The Landscape Architect’s Guide to

Portland, Oregon

Water

Rain Garden at the Oregon Convention Center

Your Guide

Carol Mayer-Reed, FASLA

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Stormwater from any roof should be captured and treated so it doesn't overwhelm our stormwater infrastructure and pollute our rivers and lakes. The Rain Garden at the Oregon Convention Center demonstrates how even massive amounts of stormwater runoff from a 5.5-acre roof can be captured and treated. It's also a display of rainwater that calls your attention to the bounty of the Northwest landscape. The garden shows us both the challenges and opportunities of treating urban stormwater.

Located in the Lloyd District on Portland's east side, the garden consists of a series of planted water basins and basalt spillways designed to collect, clean, and retain all stormwater runoff from the Convention Center building expansion roof.

Mayer/Reed designed and complete the rain garden in 2003. ZGF Architects was the building design firm and DEA and Associates were the civil engineers. The rain garden has won a number of design awards and is studied by landscape architecture students.

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Cascading Rainwater

During a typical autumn storm event in Portland, rainwater from the convention center's roof cascades into the canyon-like channel at the upper end of the garden through stainless steel scuppers.

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See the Scuppers in Action

An overlook at the building's entry allows visitors to witness the impressive volume of water delivered from just one of the four scuppers.

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Interpretation

An interpretive panel at the visitor overlook illustrates the different watersheds of the 5.5-acre roof and how the runoff is channeled to the rain garden.

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Basalt Channel

The source channel is constructed of blocky basalt and 12-foot horizontal columns of bronze basalt. Cascading rosemary, native rose, and iris flank the channel.

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Pacific Northwest Landscape

The 318-foot-long watercourse parallels the building. The garden’s verdant planting composition, terraced garden walls, and stone outcrops feature the landscape of the Pacific Northwest.

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Sediment Settles Out

Seven stone-lined, vegetated ponds allow sediments to settle out. The lowest retention pond provides final treatment and infiltration into the ground. In case of a 100-year storm event, an overflow pipe connects to the nearby Willamette River.

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Controlling the Rate of Flow

Columnar basalt weirs control the rate of flow from one pond to the next. Settlement time allows airborne pollutants such as petrochemicals and rubber from nearby freeways to be filtered through the plants roots and gravely stone layers.

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After a Rainstorm

This photo was taken immediately following a rainstorm. This downstream view highlights the stormwater ponds surrounded by a rich tapestry of adaptive and native trees, shrubs, ornamental grasses, perennials, and riparian plantings.

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Artful Infrastructure

At a more intimate level of detail, the indigenous materials of stone, water, soil, and plants speak to the goals of artful stormwater infrastructure.

Image: C. Bruce Forster