Protecting Coastal Waters

San Diego’s stormwater management strategy

Credit: iStock/ianmcdonnell

San Diego, CA, is a city with scenic coastlines along the Pacific Ocean, a world-class zoo, a long association with the US Navy, a growing population and economy, and a lively tourism industry. Managing stormwater in this beautiful city involves dealing with a myriad of challenges.

Drew Kleis works with those challenges daily. He serves as deputy director of the Storm Water Division in the City’s Department of Transportation and Storm Water. One of those challenges, he says, is “our storm drainage system itself. The city is over 100 years old, and a significant portion of the system was developed post-World War II. The infrastructure is approaching the end of its life and in need of replacement.”

Another challenge to managing stormwater in San Diego is “topography and soil. In Los Angeles and the Inland Empire, they have a blend of pervious soils that can infiltrate stormwater easily and even recharge groundwater,” says Kleis. “In San Diego, we have a series of mesa tops and canyons with impervious clay soils that drain to the ocean.”

In addition, “The mesas have natural wetlands. These vernal pools are shallow depressions that hold water [from the heavy winter and spring rains] for several months until it evaporates.”

San Diego’s weather pattern adds to the difficulty of managing stormwater there. The climate is semi-arid, but rainfalls are intense. That means detention requirements are greater on any stormwater project.

“We get rain for only three to four months a year. 85% of our rain falls from December to March,” says Kleis.

When the winter storms hit the city, San Diego’s Storm Patrol swings into action. Its members have specific strategies to implement before, during, and after storms, all aimed at minimizing flooding and damage.

Before a storm occurs, Storm Patrol members conduct final sweeps of flood-prone areas, such as Mission Valley. They deploy portable pumps and set out “No Parking” signs in these areas.

During the storms, the members are on call to respond to such situations as downed trees and blocked drains, particularly in the flood-prone locations. They move the portable pumps as needed. After the storm, they evaluate damage, the amount of flooding, and street closings, and devise ways to prepare better for the next storm.

For most of the year, when very little rain falls, San Diego still deals with pollutant-carrying runoff. Low-flow diverters—80 of them—send runoff from any source to the storm system, keeping it out of Mission Bay.

San Diego’s climate makes it more difficult to use green infrastructure there. With California’s recent years-long drought, conserving water and using it wisely is paramount for any project. Green plants need irrigation.

Then there is the intense heat, especially in hot areas such as traffic islands surrounded by asphalt. Heat stress makes even native plants wilt and die. Bioswales are frequently lined with cobblestones and very few plants.

“We’re trying to build green infrastructure in a way that doesn’t use irrigation,” says Kleis, adding that this means extensive use of native plants.

San Diego does not have a stormwater utility, which raises funds by assessing fees on the system’s commercial and residential users. Instead, California Proposition 218 requires a public vote for any increase in funds for stormwater projects.

“Most stormwater projects are challenged in funding,” he says. “Water and wastewater funds can be raised [without a public vote of agreement], but not stormwater funds.”

Given these multiple challenges, managing the division’s $4.25 ­billion operation effectively is made ­somewhat easier by its Water Asset Management Plan.

“We’re very proud of that document,” says Kleis. “It’s one of the first in the US. It integrates flood control and water-quality needs into one place. It brings all of our funding needs together so we’re more effective at setting priorities.”

Street sweeping plays an essential role in municipal stormwater management. Kleis says San Diego has done a number of studies to make its street sweeping operation as efficient and productive as possible. The studies include which types of sweepers work best on which types of streets. Hilly streets are swept with mechanical broom sweepers. On flat streets, regenerative-air sweepers are used.

San Diego’s Bannock Avenue Neighborhood Streetscape project used green infrastructure to reduce both stormwater pollutants and runoff volume into the Tecolote Canyon watershed. It involved curb cuts to divert stormwater into swales between the streets and sidewalks.

Native plants used included scarlet monkey flower, western redbud trees, and various California native grasses. The project cost $1.8 million.

The green parking lot at Kellogg Park is a $982,000 green infrastructure project. The park is in La Jolla Shores, in a location designated as an Area of Special Biological Significance (ASBS). The California State Water Resources Control Board created these special areas to protect the Pacific Ocean. They are in some of the most pristine and biologically diverse sections along the California coast.

