Overview of Stormwater BMPs in the
Pinellas County Stormwater Manual
Part 1
Pinellas County Stormwater Management Manual Training
Workshop
Presentation Outline
1. The stormwater management issue2. What is Low Impact Design?3. What are Low Impact Design BMPs?4. Pinellas County Stormwater Manual BMPs
– purpose, design criteria, construction, inspection, maintenance (Part 1)
The Stormwater Problem
Humans cause:
• Changes in land use, clearing of land
• Compaction of soil, imperviousness
• Development in floodplains, wetlands
• Alteration of natural stormwater systems
• Addition of “drainage” systems
• Addition of pollutants
Resulting in:
• Decreased recharge
• Increased speed of runoff
• Increased volume of runoff
• Increased pollutants
Hydrologic
Changes
Associated With
Urbanization
Big
Messy
ProblemCommon Pollutants
• Sediments
• Oxygen demanding substances
• Nutrients
• Pathogenic bacteria
• Heavy metals
• Oil & grease, hydrocarbons
• Fresh water
Best Management Practices (BMPs)
• Control techniques used for a given set
of conditions to manage stormwater
quantity and quality in the most cost
effective manner.
• Stormwater treatment began in 1982,
still a young field
• Florida’s ERP handbooks only include
traditional BMPs – retention basins, wet
detention ponds, sand filters
Evolution of Stormwater BMPs
• Florida based research and field monitoring
• Sponsored by DEP, FDOT, WMDs, local governments
• Focus on traditional and innovative BMPs
• Results online:
• http://www.dep.state.fl.us/water/nonpoint/pubs.htm#Urban_Stormwater_BMP_Research_Reports
• https://stormwater.ucf.edu/
• http://www.fdot.gov/research/documents.shtm
Pollutant Load =
(Concentration) * (Volume)
Stormwater volume factors:
• Rainfall variables include when, where, how long, how intense,
time between storms
• Natural stormwater variables include soils, geology, SHWT, topography, vegetation
• Human stormwater variables
include land use, site design, soil compaction, percent imperviousness, % DCIA
Stormwater
Event Mean ConcentrationsTable 5.2.3. Pinellas County Manual EMCs
Current BMPTRAINS EMCs
Minor differences in EMCs
for LDR do to difference in
EMCs for Natural
Vegetative Communities
How Do We Reduce
Stormwater Loading?
• Reduce stormwater pollutant concentrations
• Reduce stormwater volume
• Better site design – integrate stormwater into site, treat stormwater as water resource
• Use BMP Treatment Train with nonstructural and structural stormwater BMPs
• Minimize imperviousness, especially DCIA
• Reduce pollutants using source controls including public education
What Is Low Impact Development?
• Comprehensive watershed approach
• Hydrology is integrating framework
• Maintain predevelopment volume and hydrology
• Control stormwater at the source
• Combine nonstructural pollution prevention BMPs with structural BMPs
• Create multifunctional landscape and infrastructure
Pollution and Hydrologic Prevention
What Low Impact Development is Not
LID is NOT a silver bullet solution to all stormwater problems
• Additional nonstructural and structural tools in the BMP tool box
• Infiltration BMPs do not work everywhere
LID is NOT a new idea• “Designing with Nature”
1969 book by Ian McHarg
• FL stormwater program has alwayspromoted retention BMPs
Why Low Impact Design?
