From the August 2013 issue of LAM:
By Linda McIntyre
In December 2006, as the National Park Service was starting up the process of developing its National Mall Plan, Susan Spain, ASLA, and Alice McLarty, who are landscape architects with the park service, took me on a tour. As we walked along the rock-hard compacted soil underneath the iconic, yet worn and weedy, lawn panels of the Mall (the tree-lined central axis of the wider National Mall in Washington, D.C.), Spain and McLarty told me how the park service hoped to overhaul the site’s decrepit infrastructure, including, incredibly, the turf (see “Pall Over the Mall,” LAM, April 2007).
I was skeptical. How could any planted site survive more than 25 million visitors and hundreds of permitted events every year? Paving might be redone and new trees planted. But surely the public’s First Amendment right to assemble in the center of the nation’s capital—for demonstrations, festivals, tourism, and softball, to name a few of the everyday activities there—would be the death of any lawn soon after it was installed, no matter how good the intentions or design.
I was wrong. On a sweltering day early this summer, I met Spain, along with the project manager and planner Suzette Goldstein from HOK, the project’s design lead; and Michael Stachowicz, the park service’s first full-time turf manager, on the Mall to check out the first phase of this ambitious renovation. Seven years ago we saw random, borderless patches of trampled dust and weeds that were barely readable as rectangles at ground level. Now, at least on one part of the Mall, there are blocks of thick, inviting, deep-green grass cleanly edged with sleek granite curbs. There is also a set of strategies that any manager of a heavily used public green space, particularly one covered by turf, could appreciate for its comprehensiveness.
HOK started its design work in late 2010. Phase One focused on the three lawn panels closest to the U.S. Capitol and cost about $16 million, including construction costs; it finished a couple of weeks before the presidential inauguration in January. About a million people crowded onto the Mall for the event. But the new panels survived this baptism by foot beautifully, thanks to an approach designed to keep what the park service calls “America’s front yard” looking good well into the future.
The park service and its partners refer to their approach as a “three-legged stool.” The leg of turf replacement wouldn’t have any lasting impact without the other legs of maintenance and event management. The goals, they say, are to prevent damage rather than fix it and to take care of the Mall in a more efficient and sustainable way.
FIRST LEG: TURF REPLACEMENT
As every landscape architect knows, a lush green lawn that can take a lot of foot traffic is no simple thing to design and install. HOK has experience with soils and turf, but for this project the firm brought in a platoon of experts on the kinds of soil, grass, irrigation, and protection measures used on professional sports fields and other sites subject to extreme conditions. The team included Peter Landschoot, a professor of turfgrass science from Penn State University; the soil experts Norm Hummel and James Urban, FASLA; and the sports turf consultants Murray Cook and Steve Legros.
Goldstein says that after testing the existing soil and taking into account the way the lawns on the Mall are used, the team settled on amendments of coarse sand and compost. These were added to usable existing soil to make a “dirty sand mix” soil consisting of about 60 percent sand and 40 percent organic material. The high sand content helps with compaction and improves drainage, which has been extremely poor in unimproved areas of the Mall.
Athletic fields, she says, typically have even higher sand content, but that would have required more fertilization than the park service wanted to do: Heavier applications of fertilizer would be more expensive and could impair local water quality. Cook also noted in the July 2012 issue of Sports Turf magazine that faster-draining, sandier soil requires very frequent, regular irrigation all season, and the Mall’s event schedule wouldn’t allow for that kind of precision.
A foot-deep layer of this sandy loam lies just under the grass. Another four-inch course of sand, the same kind that was used in the soil amendment, was laid down below that layer for even better drainage.
The grass itself is a mix of 90 percent tall fescue and 10 percent Kentucky bluegrass. “Tall fescue/bluegrass is the best turf for this type of use in this area,” Stachowicz says. “This blend offers the best year-round traffic tolerance, disease and insect resistance, and drought tolerance. More high-performance sports fields may go with straight bluegrass, but it requires more inputs and rest periods.” The grass was installed as massive, 62-by-four-foot rolls of sod in the late summer and early fall of 2012. Public access to the new turf was blocked until the inauguration.
SECOND LEG: MAINTENANCE
Keeping the new grass thriving will be a challenge. But the project team has tried to make sure that the investment in renovating the Mall pays off for visitors well into the future.
Stachowicz is the park service’s first full-time turf manager. He has a background in turf science and golf course management, and he’s diving into the community aspect of his job—watching patterns of use in order to tweak the irrigation schedule, working with volunteers who keep the renovated area tidy, and engaging the Capitol Hill staffers and other locals who play softball and other sports on the Mall.
“I’m trying to educate them about how to use the lawns in a more sustainable way,” he says. “I’m looking out for when the areas used as pitchers’ mounds and bases get worn down. They’ve been pretty good at moving around when they need to.” The renovated space seems to be inspiring a sense of ownership among users, he told me. “People take better care of nicer areas.”
Day to day, Stachowicz is trying a lot of things—adjusting watering and fertilizing schedules, using dedicated mowers to avoid bringing in weed seeds from other park service sites—aimed at putting in place an efficient and sustainable maintenance regime. “No one thing is a cure-all,” he says.
The new design of the panels makes some aspects of maintenance easier. The granite curbs enclosing each new panel keep a nice sharp visible edge along the grass. The low curbs (mowers and wheelchairs can easily pass over them) have rounded corners instead of sharp ones, making them less vulnerable to unsightly wear from foot traffic.
