Charles County, MD Low Impact Development (LID)/ Environmental Site Design (ESD) Ordinance & Design Manual

Charles County, MD Low Impact Development (LID)/ Environmental Site Design (ESD) Ordinance & Design Manual

Presentation Highlights Background What is LID / ESD? Why adopt LID/ESD MD SWM Act 2007 Planning Process Design Objectives ESD Practices

How we got here Grant award: By the National Fish and Wildlife Foundation Partners: Charles County Government, Town of La Plata, and Town of Indian Head Grant objective: Wide scale implementation of low impact development practices in Charles County. Basis: U.S. Army Corps of Engineers Mattawoman Creek Watershed Management Plan; Port Tobacco River Watershed Restoration Action Plan; and Maryland Stormwater Management Act of 2007

Final Products Stormwater Management Ordinance Drainage Ordinance Stormwater Management Polices and Procedures Manual LID /ESD Supplement to Design Manual

Timeline Public Kick-off Meeting (January 2009) Focus Groups to Review Discuss Draft (April/May 2009) Informational Notices (June/July 2009) Briefings to Planning Commission and County Commissioners (July/August/September 2009) Submittal to Maryland Department of the Environment for their review (TBD) Public Adoption Process (public meetings and work sessions) Engineer/Inspector Training (at completion)

LID Defined What is LID / ESD? A stormwater management strategy to maintain or restore the natural hydrologic functions of a site to achieve natural resources protection objectives and fulfill environmental regulatory requirements LID employs a variety of natural and built features that reduce the rate of runoff, filter out pollutants, and facilitates the infiltration of water into the ground. LID incorporates a set of overall site design strategies as well as highly localized, small-scale scale decentralized source control techniques known as Integrated Management Practices (IMPs( IMPs) IMPs may be integrated into buildings, infrastructure, or landscape features.

Bottom Line LID and ESD now have pretty much the same meaning in MD The two terms will be used interchangeably in the rest of the presentation

MD SWM Act 2007 Why Adopt LID / ESD? Prevent soil erosion from development projects. Prevent increases in nonpoint pollution. Minimize pollutants in stormwater runoff from both new development and redevelopment. Restore, enhance, and maintain chemical, physical, and biological l integrity of receiving waters to protect public health and enhance domestic, municipal, recreational, industrial and other uses of water as specified s by MDE. Maintain 100% of the average annual predevelopment groundwater recharge volume. Capture and treat stormwater runoff to remove pollutants. Implement a channel protection strategy to protect receiving streams. Prevent increases in the frequency and magnitude of out-of of-bank flooding from large, less frequent storms. Protect public safety through the proper design and operation of stormwater management facilities.

MDE ESD Planning Process Delegated stormwater authorities will be required to use a 3 phase process 1. Concept 2. Site Development Plan 3. Final Must be a coordinated local agency effort & include SCD Planning and zoning Public Works All new developments shall be subject to the design Process for New Developments as outlined in Figure 5.1

Figure 5.1

Concept Design Phase: Site & Resources Mapping

Concept Design Phase: Site & Resources Mapping Site concept plan should identify and avoid impact to existing site environmental resources

Cul-de de-sacs Table 5.2 Better Site Design Technique Using narrower, shorter streets, ROW, sidewalks Open vegetated channels Concept Design Phase: Site Development Strategies Summary of Site Development Strategies Recommendations Street width =22 ft in low traffic volumes Open space design & clustering reduce street length ROW reduced with narrow sidewalks, sidewalks on one side only, reduce border between street & sidewalk Small radii 33 ft Landscape treatment BMP in center (Bioretention) Grass channels, biofilters for SWM Parking ratios, codes, lots Structured parking Parking lot runoff Open space Max parking ratios vs minimum; shared parking; Stall width & length; parking garages Parking lots required to be landscaped & setbacks relaxed to allow for bioretention islands & other SWM practices Flexible design criteria to enable use of clustered developments and conservation design

Table 5.2 Better Site Design Technique Setbacks & frontages Concept Design Phase: Site Development Strategies Summary of Site Development Strategies Recommendations Relax setbacks & allow narrower frontages to reduce total road & driveway length; Driveways Rooftop runoff Buffer systems Clearing & grading Tree conservation Conservation incentives Allow shared driveways & permeable pavements Direct to pervious surfaces, harvest & reuse Designate minimum buffer width & provide mechanism for long term protection Use site fingerprinting to reduce clearing, grading & earth disturbance Provide long-term protection of large tracts of contiguous forested areas; promote use of native plantings Provide incentives for conservation of natural areas through density compensation, property tax reduction, and flexibility in design process

