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170`h Trail NW Rain Garden <br />January 7, 2016 <br />Page 3 <br />Additional Considerations <br />Rain gardens are typically designed to accommodate the 1-inch rainfall event, as 90% of the pollutants <br />runoff during this size event. In this case, approximately half that volume is provided. <br />Based on the proposed depth, drawdown shouldn't be more than a few hours in the A type soils <br />common throughout the Anoka Sand Plain. <br />Rain Guardian Systems <br />The City may also want to consider the use of Rain Guardian systems. These types of systems are used <br />to prevent sediment and debris from entering the rain gardens. The sediment and debris are carried <br />from the street to the rain garden areas during rain events. Over time, the sediment and debris will <br />settle in the rain garden and prevent infiltration. The Rain Guardians trap the sediment and debris <br />before it enters the rain garden. City maintenance crews would need to clean the trapped materials on a <br />routine basis during the year. <br />Our understanding is the Rain Guardian was developed, in part, by the Anoka Conservation District and <br />are currently being distributed by Cretex. Costs can range from $1,500 to $2,500 for the units. <br />More information related to the Rain Guardian can be found on the following website: <br />http://www.raineuardian.biz/ <br />