Kellogg Park is a lovely area and popular with beachgoers, as well as an environmentally sensitive area where pollution from runoff could cause significant damage. Keeping runoff out of the ABSB required removing 18,000 square feet of asphalt and concrete from the north and south ends of the parking lot. The impervious material was replaced with permeable pavers.

A vegetated bioswale was installed on the parking lot’s east side. A filter bed was added to the west side between the parking lot and the walk leading to the beach.

Another municipal low impact development (LID) or green infrastructure project is situated at the four-corner intersection of 43rd Street, National Avenue, San Pasqual Street, and Logan Avenue. The project was created to reduce stormwater pollutants that enter Chollas Creek and San Diego Bay.

The first component of the project includes 25 filter cells located in the landscaping right of way strip between the curb and the sidewalk. Runoff from the adjacent streets’ travel lanes drains first into inlets that filter out trash, then flows through a specified soil mix that will remove metals and other roadway pollutants.

The second component that handles additional runoff from the streets is a shallow landscaped bioretention basin. It also contains the soil mix to remove metals and other roadway pollutants.

Credit: San Diego International Airport
Terminal 2 parking plaza with below-grade stormwater capture

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.

Credit: McCullough Landscape Architecture
San Diego Mesa College

“Ordinarily you would try to hide a tank. We wanted something decorated. We wanted the tank to become an element in the design of the space, and we wanted people using the culinary garden to know that this was the correct tank to use [for watering the plants],” says McCullough.

Six belowground cisterns each hold 1,700 gallons of stormwater. Annually, they account for 192,000 gallons of stormwater collected, which will be used for irrigating campus landscaping. For landscaped areas around the campus, “The primary plant we used was one that does well in a lot of situations: common dwarf mat rush,” he says.

The California native plant deer grass was used in the bioretention basins. McCullough notes that it “does well in moist conditions. It goes dormant if it dries out, but it comes back. Deer grass was used by Native Americans in this area for making baskets. They ate its seeds, too.”

For additional infiltration of stormwater runoff, large sections of permeable paving were planned for walkways and other hard surfaces. Unfortunately, the area for permeable paving had to be reduced significantly because a large swath of the area had to be accessible to, and strong enough for, fire trucks.

“After the geotechnical report was done [it revealed] that soils there were not good enough to take the weight of the fire trucks, so we had to use concrete,” says McCullough. “We installed less than 1,000 square feet of permeable pavers.”

These CalArc Narrow Modular pavers from Stepstone Inc. measure 3 inches by 18 inches by 4 inches. The pavers have a light sandblast finish and are of three different colors that go together visually.

Three bioswales were installed around the edges of the property to treat stormwater runoff. In total, the bioswales cover about 1,000 square feet.

An HDPE cellular confinement system manufactured by Hanes Geo Components was used to keep the soil in place and prevent erosion. Filled with cobblestone, this TerraCell 280 mesh is 4 inches deep.

McCullough says an interesting aspect of the project was the ­reusing
of existing gardens that had been ­created by grounds staff members
of the college.

“We stockpiled and reused rocks and boulders and felled trees [that had been part of the garden]. After the building was done, they were reinstalled. It gave the staff member pride in what they had created and an ownership in the project, an incentive to treat it with respect.”

The Commons Building and the Exercise Science Building will “become the main gateway entry to the college and [will lead] into the quadrangle when everything is finalized,” says McCullough.

“We needed an area for sunken detention basins to store heavy rains,” explains McCullough. “We kept the dirt we excavated to create two elliptical garden spaces between concrete patios.” The reserved dirt was piled up to create two domes, with trees and drought-tolerant native grass (seashore paspalum) planted on top. Students can sit on the domes, which have tiers similar to the levels of an amphitheater.

The areas where the soil was removed became the detention basins. Each basin is about 20 by 40 feet and 3 feet deep. They were planted with California field sedge and native grasses, including purple needle grass.

“You save some money if you can move soil [already on the site] around. It is much cheaper and less wasteful than having soil trucked in,” notes McCullough.

This project won an Urban Land Institute San Diego-Tijuana Healthy Places Award.

The climate and ocean proximity that give San Diego its beautiful beaches, plus the soil types, obviously pose constraints and challenges for managing stormwater there. Fortunately, as the projects and BMPs described above show, San Diego also has some creative minds at work on these challenges. SW_bug_web

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