Sometimes the answer for a city that has fought floodwaters for years isn’t more concrete, bigger pipes or taller walls.
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In Dubuque, Iowa, an old creek that was reopened became the site of an unusual experiment: 14 floating islands made partly from thousands of recycled plastic bottles.
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The islands were installed in 2017 as part of the Bee Branch Creek restoration and were designed to do more than just add greenery.
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Today, they help protect the creek, improve water quality and provide small pockets of habitat for fish, birds and aquatic life, states an online report by IECA News.
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Making a buried creek into an asset
Flooding has been a problem in Dubuque for a long time, especially in the 7-square-mile Bee Branch Watershed, where more than half of the city's residents live or work.
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Repeated flash floods damaged some 1,300 homes and businesses, with widespread destruction to buildings, roads and stormwater infrastructure, adds the report.
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The city responded by daylighting the Bee Branch, a creek that had been buried in a storm sewer about a century ago.
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The waterway's reintroduction into the landscape allowed natural features to be incorporated into the flood mitigation project.
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Before the islands were placed in the creek, four prototype designs in a variety of shapes and sizes were developed, states IECA News.
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They constructed their primary floating structures from some 67,000 recycled BPA-free water bottles.
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Also, native plants were added along with carefully selected pieces of driftwood to create year-round useful habitat.
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And, fencing around the islands protects the new vegetation from waterfowl.
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Stainless-steel cables anchor the structures to the creek bed and the flexible anchoring permits the islands to shift with changing water levels and flow directions.
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The project was partially funded by grants and donations and cost $176,000, states the report.
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More than just floating gardens
The islands perform a variety of ecological functions.
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Their construction is such that their structures interrupt the wave energy and this helps to reduce erosion along the edges of the creek.
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They also serve as barriers to slow water as it moves around the islands, allowing suspended sediment to settle and helping keep the water clear.
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Now, plants absorb nutrients, such as nitrogen and phosphorus, on the islands.
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Preventing these nutrients from entering waterways can help reduce the amount of nutrients that eventually contribute to ecological problems downstream in the Mississippi River and Gulf of Mexico.
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The plant roots and the floating structures provide space for biofilms, microorganisms that can help break down pollutants.
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The roots below the water also provide shelter to fish and juvenile aquatic species, and insects and crustaceans use the vegetation as part of the wider food web.
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And birds also use the islands as resting places and potential nesting habitat above the water.
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Keeping the islands in good health
As per the report, the project also shows that nature-based infrastructure needs ongoing maintenance.
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The islands are regularly checked for buoyancy, vegetation and anchoring systems.
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A 2019 inspection found most plants were thriving, but some had to be replaced after animal interference and parts of protective fencing needed repairs.
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Dubuque’s experience shows that careful site selection, native vegetation, durable materials, secure anchoring and regular maintenance are important factors for other communities considering similar projects.
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What started out as a piece of a flood-control project has turned into something bigger: a working part of urban ecology.
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On Bee Branch Creek, recycled plastic is now the foundation of living habitat, and the floating islands show how flood infrastructure can create room for nature, as well.
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infrastructure → live → nature
The Aporia
