STORMWATER BEST MANAGEMENT PRACTICE (BMP) CONSTRUCTED STORMWATER WETLANDS FOR STORMWATER TREATMENT...
-
Upload
terence-toby-walsh -
Category
Documents
-
view
227 -
download
3
Transcript of STORMWATER BEST MANAGEMENT PRACTICE (BMP) CONSTRUCTED STORMWATER WETLANDS FOR STORMWATER TREATMENT...
STORMWATER BEST MANAGEMENT STORMWATER BEST MANAGEMENT PRACTICE (BMP)PRACTICE (BMP)
CONSTRUCTED STORMWATER CONSTRUCTED STORMWATER WETLANDS FOR STORMWATER WETLANDS FOR STORMWATER
TREATMENTTREATMENT
JEREMY FINCH
RHETT BUTLER
OVERVIEW OF PRESENTATIONOVERVIEW OF PRESENTATION
Definition & FunctionsDefinition & Functions Characteristics of Characteristics of
Stormwater WetlandsStormwater Wetlands Natural Wetlands vs. Natural Wetlands vs.
Stormwater WetlandsStormwater Wetlands Advantages & Advantages &
DisadvantagesDisadvantages Design of Stormwater Design of Stormwater
WetlandsWetlands Practical Design Practical Design
ExampleExample
DEFINITIONS & FUNCTIONS OF DEFINITIONS & FUNCTIONS OF STORMWATER WETLANDSSTORMWATER WETLANDS
DefinitionDefinition- - Wetland Systems that are specifically designed to treat/manage Wetland Systems that are specifically designed to treat/manage the impact of development/urbanization on stormwater quality the impact of development/urbanization on stormwater quality
and quantityand quantity
FunctionsFunctions- - Improve Water Quality Improve Water Quality
(i.e. pollutant removal)(i.e. pollutant removal)
- Minimize flooding/flood control- Minimize flooding/flood control
- Establish/create wildlife habitat- Establish/create wildlife habitat
CHARACTERISTICS OF ALL CHARACTERISTICS OF ALL STORMWATER WETLANDSSTORMWATER WETLANDS
Inundated with surface or Inundated with surface or groundwater for most of groundwater for most of the yearthe year
Contains vegetation that is Contains vegetation that is adapted to saturated adapted to saturated conditionsconditions
Primary source of water is Primary source of water is runoff from urban areasrunoff from urban areas
Contains forebays, deep Contains forebays, deep pools, shallow pools, outlet pools, shallow pools, outlet control structurescontrol structures
High pollutant removal High pollutant removal efficiencyefficiency
POLLUTANT REMOVAL IN POLLUTANT REMOVAL IN STORMWATER WETLANDSSTORMWATER WETLANDS
REMOVAL PROCESSREMOVAL PROCESS POLLUTANTS REMOVEDPOLLUTANTS REMOVED
Plant UptakePlant Uptake Nutrients including nitrogen and Nutrients including nitrogen and phophorusphophorus
Microbial ProcessesMicrobial Processes Nitrogen, pathogens, organicsNitrogen, pathogens, organics
Sedimentation & FiltrationSedimentation & Filtration TSS, floating debris, trash, TSS, floating debris, trash, sediment-attached phosphorus, sediment-attached phosphorus,
pathogenspathogens
AdsorptionAdsorption Dissolved metals, soluble Dissolved metals, soluble phosphorusphosphorus
Ref: Bill Hunt
POLLUTANT REMOVAL EFFICIENCYPOLLUTANT REMOVAL EFFICIENCY
POLLUTANTPOLLUTANT REMOVAL EFFICIENCYREMOVAL EFFICIENCYTSSTSS 67%67%
Total PhosphorusTotal Phosphorus 49%49%
Total NitrogenTotal Nitrogen 28%28%
Organic CarbonOrganic Carbon 34%34%
Petroleum HydrocarbonsPetroleum Hydrocarbons 87%87%
CadmiumCadmium 36%36%
CopperCopper 41%41%
LeadLead 62%62%
ZincZinc 45%45%
BacteriaBacteria 77%77%
Ref: US EPA
NATURAL VS. STORMWATER NATURAL VS. STORMWATER WETLANDSWETLANDS
Stormwater wetlands do not perform the same functions as natural wetlandsStormwater wetlands do not perform the same functions as natural wetlands
Natural WetlandsNatural Wetlands Stormwater WetlandsStormwater WetlandsWater balance dominated by Water balance dominated by
groundwatergroundwaterWater Balance dominated by Water Balance dominated by
surface runoff from urban areassurface runoff from urban areas
Amount of standing water varies Amount of standing water varies seasonallyseasonally
Standing water year-roundStanding water year-round
Wetland boundaries can shift Wetland boundaries can shift depending on seasonal depending on seasonal groundwater changesgroundwater changes
Wetland boundaries are clearly Wetland boundaries are clearly defineddefined
