Monsanto Raingarden Pilot Project

High Performance Native Soils

Creve Coeur, Missouri
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This raingarden area helps to infiltrate 3831 gallons of water at full capacity - sufficient for a 97th percentile storm

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Through the holistic design of the stormwater basin, vegetated swale, and dry creek system, this native prairie landscape has been conceived to effectively capture and treat over 82,000 gallons of stormwater each year.

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Project metrics help to illustrate immediate benefits of the pilot project for the Client. In addition to properly treating stormwater on-site, a precedent was set for simultaneously creating biodiversity on the corporate campus.

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As plant materials mature, their groupings will naturalize and accentuate the built form

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By limiting soil disturbance, the design team was able to realize immediate cost savings for the Client. This approach meant elimination of nearly 50 dump truck trips, which would have produced over 13,000 pounds of carbon dioxide - the equivalent of 15,000 miles driven by the average car.

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Native stone materials define the ephemeral waterways

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The traditional bio-retention profile illustrates the extensive soil disturbance depths recommended, as well as the additional drainage infrastructure to be installed. This pilot project was able to eliminate the need for new subsurface drainage through a combination of extra storage capacity and the design of an adjacent vegetative swale to handle extraordinary storm events.

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The final design provides a mosiac of over 2,000 pollinator plants, incorporated into native prairie landscape, providing valuable pollinator species habitat. The existing woodland to the east provides a mature landscape component as the prairie plantings are established.

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Over 2000 pollinator-friendly plantings have been installed with a focus on attracting and accommodating monarch butterflies

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The local sewer district’s bio-retention design guidelines require removing and replacing soil to a minimum depth of 48 inches. Analysis of on-site soil profiles revealed the project could be constructed by utilizing the existing soils, resulting in a soil disturbance depth of 6 inches or less across the project site.

"The efforts taken to work with the local municipality to create a better strategy for the rain garden soil profile not only benefited the client, but also highlight why landscape architects have a critical role to play on all projects."

ASLA Awards Jury Comment

Collaborators

Civil Design, Inc.

Geotechnology, Inc.

Munie Greencare

Project Facts

Award:
Merit Award | American Society of Landscape Architects St. Louis Chapter

Size:
.5 acres

Completion:
Fall of 2016

[dtls] was contracted to design a stormwater mitigation strategy for over 3,500 square feet of roof runoff, previously held in a series of cisterns.  The [dtls] design team made an early commitment to use this project to demonstrate a transferrable process for designing a highly-functional raingarden with minimal soil disturbance.

With collaborating firms Civil Design, Inc. and Geotechnology, Inc., detailed subsurface exploration and stormwater calculations were performed to confirm that the existing native soils would deliver infiltration rates exceeding the rates required by the Metropolitan Sewer District’s design requirements for constructed raingardens.  The effective utilization of onsite soils significantly reduced construction costs for the client, while minimizing onsite disturbance.  The final design solution uses locally sourced stone creek beds to direct roof runoff into a 1,600 square foot bioretention basin for controlled stormwater infiltration into a native soil base.  Within the basin and surrounding landscape, more than 1,500 butterfly-friendly plants have been incorporated into the overall landscape design to strategically convert 17,500 square feet of manicured lawn into native prairie plantings.

The Details

  • Native Soils

  • Infiltration

  • Minimal Disturbance

  • Mitigate Run-Off

  • Continually Monitored

  • Educate

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