Added BMPs In Tool Box
• Promote development and redevelopment
through greater flexibility
• Build local economy and promote “urban
regeneration”
• Get higher levels of stormwater treatment
• Keep loads out of MS4
• Protect local taxpayers and water bodies
City of Palmetto
Urban regeneration project
Low Impact Design Projects in Florida
Madera,
Gainesville
River Forest,
Bradenton
Baldwin Park,
OrlandoTown of
Harmony
LID Site Planning Principles To Reduce
Stormwater Volume/Loads
• Consider stormwater as a resource
• Protect/avoid sensitive areas
• Minimize disturbed areas / soil compaction
• Minimize loss of vegetation and trees
• Plant more trees – intercept rainfall
• Florida-friendly landscaping
• Maximize infiltration/stormwater harvesting
• Minimize imperviousness, especially DCIA
• Integrate stormwater BMPs into landscaping
• Cluster development, increase open space
• Use innovative planning tools such as those coming in Pinellas County Code revisions
Source Controls For
Pollution Prevention• Minimize clearing, removal of trees, vegetation
• Include urban reforestation
• Minimize imperviousness, esp. DCIA
▪ Minimize soil compaction
▪ Narrow streets, pervious parking, recessed
tree islands
▪ Greenroof/cistern systems for large roofs
▪ Roof runoff to cisterns, pervious areas
• Minimize pollutants
▪ Florida-friendly landscaping design
▪ Florida-friendly fertilizers
▪ Proper use of reclaimed water
▪ Pet waste pick up and disposal
Chapter 1: IntroductionChapter 2: Site PlanningChapter 3: County Stormwater RequirementsChapter 4: Stormwater QuantityChapter 5: Stormwater QualityChapter 6: Stormwater BMPsAppendices
Increases the
number and types
of stormwater
BMPs available to
site designers
Pinellas County Stormwater Manual
• Any development or redevelopmentactivity that generates stormwater from impervious surfaces must meet Manual’s requirements
• Exemptions in Section 3.5.1
• Waivers and adjustments for sites 1 acre or less if it is technically infeasible to meet performance standards
• Minimum treatment is post-development load < pre-development
What Level of Stormwater Treatment?5.1.1. General Performance Standards
Except for exempt projects meeting the criteria in Subsection 3.5.1, the stormwater treatment system shall be designed to achieve the highest level of pollutant removal of the following performance standards:
1. Reduce the post-development annual average stormwater total nitrogen load by at least a 55% and the annual average stormwater total phosphorus load by at least 80%, OR
2. Reduce the post-development annual average stormwater total nitrogen and phosphorus loads to a level less than or equal to 90% of the loads currently discharged from the site. (Net improvement = pre-development load – 10%).
Site Planning and Source Control BMPs In
Pinellas County Manual
Site PlanningBMPs
BMP Name TreatmentCredit
SP1 Inventory Site Assets: Hydrology
SP2 Inventory Site Assets: Topography
SP3 Inventory Site Assets: Soils
SP4 Inventory Site Assets: Vegetation
SP5 Preserve Open Space
SP6 Natural Area Conservation ✔️
SP7 Cluster Design
SP8 Minimize Fill Material
SP9 Minimize Building Footprint
SP10 Minimize Total Impervious Area
✔️
SP11 Minimize DCIA ✔️
SP12 Curb Elimination and Cuts
Source Control BMPs
BMP Name Treatment Credit
SC1 Protect Surface Waters & Wetlands
SC2 Use Selective Site Clearing and Grading
SC3 Retain depression storage
SC4 Minimize Soil Disturbance and Compaction
SC5 Build with Slope
SC6 Retain Native Plants
SC7 Use Florida-friendly Landscaping and Fertilizers
✔️
Rainfall Interception Trees -See BMP 6.15
✔️
SC9 Efficient Irrigation
SC10 Non-potable Water Irrigation
SC11 Community and Homeowner Education
Structural BMPs In Pinellas County ManualStormwaterTreatment BMPs
BMP Name Treatment Credit
6.1 Retention Basin ✔️
6.2 Exfiltration Trench ✔️
6.3 Underground Storage and Retention ✔️
6.4 Treatment Swales ✔️
6.5 Vegetated Natural Buffers ✔️
6.6 Pervious Pavement ✔️
6.7 Green Roof with Cistern ✔️
6.8 Wet Detention ✔️
6.9 Stormwater Harvesting ✔️
6.10 Up-Flow Filter ✔️
6.11 Managed Aquatic Plants (MAPS) ✔️
6.12 Biofiltration with BAM ✔️
6.13 Rain Gardens ✔️
6.14 Rainwater Harvesting ✔️
6.15 Rainfall Interceptor Trees ✔️
Improved Site Planning BMPs
SP5 - Preserve Open Space
SP6 – Natural Area Conservation,
retain tree canopy
SP7 - Cluster development*
SP9 - Minimize building footprint*
SP10 - Minimize total imperviousness*
SP11 - Minimize DCIA*
SP12 - Curb elimination & curb cuts*
NATURAL AREA CONSERVATION
• Credit for preserving natural areas
Planting trees in urban
areas intercepts and
evaporates rain and
reduces stormwater
volume and loads
The Stormwater Benefits Of Trees
Interceptor Trees
BMP 6.15.3
Up to 18% reduction in
stormwater volume
NEED MORE DATA
AND SITES!
