Implementing Low Impact Development in Utah - An Engineer’s Perspective PRESENTED BY: CRAIG BAGLEY, P.E., CFM BOWEN, COLLINS & ASSOCIATES

What is Low Impact Development?  A comprehensive, landscape-based approach to sustainable development  A management strategy to maintain pre-development natural systems, hydrology and ecology  A cost-effective, flexible approach based on a set of simple techniques  A collection of practices that have been implemented nationwide

What is Low Impact Development?  NOT rocket science  NOT formulaic  NOT the answer to every storm water challenge  NOT yet finished evolving  NOT very common in Utah

Typical pre-development conditions: Runoff = 10% Infiltration = 50%

Typical post-development conditions: Runoff = 55% Infiltration = 15%

LID Principles  Work with the landscape and natural systems  Focus on prevention (flood, erosion, pollution, etc.)  Micromanage stormwater – treat near source  Keep it simple  Design multi-functional features (filter, treat, infiltrate)  Maintain and sustain

1.Use existing natural systems as the integrating framework for site planning Land use planning and watershed planning Identify environmentally sensitive resources: wetlands, mature trees, slopes, drainageways, permeable soils, waterway buffers Mimic pre-development hydrology

2.Focus on prevention Minimize clearing and grading Cluster buildings and reduce building footprints Reduce road widths, use shared driveways, reduce parking area Align roads to minimize impact Use green rooftops Use permeable paving

Create subwatersheds and “micromanage” runoff in a treatment train of small structures Flatten slopes, lengthen flow paths, maximize sheet flow Maintain natural flow paths, use open drainage Use LID techniques to manage frequent, low-intensity storms 3.Treat stormwater close to the source

Open drainage systems and filter strips Disconnection of roof runoff Rain barrels Street sweeping Reduce construction disturbance 4. Emphasize simple, nonstructural, low-tech, low-cost methods

Use stormwater management components that provide filtration, treatment, and infiltration. Provide open space and wildlife habitat. Store water for landscape use Reduce heat island effect Enhance site aesthetics 5.Create a multifunctional landscape

Reduce use of pesticides and fertilizers. Use drought-resistant plants. Maintain rain gardens and bioretention areas. Provide adequate funding for public works departments 6.Maintain and sustain

Key LID Strategies  Conserve natural hydrology, trees and vegetation  Preserve stream and wetland buffers  Minimize impervious surfaces (DCIA)  Micromanage stormwater  Plant ecological landscaping

LID Advantages over Conventional Means  Reduces need for large detention facilities and flood control structures  Reduces pollutant loading to receiving waters  Reduces stream bank erosion associated with peak flow and volume  Provides visual amenity  Costs less to construct (less pipe, less pavement, smaller facilities)

Conventional LID BMPs/Integrated Management Practices  Bioretention  Dry wells  Filter/buffer strips  Vegetated swales  Rainwater harvesting  Infiltration trenches  Reducing roads and parking areas  Permeable pavement

LID Design Process  Develop site plan  Perform hydrologic analysis  Evaluate/select BMPs/Integrated management practices  Develop erosion and sediment control measures

LID Site Planning  Define development envelope  Reduce/minimize total impervious area on site  Disconnect impervious areas  Modify/increase flow paths

LID Hydrologic Analysis  Delineate drainage basin and sub-basin areas  Define the design storm characteristics  Select modeling techniques  Estimate runoff from pre-development conditions (baseline)  Estimate runoff from propsed new development without BMPs  Evaluate alternative BMPs to mitigate impacts of development on stormwater

Select LID BMPs/Integrated Management Practices  Define needed hydrologic controls to mitigate  Evaluate site constraints  Screen potential BMPs  Evaluate impacts of implementing BMPs on post-developed model  Select BMPs to implement  Incorporate additional controls if necessary

Select Erosion & Sediment Control Methods  Plan and phase construction  Select appropriate erosion control measures  Select sediment control measures  Identify needed maintenance activities

LID Planning/Design Considerations  Space requirements  Soil characteristics  Slopes (hillside, channel, etc.)  Depth to water table or bedrock  Proximity to building foundations & wells  Maximum depth AND Maintenance costs

Low Impact Site Design Example Conservation of natural hydrology, trees, vegetation Stream & wetland buffers Minimize impervious surfaces Stormwater micromanagement Ecological landscaping Typical Subdivision Conservation

Low Impact Site Design Example Open Space Residential Design 1. Identify Conservation Areas

Low Impact Site Design Example Open Space Residential Design 1. Identify Conservation Areas 2. Locate House Sites

Low Impact Site Design Example Open Space Residential Design 1. Identify Conservation Areas 2. Locate House Sites 3. Align Roads & Trails

1. Identify Conservation Areas 2. Locate House Sites 3. Align Roads & Trails 4. Draw the Lot Lines Open Space Residential Design Low Impact Site Design Example

Buildings and Roadways Low Impact Site Design Example Cluster buildings within the development envelope Design buildings with smaller footprints Roadways should follow existing grades. Use parking structures Separate parking areas

Buildings and Roadways Low Impact Site Design Example Cluster buildings within the development envelope Design buildings with smaller footprints Roadways should follow existing grades. Use parking structures Separate parking areas

Stormwater Management Low Impact Site Design Example Minimize directly connected impervious area Create multiple sub-basins Increase time of concentration Use a “treatment train” of LID techniques to deal with frequent, low-intensity storms.

