How San Diego’s Stormwater Management Strategy Protects Coastal Waters | Stormwater Solutions
How San Diego’s Stormwater Management Strategy Protects Coastal Waters | Stormwater Solutions
An Airport on the Bay
San Diego International Airport is located close to San Diego Bay. It is the busiest single-runway airport in the US, but it occupies only 661 acres.
“We’re very site-constrained,” says Brendan Reed, environmental affairs director for the airport.
Fifteen stormwater outfalls at the edge of the airport’s land send runoff into San Diego Bay. The airport is the last stop at the end of a large municipal drainage system.
The relatively small space, proximity to the bay, and high demand for flights add to the challenges Reed and Richard Gilb, manager of environmental affairs for the airport, face. They also must consider the same climate, soil, and storm patterns faced by the City’s stormwater officials.
To better meet those challenges, “About two years ago we spent a year looking at our water use and constraints,” says Reed. “We developed our Water Stewardship Plan focusing on three items: water quality, water usage, and flood resilience.”
He adds that the plan is the result of input from consultants Haley & Aldrich and from every department at the airport. “It explains where we want to end up in 20 years, with synergy between those three items.”
Using green infrastructure or LID to manage stormwater at the airport isn’t easy. Given the climate and rainfall amount, it is difficult to make it cost effective.
“Given our small size, we don’t have a lot of landscaping. There’s no grass along the runways, for example. Our site on soil with lots of clay has handicapped our ability to put in LID,” says Gilb. One example that has worked is “two and three-quarters acres of bioswales within a total area of 25 acres at the rental car site. With our desert semi-arid climate, we have more xeriscaping and rock,” he says.
A side effect of the xeriscaping is that “as much as we’d like to capture rain, we don’t need a lot of irrigation,” he explains.
The San Diego airport qualifies for a Phase 1 NPDES stormwater permit. “Not too many airports are managed by these permits,” notes Gilb. “We get to run with the big dogs.”
Describing California’s stringent multi-sector general stormwater permit, Gilb explains that BMPs under the new permit are more specific and are tied to performance. “In the past, permit holders just had to put in LID somewhere that met some basic performance. But recently—beginning in February, 2016—there is a hierarchy for post-construction BMPs. Harvesting and reusing [stormwater] is at the top tier. If you can’t do that, you’re supposed to infiltrate it.”
The bottom tier of the hierarchy is to substitute offsite measures for onsite harvesting or infiltration. This route is costly, because it requires purchasing the right to claim performance of a BMP located elsewhere.
Despite the site and climate constraints, Gilb says the airport has a very good chance of meeting that top tier. It will harvest the stormwater, but instead of using it for landscaping irrigation, the airport will use it in the central plant’s cooling towers. Water will be harvested at a new three-story parking garage with 2,900 stalls. When the facility is finished in June 2018, it will capture and treat approximately 2 million gallons of stormwater in a year. Storage capacity is 107,000 gallons.
The runoff flows into reinforced concrete pipes 36 inches in diameter. Demand for water for the cooling towers is constant. By using this reclaimed and treated water instead of potable water, the airport will reduce its water bill considerably.
Another stormwater feature at the airport is the San Park II. This 16-acre parking facility sits along the Pacific Coast Highway. Beneath its 2,003 parking spaces are 12 Modular Wetlands units from Bio Clean of San Diego. The MWS Linear model installed saves space and treats pollutants to a higher level than does bioretention. It functions as a horizontal-flow biofilter. Because the units are placed at traffic grade level, they have no effect on the parking lot space or design.
The subsurface system operates in three stages. Pretreatment collects trash and sediment, making their removal easy for cleaning crews. Compared to using traditional LID measures, the airport saved more than a half-acre of land, which made more parking spaces possible.
Sea level rise is a topic mentioned more and more often in stormwater management. As in other coastal communities, San Diego stormwater officials have been studying it and its potential effects.
Reed says that sea level rise would cause
“further intrusion up our stormwater drains, creating a tail water
condition. Hence, any way to capture and reuse, or to infiltrate
—to get water out of the outfall drains—is worth considering.”
About five years ago, a conference on a regional adaptation strategy for San Diego was held. The airport “worked with the Port of San Diego, the City, the US Navy, and other stakeholders to study the impact sea level rise would have on the built environment and the natural environment here,” says Reed.
He adds, “We’ve done some modeling on sea level rise. We were using two feet rise, working with consultants. Some of that work is in our water stewardship plan.”
Gilb says that managing stormwater at the airport currently costs about $2 million per year. He and Reed anticipate that cost increasing as the airport staff works through the water stewardship plan and future redevelopment.
“We have a pretty significant redevelopment project, covering almost half the site [planned for the future]. “Because of that pretty large planned construction, we’re more connected to the idea of a stormwater capture system that will allow us flexibility in how we capture and reuse the water,” says Reed.
Student Housing on Campus
The Charles David Keeling Apartments provide student housing on West Campus of the University of California at San Diego (UCSD). The complex is named in honor of the late Scripps Institute of Oceanography professor who first suggested human behavior’s contribution to the rising level of carbon dioxide.
“It is the first LEED Platinum project at UCSD,” says project manager Greg Kump of Nasland Engineering in San Diego. The cost of the project was about $50 million. Work took place from 2008 through 2011.
The site covers about 2 acres. Several green infrastructure components for managing stormwater contributed points toward the project’s total score for its LEED certification.
Virtually all of the site’s stormwater is handled onsite, but not all of it is treated. Keeping the runoff onsite prevents it from flowing to nearby Skeleton Canyon, a biologically sensitive area.
A bioinfiltration basin was added to the interior courtyards for stormwater treatment. A roof drain went underneath this area, but it is exposed by way of a metal grating so that people walking through the area can see the downspout in action and understand the stormwater’s path.
“We had to do a lot of soil remediation in our stormwater treatment [installations],” says Kump. “We put in more organic material to help plants grow.”
The green roof is the most impressive LID feature. Planted with succulents and other native plants plus some low-growing shrubs such as English stonecrop, the rooftop draws students and visitors to spend leisure time there.
“From there you can see all of the water parts: the LID basin on the west side, the bioswales in the middle courtyard, and the stormwater areas on the southside,” says Kump.
Perforated pipes under the green roof carry runoff not used by the plants to the complex’s mechanical room. This water is reused for irrigation.
The project won a number of awards, including an Engineering Excellence Small Firm Merit Award from ACEC California, Outstanding Environmental Engineering Project from ASCE Region 9, Outstanding Chapter Project of the Year from the American Public Works Association, and an Award of Merit from ASCE.
San Diego Mesa College
San Diego Mesa College has worked to create a sustainable campus, aiming for a LEED Silver certification. Its ongoing revitalization will finish with a new entrance to the campus. Newly constructed facilities save energy and manage stormwater in an impressive way.
“This project was a long time in the making. Institutional projects take time. We started in 2010 and finished in June 2016,” says David McCullough, principal with San Diego’s McCullough Landscape Architecture.
“One of the things we did, in conjunction with the architects and mechanical engineers, was to capture rainwater from the roof,” he says. “The challenge of the project was to coordinate the various elements.”
Part of the roof is adjacent to the college’s Department of Culinary Arts. Planters were installed for the culinary students to use in growing vegetables and herbs for dishes served in the student-run café.
A tank to collect HVAC condensate to use for irrigating plants growing around the building was installed. The building’s loading dock was built up, and a void for this water was created within the concrete structure. (HVAC condensate can be used to irrigate landscaping plants, but not for plants that will be eaten). Another 700-gallon tank was installed on the roof to capture rainwater that is used to irrigate the plants that the students are growing.
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