Biological Pollutant Removal
Plant / Soil Flora / Soil Chemistry
• Phytoremediation
– Translocate
– Accumulate
– Metabolize
– Volatilize
– Detoxify
– Degrade
• Bioremediation
Trees Are Stormwater BMPs!
Urban Ecosystem Analysis, Jacskonville
• American Forests (www.americanforests.org)
I-TREE TOOLS
http://www.itreetools.org/
Using Low Impact Development
To Reduce Imperviousness
• Cluster development
• Tailor and decrease road width
• Minimize road length
• Use pervious pavements for parking
• Reduce required parking spaces
• Reduce parking space size
• Use one way angled parking
• Minimize paved driveways/size
• Side walks on one side only
Requires Land Development Code revisions
Currently underway
Reducing Imperviousness
In Parking Lots
Nonstructural tools• Reduce required parking spaces • Reduce parking space size• Use one way angled parking
BUT, THIS MAY REQUIRE CODE OR
CULTURAL CHANGE
Structural tools• Use pervious pavements for parking
▪ Pervious concrete▪ Turf block/pavers▪ Geoweb and sod
THE INFLUENCE OF DCIA
ON STORMWATER VOLUME
Agriculture land use (pasture)
No DCIA, CN for D soils = 90 C = .266
SF residential land use
¼ acre lots - DCIA = 40%, CN for lawns, D soils = 90 C = .489
Zone 4
Mean Annual Runoff Coefficients (C Values) as a Function
Of DCIA Percentage and Non-DCIA Curve Number (CN)
Reducing Parking Lot
Imperviousness And DCIA
Disconnecting Directly Connected Impervious
Areas (DCIA)
RECESSED ROAD MEDIANS AS BMPs
Source Control BMPs
SC1 – Protect waters/wetlands
SC2 - Retain depression storage
SC3 – Selective clearing/grading
SC4 - Minimize compaction
SC5 - Build with slope
SC6 - Retain native plants
SC7 - Florida-friendly landscape*
SC8 - Rainfall interception trees*
SC9 - Install efficient irrigation
SC10 - Harvest and use stormwater*
SC11 - Public education
Source Controls For
Pollution Prevention
• Minimize clearing, removal of trees, vegetation
• Include urban reforestation
• Minimize imperviousness, esp. DCIA
▪ Minimize soil compaction
▪ Narrow streets, pervious parking, recessed tree
islands
▪ Greenroof/cistern systems for large roofs
▪ Roof runoff to cisterns, pervious areas
• Minimize pollutants
▪ Florida-friendly landscaping design
▪ Florida-friendly fertilizers
▪ Proper use of reclaimed water
▪ Pet waste pick up and disposal
Land Clearing, Vegetation Removal
And Soil Compaction
80% compaction on first
pass of equipment
Soil Compaction And Infiltration Rates
SOIL TYPE INFILTRATION RATE
(in/hr)
Pitt et. al. Gregory
Sandy soils 13.0 14.8 – 25
Compacted sandy soils 1.4 0.3 - 6.9
Clay soils 9.8 NA
Compacted or wet clay
soils
0.2 NA
Source: Pitt, Chen, and Clark, 2001; Gregory, 2006
Florida-friendly
Landscaping Principles
1. Right plant, right place
2. Water efficiently, use
stormwater
3. Fertilize properly
4. Mulch
5. Attract wildlife
6. Manage yard pests properly
7. Recycle clippings and leaves
8. Reduce runoff
9. Protect the waterfront
http://www.floridayards.org
Use Florida-friendly Fertilizers
Get 3% Load Reduction CreditFollow requirements in Pinellas County Landscape Maintenance and Fertilizer Use and Application Ordinance (2010):
• Only apply Oct 1 to May 31
• No phosphorus unless soil test need
• Granular must be 50% slow release
• Liquid app rate < 0.5 lbs N/1000 sf
• Spring app rate = 2 lbs N/1000 sf
• Winter app rate = 1 lb N/1000 sf
• Annual app rate = 4 lbs N/1000 sf
• Commercial fertilizer applicators and landscape maintenance professionals must be certified
PET WASTE: A Major Source Of
Nutrients And Bacteria Pollutants
Animal Average fecal
coliform per
gram of feces
Fecal coliform
load per day
Human 13,000,000 1,921,920,000
Dog 23,000,000 7,728,000,000
Cow 230,000 5,358,080,000
Horse 12,600 293,529,600
• Pets deposit up to 0.5 lbs/day of pet waste
• Contributes to bacterial and nutrient
pollution
RAINFALL INTERCEPTOR TREES
Interceptor Tree BMP
Up to 18% reduction in
stormwater volume
Interim BMP, Need more data!
