Biofiltration Swale Design Guidance
Biofiltration SwaleDesign GuidanceSeptember 2012California Department of TransportationDivision of Environmental AnalysisStorm Water Program1120 N StreetSacramento, index.htmCaltrans Storm Water Quality HandbookBiofiltration SwaleDesign Guidance
For individuals with sensory disabilities, this document is available in alternateformats upon request. Please call or write to Storm Water Liaison, CaltransDivision of Environmental Analysis, P.O. Box 942874, MS-27, Sacramento, CA94274-0001. (916) 653-8896 Voice, or dial 711 to use a relay service.Caltrans Storm Water Quality HandbookBiofiltration SwaleDesign Guidance
Table of Contents1.INTRODUCTION. 11.1.1.2.2.BASIS OF BIOFILTRATION SWALE DESIGN . 32.1.2.2.3.LAYOUT . 11SITE SPECIFIC DESIGN ELEMENTS. 11PS&E PREPARATION. 135.1.5.2.5.3.6.PRELIMINARY DESIGN PARAMETERS . 5PRELIMINARY CALCULATIONS. 6OTHER COMMENTS . 8BMP LAYOUT AND DESIGN. 114.1.4.2.5.DESIGN CRITERIA . 3RESTRICTIONS . 4GETTING STARTED . 53.1.3.2.3.3.4.OVERVIEW . 1BIOFILTRATION SWALES – A BRIEF DESCRIPTION . 1PS&E DRAWINGS . 13SPECIFICATIONS . 14PROJECT COST ESTIMATES . 15REFERENCES. 17A BIOFILTRATION GUIDANCE-VEGETATION. 18A.1 OVERVIEW . 18A.2SOIL TESTING & INVESTIGATION . 18A.3SOIL AND PLANTING AREA PREPARATION . 19A.4IRRIGATION STRATEGIES . 20A.5PLANTING STRATEGIES . 20A.6RESTRICTIONS FOR PLANT SELECTION . 22A.7DRAINAGE FACILITIES . 22A.8PLANT ESTABLISHMENT PERIOD (PEP) . 22A.9DEFINITIONS: . 23A.10 ADDITIONAL RESOURCES . 23Caltrans Storm Water Quality HandbookBiofiltration SwaleDesign Guidancei
Table of ContentsLIST OF TABLESTABLE 2-1 BIOFILTRATION SWALE DESIGN CRITERIA . 3TABLE 3-1 MANNING’S EQUATION SOLVED FOR PARTICULAR CONDITIONS BY ASSUMING DEPTH VALUES . 7LIST OF FIGURESFIGURE 1-1 SCHEMATIC OF BIOFILTRATION SWALE AND STRIP . 2FIGURE 1-2 TYPICAL SWALE (SR-78/MELROSE DRIVE) . 2FIGURE 3-1 TYPICAL BIOFILTRATION SWALE CROSS-SECTION . 6LIST OF BsecUSCSWQFBest Management PracticefeetHighway Design ManualHydraulic Residence TimeHydrologic Soil Groupinchesmaximum extent practicablemaximumminimumNational Pollutant Discharge Elimination SystemProject Planning and Design Guide – Storm Water Quality HandbookPlans, Specifications and EstimateRegional Water Quality Control BoardsecondUnified soil classification systemWater Quality FlowCaltrans Storm Water Quality HandbookBiofiltration SwaleDesign Guidanceii
SECTIONONEIntroduction1. Introduction1.1. OverviewThis document provides guidance to Caltrans Project Engineers and Landscape Architectsfor incorporating Biofiltration Swale Treatment Best Management Practices (BMPs) intoprojects during the planning and design phases of Caltrans highways and facilities. Theprimary functions of this document are to: Describe the design criteria of Biofiltration Swales (“Bioswales”);Present detailing standards and siting limitations;Present the formulas used to design Bioswales; andReview the required elements for implementing Bioswales into PS&Epackages.The Project Engineer and the District Landscape Architect have different perspectives andresponsibilities during the design of Biofiltration Swales. In this document, guidanceaddressed to the Project Engineer is provided in the numbered sections, while guidance tothe Landscape Architect is provided in the Appendix (separate attachment); the latterguidance is considered the best available at this time, but the Headquarters Office ofRoadside Management will develop and issue additional guidance as needed.1.2. Biofiltration Swales – A Brief DescriptionBiofiltration Swales are one of several BMPs for treatment of stormwater runoff fromproject areas that are anticipated to produce pollutants of concern (e.g., roadways, parkinglots, maintenance facilities, etc.). Bioswales are vegetated, typically trapezoidal channels,which receive and convey storm water flows while meeting water quality criteria and otherflow criteria. Pollutants are removed by filtration through the vegetation, uptake by plantbiomass, sedimentation, adsorption to soil particles, and infiltration through the soil.Pollutant removal capability is related to channel dimensions, longitudinal slope, and typeof vegetation. Bioswales are effective at trapping litter, Total Suspended Solids (soilparticles), and particulate metals (Caltrans, 2007).The following list demonstrates some advantages of utilizing a Bioswale as a TreatmentControl BMP.1. When properly implemented, Bioswales are aesthetically pleasing. Due to thepresence of its vegetation, the public views Bioswales as a “landscaped roadside”which would make placement more acceptable than other Treatment BMPs usingconcrete vaults.2. Bioswales were determined to be an effective Treatment BMP in reducing sedimentand heavy metals, as described in the BMP Retrofit Pilot Program Final Report(Caltrans, 2004).Caltrans Storm Water Quality HandbookBiofiltration SwaleDesign Guidance1
