Slowing Storm Water with the Right Plants

Water Retention Basin

Water Retention Basin

It is encouraging to see that those once boring and not exactly effective retention basins are morphing into bioretention basins, rain gardens and constructed wetlands. For quite some time new science, research and an understanding of the way plants and water work together, a need to manage water more effectively, as well as the likelihood that we will all experience flooding at some point now, has led to the development (and implementation!) of Best Management Practices (BMP). These BMP for storm water management provide more informed and specific ideas for planting. Of course they provide more informed instructions for design and installation as well, but we are a plant nursery – so we are going to focus on the plants.

As the weather forecasters threaten rain for the weekend (finally!) perhaps it is time to talk about the plants you can use to create a more effective storm water catchment area.  Turns out the backyard rain garden and the bioretention basin for a development or shopping center have some features in common. Yes, they both capture storm water runoff, slow it down and let it recharge into groundwater. As it filters through the soil the runoff is cleaned and purified. The other characteristics these have in common are hydrologic zones. Hydrologic zones describe the degree to which an area is inundated by water. Of course plants have different tolerances for water. Knowing the zones you are working with will help you with plant selection and help ensure a successful storm water retention cell. The basin in the photo above is planted only with turf grass, so it is easy to see the different possible levels of water that may end up there.

When you take a closer look at these rain gardens and bioretention basins here is what you may see from the bottom of the basin to the top:

  • Zone 1 – Deep Water Pool – 1-6′ Deep Permanent Pool of Water
  • Zone 2 – Shallow Water Bench (low marsh) – 6″ – 1′ Deep
  • Zone 3 – Shoreline Fringe (high marsh) – Regularly Inundated
  • Zone 4 – Riparian Fringe – Periodically Inundated
  • Zone 5 – Floodplain Terrace – Infrequently inundated
  • Zone 6 – Upland Slopes – seldom or never inundated

All basins do not have all of these zones. The good news for you is that at New Moon we have plants for all of these zones! Of course there are more than 5 plants suitable for each zone (we are pretty sure there are at least 2 Carex for each zone alone!)- to see what else will work, use our plant finder or our hydric plant list which shows you what plants will take wet conditions in various sun exposures.

Zone 1 – Deep Water – often not planted and often colonized by plants brought in by water fowl, wind etc. If installed, planting is to reduce sedimentation and improve oxidation which creates an excellent aquatic habitat. Submergent plant species are suitable for this space.

Acorus americanus

Acorus americanus

Zone 2 – Shallow Water – ideal growth for many emergent wetland species.  Plants suitable for this area include:

Asclepias incarnata

Asclepias incarnata

Zone 3 – Shoreline Fringe – basically the shoreline of a pond or wetland, extends vertically  one foot in elevation from the normal pool. Typically inundated during storm events. The plants in this zone need to be able to take frequent and prolonged inundation as well as summer droughts.

Caltha palustris

Caltha palustris

Zone 4 – Riparian Fringe – plants must be able to withstand periodic inundation of water after storms as well as drought during warm months. Plants in this area are used to help stabilize the ground from erosion.

Lobelia cardinals stands out among the ferns

Lobelia cardinals stands out among the ferns

Zone 5 – Floodplain Terrace – periodically inundated but the waters recede in less than a day, plants installed here stabilize steep slopes and provide food and cover for water fowl.

Aquilegia canadensis

Aquilegia canadensis

Zone 6 – this is the area beyond the 100 year flood zone. This area may contain infrastructure such as sidewalks, roads and little or no water inundation will occur. These plants help control and slow water heading into the basin or rain garden.

Polemonium reptans (Jacob's Ladder)

Polemonium reptans (Jacob’s Ladder)

Knowing the zones of your project will help you diversify your planting while adding some seasonal beauty to these functional spaces.

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3 comments

  1. Great post. We have a demonstration garden at the UNC Charlotte Botanical Gardens that the public can visit. We are calling it a “bioswale” since it slows and filters the runoff from a huge campus parking lot.

  2. […] know that native plants provide many ecosystem services. From stormwater management to sustaining pollinators we know they are invaluable to our ecosystem. But have you considered […]

  3. […] you will recall in our earlier post about slowing storm water with the right plants we mentioned the various zones found in retention basins and bioswales. The plants people are […]

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