The rain garden soil media was mixed and placed on-site using light construction equipment, and is comprised of 83% sand, 8.5% onsite topsoil, and 8.5% shredded leaf mulch. The media was designed to allow water to permeate through very quickly while still providing enough soil and organic matter for plants to thrive. Beneath the soil layer is an 8" layer of crushed gravel, which provides storage capacity for the captured water and a base for the 4" perforated underdrain. After entering the underdrain, water flows into the gravel bed detention area.
The entire rain garden basin is wrapped in a non-woven geotextile fabric. This fabric allows water to infiltrate freely but prevents fine particles found in the in-situ clay soils from migrating into the growing media and causing clogging and failure. The same type of fabric separates the soil layer from the crushed gravel layer. WSSI has never experienced failure due to the fabric clogging.
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