Saturday, 15 July 2006

Soil and Site Assessment Card for Connecticut Rain Gardens.

Marjorie Faber, USDA NRCS, 100 Northfield Drive, 4th Floor, Windsor, CT 06095-1325

Soil and site assessment cards were prepared to help people without soil science backgrounds evaluate possible rain garden locations. The evaluations are conducted using common low technology items.

Rain gardens are shallow lowlying areas which collect rain water from lawns, rooftops, and paved surfaces such as driveways, streets, and parking lots. The water is guided into the rain garden, where it can infiltrate into the ground. These perennial gardens are planted with both water and drought tolerant plants. The rain gardens are designed to stay wet for only a few hours after a storm. By keeping storm water off paved surfaces and fertilized lawns, rain gardens can reduce the amount of polluted storm water that reaches waterways. Rain gardens also help recharge groundwater supplies, reduce the amount of storm water entering sewer systems and leaving the site, provide wildlife habitat, and attract butterflies and birds.

To help people select the location of the rain garden and determine the size needed, the Soil and Site Assessment Card for Connecticut Rain Gardens was created. This field matrix was developed collaboratively by local gardeners, USDA NRCS, and conservation partners. The assessment consists of three steps: 1) evaluating the site and selecting the proper location for the rain garden, 2) examining the soils in the proposed rain garden, and 3) determining the size and shape of the rain garden. Each of these three steps is further divided into a list of indicators for the user to evaluate as either favorable or unfavorable on their site.

An example of a site indicator is: “Distance from foundation”. The favorable condition is: “More than 20 feet” and the unfavorable condition is “Less than 20 feet”. Comments for this indicator are “This distance is necessary to prevent water from seeping into the basement or causing frost damage.”

An example of a soil indicator is: “Soil compaction”. The favorable condition is “Loose soil at least 2 feet deep” and the unfavorable condition is “Wire flag or probe cannot be inserted into the soil at all”. Comments for this indicator are “If the soil is compacted, loosen it OR replace with a mix of 50-60% sand, 20-30% compost, and 20-30% topsoil.”

The shape and size of the rain garden is determined using indicators and a sizing worksheet. An example of a sizing indicator is “Width of rain garden”. The favorable condition is “10 feet is ideal”. The unfavorable condition is “Less than 15 feet if slope is more than 8%”. Comments for this indicator are “The longer side of the rain garden should face upslope”.

A rain garden sizing worksheet is also included to be used with the size and shape assessment indicators. The sizing worksheet considers the slope, soil texture, and drainage area (roof area, for example) to calculate the size of the rain garden.

The assessments are designed for people to do general evaluation of property, but are not a substitute for detailed, on-site investigations by professionals. Users are cautioned that the scorecard is intended to be used for infiltrating rain water and not other water, such as from animal waste, car washing, cleaning pesticide containers, or their residential/commercial uses which discharge water.

The site and soil assessment cards for rain gardens have been demonstrated at various local workshops and have been successfully utilized by Connecticut residents who are planning their own rain garden.

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