Minimization of Development Impacts: Site fingerprinting Large lots Reduced clearing & grading costs Preserves natural soils & vegetation Vegetative buffer

Design Objectives The criteria for sizing ESD practices are based on capturing and retaining enough rainfall so that the runoff leaving a site is reduced to a level equivalent to a wooded site in good condition as determined using United States Department of Agriculture (USDA) Natural Resource Conservation Service (NRCS) methods (e.g., TR-55). The basic principle is that a reduced runoff curve number (RCN) may be applied to post-development conditions when ESD practices are used. The goal is to provide enough treatment using ESD practices to address channel protection (Cpv) requirements by replicating an RCN for woods in good condition for the 1-year rainfall event. This eliminates the need for structural practices (MDE, Chapter 3). If the design rainfall captured and treated using ESD is short of the target rainfall, a reduced RCN may be applied to post-development conditions when addressing stormwater management requirements. The reduced RCN is calculated by subtracting the runoff treated by ESD practices from the total 1-year 24-hour design storm runoff.

ESD Practices Group 1: Alternative Surfaces A-1 Green Roofs A-2 Permeable Pavements Group 2: Nonstructural Practices N-1 Disconnection of rooftop runoff N-2 Disconnection of non-rooftop runoff N-3 Sheetflow to conservation area Group 3: Micro-scale Practices to Treat Runoff M-1 Rainwater Harvesting M-2 Submerged Gravel wetlands M-3 Landscape Infiltration M-4 Infiltration Berms M-5 Dry wells M-6 Micro-bioretention M-7 Rain gardens M-8 Swales M-9 Enhanced Filters

A-1 1 Green Roofs Also known as vegetated roofs, roof gardens, or eco-roofs. May be used in place of traditional flat or pitched roofs to reduce impervious cover and more closely mimic natural hydrology. Green roofs produce less heat than conventional systems. Therefore, they may be used to help mitigate stormwater impacts and temperature increases caused by new development. There are two basic green roof designs that are distinguished by media thickness and the plant varieties that are used: Extensive Intensive

Extensive Green Roofs Extensive green roofs more common lightweight system media layer is 2-6 inches thick. limits plants to low-growing, hardy herbaceous varieties may be constructed off-site as a modular system with drainage layers, growing media, and plants installed in interlocking grids. Conventional construction methods may also be used to install each component separately Hamilton Apartments Ecoroof - 1999 first large scale stormwater monitoring and education site in USA

A-1 1 Green Roofs Design Considerations Infrastructure Structure Waterprooofing Drainage Conveyance Treatment Landscaping Construction Considerations Waterproofing Slope stabilization Installation Inspection Maintenance

A-2: Permeable Pavements Permeable pavements are alternatives that may be used to reduce imperviousness MDE groups into 3 categories Porous bituminous asphalt Porous concrete Interlocking concrete paving blocks (grid pavers) Benefits Reduce impervious cover Provide water quality and groundwater recharge benefits Mitigate temperature increases

Permeable Pavement Types

MDE: Typical Sections

A-2: Permeable Pavements Design Considerations: Space / Topography / Soils / Drainage area / Hotspot Runoff Structure Conveyance / treatment / landscaping / setbacks Construction Considerations Erosion and sediment control Soil compaction Under-drains drains Inspection Maintenance

Porous Pavement

Permeable Pavement DC Navy Yard Eco-Stone

A-3: Reinforced Turf Reinforced turf consists of interlocking structural units with interstitial areas for placing gravel or growing grass. These systems are suitable for light traffic loads and are commonly used for emergency vehicle access roads and overflow or occasionally used parking.

Turfstone

GEOBLOCK

GREEN GEOBLOCK

A-3: Reinforced Turf Design Considerations: Space / Topography / Soils / Drainage area / Hotspot Runoff Structure Conveyance / treatment / landscaping / setbacks Construction Considerations Erosion and sediment control Soil compaction Under-drains drains Inspection Maintenance

Group 2: Nonstructural Practices N-1. Disconnection of Rooftop Runoff N-2. Disconnection of Non-Rooftop Runoff N-3. Sheetflow to Conservation Areas

Group 2: Nonstructural Practices Disconnecting impervious cover and treating urban runoff closer to its source are the next steps in the design process for implementing ESD. Using nonstructural techniques (e.g., disconnection of rooftop runoff, sheetflow to conservation areas) and micro-scale practices (e.g., rain gardens, bio-swales) throughout a development is an effective way to accomplish this goal. Nonstructural practices may be used to disconnect impervious cover and direct runoff over vegetated areas to promote overland filtering and infiltration. Whether runoff is directed over permeable areas or captured in small water quality treatment practices, there are reductions in both volume and pollutants delivered to receiving streams. These practices may be used to address the ESD design criteria

Group 2: Nonstructural Practices Nonstructural and micro-scale practices are an integral part of the ESD stormwater management plans. The use of these practices must be documented at the concept, site development, and final design stages and verified with as-built certification. If practices are not implemented as planned, then volumes used to design structural practices must be increased appropriately to meet the ESD sizing criteria.