Use to meet PCSWM Net Improvement
Structural BMPs in Pinellas County
Stormwater Manual
Retention BMPs
• Basins
• Exfiltration trenches
• Underground retention storage
• Swales
• Vegetated natural buffers
• Rain gardens
• Pervious pavements
Harvest & Reuse BMPs
• Greenroof/cistern
• Rainwater harvesting
• Wet detention
• Stormwater harvesting
Filtration BMPs
• Managed aquatic plants
• Upflow filters
• Biofiltration with BAM
LID BMPs And Getting An Environmental
Resource Permit
LID BMP SWFWMD ACCEPTABILITY
Rain garden (bioretention) Retention BMP
Swales Retention BMP
Vegetated Natural Buffers Check with staff
Pervious pavements Retention BMP
Green roof with cistern Retention and reuse BMP
Rainwater harvesting Retention BMP, not rain barrel
Stormwater harvesting Check with staff
Biofiltration with BAM Filtration BMP
6.1. Retention (Infiltration) Practices
DESCRIPTION: Family of practices where the stormwater is infiltrated or evaporated rather than discharged.
PURPOSE:• Reduce total volume
• Reduce pollutants
POLLUTANT REMOVAL:• Percolation, evaporation
• Filtering and adsorption
• Effectiveness = % annual runoff retained
Retention BMP Treatment Volume and
Load Reduction Effectiveness
Required Treatment VolumeSWFWMD – off-line - 0.5” runoff
-- on-line – runoff from 1” rain-- OFW - 50% more volume
Treatment effectiveness varies from 42.6% to 94%
Retention BMP Treatment Volume to get
80% Load Reduction Effectiveness
Required Treatment Volume from tables
varies from 0.23” to 1.59”
Getting Good Infiltration Data for
Retention BMP Design
• See Appendix A of Manual
• Measure at proposed bottom elevation
• Allowable data
▪ Mass balance field data
▪ Double ring infiltrometer *
▪ Lab permeability tests *
▪ NRCS soil survey - planning only
* Use half of the value
Retention BMP Design Criteria
• Determine Required Treatment Volume from Tables based on required % load reduction
• Ensure both RTV and flood control volumes can be stored safely
• Recover RTV within 24-36 hrs if vegetated• SHGWT at least 2’ beneath bottom of retention
BMP, must consider mounding• Sides and bottom must be stabilized by
Florida-friendly vegetation, other pervious materials or as approved
• Do not construct within 50 feet of potable well or within 15 feet of OSTDS (Note: setback to private potable well is 75’)
Retention BMP Construction
• Locate and mark locations of all retention BMPs
• Prevent traffic and equipment from entering to
minimize soil compaction
• Excavate with lightweight equipment with tracks
not tires
• Initially excavate to within 12” of design bottom
• Do not use for erosion/sediment control during
construction
• Once drainage area stabilized, remove
accumulated materials and excavate to final
bottom elevation. Deep rake or till the bottom to
compensate for compaction.
