HOW TO: CAPITALIZE AND REDUCE STORMWATER RUNOFF IN YOUR LANDSCAPES
Reducing the amount of stormwater runoff from roadways, parking lots and rooftops, which can become polluted with oil and other vehicular fluids, deicing chemicals, brake dust and other debris, is possible on a small scale. New terms, such as bioswale and rain gardens, are popping up everywhere as possible methods for reducing non-point source pollution in the groundwater. Incorporating planting areas within and adjacent to parking lots, entry drives and sidewalks can upgrade the landscape while catching, utilizing and filtering runoff prior to entering groundwater.
Aesthetics always comes first. No matter how you plan to reduce and utilize runoff, keep in mind that the results of your efforts will be continuously on display. The very unattractive detention ponds surrounded with riprap, located strategically on the corner of some upscale shopping areas, are difficult to hide. Consider entering the property from all areas and how your remedy will be viewed. Frame areas that are attractive; areas that are unattractive should be altered, if possible, hidden at the least.
Instead of creating raised planters with curbs and bump-outs, flatten the pavement at the edges and prep the soil within to accept runoff. Use pervious pavers where attractive and possible. These come in many forms but all have holes through them that allow water to filter down. The fill materials must meet specifications for infiltration, percolation and compaction resistance. Most clay soils will not qualify. Cornell University has a proven soil specification that can be used in many high traffic areas.
A minimum five percent of the entire paved surface should incorporate some type of soil drainage within the property. Buffer zones adjacent to parking lots and drives can slow water movement, allowing more time for infiltration.
Parking blocks will help prevent drivers from driving right into your planting. Recycled plastic blocks work as well as concrete blocks.
Prior to installation, till soils deep enough to break through any compaction layers and rejoin the soil and drainage system below. If the soil holds water too long, mosquitoes may become a problem. Test the area after tilling. If it still holds water, till or disk again, only deeper.
Choose plant materials that are salt- and flood-tolerant, where needed. Go beyond choosing genus and species — some cultivars are more tolerant than others. For example, red maples are generally flood-tolerant; however, ‘Red Sunset,’ ‘Schlesinger’ and ‘Bowhall’ had the highest flood tolerance of cultivars tested. Many flood-tolerant plants do not prefer to have wet feet; rather, they are tolerant of low oxygen conditions (not surprisingly, many are also drought-tolerant, which will help with the extremes of wet and dry).
There are a lot of recommendations for using native plant material in bioswales and rain gardens. Keep in mind that in public areas, using native plants for native-plant-sake may not develop into an attractive planting. Natives are an excellent choice if they fulfill the design criteria set out and your clients are accepting of their look. Some natives can become more attractive with increased cultural practices (pinching, deadheading, etc.).
Selected plant materials should not cause additional maintenance issues, such as dropping branches and fruit. Again, select species or cultivars that are less likely to drop things. Check with your local nurseries, and Extension offices for appropriate plants for your area. Don't discount annuals in your search for plant material. They can look nice during the summer months and the empty bed during winter can still catch and filter runoff.
Consider site lines for traffic safety. Choose plant material that will not block views and cause wrecks.
Select plant material carefully for maintenance requirements. If your staff is already stretched to maintain the “official” planting areas, you will not want to install high-input plants. Perennials are often talked of as the “low maintenance” way to go, but many perennials need frequent deadheading and division. Stella D'Oro daylilies are an attractive plant, but the frequent deadheading and removal of yellowing leaves puts them in the “high maintenance” category. Ornamental grasses are an easy way to go. For 10 months of the year, they are either newly emerged, flowering or fading into the winter landscape. You will need to cut back foliage once per year — doesn't get easier than that.
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