My WebLink
|
Help
|
About
|
Sign Out
Home
Browse
Search
JAWRA article - Rain Gardens
CWCB
>
Water Conservation
>
DayForward
>
JAWRA article - Rain Gardens
Metadata
Thumbnails
Annotations
Entry Properties
Last modified
12/16/2009 7:51:12 AM
Creation date
12/15/2009 4:10:06 PM
Metadata
Fields
Template:
Water Conservation
Project Type
General OWC
Title
Performance Assessment on Rain Gardens
Date
12/15/2009
Water Conservation - Doc Type
Reports
Supplemental fields
Drought Mitigation - Doc Type
News Article
There are no annotations on this page.
Document management portal powered by Laserfiche WebLink 9 © 1998-2015
Laserfiche.
All rights reserved.
/
13
PDF
Print
Pages to print
Enter page numbers and/or page ranges separated by commas. For example, 1,3,5-12.
After downloading, print the document using a PDF reader (e.g. Adobe Reader).
Show annotations
View images
View plain text
ASLESON, NESTINOEN, GULLIVER, HOZALSKI, AND NIEI3ER <br />computed coefficient of variation (CV) values was used <br />to determine the appropriate distribution for the mea- <br />sured Ksat values. Possible outliers were not removed <br />due to the highly heterogeneous soil expected in vege- <br />tative landscapes and the uncertainty involved with <br />removal of such data points. <br />The median or mean Ksat value from the infiltrom- <br />eter results; the surface area, A (m and volume, V <br />(m of the water in the rain garden at the time of <br />the test were used to predict the drain time, t, using <br />the following equation: <br />V <br />Drain Time = (2) <br />Ks.tA <br />Equation (2) will provide a rough estimate of the <br />drain time, subject to the following assumptions: <br />(1) The mean piezometric head over the soil, repre- <br />sented by VIA, is appropriate to estimate drain <br />time, and <br />(2) The soil is saturated at the conclusion of filling, <br />when drain time measurements commenced. <br />Synthetic Drawdown Tests <br />The flow rate needed to fill a rain garden with water <br />for the simulated runoff assessment was calculated to <br />determine if an adequate supply of water was avail- <br />able. The parameters necessary to estimate this flow <br />rate include the surface area of the basin, the esti- <br />mated or measured infiltration rate, and the storage <br />capacity of the basin. After filling the rain garden with <br />water to the highest level possible, the water level vs. <br />time was recorded using a staff gauge and a stop <br />watch. Measurements also were collected every second <br />and averaged over 10 s intervals with an ultrasonic <br />sensor (MassaSonic, M -5000) mounted to a postset at <br />the lowest point in the basin. The time required to fill <br />each rain garden was —30 min. Measurements of <br />water level began as soon as the inflow was turned off. <br />The reported drain times are based on the actual vol- <br />ume of water used during the synthetic drawdown test <br />and not the maximum capacity of each site. <br />RESULTS AND DISCUSSION <br />Visual Inspection <br />All of the rain gardens contained various species of <br />native perennial vegetation. Four of the sites con- <br />tained new plantings and were considered to be in <br />good health based on their early stage in develop- <br />ment. Four rain gardens suffered from an obvious <br />lack of infiltration observed during a visual inspec- <br />tion, including ponded water, the presence of hydric <br />soils and wetland plants, and a lack of plant growth <br />on compacted soil. These rain gardens failed the <br />Level 1 inspection and will require rehabilitation. <br />Vegetation health at the Cottage Grove (7) site was <br />rated as poor based on the presence of failing trees. <br />Nevertheless, the prairie grasses and perennial <br />plants appeared to be established and growing well. <br />With the exception of the four sites determined to be <br />nonfunctional and the Cottage Grove (7) site, the <br />other sites bad well - established vegetation that <br />appeared to be healthy. <br />The results of the inspection of the soils at each <br />rain garden are provided in Table 2. Rain gardens <br />typically have mulch covering the soil surface for <br />moisture and weed control. The topsoil of several rain <br />gardens consisted of a sandy loam soil. Examining <br />the soil profile, as described in the methods section <br />for visual inspection, of the rain gardens is important <br />for the detection of restrictive soil layers that may be <br />present due to improper construction or have formed <br />over time due to prolonged saturation. Soil profiles <br />can give especially useful information as it is possible <br />that a restrictive layer contributes to the desired <br />drain time not being met. At the UM — St. Paul (6) <br />campus rain garden, for example, a lower permeabil- <br />ity silt loam soil layer was found to underlay the <br />sandy loam topsoil, which was later found to be an <br />adjustment made during construction. Two other rain <br />garden sites [Thompson Lake (11) and UM — Duluth <br />(12)] had an underlying native soil of finer texture <br />(silt loam and clay) than the overlying topsoil (loamy <br />sand and sandy loam). These two sites were designed <br />with underdrains to compensate for the restrictive <br />layer. The soil profile at the Cottage Grove (7) site <br />consisted of forty inches of sand overlying gravel. The <br />poor retention of water and nutrients in the sandy <br />soil were a potential cause of the failing plants <br />observed during inspection of the vegetation. <br />Two sets of samples were taken for the UM — <br />Duluth (12) rain garden as it contained two different <br />types of soil. The mean bulk densities of the Cottage <br />Grove (7) rain garden (Table 2) and the coarse sand <br />overlying the underdrain system at the UM — Duluth <br />(12) rain garden were 1.57 and 1.53 g /cm respec- <br />tively, which are typical values for sand. There was <br />several bulk densities of — 1.0 -1.2 g /cm which is <br />indicative of loamy soils and was expected based on <br />the texture of the topsoils in the rain gardens. Sandy <br />soils with a relatively low volume of pores may have <br />a bulk density of —1.6 g /cm whereas aggregated <br />loams and clay soils fall below 1.2 g /cm (Hillel, <br />JAWRA 1024 JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION <br />
The URL can be used to link to this page
Your browser does not support the video tag.