• Vegetate and landscape per plans.
Retention BMP Maintenance Inspection
• Standing water or soggy soils,
cattails
• Erosion and sedimentation
• Vegetation - coverage, growth,
type
• Soil compaction or smearing
• Pretreatment BMPs
• Contributing area stabilization
• Inlets, discharge – sediment,
litter, debris, vegetation
Retention BMP Maintenance Activities
Objective – maintain or restore percolation rate
• Remove accumulated solids
• Mowing and removal of vegetation
• Repair erosion, vegetative stabilization
• Tilling, disking, aerating the bottom
• Check structures
• Clear debris from structures
• Clean pretreatment BMPs
6.2. Exfiltration Trench
DESCRIPTION: An underground retention system consisting of an inlet and perforated pipe within a gravel envelope where the stormwater is infiltrated rather than discharged.
PURPOSE:• Reduce total volume
• Reduce pollutants
POLLUTANT REMOVAL:• Percolation, evaporation
• Filtering and adsorption
• Effectiveness = % annual runoff retained
Exfiltration Trench Design Criteria
1. Follow retention BMP requirements
2. 12” minimum perforated pipe diameter with
minimum of 3’ of trench
3. Pipe not exceed 45º bend
4. Aggregate must be washed to remove fines
5. Trench enclosed within filter fabric
6. Must have OM access via manhole, inspection
ports, or observation wells
7. Pretreatment baffle trash tee at inflow and 24”
sump with 12” weep hole
Exfiltration Trench Pretreatment Details
Exfiltration Trench Construction
Recommendations
• Follow retention BMP recommendations
• Minimize soil and debris entry into trench
• Excavate with backhoe to minimize soil
compaction
• Inspect trench bottom and sides to remove
tree roots and other items that tear fabric
• Inspect aggregate to ensure size and
washed
• Block inflows to trench until contributing
area is stabilized
Exfiltration Trench Maintenance Activities
Objective – maintain or restore percolation rate
• Inspect and monitor sediment accumulation in
pipe and storage volume recovery
• Inspect pre-treatment BMPs and clean as needed
• Check structures and clear debris from
structures
• If needed, remove sediment from pipe by
suctioning or high pressure jet washing
• If clogged, total replacement may be required
6.3. Underground Storage and Retention System
DESCRIPTION: An underground retention system consisting of an inlet and modular storage units with an open bottom allowing the stormwater to be infiltrated rather than discharged.
PURPOSE:• Reduce total volume
• Reduce pollutants
POLLUTANT REMOVAL:• Percolation, evaporation
• Filtering and adsorption
• Effectiveness = % annual runoff retained
Underground Retention Design Criteria
1. Follow Exfiltration Trench BMP requirements
2. Follow manufacturer’s recommendations
3. 12” minimum perforated pipe diameter with
minimum of 3’ of trench
4. Pipe not exceed 45º bend
5. Aggregate must be washed to remove finesds
6. Trench enclosed within filter fabric
7. Must have OM access via manhole, inspection
ports, or observation wells
8. Pretreatment baffle trash tee at inflow and 24”
sump with 12” weep hole
6.13. LID BMP Rain Garden
• Small retention depressions integrated
into the landscaping with deep rooted
Florida-friendly vegetation.
• http://lowimpactdevelopment.org/raingard
en_design/whatisaraingarden.htm
Rain Garden Design Criteria
• Contributing DA <3 acres
• Ponding depth – 4 to 10 inches
• Location – sunny, on slopes <10%, at
least 10’ from buildings
• Vegetation – See table of plants. Depends
on planting zones, dry to wet zones, need
a good plan
• Mulch – use materials that won’t float
Rain Garden Design Considerations
• Contributing DA (<3 acres)
• Ponding depth (4 to 10 inches)
• Retention or detention system?
• BAM used? If yes, which one and %
removal
• Sustainable void space - .20
• Water above media volume? (ponding d)
• Media volume?
