Sports Complex combined. Since 2003, however, the average irrigation requirement has been approximately 350 acre-feet, 150 acre-feet of harvested stormwater, and 200 acre-feet of reclaimed water.

As technologically feasible and economically viable as stormwater harvesting appears to be, at Overland Partners Bob Shemwell cautions that harvesting involves a “balancing act. You want to negate the problems that urbanization creates. But you also want to be putting water back into the environment. You don’t want to erode or pollute, but you also have to make sure you’re putting adequate water back into the watershed. If you’re not careful, you can get too greedy.”

Journalist Penelope Grenoble O’Malley is a frequent contributor to environmental publications.

WE March/April 2007