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Turning the Red River green

February 1st, 2009 / By: / Erosion Control, Erosion Control Materials, Feature, Reinforcement

The Red River of the North submerged 2 Upper Midwest towns 12 years ago. Now geotextile matting is part of the foundation for a sweeping urban levee and greenway.

Introduction

Today, the Greater Grand Forks Greenway is a large, beautiful park bordering the Red River of the North in the twin cities of Grand Forks, N.D., and East Grand Forks, Minn. (commonly known as Greater Grand Forks).

At 2,200 acres (9km2), the “Town Green” is more than twice the size of New York City’s Central Park. One of the prominent features of the Greenway is the extensive, 20-mile (32km) system of pathways that are used by bikers, walkers, joggers, and in-line skaters.

In 2007, the system was designated as a National Recreation Trail by the National Park Service. There are several city parks and golf courses along the Greenway. Other amenities include wildlife observation areas, a campground, fishing areas, interpretive displays, wildflower gardens, and fields for various athletics including softball, basketball, and disc golf.

The Greenway was developed after the devastating Red River flooding and fires of 1997. The land encompasses major portions of the 2 communities that used to sit in the floodplain. During the years following the flood, several neighborhoods were removed to make way for a massive new dike system. The Greenway includes the lands that sit between these new dikes and the river. Today, the Greenway serves the dual purpose of holding back river waters during floods and providing recreational opportunities for area residents throughout the year.

Background

On the riverfront in Grand Forks, N.D., in a park called the Town Green, is a concrete obelisk that commemorates floods. The tip of that obelisk, 55ft (16.5m) above the Red River of the North’s normal water elevation, is for 1997. That year, the so-called “Flood of the Millennium” inundated the downtowns of Grand Forks and East Grand Forks, Minn., forced the evacuation of more than 50,000 people, triggered fires that burned 6 city blocks, and caused a total of more than $2 billion in damage.

Almost immediately after the floodwaters subsided, the federal government, through the U.S. Army Corps of Engineers, offered $100 million and agency expertise to raise the levees and clear land to ensure that such a disaster would not happen again.

The cities said no.

Instead, they created a master plan for a 350-acre recreational area that would stretch along 3 miles (4.8km) of both states’ waterfronts and include parks, trails, and sports fields. The objective was flood control, not as functional imposition, but as local amenity. The project ultimately received more than $450 million in federal assistance, which was supplemented by local and state funding.

Bring in the TRM

Now, 12 years later, the Red River Greenway is complete, and the obelisk in the Town Green looks out over art and music festivals, the afternoon lunch crowd, and a wide, sluggish river fringed with native prairie landscape.

Yes, native prairie, not stone armoring. While the large scope and cost of this project were certainly unusual, so, too, is the aesthetic. “One of the concerns early on,” remembers Tom Whitlock, ASLA, a landscape architect with Minneapolis-based Damon Farber Associates, “was that [residents] wanted the whole shoreline natural. They didn’t want to riprap the edge.”

Whitlock worked on the project from its inception in the fall of 1997, and has outlasted Army Corps project managers, city officials, and multiple consultants. He remembers being all for the idea, since this is likely what the Red River Valley would have looked like before European settlement. But Whitlock saw some immediate concerns, namely the fact that the Red would surely flood again and rip out whatever was planted there.

To satisfy community desires and Army Corps mandates, Whitlock and his team devised a simple detail that relies heavily on geosynthetic turf reinforcement mat (TRM). The sloping flood levees that rise from the edges of the water were left uncompacted, but were scarified to loosen the soil. Then a nondegradable, erosion-control TRM was rolled out on the slopes and anchored at the bottom with a 5ft (1.52m) width of riprap (see “Geosynthetics in the Greater Grand Forks Greenway”).

Vegetation

Two different plant mixes were developed for the reinforced slopes, depending on proximity to the typical waterline.

The “shoreline mix” leans heavily on big bluestem grass and also includes milkweed, aster, several sedges, wild rye, bulrushes, switchgrass, and a locally appropriate variety of other wildflowers. The “upland mix” includes mostly little bluestem grass, wild rye, and switchgrass, with some big bluestem, black-eyed susans, coneflowers, primroses, and other prairie wildflowers.

The plants have thrived, covering the banks of the river in a native carpet, camouflaging the levees. “The result is this lush landscape,” said Whitlock. “You can’t even tell the fabric is there.”

But the geosynthetic matting most certainly is there and it is working. During construction of the Greenway in the early 2000s, the Red River flooded again (2001). The waters rose up over the restored prairie banks, up over the Town Green, almost to the top of the obelisk. When the waters receded, the prairie/levee blanket was largely intact, and the plants rebounded easily throughout the summer. That flood turned out to be the 3rd-highest on record, but Whitlock recalled: “It was a nonevent.”

The return of a true ‘prairie river’

After the heart-wrenching flooding and fires of 1997, the residents of Grand Forks and East Grand Forks wanted a return to their prairie roots.

They wanted to see flowers and waving grasses on the edge of the Red instead of stone-clad slopes hemming in their river with an engineered look. The geosynthetic reinforcement matting that landscape architects used is making that happen.

Though it is virtually invisible, geosynthetic materials are facilitating the restoration of a native landscape in a place where that is hardly ever done. Today, one of the great prairie rivers of North America actually looks like a prairie river.

Adam Regn Arvidson is a landscape architect and freelance writer based in Minneapolis. He is founder of Treeline, a design/writing consultancy that focuses on environmentally sustainable projects. Ron Bygness, editor of Geosynthetics magazine, also contributed to this article.

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