N-1: Disconnection of rooftop runoff Rooftop disconnection involves directing flow from downspouts onto vegetated areas where it can soak into or filter over the ground. This disconnects the rooftop from the storm drain system and reduces both runoff volume and pollutants delivered to receiving waters. To function well, rooftop disconnection is dependent on several site conditions (e.g., flow path length, soils, slopes). Disconnected downspout Connected downspout

MDE: Typical Details

N-1: Disconnection of rooftop runoff Design Considerations: Space / Topography / Soils / Drainage area / Reconnections Conveyance / treatment / landscaping Construction Considerations Erosion and sediment control Site disturbance Inspection Maintenance

N-2 2 Disconnection of Non-Rooftop Runoff Directs flow from impervious surfaces to vegetated areas where it can soak into or filter over ground Disconnects surfaces from storm drain system, reducing both runoff volume and pollutants delivered to receiving waters Commonly applied to smaller or narrower impervious areas, driveways, open section roads, small parking lots Dependent on site condition: Permeable flow path length / soils s / slopes compaction

MDE: Typical Details

MDE: Typical Details

N-2: Disconnection of non-rooftop runoff Design Considerations: Space / Topography / Soils / Drainage area / Reconnections Conveyance / treatment / landscaping Construction Considerations Erosion and sediment control Site disturbance Inspection Maintenance

N-3: Sheetflow to conservation area Flow from pervious and impervious surfaces is directed to vegetated buffers (infiltration, filtering) Effective when development adjacent to protected areas Dependent on site conditions: Buffer size Contributing flow path lengths Slopes Compaction

Sheetflow to conservation area

M-1: Rainwater harvesting Group 3: Micro-scale Practices to Treat Runoff M-1 Rainwater Harvesting M-2 Submerged Gravel wetlands M-3 Landscape Infiltration M-4 Infiltration Berms M-5 Dry wells M-6 Micro-bioretention M-7 Rain gardens M-8 Swales M-9 Enhanced Filters

M-1: Rainwater Harvesting (Cisterns & Rain Barrels) Intercept and store rainfall for future use Stored water used for outdoor landscaping irrigation, car washing, non-potable water supply Promotes conservation Reduces runoff volumes and discharge of pollutants

MDE: Typical Details

MDE: Typical Details

Cistern schematic and applications

M-1: Rainwater Harvesting: (Design & Construction) Design Considerations: Space Topography Drainage Area Operation Conveyance Treatment Distribution System Dewatering Observation Well Safety Mosquitoes Setbacks Construction Considerations: Site Disturbance Storage Tanks Pressurization Maintenance Inspection

M-1: Rainwater Harvesting: Cost Rainbarrels Do-it it-yourself rain barrels can be constructed for under $30. Ready-made 55 gallon to 90 gallon rain barrels generally cost from $50 to $300 uninstalled. Cisterns Costs for a cistern, not including installation, range from about t $250 for a 200-gallon cistern to $5,000 for a 10,000-gallon cistern.

M-2: Submerged gravel wetlands A submerged gravel wetland is a small-scale scale filter using wetland plants in a rock media to provide water quality treatment. Runoff drains into the lowest elevation of the wetland, is distributed throughout the system, and discharges at the surface. Pollutant removal is achieved in a submerged gravel wetland through biological uptake from algae and bacteria growing within the filter media. Wetland plants provide additional nutrient uptake and physical and chemical treatment processes allow filtering and absorption of organic matter.

