BMP Training Module 4 BMP Training Module 4 Extended Dry Detention Basin Extended Dry Detention Basin and Infiltration Practices and Infiltration Practices Sponsored by: MARC Sponsored by: MARC Presenters: Presenters: Andy Sauer, P.E. (CDM) Andy Sauer, P.E. (CDM) Brenda Macke, P.E. (CDM) Brenda Macke, P.E. (CDM) February 20, 2009
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Review watershed planning and BMP value rating process Review watershed planning and BMP value rating process (Module 1)(Module 1)
Overview of extended dry detention basins (EDDB) Overview of extended dry detention basins (EDDB)
Best Management Practice Best Management Practice (BMP)(BMP)
BestBest – State of the Practice – State of the Practice No definitive answerNo definitive answer Past experience, testing, research, Past experience, testing, research, Unique to siteUnique to site
ManagementManagement – Responsible Parties – Responsible Parties Improve water quality, meet NPDES Phase IIImprove water quality, meet NPDES Phase II Jurisdictional specificJurisdictional specific Meet specific requirements of a regionalMeet specific requirements of a regional
PracticePractice – Action or Implementation – Action or Implementation Practice = defined to carry out, apply, or to Practice = defined to carry out, apply, or to
do or perform often. do or perform often.
Basic BMP PrinciplesBasic BMP Principles
PlanPlan for stormwater management for stormwater management Sustainable and “be green”Sustainable and “be green” Provide a level of serviceProvide a level of service Improve water qualityImprove water quality
Water Quality Volume (WQv)Water Quality Volume (WQv)
Water Quality Volume Water Quality Volume (WQv): The storage needed (WQv): The storage needed to capture and treat 90% of to capture and treat 90% of the average annual storm the average annual storm runoff volumerunoff volume
Water Quality Storm: The Water Quality Storm: The storm event that produces storm event that produces ≤ ≤ 90% volume of all daily 90% volume of all daily storms in a year storms in a year
Extended dry detention Extended dry detention basin design and infiltration basin design and infiltration system design is based on system design is based on the WQvthe WQv
WQv
2003 Kansas City Precip events
05
1015202530354045
0.1
0.3
0.5
0.7
0.9
1.1
1.3
1.5
1.7
1.9
2.1
2.3
2.5
2.7
Daily Precipitation (in)
# o
f d
ays
> o
r=
Kansas City Water Quality Kansas City Water Quality StormStorm
Water Quality Storm = 1.37 in
Young and McEnroe
(http://kcmetro.apwa.net)
Why Use the WQv to size Why Use the WQv to size BMP?BMP?
Retain runoff long enough to get Retain runoff long enough to get water quality benefitswater quality benefits InfiltrateInfiltrate Maintain vegetationMaintain vegetation
Reducing erosive flows from Reducing erosive flows from smaller runoff eventssmaller runoff events Less applicableLess applicable
Water Quality Volume Water Quality Volume CalculationCalculation
Two methodsTwo methods Short-Cut MethodShort-Cut Method
• Sites < 10 acresSites < 10 acres
• Only 1 predominant cover typeOnly 1 predominant cover type
Small Storm Hydrology MethodSmall Storm Hydrology Method• Larger or more heterogeneous drainage Larger or more heterogeneous drainage
areasareas
WQv Short-cut ExampleWQv Short-cut Example
GivenGiven Tributary area (ATributary area (ATributaryTributary) = 2.5 acres) = 2.5 acres %impervious = 80%%impervious = 80%
Why the term “Extended” Why the term “Extended” Detention?Detention?
