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Constructed Wetlands

A constructed wetland is a man made management practice that provides a natural way to treat and remove pollutants from stormwater runoff before it enters a stream, river, or lake. As stormwater is captured in the wetland, pollutant removal is achieved through various mechanisms. Vegetation aids in this process helping to slow, settle and uptake nutrients through biochemical reactions.

Urbanized landscapes generate large quantities of stormwater runoff during rain storms. As stormwater flows off buildings and homes, into streets, down storm drains, and into local water bodies, it picks up pollutants that negatively affect water quality. Constructed wetlands provide an opportunity to manage the quantity and quality of stormwater runoff from a large area of urban development. Without the use of stormwater wetlands or other stormwater management practices, polluted water would flow directly into water bodies.

The Iowa Department of Agriculture and Land Stewardship has excellent information regarding constructed wetlands. For success stories and more, visit the Clean Water Iowa website.

Design Components

  1. Forebay. Eroded soil is captured from incoming runoff before entering the wetland. Over time, buildup of eroded soils can be removed from the forebay allowing for easier maintenance. This prevents damage to the wetland and plants and increases overall longevity of the wetland.
  2. Microtopography. A series of small berms and depressions designed to increase the distance water has to travel. This “stormwater maze” forces water to weave slowly through the wetland promoting pollutant removal.
  3. Areas of Shallow Water. Varying depths of water promote plant growth allowing for biological uptake which helps remove pollutants.
  4. Pools. Deep pools reduce the suspension of sediment, reduce thermal pollution, and increase habitat.
  5. Outlet. A primary function of a stormwater wetland is to help slow down stormwater. Aligning with this goal, the outlet of the wetland is intentionally designed to release water slowly to improve downstream environmental conditions.