Pinellas County Stormwater Management Manual Training Workshop. Overview of Stormwater BMPs in the Pinellas County Stormwater Manual Part 1

Transcription

1 Pinellas County Stormwater Management Manual Training Workshop Overview of Stormwater BMPs in the Pinellas County Stormwater Manual Part 1

2 Presentation Outline 1. The stormwater management issue 2. 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)

3 Resulting in: Decreased recharge Increased speed of runoff Increased volume of runoff Increased pollutants 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

4 Hydrologic Changes Associated With Urbanization

5 Big Messy Problem Common Pollutants Sediments Oxygen demanding substances Nutrients Pathogenic bacteria Heavy metals Oil & grease, hydrocarbons Fresh water

6 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

7 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: bs.htm#urban_stormwater_bmp_research_ Reports m

8 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

9 Table Pinellas County Manual EMCs Stormwater Event Mean Concentrations Current BMPTRAINS EMCs Minor differences in EMCs for LDR do to difference in EMCs for Natural Vegetative Communities

10 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

11 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

12 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 always promoted retention BMPs

13 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

14 Low Impact Design Projects in Florida Madera, Gainesville Baldwin Park, Orlando Town of Harmony River Forest, Bradenton

15 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

16 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

17 Chapter 1: Introduction Chapter 2: Site Planning Chapter 3: County Stormwater Requirements Chapter 4: Stormwater Quantity Chapter 5: Stormwater Quality Chapter 6: Stormwater BMPs Appendices Increases the number and types of stormwater BMPs available to site designers

18 Pinellas County Stormwater Manual Any development or redevelopment activity that generates stormwater from impervious surfaces must meet Manual s requirements Exemptions in Section Waivers and adjustments for sites 1 acre or less if it is technically infeasible to meet performance standards Minimum treatment is postdevelopment load < pre-development

19 What Level of Stormwater Treatment? 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%).

20 Site Planning and Source Control BMPs In Pinellas County Manual Site Planning BMPs BMP Name Treatment Credit Source Control BMPs BMP Name Treatment Credit SP1 SP2 SP3 SP4 SP5 Inventory Site Assets: Hydrology Inventory Site Assets: Topography Inventory Site Assets: Soils Inventory Site Assets: Vegetation Preserve Open Space SP6 Natural Area Conservation SP7 SP8 SP9 SP10 Cluster Design Minimize Fill Material Minimize Building Footprint Minimize Total Impervious Area SP11 Minimize DCIA SP12 Curb Elimination and Cuts SC1 SC2 SC3 SC4 SC5 SC6 SC7 SC9 SC10 Protect Surface Waters & Wetlands Use Selective Site Clearing and Grading Retain depression storage Minimize Soil Disturbance and Compaction Build with Slope Retain Native Plants Use Florida-friendly Landscaping and Fertilizers Rainfall Interception Trees - See BMP 6.15 Efficient Irrigation Non-potable Water Irrigation Community and Homeowner

21 Structural BMPs In Pinellas County Manual Stormwater Treatment 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

22 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*

23 NATURAL AREA CONSERVATION Credit for preserving natural areas

24 The Stormwater Benefits Of Trees Planting trees in urban areas intercepts and evaporates rain and reduces stormwater volume and loads Interceptor Trees BMP Up to 18% reduction in stormwater volume NEED MORE DATA AND SITES!

25 Biological Pollutant Removal Plant / Soil Flora / Soil Chemistry Phytoremediation Translocate Accumulate Metabolize Volatilize Detoxify Degrade Bioremediation

26 Trees Are Stormwater BMPs! Urban Ecosystem Analysis, Jacskonville American Forests (

27 I-TREE TOOLS

28 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

29 Reducing Imperviousness In Parking Lots Nonstructural tools Reduce required parking spaces Reduce parking space size Use one way angled parking Structural tools Use pervious pavements for parking Pervious concrete Turf block/pavers Geoweb and sod BUT, THIS MAY REQUIRE CODE OR CULTURAL CHANGE

30 THE INFLUENCE OF DCIA ON STORMWATER VOLUME Zone 4 Mean Annual Runoff Coefficients (C Values) as a Function Of DCIA Percentage and Non-DCIA Curve Number (CN) 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

31 Reducing Parking Lot Imperviousness And DCIA

32 Disconnecting Directly Connected Impervious Areas (DCIA)

33 RECESSED ROAD MEDIANS AS BMPs

34 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

35 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

36 Land Clearing, Vegetation Removal And Soil Compaction 80% compaction on first pass of equipment

37 Soil Compaction And Infiltration Rates SOIL TYPE INFILTRATION RATE (in/hr) Pitt et. al. Gregory Sandy soils Compacted sandy soils Clay soils 9.8 NA Compacted or wet clay soils 0.2 NA Source: Pitt, Chen, and Clark, 2001; Gregory, 2006

38 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

39 Use Florida-friendly Fertilizers Get 3% Load Reduction Credit Follow 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

40 PET WASTE: A Major Source Of Nutrients And Bacteria Pollutants Pets deposit up to 0.5 lbs/day of pet waste Contributes to bacterial and nutrient pollution 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, ,529,600

41 RAINFALL INTERCEPTOR TREES Interceptor Tree BMP Up to 18% reduction in stormwater volume Interim BMP, Need more data! Use to meet PCSWM Net Improvement

42 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

43 LID BMPs And Getting An Environmental Resource Permit LID BMP Rain garden (bioretention) Swales Vegetated Natural Buffers Pervious pavements Green roof with cistern Rainwater harvesting Stormwater harvesting Biofiltration with BAM SWFWMD ACCEPTABILITY Retention BMP Retention BMP Check with staff Retention BMP Retention and reuse BMP Retention BMP, not rain barrel Check with staff Filtration BMP

44 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

45 Retention BMP Treatment Volume and Load Reduction Effectiveness Required Treatment Volume SWFWMD off-line runoff -- on-line runoff from 1 rain -- OFW - 50% more volume Treatment effectiveness varies from 42.6% to 94%

46 Retention BMP Treatment Volume to get 80% Load Reduction Effectiveness Required Treatment Volume from tables varies from 0.23 to 1.59

47 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

48 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 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 )

49 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.

50 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

51 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

52 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

53 Exfiltration Trench Design Criteria 1. Follow retention BMP requirements 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

54 Exfiltration Trench Pretreatment Details

55 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

56 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

57 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

58 Underground Retention Design Criteria 1. Follow Exfiltration Trench BMP requirements 2. Follow manufacturer s recommendations 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

59 6.13. LID BMP Rain Garden Small retention depressions integrated into the landscaping with deep rooted Florida-friendly vegetation. en_design/whatisaraingarden.htm

60 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

61 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

62 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

63 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

64 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

65 5.8 LID BMP Vegetated Natural Buffers

66 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

67 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

68 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 hrs

69 5.7 LID BMP - Swale Chapter (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

70 Use of Swales Types: Linear retention treatment swale Conveyance swales Uses: 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

71 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

72 Conveyance Swale Design

73 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

74 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

75 Pinellas County Stormwater Management Manual Training Workshop Questions, Remarks, and Discussion Break is next