The Morton Arboretum: Meadow Lake and Permeable Main Parking Lot
Landscape Performance Benefits
- Retains virtually 100% annual rainfall on the site, as supported by 10 years of observations. Only one unprecedented rain event resulted in flooding.
- Improved water quality in Meadow Lake by helping to reduce Total Suspended Solids (TSS) by 84% and Total Phosphorus by 39%. Both reductions contribute to the penetration of sunlight and dissolved oxygen, and the increase in aquatic macrophytes.
- Saves approximately 327,700 gallons of potable water for the peak month of July by using nonpotable lake water for irrigation.
- Increased the Biomass Density Index — a measure of the density of plant layers covering the ground — by 10% around Meadow Lake and the parking lot.
- Prevents the establishment of all invasive species around Meadow Lake through ongoing monitoring and integrated pest management.
- Reused approximately 31,000 cu yd of excavated soil and fill materials from the parking lot site to create a portion of a berm to buffer the Arboretum from the adjacent highway.
- Supplements the Arboretum topsoil production with nearly 100% or 138 cu yd of the site’s plant debris and clippings composted annually.
- Educates the Arboretum’s 850,000 annual visitors about the stormwater management features with 34% of Arboretum members and 32% of volunteers surveyed saying that they learned something new from the interpretive signs.
- Draws people to the lake, with over 85% of volunteers and 83% of members saying that they visit Meadow Lake every time they visit the Arboretum. Reasons include physical exercise, mental restoration and to experience nature.
- Saves approximately $3,300 annually and over 235 maintenance hours through efficient seasonal burning versus only hand weeding around Meadow Lake.
- Reduces parking lot maintenance costs by approximately $25,100 per year when averaged over 50 years by eliminating seal coating, striping and resurfacing.
At a Glance
The Morton Arboretum
Stormwater management facility
Former Land Use
4100 Illinois Route 53
Lisle, Illinois 60532
$7.4 million (Meadow Lake: $3.6 million, parking lot: $3.8 million)
The Morton Arboretum Meadow Lake and Permeable Main Parking Lot replaced a former degraded retention pond and asphalt parking lot with a functioning wetland system and permeable lot whose stormwater flow is now integrated with aquatic ecology. The entire project was the beginning of a 20-year capital improvement master plan, aimed at expanding facilities and sites to demonstrate sustainable design to visitors. The Arboretum now receives 850,000 visitors annually. All visitors to the Arboretum pass through the high-performance parking area to reach the Visitor Center. The adjacent Meadow Lake has become an active area for walkers, joggers, and educational programming. The permeable parking lot, the largest of its kind in the Midwest when it was installed, infiltrates and collects rainwater through a subsurface gravel bed, channels water through bioswales, and directs overflow to a final cleansing via the wetland area within the restored lake system. The permeable parking lot was partially supported by a US-EPA grant, and the complete project site is certified by the Sustainable SITES Initiative.
Historically, The Morton Arboretum was known for being a research institution, and less known as an educational and outreach facility. With an interest in expanding its mission, the Arboretum leadership decided to upgrade its facilities to accommodate increased programming and visitors. To complement a new Visitor Center, the Arboretum also needed to upgrade an adjacent stormwater detention area and to enlarge the main visitor parking lot. However, there was concern about adding parking to the site, since additional parking would impact the quality of the site from a landscape aesthetic and ecological performance perspective, counter to the mission of the Arboretum.
In working through the design challenges of mitigating site impact, the design team proposed to the Arboretum that there might be an opportunity to accommodate increased visitors, programming and parking while also developing a higher-performing site. By removing the existing asphalt parking lot and installing a larger permeable parking lot, the new lot design would reduce total runoff, leading to improved water quality in a restored Meadow Lake. The parking lot then became integrally tied to the lake, with stormwater filtering through bioswales and a wetland before entering the main body of the lake. The project represents a design decision process that expanded the project footprint but, through ecological design, increased overall site performance.
- A 205,600-sf permeable parking lot with 477 car and 11 bus spaces is composed of a concrete paver system underlain by a 4-ft-gravel bed that stores and slows stormwater.
- Runoff from the parking lot is directed into 38,936 sf of bioswales where it infiltrates, and any overflow is directed into the adjacent constructed wetland at Meadow Lake.
- Meadow Lake was enhanced to create a 7-acre functioning wetland and habitat system. Previously, it was a degraded retention pond with undercut banks and no edge plantings that was not conducive for human interaction.
- 68,000 plants of 165 species, 98% of which are native, increase the habitat value of Meadow Lake. Wetland plantings demonstrate submergent, emergent, and wet mesic plant zones, and unique plants such as Dirca palustris (leatherwood) were propagated from the surrounding Arboretum grounds.
- Dense massing and drifts of native species provide a legible, garden-like ecological edge to Meadow Lake.
- A 35-foot slurry wall extending to bedrock surrounds Meadow Lake to prevent groundwater from entering the lake, since the groundwater contains higher than average amounts of naturally-occurring phosphorus due to underlying bedrock.
- During peak growth season from April to November, high efficiency pop-up head irrigation supplements the parking lot bioswale display gardens using non-potable water from Meadow Lake.
- Two 15- to 25-ft-wide limestone stepped-terraces gradually descend 3 ft and10 ft down to the lake, allowing direct interaction with the water’s edge and a feeling of immersion within the landscape. Turtles and frogs frequent this edge and provide an opportunity for people to observe them up-close.
- The life cycle cost for the parking lot demonstrates that interlocking permeable concrete pavers are less expensive than asphalt pavement over time. The permeable pavement system had a higher upfront installation cost in 2004 of $42 per sq yd, compared to $17 per sq yd for an asphalt lot. But the real costs of both systems accumulate with maintenance: Over a 50-year period, maintenance costs for an interlocking permeable concrete pavers system are projected to be $45 per sq yd, compared to $80 per sq yd for asphalt. Based on these forecasted annual costs, year 23 is projected as the break-even point for the permeable pavement system.
- The bioswales in the parking lot, which were designed to infiltrate stormwater, have drained too well because of a high percentage of sand in the soil mix. As a result, they require supplemental irrigation through non-potable water from Meadow Lake during times of drought. The Arboretum is now working on its operations headquarters site within the Arboretum grounds. It will be implementing a similar permeable parking lot design and will specify a less-sandy soil mix to hold water longer.
- The Arboretum is a research institution staffed with scientists, researchers and management specialists who conduct maintenance and operations in-house. The Meadow Lake and Permeable Main Parking Lot participated in the Sustainable SITES Pilot Program, but because construction of the project had been completed five years before the start of the program, there was some difficulty in providing exact documentation for some of the SITES credits. The project received a SITES One-Star certification when it probably could have qualified for a higher designation if these records had been available. The Arboretum has since documented its site development and construction processes so they are able to transfer these beneficial practices and contracts to other Arboretum projects, enabling future certification and recognition.
Landscape Architect: The Morton Arboretum
Civil Engineer (Meadow Lake): Montgomery Watson Harza Engineers
Civil Engineer (Parking Lot): Christopher B. Burke Engineering, Ltd.
Environmental Consultant: Baetis Environmental Services
Native Planting Consultant: Living Habitats
Construction Management: Featherstone
General Contractor: V3 Construction Corporation
Contractor/Installer: LPS Pavement Company
Role of the Landscape Architect
Scott Mehaffey, landscape architect for The Morton Arboretum during the project period, provided schematic design for the lake and parking lot. Conservation Design Forum provided design development feasibility for the project, including services to obtain grant funding to support construction. Design development and construction administration were provided by other disciplines.