Extended: Designed to release the WQv over a period of 40 hours Extended: Designed to release the WQv over a period of 40 hours
Allows time for more particles and associated pollutants to Allows time for more particles and associated pollutants to settle outsettle out
Reduces the downstream velocity and erosive conditionsReduces the downstream velocity and erosive conditions More closely imitates natural release rates and durationMore closely imitates natural release rates and duration
Geomorphic Effects of Geomorphic Effects of Uncontrolled Urban RunoffUncontrolled Urban Runoff
0.1
1
10
100
1000
§� · q· B Ú y·
Exceedance Frequency for Exceedance Frequency for DetentionDetention
7-yr
2/yr
20/yr
Storm Return Interval more frequent than 1-yr
1-yr 10-yr 100-yr2-yr
Undeveloped
DevelopedUncontrolled
6/yr
F
low
40-Hour Drawdown Impacts40-Hour Drawdown Impacts
Storm Return Interval
more frequent than 1-yr
1-yr 10-yr 100-yr2-yr
F
low
Undeveloped
DevelopedUncontrolled
DevelopedControlled
0.80 psf
0.26 psf
0.1
1
10
100
1000
0.01 0.1 1 10 100
•10-year control•1-year control•WQv – extended detention with 40 hr drawdown
March 2008 ManualMarch 2008 ManualExtended DetentionExtended Detention
Water Quality (40-hr)Water Quality (40-hr) Pollutant removal throughPollutant removal through
• SettlingSettling• Biological uptake (more for Biological uptake (more for
wetland)wetland)• Detain and promote Detain and promote
conditions for full range of conditions for full range of hydrologyhydrology
Can meet flood control Can meet flood control objectivesobjectives
EDDB Major ComponentsEDDB Major Components
EDDB Inlet/ForebayEDDB Inlet/Forebay
Forebay
Traps sediment and trash and slows inflow velocitiesTraps sediment and trash and slows inflow velocities Forebay (optional) should be at least 10% of WQv and Forebay (optional) should be at least 10% of WQv and
separated from the main basin by an acceptable barrier. separated from the main basin by an acceptable barrier. Use energy dissipaters at inlets to reduce scour potentialUse energy dissipaters at inlets to reduce scour potential
EDDB Inlet/ForebayEDDB Inlet/Forebay
EDDB Pilot ChannelEDDB Pilot Channel
Pilot Channel
EDDB Pilot ChannelEDDB Pilot Channel
Conveys low flows Conveys low flows to the outlet to the outlet
Recommend lining Recommend lining with riprap with riprap
Olathe, KS
EDDB Main BasinEDDB Main Basin
Main Basin
EDDB Main BasinEDDB Main Basin
Designed to hold the WQv Designed to hold the WQv with a depth of 2 to 5 ftwith a depth of 2 to 5 ft
Does not maintain a Does not maintain a permanent poolpermanent pool
Shallow basins with larger Shallow basins with larger surface area have higher surface area have higher performanceperformance
Basin bottom should be at Basin bottom should be at least 2 ft above the wet least 2 ft above the wet season water tableseason water table
For KC Metro, can be used for For KC Metro, can be used for limited passive recreation limited passive recreation such as trailssuch as trails
EDDB Outlet StructureEDDB Outlet Structure
Outlet
EDDB Outlet StructureEDDB Outlet Structure
Release the WQv over a Release the WQv over a period of 40 hrperiod of 40 hr
Protected by well screens, Protected by well screens, trash racks or gratestrash racks or grates
Located as far from inlet as Located as far from inlet as possiblepossible
Various outlet structure Various outlet structure typestypes Single OrificeSingle Orifice
Perforated Riser or PlatePerforated Riser or Plate
Design an EDDB for a 26-acre commercial development. Design an EDDB for a 26-acre commercial development. Size the EDDB to capture the WQv.Size the EDDB to capture the WQv. Size an outlet structure to release the WQv over 40 Size an outlet structure to release the WQv over 40
hours.hours.
Step 1:Step 1: Calculate Water Calculate Water Quality Storage Volume WQvQuality Storage Volume WQv
Two methodsTwo methods Short-Cut MethodShort-Cut Method
• Sites < 10 acresSites < 10 acres• Only 1 predominant cover typeOnly 1 predominant cover type
Small Storm Hydrology MethodSmall Storm Hydrology Method• Larger or more heterogeneous drainage Larger or more heterogeneous drainage
areasareas
As tributary area is 26 acres, Small Storm As tributary area is 26 acres, Small Storm Hydrology Method will be used.Hydrology Method will be used.