SECTIONONEIntroduction3. In that same report Bioswales were determined to be cost effective and, togetherwith Biofiltration Strips, were among the least expensive Treatment BMP pervolume of runoff treated.4. Bioswales also are well suited to being part of a “treatment-train” system of BMPsand should be considered whenever siting other BMPs that could benefit frompretreatment, especially Biostrips, Infiltration Basins, Infiltration Trenches, andWet Basins.Schematics of a Biofiltration Swale adjacent to a Biofiltration Strip are shown below.Figure 1-1 Schematic of Biofiltration Swale and StripFigure 1-2 Typical Swale (SR-78/Melrose Drive)Caltrans Storm Water Quality HandbookBiofiltration SwaleDesign Guidance2
SECTIONTWOBasis of Biofiltration Swale Design2. Basis of Biofiltration Swale Design2.1. Design CriteriaTo perform as an effective Treatment BMP, the Biofiltration Swale must meet certaindesign criteria; the primary factors to be incorporated into the design are found in belowTable 2-1.Table 2-1 Biofiltration Swale Design CriteriaParameterMin. ValueMax. ValueFlow Rate(See Note 1)For water qualitytreatment: WQFBottom Width(See Note 2)0 ft, as v-ditch2 ft, as trapezoidFor roadway drainage (“Design Event”)(HDM Topic 831)Consult with District Hydraulics andDistrict Maintenance(See Note 3)3H:1V with DistrictMaintenance approval1% to 2% preferred. 6% maximum. Theresulting depth, velocity and HRT mustmeet the Interrelationship formulaSide Slope (sides of the Bioswale,in cross section)4H:1VLongitudinal Slope0.25%Hydraulic Residence Time (HRT)at WQF5 minutesNo maximumAs required byminimum HRTNo maximumNo minimum6 inches (See Note 4)VelocityNo minimumDuring WQF: 1.0 ft/sec (See Note 4)During HDM flow: 4.0 ft/sec (HDMTable 873.3E)(See Note 5)Interrelationship Formula for HRT,depth, and velocity1300 sec2/ft2No maximumLength of flow pathFlow Depth during WQFManning's n valueDuring WQF: 0.20 to 0.30 but 0.24 recommendedDuring HDM flow: 0.05 (HDM Table 864.3A)There is no minimum set of this parameter at this time set forwater treatment purposes.Hydraulic conductivity of the soilsin the Biofiltration SwaleNotes:1. Bioswale should be designed based on both the WQF and peak flow of the HDM design storm,unless bypass of the larger flows are made.2. Consult with District Maintenance for whatever bottom width is proposed. If the smallest mower onhand in the District is 4-feet wide, that is the minimum bottom width.3. From HDM Topic 863: “For large flows, consideration should be given to using a minimum bottomwidth of 12 feet for construction and maintenance purposes, but depths of flow less than one footare not recommended.” However, smaller bottom widths are preferred for water quality purposes,in order to limit the tendency at low flows to concentrate into smaller rivulets.4. Maximum value may be limited if HRT less than 10 minutes, using the Interrelationship Formula.Higher if protected from erosion.Caltrans Storm Water Quality HandbookBiofiltration SwaleDesign Guidance3
SECTIONTWOBasis of Biofiltration Swale Design2.2. RestrictionsSuccessful implementation and utilization of a Bioswale as a Treatment BMP will requireproper siting of the Bioswale by coordinating with District Hydraulics and DistrictLandscape Architect. Therefore, it is important to take note of siting restrictions whendesigning the Bioswale. Bioswales should not be designated as a Treatment BMP if designis outside the range of values presented in Table 2-1, without the approval of the DistrictDesign NPDES Coordinator. Bioswales in arid regions will require installation of a temporary (or permanent)irrigation system to ensure approximately 70 percent vegetative coverage,and/or must be planted with vegetation that will go dormant outside of the rainyseason; consult with the District Landscape Architect to verify that water isavailable for irrigation. Also assess feasibility. Refer to Section 2.4.2.1 of thePPDG. A permanent irrigation system for a Bioswale should only berecommended if the planting that requires it is specified for aesthetic reasons aspart of a landscape plan and there are other irrigated elements in the plan. In extremely arid places where permanent irrigation would be required,Bioswales would not be recommended. Consult with District Design NPDES Coordinator if Bioswales are proposed atlocations having contaminated soils or above contaminated groundwaterplumes. Bioswales can be used to effectively attenuate some flows depending on the siteconditions and site hydrology. Amended soils and vegetation seeding, withcorrectly designed Bioswales, help in the attenuation of flows. Bioswales are not generally subject to setback restrictions as an InfiltrationDevice is; however, if unusual geotechnical conditions exist, or if a Bioswale isproposed above a retaining wall and the soils are known to be especiallyerodible or permeable, consult with Geotechnical Design.Caltrans Storm Water Quality HandbookBiofiltration SwaleDesign Guidance4