Each panel was regraded and is now crowned slightly (1 to 1.5 percent). The crowning promotes surface drainage, and the regrading makes it easier to keep the grass at a uniform height. This subtle surface manipulation, which I didn’t notice until Goldstein pointed it out, also reduces the visual impact of the roads that slice through the Mall: When you stand on Seventh Street, looking east toward the Capitol, the three panels of lawn look much more like a continuous green carpet than the unimproved ones to the west. Even cars on the intersecting roads blend in more when you don’t see the pavement they’re traveling on.
Heavy-duty lateral drainpipes were installed four feet below the grass, out of danger from tent stakes. The pipes carry stormwater that runs off the lawn and sidewalks into a pair of cisterns that each hold 250,000 gallons of water for irrigation. When the next phase of the project is finished, there will be four of these cisterns.
The pipes of the old, inefficient irrigation system, which hadn’t been in use for at least 30 years, were closer to grade and heavily damaged by tent stakes. Now only stakes with a maximum depth of three feet are allowed for events.
The flush-mounted sprinkler heads throw water 80 or 90 feet, Stachowicz says. This means there are relatively few of them, making them easy to map for maintenance—the heads run in only three lateral rows across each panel—and easier for people setting up event tents to avoid.
Before the collected stormwater in the new system is used for irrigation, it passes through a set of screens that filter out particulates in a high-tech underground pump house. Ultraviolet light is used to disinfect the water before it’s sprayed on the lawn.
The system’s sophisticated computers are tied in to a weather station, and they help control the amount of watering based on how much rain has fallen and how much soil moisture has been lost to evapotranspiration by the grass. Stachowicz can plug in to the system and turn it on and off with his smartphone.
THIRD LEG: EVENT MANAGEMENT
There are more events on the Mall every year than there are days—more than twice as many. Limiting the damage from these activities, while keeping the Mall open and available as a unique public space, is perhaps the most challenging part of the project. So the park service is changing the way it manages events on the Mall.
It’s a delicate balance, because the Mall is, in the words of the U.S. Court of Appeals for the District of Columbia Circuit, the place where “the constitutional rights of speech and peaceful assembly find their fullest expression.”
Not wanting to spring an unpleasant surprise on the event planners who count on Mall access, the park service has reached out to them by holding meetings and explaining the reasoning behind the changes. Groups seeking permits—this is done a year in advance—now have to provide more detailed information about the scale of an event and the infrastructure it will require.
These and other changes are set out in a new operations and maintenance manual developed by the park service and the project team. The manual touches on day-to-day management but mostly focuses on events.
It sets out new limitations on use, especially on renovated lawn areas, and establishes time frames for events, geared to the number of people expected to attend, that allow for the preparation, protection, and recovery of the turf before and afterward. No vehicles of any kind (including golf carts as well as cars and heavy equipment) are allowed on the lawns and curbs, nor are most tents and other temporary structures (permits can be issued for these in some circumstances if detailed protective measures are put in place). The next phases of the project will expand paved areas to accommodate these uses, and new policies will allow for the occasional closure of Madison and Jefferson Drives, which run lengthwise along the north and south sides of the Mall.
Red flags and signs, based on a successful system developed for Central Park, indicate when regular users, such as softball teams, should steer clear of an area because of maintenance activities or conditions such as heavy frost or saturated soil.
Turf protectors—interlocking, translucent plastic squares that let some light and air get through to the grass—have to be used to protect the lawns when big crowds are expected or when the park service determines that a temporary structure can be set up on the turf. The manual details the characteristics of acceptable products and provides for monitoring while the protectors are in place and a period of recovery afterward. The recovery period, during which part or all of a lawn panel is closed to foot traffic, can last as long as eight weeks if Stachowicz determines that’s what’s needed.
The manual was designed to be updated often as Stachowicz and others work with the new turf and the new rules. “What’s impressive is that it brings together management, policy, permitting, everything in one place,” Stachowicz says. “I’m sure things will change over time, but as a framework it’s a great document.” Patrick MacDonald, the manager of this project for the park service, says the manual is something new for him and his colleagues. “In 35 years in the park service, I’ve never been involved in this kind of support document.”
This new system was put to the test during President Obama’s second inauguration in January. The new turf panels were overlaid with what the project team says is the biggest single installation ever of protective covers. The covers, some of which had to be borrowed from sports stadiums around the country, were hand carried onto the Mall a few days before the ceremony. When they were taken up afterward, the team let out a collective sigh of relief: The system worked.
The new strategy, including the measures detailed in the manual, was given a political boost when then-Secretary of the Interior Ken Salazar, Honorary ASLA, issued a secretarial order in January that formally directs the park service to implement the policies set out in the manual.
Although the renovated lawn panels are in good shape and the new strategy is working well so far, everyone involved with the project knows there are plenty of challenges ahead. The closure of the remaining lawn panels during the next phases of construction will put heavy pressure on the renovated ones. No matter how good Stachowicz is at his job, managing all of this turf for so many users is a tall order for one guy. He’s supposed to have a staff to work with, eventually, but as it is for so many government activities these days, it’s not clear when funding will be available. The second and third phases of the project are also dependent on Congress’s appropriating the funds (construction documents for these phases are due to be finished later this year, with funding for the second phase planned to come through in fiscal year 2014).
But the progress so far has been impressive. “We’ve built up to people understanding that we had a problem and we needed a multipronged solution,” Spain says. When the park service was developing the plan, a few commenters suggested using artificial turf or even green-painted concrete instead of real grass. But as the process went on, she says, “It was clear that this was a valued landscape, and most people didn’t want anything artificial here. They wanted something authentic, of an appropriate quality for a place where people learn about American values and the heroes and symbols of our nation.”
Linda McIntyre is a former staff writer and a frequent contributor to LAM.