Equation: WQvEquation: WQv
Small Storm Hydrology MethodSmall Storm Hydrology Method
WQv = (P)*(Weighted Rv)WQv = (P)*(Weighted Rv)
Weighted Rv = Weighted Rv = ΣΣ(Rv(Rvii*Ac*Acii)/Total area (ac))/Total area (ac)
• RvRvii = Volumetric runoff coefficient for cover type (Table = Volumetric runoff coefficient for cover type (Table
7)7)
• AcAc ii = Area of cover type i (ac) = Area of cover type i (ac)
Rv TableRv TableTABLE 7
VOLUMETRIC COEFFICIENTS FOR URBAN RUNOFF FORDIRECTLY CONNECTED IMPERVIOUS AREAS
(CLAYTOR AND SCHUELER 1996)
Rainfall Rainfall (inches)(inches)
Flat roofs and Flat roofs and large unpaved large unpaved
parking lotsparking lots
Pitched roofs and Pitched roofs and large impervious large impervious
areas areas (large parking lots)(large parking lots)
Small Small impervious impervious areas and areas and
Note: a reduction factor may be applied to the Rv values for disconnected surfaces, consult the BMP hydrology section
Water Quality Control Water Quality Control Volume Volume
Cover TypeCover Type RvRv Area (acres)Area (acres)
Flat roofsFlat roofs 0.870.87 1.61.6
Parking lotsParking lots 0.980.98 8.88.8
Narrow streetsNarrow streets 0.750.75 3.33.3
Silty soilSilty soil 0.140.14 12.312.3
( )∑ ∑ =×
×+×+×+×=××= inP
AreaTotal
AcRvWQv ii 749.037.1
26
3.1214.3.375.8.898.6.187.
Water Quality Storage Water Quality Storage VolumeVolume
Convert WQv from inches to ac-ft by converting Convert WQv from inches to ac-ft by converting inches to feet and multiplying by the tributary areainches to feet and multiplying by the tributary area
Add 20 percent to account for silt and sediment Add 20 percent to account for silt and sediment depositiondeposition
Outlet sized to release Outlet sized to release WQWQvv (ac-ft) within 40 (ac-ft) within 40
hourshours Locate outlet as far away Locate outlet as far away
from inlet as possiblefrom inlet as possible Avoid short-circuitingAvoid short-circuiting
The facility must bypass The facility must bypass 1% storm event1% storm event
Provide at least 1ft of Provide at least 1ft of freeboard above WQfreeboard above WQVV
stage stage
Option 1:Option 1: Single Orifice Outlet Single Orifice Outlet
Single Orifice OutletSingle Orifice Outlet
i.i. Depth of water quality volume at outlet (ZDepth of water quality volume at outlet (ZWQWQ)) Dependent on site conditions – designer determinedDependent on site conditions – designer determined
ii.ii. Average head of WQv over invert of orifice, HAverage head of WQv over invert of orifice, HWQ WQ (ft)(ft)
HHWQWQ = 0.5*Z = 0.5*ZWQWQ
iii.iii. Average water quality outflow rate, QAverage water quality outflow rate, QWQWQ (cfs) (cfs)
iv. Set orifice coefficient (Co) depending on orifice plate thickness
� Do must be > or = 4 inches to prevent clogging
� Co = 0.66 if plate thickness is < Do