Complex topographyComplex topography Simple topographySimple topography
Self-maintainingSelf-maintaining Requires year-round maintenanceRequires year-round maintenance
High Wildlife potentialHigh Wildlife potential Low to Moderate Wildlife PotentialLow to Moderate Wildlife Potential
Occurs naturallyOccurs naturally Constructed & Designed specifically Constructed & Designed specifically for urban stormwater runofffor urban stormwater runoff
Ref: NCDENR
ADVANTAGES & DISADVANTAGESADVANTAGES & DISADVANTAGES
ADVANTAGESADVANTAGES- Removes multiple pollutants from stormwater runoff- Removes multiple pollutants from stormwater runoff
- Improves overall water quality- Improves overall water quality
- If designed & constructed properly, can be aesthetically pleasing- If designed & constructed properly, can be aesthetically pleasing
- Reduce flooding potential in downstream areas due to - Reduce flooding potential in downstream areas due to
development upstreamdevelopment upstream
DISADVANTAGESDISADVANTAGES- Can occupy large areas of developable land- Can occupy large areas of developable land
- Can dry out and become nuisance if drainage area is too small- Can dry out and become nuisance if drainage area is too small
- Mosquito/Snake habitat- Mosquito/Snake habitat
- May be difficult to establish native wetland plants- May be difficult to establish native wetland plants
DESIGN OF STORMWATER DESIGN OF STORMWATER WETLANDSWETLANDS
Optimal LocationOptimal Location- - Where water availability is Where water availability is
highhigh
- Flat topography- Flat topography
- Areas where seasonal high - Areas where seasonal high
water table is approx. 6” water table is approx. 6”
above bottom of wetlandabove bottom of wetland
- Areas where soil studies - Areas where soil studies
show that the underlying show that the underlying
soils have an low infiltration soils have an low infiltration
rate to maintain a rate to maintain a
permanent pool of waterpermanent pool of water
NOTE: THE FOLLOWING DESIGN PROCEDURE VARIES REGIONALLY. THIS IS ONE DESIGN PROCEDURE SUMMARIZED FROM THE SOURCES SHOWN IN THE REFERENCES AT THE END OF THIS PRESENTATION. IT IS IMPORTANT TO NOTE THAT THIS IS ONE OF MANY POSSIBLE DESIGN PROCEDURES FOR STORMWATER WETLANDS
DESIGN OF STORMWATER WETLANDSDESIGN OF STORMWATER WETLANDS (continued)(continued)
DESIGN REQUIREMENTSDESIGN REQUIREMENTS- Must have a p- Must have a permanent pool ermanent pool
of water (for stormwater of water (for stormwater wetlands, we use 3 feet)wetlands, we use 3 feet)
- Must meet required surface - Must meet required surface area to drainage area ratioarea to drainage area ratio
Schematic Ref: Bill Hunt
Ref: NCDENR
DESIGN OF STORMWATER WETLANDSDESIGN OF STORMWATER WETLANDS (CONTINUED)(CONTINUED)
- Must detain volume of runoff resulting from the 1” storm (i.e. - Must detain volume of runoff resulting from the 1” storm (i.e. first flush runoff) above the permanent pool. This volume is first flush runoff) above the permanent pool. This volume is
calculated using the SCS Curve Number method shown below:calculated using the SCS Curve Number method shown below:
)8.0(
)2.0( 2
SP
SPmeRunoffVolu
Where: P = Precipitation (in) 1” storm
S = Ultimate Storage Capacity (in/in)
• Must drawdown the 1” storm over a period of 2 to 5 days
• Should contain a sediment forebay for initial settling
• To function properly as a wetland, 35% of the total wetland area should have a depth 0-9”
• To function properly as a wetland, 35% of the total wetland area should have a depth 9-18”
• To function property as a wetland, 30% of the total wetland area should be “shallow land”
FOREBAYFOREBAY Placed where runoff enters the wetland (i.e. storm drainage)Placed where runoff enters the wetland (i.e. storm drainage) Serves as a preliminary “screening” device to prevent Serves as a preliminary “screening” device to prevent
degradation of primary wetland functions degradation of primary wetland functions traps sediments, traps sediments, larges pieces of debris, etc.larges pieces of debris, etc.
