JAWRA article - Rain Gardens

• Project Type: General OWC
• Title: Performance Assessment on Rain Gardens
• Date: 12/15/2009
• Water Conservation - Doc Type: Reports

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