� Co = 0.80 if plate thickness is > Do
Single Orifice Outlet Single Orifice Outlet
v.v. Orifice diameter (DOrifice diameter (Doo) must be greater than 4 ) must be greater than 4 inches, otherwise use weir or riserinches, otherwise use weir or riser
( )WQoWQo H * g * 2 * * C / Q * 2 * 12 D π=
Single Orifice Outlet SizingSingle Orifice Outlet Sizing
Do=12*2*(0.49/(0.66*π*(2*32.2*1.5)0.5))0.5
Option 2: Option 2: Perforated Riser or Perforated Riser or Plate OutletPlate Outlet
Photo taken by Larry Roesner
Photo taken by Larry Roesner
Perforated Riser or Plate Perforated Riser or Plate OutletOutlet
Calculate outlet area per row of Calculate outlet area per row of perforations (Aperforations (Aoo))
AAoo (in (in22) = WQ) = WQvv / (0.013 * Z / (0.013 * ZWQWQ22 + 0.22 * Z + 0.22 * ZWQWQ – 0.1) – 0.1)
Assuming a single column calculate the Assuming a single column calculate the diameter of a single perforation for each diameter of a single perforation for each rowrow
DD11 = (4 * A = (4 * Aoo / / π)π)1/21/2
If DIf D11 is greater than 2 inches add more is greater than 2 inches add more
columnscolumns
nc = 4
Perforated Riser or Plate Perforated Riser or Plate OutletOutlet
= 1.62/(0.013*3.02+0.22*3.0–0.1)
= (4*2.4/π)1/2
Perforated Riser or Plate Perforated Riser or Plate OutletOutlet
Use number of columns to determine exact Use number of columns to determine exact perforation diameterperforation diameter
DDperfperf = (4 / = (4 / ππ * A * Aoo / n / ncc))1/21/2
Using a 4” center to center vertical spacing and Using a 4” center to center vertical spacing and ZZWQWQ, determine number of rows (n, determine number of rows (nvv))
nnvv = Z = ZWQWQ / 4 / 4
nv = 5
Perforated Riser or Plate Perforated Riser or Plate OutletOutlet
i.i. Depth of water quality volume at outlet (ZDepth of water quality volume at outlet (ZWQWQ)) Dependent on site conditions – designer determinedDependent on site conditions – designer determined
ii.ii. Calculate HCalculate HWQWQ over weir notch over weir notch
HHWQWQ=0.5*Z=0.5*ZWQWQ
iii.iii. Calculate the average water quality pool outflow Calculate the average water quality pool outflow rate Qrate QWQWQ (cfs) (cfs)
Volume (VolVolume (VolFBFB) should be at least 10% of WQv) should be at least 10% of WQv
Sides and bottom paved or hardenedSides and bottom paved or hardened
Surface area (ASurface area (AFBFB):):
AAFBFB = Vol = VolFBFB / Z / ZFBFB
Forebay (Optional)Forebay (Optional)
= 0.10*6.23
= 0.62/3.0
EDDB Design ActivityEDDB Design Activity
ActivityActivity
Design an extended dry detention basin (EDDB) to capture the Design an extended dry detention basin (EDDB) to capture the WQv from a 52-acre development. Design a single orifice WQv from a 52-acre development. Design a single orifice outlet to release the WQv over 40-hours.outlet to release the WQv over 40-hours.