SECTIONTHREEGetting Started3. Getting StartedThis section presents the process and parameters incorporated into the design of aBioswale. Before selecting, sizing, and laying out the Biofiltration Swale, existing siteconditions are evaluated to obtain and assess the necessary design parameters that will beused to determine if a Bioswale is applicable and later in the design process. It is assumedthat the proposed site has already met the requirements in PPDG Checklists T-1, Parts 1and 2, and that PPDG Appendix B-2 has been reviewed.3.1. Preliminary Design Parameters3.1.1.Rainfall CharacteristicsObtain site Water Quality Flow information for the Bioswale; other hydrologic data suchas the event intensity, duration, and frequency should also be obtained for the design of theBioswale when it is used for the conveyance of the larger events from the tributary area.A.Flow in the Bioswale under the WQF intensity: QWQFThe Biofiltration Swale is a flow-based Treatment BMP that is designed to convey andtreat the runoff during WQF intensity events, as long as the flow depth, velocity, HRT, andthe Interrelationship Formula all met.The WQF intensity for the project area may be found in the PPDG, Section 2.4.2.2, or byreferring to the Basin Sizer program that has been created for Caltrans use, at this er/Basinsizer.htmThe Rational Formula should be used to calculate the runoff entering the bioswale, asshown below:QWQF C x I x AWhereQWQFCIASee Footnote 1 Water Quality Flow rate (cfs) runoff coefficient WQF rainfall intensity (in/hr) tributary area to the Bioswale (acres)B.Flow in the Bioswale during the Design Event: QThe Bioswale must be designed to convey larger during rainfall intensities greater than theWQF, and in fact must handle the peak drainage from the roadway unless an upstream1In metric units: QWQF 0.28 C x I x A where QWQF is m3/sec, C as above, intensity I as mm/hr, and area Aas square kilometers.Caltrans Storm Water Quality HandbookBiofiltration SwaleDesign Guidance5
SECTIONTHREEGetting Startedbypass for the larger events is provided. Absent such diversion, the “Design Event” for theBioswale must be consistent with the intensity, duration, and frequency of the rainfallevent used in the roadway drainage design for that tributary area contributing runoff to theTreatment BMP, as discussed in HDM Topic 831.2 Additionally, the placement of theBioswale must not impede the effective drainage of the roadway upstream. Lastly, if theBioswale is placed with a curve rather than a linear alignment, and is carrying the DesignEvent, consult HDM Topic 866, Freeboard Considerations.Note that, notwithstanding the above, there is no overflow release device from theBioswale, as must be considered for volume-based Treatment BMPs.3.2. Preliminary CalculationsIn order to utilize the Bioswale, the following calculations/analyses need to be performed:A.Flow depths and velocities at WQF and during Design EventThe flow depth during WQF and the Design Event can be calculated using Manning’sEquation, as shown below. Refer to Figure 3-1 for an illustration of the variables used inthe equation.Q (1.486/n) x A x R2/3 x S1/2whereQ flow at defined event (QWQF or Q25)n Manning’s coefficient; recommend using “n” 0.24 for QWQF and 0.05for the Design Event Q25A Cross-sectional area of the flow in the channelR Hydraulic Radius “A” / Wetted Perimeter (“P”) See Footnote 3S longitudinal slope, length drop per unit length runFigure 3-1 Schematic for Manning’s Equation terms2For convenience in this document, this flow will be referred to as Q25, although other recurrence intervalsmight have been used, as described in HDM 830, Roadway Drainage; confer with District Hydraulics.3The depth of flow is shown in various sources as “y” or “d”, but with no difference in meaning.Caltrans Storm Water Quality HandbookBiofiltration SwaleDesign Guidance6