Deepest part of wetland Deepest part of wetland usually 2-2.5’ deep usually 2-2.5’ deep Must allow access to forebay for maintenance purposes Must allow access to forebay for maintenance purposes
(sediment cleanout, etc.)(sediment cleanout, etc.) Designed to occupy approximately 10% of total wetland areaDesigned to occupy approximately 10% of total wetland area
Forebay Ref: Bill Hunt
SHALLOW POOLSSHALLOW POOLS Typically 0-9” deepTypically 0-9” deep Area where primary wetland functions occur (i.e. Area where primary wetland functions occur (i.e.
denitrification, sedimentation, filtration, adsorption, etc.)denitrification, sedimentation, filtration, adsorption, etc.) Water velocity decreases dramatically here, thus causing Water velocity decreases dramatically here, thus causing
pollutants to settle out of stormwaterpollutants to settle out of stormwater Area where majority of wetland vegetation growsArea where majority of wetland vegetation grows Designed to be a long, winding flowpath occupying Designed to be a long, winding flowpath occupying
approximately 35% of total wetland areaapproximately 35% of total wetland area During low flow conditions, this is path the water takes During low flow conditions, this is path the water takes
through the wetlandthrough the wetland
Shallow Pool Ref: Bill Hunt
DEEP POOLSDEEP POOLS Typically 9-18” deepTypically 9-18” deep Designed to occupy approximately 35% of total wetland Designed to occupy approximately 35% of total wetland
areaarea Contains water in times of droughtContains water in times of drought Where animal habitats (i.e. fish) are locatedWhere animal habitats (i.e. fish) are located Area with least amount of vegetationArea with least amount of vegetation
Deep Pool Ref: Bill Hunt
SHALLOW LANDSHALLOW LAND Designed to be dry except during storm eventsDesigned to be dry except during storm events 0-12” above normal pool0-12” above normal pool Supports a wide variety of vegetationSupports a wide variety of vegetation Designed to occupy approximately 30% of the total Designed to occupy approximately 30% of the total
wetland areawetland area Supports various types of wildlifeSupports various types of wildlife
Shallow Land Ref: Bill Hunt
STORMWATER WETLAND OUTLET STORMWATER WETLAND OUTLET STRUCTURESTRUCTURE
Designed to store the 1” Designed to store the 1” storm runoff volumestorm runoff volume
Contains siphon/drawdown Contains siphon/drawdown device designed to device designed to drawdown the 1” storm drawdown the 1” storm volume over 2 to 5 daysvolume over 2 to 5 days
Passes higher flows (i.e. Passes higher flows (i.e. 100-year storm) during 100-year storm) during extreme storm events extreme storm events safely through the wetlandsafely through the wetland
Typically riser-barrels or Typically riser-barrels or weir overflow structuresweir overflow structures
STORMWATER WETLAND VEGETATION STORMWATER WETLAND VEGETATION GUIDELINESGUIDELINES
Avoid non-native species or aggressive plantsAvoid non-native species or aggressive plants Select plants that can adapt in saturated Select plants that can adapt in saturated
conditions and withstand long term inundationconditions and withstand long term inundation Include species that are evergreen (meaning not Include species that are evergreen (meaning not
dormant during winter time)dormant during winter time) Can use donor soils (if necessary) from natural Can use donor soils (if necessary) from natural
wetlands to establish vegetationwetlands to establish vegetation
BLACK WILLOW
RICE CUT GRASS
SMARTWEED
Ref: US EPA & Bill Hunt
MAINTENANCE OF STORMWATER WETLANDSMAINTENANCE OF STORMWATER WETLANDS Stormwater wetlands should be Stormwater wetlands should be
inspected after each rainfall inspected after each rainfall eventevent
Check for clogging of the outlet Check for clogging of the outlet structure, or too rapid of a structure, or too rapid of a drawdown drawdown
Erosion/scour of wetland Erosion/scour of wetland embankmentsembankments
Erosion in areas where the Erosion in areas where the stormwater runoff enters the stormwater runoff enters the wetland (i.e. storm drainage wetland (i.e. storm drainage pipes, etc.)pipes, etc.)