Provides 100% load reduction for captured runoff Provides 100% load reduction for captured runoff volumevolume
Flood control via peak discharge attenuationFlood control via peak discharge attenuation
Control of channel erosion by reducing Control of channel erosion by reducing downstream flow velocitiesdownstream flow velocities
DisadvantagesDisadvantages
Sediment can clog an infiltration facilitySediment can clog an infiltration facility
Tributary area should be stabilizedTributary area should be stabilized
Not suitable in areas with high water table (1-Not suitable in areas with high water table (1-2 feet from ground surface)2 feet from ground surface)
Soils must have a minimum saturated Soils must have a minimum saturated hydraulic conductivityhydraulic conductivity
Risk of contaminating groundwaterRisk of contaminating groundwater
Infiltration Practices Infiltration Practices
CautionCaution
Infiltration capacity of soils in the MARC region Infiltration capacity of soils in the MARC region is general low (<0.5 in/hr)is general low (<0.5 in/hr)
High water tables are also a common concern High water tables are also a common concern related to these practicesrelated to these practices
Be very careful in site selection for infiltration Be very careful in site selection for infiltration basins or trenchesbasins or trenches
Plant native vegetation on side slopes and Plant native vegetation on side slopes and bottom of infiltration basinbottom of infiltration basin Can increase infiltration rateCan increase infiltration rate
Use plants listed in the BMP Manual Appendix A Use plants listed in the BMP Manual Appendix A “Recommended Plant Materials for BMPs”“Recommended Plant Materials for BMPs”
Select species that can withstand drought and Select species that can withstand drought and long periods of ponding long periods of ponding
Regular inspectionsRegular inspections Preferably once per monthPreferably once per month Assess length of time water is ponded following a Assess length of time water is ponded following a
stormstorm Stabilize areas of erosion in tributary areaStabilize areas of erosion in tributary area Remove trash and debris at beginning and end of Remove trash and debris at beginning and end of
wet seasonwet season Remove dry sediment from basin Remove dry sediment from basin
Use light equipment Use light equipment Wait until sediment Is cracking and readily Wait until sediment Is cracking and readily
separating from bottomseparating from bottom Weed trimming to maintain plantsWeed trimming to maintain plants
Infiltration TrenchInfiltration Trench
Infiltration Trench Plan ViewInfiltration Trench Plan View
Pretreatment increases the life of the trenchPretreatment increases the life of the trench Remove as much of the suspended solids as Remove as much of the suspended solids as
possiblepossible Grit ChambersGrit Chambers Swales with check damsSwales with check dams Filters stripsFilters strips Sediment ForebaysSediment Forebays
Convey flows over Convey flows over the WQv around or the WQv around or over the trench over the trench safelysafely
Prevent erosionPrevent erosion
Infiltration Trench Infiltration Trench
Infiltration Trench
Infiltration TrenchInfiltration Trench
Designed to Infiltrate the WQv within 72 hours (24 Designed to Infiltrate the WQv within 72 hours (24 hours recommended)hours recommended)
Filled with clean stone 1.5-2.5 inches in diameterFilled with clean stone 1.5-2.5 inches in diameter Lined with filter fabricLined with filter fabric Under drain can be incorporated Under drain can be incorporated
Use non-woven filter fabric layer close to the surface Use non-woven filter fabric layer close to the surface to prevent majority of substrate from getting clogged to prevent majority of substrate from getting clogged with sedimentwith sediment
Line the trench walls and bottom with filter fabricLine the trench walls and bottom with filter fabric
Infiltration Trench Infiltration Trench Monitoring WellMonitoring Well
Used to monitor the Used to monitor the infiltration rateinfiltration rate
Determine if trench Determine if trench needs cleaningneeds cleaning
4 to 6 inch diameter 4 to 6 inch diameter PVCPVC
Anchored to bottom of Anchored to bottom of trenchtrench
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OutletOutlet
Commercial Area DrainageCommercial Area Drainage
Riprap covered outlet
Overflow Weir
Infiltration Trench ExampleInfiltration Trench Example
Infiltration Trench ExampleInfiltration Trench Example
Tributary area must be less than 5 acresTributary area must be less than 5 acres If runoff comes in as sheet flow orient the trench If runoff comes in as sheet flow orient the trench
perpendicular to the flowperpendicular to the flow If runoff is channelized orient the channel parallel If runoff is channelized orient the channel parallel
