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JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION' , <br />VoL'45 No. 41 AMERICAN WATER RESOURCES ASSOCIATION <br />s� <br />PERFORMANCE ASSESSMENT OF RAIN GARDENS' <br />August 2009 <br />Brooke C. Asleson, Rebecca S. Nestingen, John S. Gulliver, Raymond M. Hozalski, and John L. Nieber <br />ABSTRACT: The most widely used approach for evaluating the performance of stormwater best management <br />practices (BMPs) such as rain gardens is monitoring, but this approach can involve a long time period to observe <br />a sufficient number and variety of storm events, a high level of effort, and unavoidable uncertainty. In this <br />paper, we describe the development and evaluation of three approaches for performance assessment of rain <br />gardens: visual inspection, infiltration rate testing, and synthetic drawdown testing. Twelve rain gardens in <br />Minnesota underwent visual inspection, with four determined to be nonfunctional based on one or more of the <br />following criteria: (1) presence of ponded water, (2) presence of hydric soils, (3) presence of emergent (wetland) <br />vegetation, and (4) failing vegetation. It is believed that these rain gardens failed due to a lack of maintenance. <br />For the remaining eight rain gardens, an infiltrometer was used to determine the saturated hydraulic conductiv- <br />ity (K of the soil surface at several locations throughout each basin in what is termed infiltration rate testing. <br />The median K sat values for the rain gardens ranged from 3 to 72 cm/h. Synthetic drawdown testing was per- <br />formed on three rain gardens by filling the basins with water to capacity where possible and recording water <br />level over time. The observed drain times for two of those rain gardens were in good agreement with predictions <br />based on the median of the infiltrometer measurements. The observed drain time for the third rain garden was <br />much greater than predicted due to the presence of a restrictive soil layer beneath the topsoil. The assessment <br />approaches developed in this research should prove useful for determining whether the construction of the rain <br />garden was performed properly, a rain garden is functioning properly, and for developing maintenance tasks <br />and schedules. <br />(KEY TERMS: rain garden; bioretention practice; infiltration; best management practices; runoff, stormwater <br />management.) <br />Asleson, Brooke C., Rebecca S. Nestingen, John S. Gulliver, Raymond M. Hozalski, and John L. Nieber, 2009. <br />Performance Assessment of Rain Gardens. Journal of the American Water Resources Association (JAWRA) <br />45(4):1019 -1031. DOI: 10 . 1688.2009.00344.x <br />INTRODUCTION <br />Urbanization of a watershed has significant nega- <br />tive effects on downstream aquatic systems including <br />degradation of both form and function (Booth and <br />Jackson, 1997). The increase in runoff caused by <br />increases in impervious land area during urbaniza- <br />tion results in an increase in flood frequency and can <br />decrease base flows (Wang et al., 2001). These <br />'Paper No. JAWRA -08- 0016 -P of the Journal of the American Water Resources Association ( JAWRA). Received January 18, 2008; accepted <br />April 8, 2009. © 2009 American Water Resources Association. Discussions are open until six months from print publication. <br />2 Respectively, Project Manager (Asleson), Watershed Section, Minnesota Pollution Control Agency, 520 Lafayette Road N., St. Paul, Min- <br />nesota 55155; Water Resources Engineer (Nestingen), Short Elliott Hendrickson Inc., St. Paul, Minnesota; Professor (Gulliver), Associate <br />Professor (Hozalski), Department of Civil Engineering, University of Minnesota, Minnesota; Professor (Nieber), Department of Bioproducts <br />and Biosystems Engineering, University of Minnesota, St. Paul, Minnesota (E- Mail /Asleson: brooke <br />JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION 1019 JAWRA <br />