Sediment accumulation in the Sediment accumulation in the forebay forebay
Condition of outlet structureCondition of outlet structure Prevention of woody vegetation Prevention of woody vegetation
on the wetland bermon the wetland berm Any additional Any additional
fertilizing/seeding to maintain fertilizing/seeding to maintain healthy vegetation healthy vegetation Ref: NCDENR
QUESTIONS?QUESTIONS?
PRACTICAL STORMWATER WETLANDS PRACTICAL STORMWATER WETLANDS DESIGN EXAMPLEDESIGN EXAMPLE
Development RequirementsDevelopment Requirements Example Project: Residential development consisting of mult-Example Project: Residential development consisting of mult-
family townhomes, associated streets, parking, and sidewalksfamily townhomes, associated streets, parking, and sidewalks
Detention of 2- & 10-year post-development peak flowrates back Detention of 2- & 10-year post-development peak flowrates back to pre-development levelsto pre-development levels
Reduction of nitrogen loading rate down to at least 6 lbs/ac/yr Reduction of nitrogen loading rate down to at least 6 lbs/ac/yr (must then buydown to 3.6 lbs/ac/yr)(must then buydown to 3.6 lbs/ac/yr)
Removal of 85% of the total suspended solids from the stormwater Removal of 85% of the total suspended solids from the stormwater runoff resulting from the developmentrunoff resulting from the development
Safe passage of the 100-year storm event through the wetlandSafe passage of the 100-year storm event through the wetland
EXAMPLE STORMWATER WETLANDS EXAMPLE STORMWATER WETLANDS DESIGN DESIGN (CONTINUED)(CONTINUED)
STEP #1STEP #1- Determine the stormwater wetlands drainage area- Determine the stormwater wetlands drainage area
EXAMPLE STORMWATER WETLANDS EXAMPLE STORMWATER WETLANDS DESIGN DESIGN (CONTINUED)(CONTINUED)
Watershed CharacteristicsWatershed CharacteristicsPRE-DEVELOPMENTPRE-DEVELOPMENT
- Total Drainage Area = 12.27 acres- Total Drainage Area = 12.27 acres
- SCS Curve Number = 72 (Hydrologic soil - SCS Curve Number = 72 (Hydrologic soil
group C)group C)
- Pre-development time of concentration = - Pre-development time of concentration =
10.5 minutes10.5 minutes
- 2-Year pre-development peak flowrate = 20 cfs - 2-Year pre-development peak flowrate = 20 cfs
- 10-Year pre-development peak flowrate = 39 cfs- 10-Year pre-development peak flowrate = 39 cfs
POST-DEVELOPMENTPOST-DEVELOPMENT
- Total Drainage Area = 11.22 acres- Total Drainage Area = 11.22 acres
- SCS Curve Number = 78 (Hydrologic soil group C)- SCS Curve Number = 78 (Hydrologic soil group C)
- Post-development time of concentration = 5 - Post-development time of concentration = 5
minutesminutes
EXAMPLE STORMWATER WETLANDS EXAMPLE STORMWATER WETLANDS DESIGN DESIGN (CONTINUED)(CONTINUED)
CALCULATION OF 1” STORM RUNOFF VOLUMECALCULATION OF 1” STORM RUNOFF VOLUME-- Precipitation amount = 1”Precipitation amount = 1”- Directly connected impervious area = 5.67 acres (CN = 98)Directly connected impervious area = 5.67 acres (CN = 98)
101000
CN