Stormwater Management Low Impact Site Design Example Minimize directly connected impervious area Create multiple sub-basins Increase time of concentration Use a “treatment train” of LID techniques to deal with frequent, low-intensity storms.

Low Impact Site Design Examples

Roadways and Parking Areas Road Profile Narrower roadways ( feet) Permeable parking lanes Open section roadways Alternative curb designs

Roadways and Parking Areas Alternative Turnarounds Smaller cul-de-sacs Bioretention islands One-way-loops Hammerhead turnarounds

Roadways and Parking Areas Parking Lots Create multiple small lots Allow shared parking Reduce requirements near transit Require compact spaces Set parking maximums

Roadways and Parking Areas Parking Lots Create multiple small lots Allow shared parking Reduce requirements near transit Require compact spaces Set parking maximums

Permeable Paving Grass pavers Paving stones Porous asphalt Pervious concrete Runoff reduction

Permeable Paving Parking stalls Overflow parking Driveways Walkways and plazas Applications

Bioretention Excavation filled with engineered soil mix Herbaceous perennials, shrubs, trees Ponded water infiltrates within 72 hours Overflow outlet and optional underdrain Treatment, retention, infiltration, landscaping

Bioretention Parking lot islands Median strips Rooftop runoff Applications

Bioretention Applications Urban retrofits High-density areas

Vegetated Swales Roadside swales “country drainage” Parking lots Low-angle slopes only Opportunity for snow storage Conveyance, treatment, infiltration

Vegetated Swales Conveyance, treatment, infiltration

Grassed Filter Strips Pretreatment and Attenuation Low-angle vegetated slopes Adjacent to parking lots and roadways Opportunity for snow storage

Grassed Filter Strips

Infiltration Trenches / Dry Wells Infiltration and Volume Reduction Runoff stored in void space; slowly percolates into the ground Excellent for rooftop runoff Pretreatment is critical for surface runoff

Infiltration and Volume Reduction Infiltration Trenches / Dry Wells

Runoff Reduction and Water Conservation Rain Barrels and Cisterns Downspouts directed to tanks or barrels UT – up to 2500 gal/lot Excess diverted to drywell or rain garden Landscaping, car washing, other nonpotable uses

Runoff Reduction and Water Conservation Rain Barrels and Cisterns

Runoff Reduction, Treatment, Attenuation Stormwater Planters “Bioretention in a Box” Vegetative uptake of stormwater pollutants Pretreatment for suspended solids Aesthetically pleasing Reduction of peak discharge rate

Stormwater Planters

LID BENEFITS Lower Peak Discharge Rates Reduced Runoff Volume

LID BENEFITS Improved Water Quality Increased Aquifer Recharge

ConventionalLow Impact Grading/Roads $569,698$426,575 Storm Drains $225,721$132,558 SWM Pond/Fees $260,858$ 10,530 Bioretention/Micro —$175,000 Total$1,086,277$744,663 Unit Cost$14,679$9,193 Lot Yield7481 Lower Construction Costs Higher Lot Yield

Important Design Considerations Selection of pretreatment prior to infiltration Wellhead protection Emergency access Snow removal issues Overflow/bypass controls Mosquito issues and concerns

Important Design Considerations Select appropriate cold climate techniques Ensure adequate emergency access Prioritize pedestrian safety Define ownership: public, private, mix? Develop monitoring and inspection plan Assign maintenance responsibilities

QUESTIONS?

LID IMPLEMENTATION Long-Term Maintenance All stormwater systems require maintenance LID maintenance often simple, low cost Ensure adequate funding for PW Depts Homeowner/landscaper education Consider requiring permanent sureties

LID IMPLEMENTATION Review of Local Codes Zoning Bylaw and Site Plan Review Subdivision Rules and Regulations Board of Health Regulations Wetland Regulations Building Codes

LID IMPLEMENTATION Stormwater/LID Bylaw Replace the “patchwork” of stormwater codes with a single set of local standards Establish Stormwater Permitting Authority to review all projects over a certain size Specify performance standards Utilize expert review when necessary Permit/promote the use of LID techniques Require a maintenance plan

LID IMPLEMENTATION Collaboration is Critical! Local boards Public works officials Fire department and emergency response Developers and builders Consultants and engineers Business interests and property owners Environmental advocates