MDE: Typical Details

Gravel Wetland: Schematic

M-2: Gravel Wetland: (Design & Construction) Design Considerations: Space Topography Soils Drainage Area Hotspot Runoff Conveyance Treatment Flow Splitter Observation Well Treatment Cells Wetland Vegetation Construction Considerations: Site Disturbance Erosion and Sediment Control Gravel Media Inspection Maintenance

Design Example: As-built

Performance

M-3: Landscape infiltration Landscape infiltration (planters) uses on-site vegetation to capture, store and treat stormwater Rainwater is stored, filters through the planting soil and gravel media below, and then infiltrates into native soil. Practices can be integrated into overall site design Storage is provided in constructed planters made of stone, brick, concrete, or in natural areas excavated and backfilled with stone and topsoil

MDE: Typical Details

Landscape Infiltration

Landscape Planters

M-3: Landscape Infiltration Design Considerations: Space Topography Soils Drainage Area Hotspot Runoff Conveyance Treatment Flow Splitter Infrastructure Observation Well Construction Considerations: Soil Compaction Erosion and Sediment Control Gravel & Filter Media Planter Boxes Filter Cloth Landscape Installation Inspection Maintenance

M-4: Infiltration Berms A mound of earth composed of soil and stone that is placed along the contour of a relatively gentle slope. This practice may be constructed by excavating upslope material to create a depression and storage area above a berm or earth dike. Stormwater runoff flowing downslope to the depressed area filters through the berm in order to maintain sheetflow. Infiltration berms should be used in conjunction with practices that require sheetflow (e.g., sheetflow to buffers) or in a series on steeper slopes to prevent flow concentration.

MDE: Typical Details

M-4: Infiltration Berms Design Considerations: Space Topography Soils Drainage Area Hotspot Runoff Conveyance Treatment Storage Capacity Plant Materials Construction Considerations: Soil Compaction Erosion and Sediment Control Gravel & Filter Media Landscape Installation Inspection Maintenance

M-5: Dry wells An excavated pit or structural chamber, filled with gravel or stone, provides temporary storage of stormwater runoff from rooftops Storage area may be a shallow trench or deep well Rooftop runoff is stored and infiltrates into soil Pollutant removal ability related to volume of flow MDE: Typical Details

M-5: Dry well Design Considerations: Space Topography Soils Drainage Area Hotspot Runoff Conveyance Treatment Landscaping Underground distribution system Setbacks Operation Construction Considerations: Soil Compaction Erosion and Sediment Control Gravel Media Landscape Installation Dry well bottom Underground distribution system Inspection Maintenance

M-6: Micro-bioretention Practice captures and treats runoff from discrete impervious areas by passing through a filter bed mixture of sand, soil & organic matter Filtered stormwater is either returned to the conveyance system or partially infiltrated into soil Micro-bioretention practices are versatile and may be adpated for use anywhere there is landscaping MDE: Typical Details

MDE: Typical Details

MDE: Typical Details

M-6: Micro-bioretention Design Considerations: Space Topography Soils Drainage Area Hotspot Runoff Conveyance Treatment Landscaping Infrastructure Construction Considerations: Soil Compaction Erosion and Sediment Control Filter Media Landscape Installation Underdrain installation Inspection Maintenance

M-7: Rain gardens Shallow excavated landscape feature or saucer shaped depression that temporarily holds runoff for a short period of time Consists of the following components: Absorbent planted soil bed A mulch layer A gravel filter chamber Planting materials (shrubs, grasses, flowers) Overflow conveyance systems Captured runoff filters into soil over 24-48 hours

MDE: Typical Details

On Lot Bioretention Functional Landscape

M-7: Rain garden Design Considerations: Topography Soils Drainage Area Location Conveyance Treatment Landscaping Infrastructure Construction Considerations: Erosion and Sediment Control Planting Soil Landscape Installation Inspection Maintenance

M-8: Swales Channels that provide conveyance, water quality treatment & flow attenuation of stormwater runoff Pollutant removal through vegetative filtering, sedimentation, biological uptake, & infiltration into soil media 3 design variants: Grass swales Wet swales Bio-swales Micro-scale practices are small water quality

MDE: Typical Details

MDE: Typical Details

M-8: Swales Design Considerations: Topography Soils Drainage Area Hotspot runoff Conveyance Treatment Landscaping Location grass swales bioswales check dams Construction Considerations: Erosion and Sediment Control Inspection Maintenance

M-9: Enhanced Filters Modification that takes advantage of soil conditions below a specific practice ( e.g., micro-bioretention) to provide water quality treatment and gw recharge in a single facility. Uses stone reservoir under conventional filtering device to collect runoff, remove nutrients anaerobically,, and allow infiltration into the soil

MDE Typical Details

M-9: Enhanced Filters Design Considerations: Space Soils Hotspot runoff Conveyance Treatment Observation well Setbacks Infrastructure Construction Considerations: Erosion and Sediment Control Soil compaction Reservoir installation Inspection Maintenance

Comments / Questions?