SECTIONTHREEGetting StartedWhile Q, n, and S are known values in the equation, based on the project’s specifics, thearea and wetted perimeter (and therefore the hydraulic radius) are unknowns. For thisreason, it is easier to set up as a spreadsheet and assign various depths, which allows thearea, the wetted perimeter, and the hydraulic radius to be calculated. From these values Qcan be calculated for each of the depths as illustrated on Table 3-1 4. The row thatrepresents the site is the row that has the nearest Q that has been calculated to enter theBioswale during WQF events, from which the depth and velocity can be read. Varioushydraulic references present such parametric tables for trapezoidal cross sections.For example, with the site parameters shown in the upper row (note that Manning’s n is forthe WQF conditions), and with the QWQF as 0.51 cfs, the depth in the Bioswale would beapproximately 2.4 inches, and the velocity would be 0.23 ft/sec.depthVelocityinches(ft/s)PRQWQFy ( Depth)A(feet)(feet)(ft3 / sec)(ft)(ft2)max 6 inchesmax 1.0 1Table 3-1 Manning’s Equation solved for particular conditions by assuming depth valuesThe same spreadsheet or parametric table would be used when analyzing the flow duringthe Design Event, except that the Q25 and Manning’s n as 0.05 would be used. Note: Thehigher of the two flow depths calculated should be used to set the constructed depth of theBioswale, including any freeboard that may be required.The geometric parameters set during this step, the base width, side slope ratio, andlongitudinal slope, are accepted at the trial values, pending the check for HydraulicResidence Time and the Interrelationship Formula.B.Hydraulic Residence TimeThe minimum travel time within the Bioswale, termed the Hydraulic Residence Time[HRT]) is 5 minutes. This can be checked after the proposed Bioswale site is analyzedusing Manning’s Equation, as discussed above. The velocity associated with the QWQF isdetermined, and the HRT calculated using the proposed length of the Bioswale:4A downloadable spreadsheet can found on the OSWMD intranet websiteCaltrans Storm Water Quality HandbookBiofiltration SwaleDesign Guidance7
SECTIONTHREEGetting StartedHRT L / (60 x VWQF)whereL proposed length of the Bioswale (ft)HRT Hydraulic Residence Time (minutes)VWQF
Present the formulas used to design Bioswales; and Review the required elements for implementing Bioswales into PS&E packages. The Project Engineer and the District Landscape Architect have different perspectives and responsibilities during the design
4.3-j ROCK LINED AND VEGETATED SWALE Alternative Names: Permanent Waterway, Drainage Ways, Riprap Channel BMP DESIGN APPROACH . Rock Lined swale surrounded by vegetation. DESCRIPTION Rock lined and vegetated swales are conveyance systems designed, shaped, and lined to convey surface r
3. Select swale geometry (typically 3:1 or 4:1 side slopes). 4. Assume Manning’s n value from Table 8.1 depending on chosen liner type. 5. Use equations 8-3, 8-4, and 8-5 to determine D, the depth of swale when flowing full during 10 year storm). 6. Use D to calculate swale area as define in Sectio
grease as noted in the PPDG and TC-31 of the California Stormwater Quality Association (CASQA) manual (CASQA 2003). They are in the medium effective range for organics and trash, and in the low effective range for nutrients and bacteria (CASQA 2003, TC-31). The effectiveness of Biofiltration Strips can be
Mathematical Modeling of GAC Biofiltration System 213 Korean J. Chem. Eng.(Vol. 21, No. 1) biofilter dynamics. MATHEMATICAL MODEL DEVELOPMENT A simple mathematical model was developed to evaluate the or-ganic removal efficiency of the GAC biofiltration system. A sys-tematic representation of the mass balance in a biologically acti-
(Table 5.72 of the CIRIA SuDS manual) 47 Table 7.3 - Further information sources 48 Table 9.1 - Swale - Dos and Don'ts 59 Table 9.2 - Swale maintenance requirements. 61 Table 9.3 - Filter Strips - Dos and Don'ts 64 Table 9.4 - Filter strip maintenance activities 65 Table 9.5 - Other pond design criteria (CIRIA 2013) 68
Pervious Concrete Turf Block Flexi-Pave . Grassed Swale . Grassed Swale Design Considerations Shallow depth of flow Gradual side slopes Gradual longitudinal slope . Annual Cost Projection . Low Impact Development (LID) Examp
storm and a minimum hydraulic retention time of four minutes. A treatment swale shall be designed such that the treatment volume has a HRT of at least four minutes and has a ponding depth of less than six inches (to ensure flow though grass vegetation) for a 0.75 in/hr storm intensity. Maximum longitudinal slope shall be 7%.
influence of ideological values on the policies and practices of America’s criminal justice systems. Recently, however, a trend toward critical analysis of the behavior of police, courts, and corrections has emerged that focuses exclusively on ideology as the analytical tool of choice. For example, Barlow (2000), and Bohm and Haley (2001) include extensive discussion of the influence of .