to the channelto the channel Don’t use limestone or shale as backfill materialDon’t use limestone or shale as backfill material Surrounding soil should be less than 40% claySurrounding soil should be less than 40% clay
Calculate the volume of the trench (VCalculate the volume of the trench (VTRTR) )
VVTRTR = WQv / n = WQv / n
where:where:
WQv = water quality volume (ftWQv = water quality volume (ft33) ) n = void space in trench media (0.4 for clean n = void space in trench media (0.4 for clean
Calculate bottom area (A) Calculate bottom area (A)
A = 12 * WQv / (f * t)A = 12 * WQv / (f * t)
where:where: WQv = water quality volume (ftWQv = water quality volume (ft33) ) f = percolation rate of surrounding soil (in/hr)f = percolation rate of surrounding soil (in/hr) t = retention time (hr)t = retention time (hr)
Regular inspectionsRegular inspections Preferably once per monthPreferably once per month Assess length of time water is ponded following a Assess length of time water is ponded following a
storm (monitoring well)storm (monitoring well) Stabilize areas of erosion in tributary areaStabilize areas of erosion in tributary area Remove trash and debris at beginning and end of Remove trash and debris at beginning and end of
If sediment is visible in top layer, remove top If sediment is visible in top layer, remove top layer of stone, filter fabric and sediment layer of stone, filter fabric and sediment Wash stoneWash stone Reinstall filter fabric and washed stone Reinstall filter fabric and washed stone
If standing water persists for more than a few If standing water persists for more than a few daysdays Remove and clean or replace all stone aggregate Remove and clean or replace all stone aggregate Replace filter fabricReplace filter fabric
Reinforced slab, suitable Reinforced slab, suitable for heavy loadsfor heavy loads
Poured on sitePoured on site
Lenexa, KS www.lowimpactdevelopment.org
Precast Concrete GridsPrecast Concrete Grids
Permeable Concrete Permeable Concrete pavers with void areas pavers with void areas separating piecesseparating pieces
Higher percentage of Higher percentage of permeable surfaces permeable surfaces
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Modular Unit PaversModular Unit Pavers
Pavers themselves are impermeable Pavers themselves are impermeable Porous material places in gaps between paversPorous material places in gaps between pavers
Concrete Promotions Demo
GeowebsGeowebs
Traditionally used for soil Traditionally used for soil stabilizationstabilization
System must be able to sustain traffic loadSystem must be able to sustain traffic load 15% Void space with infiltration rates > 12in/hr15% Void space with infiltration rates > 12in/hr Subbase – 36 to 42% voids compacted at 95 Subbase – 36 to 42% voids compacted at 95
proctorproctor Subbase – ¾ inch clean rock with < 2% passing Subbase – ¾ inch clean rock with < 2% passing
#200 sieve#200 sieve A minimum subbase thickness of 8 inchesA minimum subbase thickness of 8 inches Use non-woven geotexile fabric between subbase Use non-woven geotexile fabric between subbase
and soiland soil Use a uniform grade material to maximize voidsUse a uniform grade material to maximize voids
Only use certified ready-mix companiesOnly use certified ready-mix companies Request certified contractor orRequest certified contractor or
Require test placement (4 ydRequire test placement (4 yd33) to verify mix and ) to verify mix and installation proceduresinstallation procedures
Do not use pervious pavements in areas where Do not use pervious pavements in areas where heavy trucks will turnheavy trucks will turn
2:1 impervious to pervious area is good rule of 2:1 impervious to pervious area is good rule of thumbthumb
Use an underdrain to dewater subbase for events Use an underdrain to dewater subbase for events greater than the water quality eventgreater than the water quality event
Calculate the minimum required surface area Calculate the minimum required surface area (SA(SAminmin) to infiltration the WQv into the soil) to infiltration the WQv into the soil
where:where:• WQv = water quality volume (ftWQv = water quality volume (ft33) ) • f = percolation rate of surrounding soil (in/hr)f = percolation rate of surrounding soil (in/hr)• t = retention time (hr)t = retention time (hr)
Size a permeable pavement parking area to Size a permeable pavement parking area to capture and infiltrate a WQcapture and infiltrate a WQvv 0f 1.37 inches over a 0.5 0f 1.37 inches over a 0.5
acre tributary areaacre tributary area Assume 100% impervious tributary areaAssume 100% impervious tributary area Short-cut MethodShort-cut Method
Water quality volume to be infiltrated in 12 hrs into Water quality volume to be infiltrated in 12 hrs into subsurface soils with infiltration rate of 0.35 in/hrsubsurface soils with infiltration rate of 0.35 in/hr