Treatment Volume will
be calculated from
above information
Rain Garden Construction
• Determine final shape and location after locating utilities, mark on ground
• Excavate the garden, use soil for berm
• Prepare and add soil/media mixture (BAM)
• Install plants per the design, 1’ On Center
• Apply mulch (if used)
• Water plants regularly
• Check conveyance inflow,
water storage, and
infiltration rate
Rain Garden Maintenance
• In first year, water and weed regularly
• Inspect at start and end of rainy season
• Check infiltration rate after rainy season
• Each spring, remove dead vegetation
and replenish mulch
• Weed and maintain plants as needed
• Remove sediment, trash, debris
• Repair erosion, as needed
6.5. LID BMP – Vegetated Natural Buffers
• A vegetated area with soil and water
table conditions that allow filtering and
infiltration of overland flows.
• Used to treat rear roof and yard runoff
when impractical to route to main
stormwater system.
• Treatment based on retention volume
that is infiltrated
5.8 LID BMP – Vegetated Natural Buffers
Vegetated Natural Buffers Design Criteria
• Infiltrate required treatment volume
• SHGWT > two feet below bottom
• 1” minimum infiltration rate
• 25’ minimum flow length, = length of CA
• 100’ maximum width
• 6:1 maximum slope
• Legal easement for VNB
Vegetated Natural Buffers Construction
• Verify location and dimensions of VNB
• Install erosion and sediment controls and divert flows until contributing area construction is complete/stabilized
• Mark VNB boundaries to prevent compaction from equipment
• Install upstream level spreader
• Ensure vegetation is healthy, add Florida-friendly plants as needed
Vegetated Natural Buffers
Inspection and Maintenance
• Inspect during or soon after a storm to visually check sheet flow and flow paths
• Eliminate channelized flow areas and restore vegetation, if needed
• Eliminate erosion, remove sediment, restore vegetation, as needed
• Identify damage from vehicles, foot traffic, or encroachment
• Ensure infiltration within 24 – 36 hrs
5.7 LID BMP - Swale
Chapter 403.803 (14), Florida Statutes
A manmade trench which:
• Has a top width-to-depth ratio of 6:1 or greater
• Has areas of standing or flowing water only
after a rain
• Is planted with vegetation suitable for soil
stabilization, stormwater treatment, nutrient uptake
• Designed for soil erodibility, soil percolation, slope,
slope length, and the drainage area
• Designed to prevent erosion and reduce pollutants
Use of Swales
Types:• Linear retention treatment swale• Conveyance swalesUses:• Along streets, rural road sections• Residential subdivisions• Pretreatment (BMP Treatment
Train)▪ Any land use type, parking lots▪ Before infiltration trenches,
wet ponds• With enhancements
▪ Swale blocks▪ Shallow longitudinal slopes
(settling)▪ Raised driveway culverts
Swale Design Criteria
OBJECTIVES
• Conveyance and Water quality
DESIGN CONSIDERATIONS• Depends on type of swale
• Soil infiltration - HSG A,B soils
• Pavement edge protection
• Slope - flat as possible
• Cross-section - triangular, trapezoidal
• Side slopes - 3:1 or flatter
• Bottom width – usually at least 2 feet
• Vegetation - lawn grasses, native grasses, wildflowers, shrubs
Conveyance Swale Design
Swale Construction
• Verify location and prevent equipment
• Minimize soil compaction
• Construct first, mulch and establish vegetation
• Divert flows until DA stabilized
• Stabilization recommendations
▪ 0 - 4% Seed with erosion blanket
▪ 4 - 8% Staked sod
▪ >8% Staked sod, swale blocks
• Do not use muck grown sod
Swale Inspection and Maintenance
Inspection
• Check treatment volume recovery time and
percolation rates; check for standing water
• Monitor erosion and sediment accumulations
• Check vegetation cover and health
• Check flow path for obstructions, damage
Maintenance
• Restore percolation rate if needed
• Remove trash, debris, sediments
• Maintain healthy vegetative cover
• Mowing – as needed, keep grass 3 - 5” long
• Repair any erosion
• Disk, till, or aerate bottom if needed
• Maintain swale blocks, outlets, and pavement
Break is next
Questions, Remarks, and Discussion
Pinellas County
Stormwater Management
Manual Training
Workshop