ityorageCapacUltimateSt
1098
1000ityorageCapacUltimateSt
204.0ityorageCapacUltimateSt
)8.0(
)2.0( 2
SP
SPmeRunoffVolu
)204.0*8.0"1(
)204.0*2.0"1( 2
meRunoffVolu
meRunoffVolu 0.79 inches = 16,279 cubic feet
EXAMPLE STORMWATER WETLANDS EXAMPLE STORMWATER WETLANDS DESIGN DESIGN (CONTINUED)(CONTINUED)
Other non-connected area = 5.55 acres (CN=74)Other non-connected area = 5.55 acres (CN=74)
101000
CN
ityorageCapacUltimateSt
1074
1000ityorageCapacUltimateSt
51.3ityorageCapacUltimateSt
)8.0(
)2.0( 2
SP
SPmeRunoffVolu
)51.3*8.0"1(
)51.3*2.0"1( 2
meRunoffVolu
meRunoffVolu 0.023 inches = 467 cubic feet
EXAMPLE STORMWATER WETLANDS EXAMPLE STORMWATER WETLANDS DESIGN DESIGN (CONTINUED)(CONTINUED)
Total Runoff from 1” storm = 16,279 cubic Total Runoff from 1” storm = 16,279 cubic feet + 467 cubic feetfeet + 467 cubic feet
Total Runoff from 1” storm = 16,746 cubic Total Runoff from 1” storm = 16,746 cubic feetfeet
This volume must be stored on top of the This volume must be stored on top of the permanent pool, and should be drawn permanent pool, and should be drawn down over a period of 2 to 5 daysdown over a period of 2 to 5 days
EXAMPLE STORMWATER WETLANDS EXAMPLE STORMWATER WETLANDS DESIGN DESIGN (CONTINUED)(CONTINUED)
CALCULATION OF WETLANDS SURFACE AREACALCULATION OF WETLANDS SURFACE AREA Total Impervious Area = 5.67 acresTotal Impervious Area = 5.67 acres Total Drainage Area = 11.22 acresTotal Drainage Area = 11.22 acres % Impervious = 51%% Impervious = 51% Assumed average depth = 3.00 feetAssumed average depth = 3.00 feet Using table below, required wetlands surface area = 10,157 Using table below, required wetlands surface area = 10,157
square feet (interpolation required)square feet (interpolation required)
EXAMPLE STORMWATER WETLANDS EXAMPLE STORMWATER WETLANDS DESIGN DESIGN (CONTINUED)(CONTINUED)
PREPARE STORMWATER WETLANDS GRADING PLANPREPARE STORMWATER WETLANDS GRADING PLAN
EXAMPLE STORMWATER WETLANDS EXAMPLE STORMWATER WETLANDS DESIGN DESIGN (CONTINUED)(CONTINUED)
Specify stormwater wetlands vegetation planting planSpecify stormwater wetlands vegetation planting plan
REFERENCESREFERENCES
Doll, Barbara A; Hunt, William F. Doll, Barbara A; Hunt, William F. Urban Waterways: Urban Waterways: Designing Stormwater Wetlands for Small Watersheds.Designing Stormwater Wetlands for Small Watersheds.
North Carolina Cooperative Extension Service.North Carolina Cooperative Extension Service. USEPA.USEPA. EPA Stormwater Technology Fact Sheet: EPA Stormwater Technology Fact Sheet:
Stormwater WetlandsStormwater Wetlands. EPA 832-F-99-025, September 1999.. EPA 832-F-99-025, September 1999. Harris County Texas Stormwater BMP Manual. Harris County Texas Stormwater BMP Manual.
“Constructed Wetlands for Stormwater Treatment”. 2001 “Constructed Wetlands for Stormwater Treatment”. 2001 Edition.Edition.
NCDENR Division of Water Quality. NCDENR Division of Water Quality. Stormwater Best Stormwater Best Management Practices.Management Practices. April 1999 Edition. April 1999 Edition.