state of stormwater management practice in florida

State of Stormwater Management Practice in Florida

Inter-American Development Bank User Charge Based Funding Mechanisms for Stormwater Management

James D. Hunt, P.E.City of Orlando, FloridaDivision Manager, Streets & Stormwater Services Division

The Stormwater Balancing Act

cost of stormwater improvements

probability of damage occurring

Stormwater Design Hierarchy

1. Road cross-section:

2. Catch basin capacity:

3. Storm sewer design:

4. Minimum road elev:

5. Pond design:

6. Building elevs:

7. Landlocked ponds:

3-yr storm

5-yr storm

10-yr, 6-hr storm

25-yr, 24-hr storm

25-yr, 24-hr storm

100-yr, 72-hr storm

25-yr, 96-hr storm

Evolution of Stormwater Management

• Flood protection (rate controlled)

• Flood protection (volume controlled)

• Pollution abatement

• Wetland preservation & enhancement

• Wetland creation

• Groundwater issues

• Re-use

What is a Best Management Practice (BMP)?

A cultural or engineering technique, or management strategy, that has been determined and accepted to be an effective and practical means of preventing or reducing non-point source pollution in a local area.

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Rainfall Probability Histogram

Origins of Pollution Abatement Criteria

• 90% of all rainfall events are less than one inch• 80% of rainfall volume is received from events

less than one inch in depth• assumes each event completely removes pollutants

from drainage catchment and delivers them for treatment

Stormwater Treatment Train

Low impact development

Roadside swales

Inlet filters

Baffle boxes

End-of-pipe treatment

Dry pre-treatment ponds

Wet detention ponds

Master (regional) facility

Wetland filter

Close to source

Regional system

Low Impact Development

• Control occurs closer to source• Reduce maintenance obligations• Still need educational outreach• Still need enforcement• Contrary to compact development?• Cheaper to prevent pollution from entering

receiving waters than to remove pollutants from receiving waters

LID Design Features

• Vegetative cover

• Green roofs

• Rain gardens

• Roadside swales

• Disconnected impervious area

• Stormwater reuse

Retention Ponds

• Typically dry (may be wet)

• Designed to store a specific amount of runoff (usually from the first inch of rainfall in the drainage area)

• Will usually return to dry state or designed water elevation through percolation and evaporation in 72 hours

Dry Retention Pond

Dry Retention Pond

Detention Ponds

• Designed to fill up with runoff and then allow the water to pass through the pond at a slow, controlled rate by way of an outfall structure to the receiving water body

Dry Detention Pond

Dry Detention Pond

Underdrains

• Perforated pipe surrounded with filter fabric material and a specific medium (sand or gravel) for percolation

• Transports groundwater and percolated stormwater into perforated pipe that discharges into a control structure

• Typically installed in poor draining soils and wet areas

• Designed to keep ponds dry or at a certain elevation

Underdrains

Underdrains

Wet Detention Pond Design

• Greater treatment volume

• Slow volume recovery

• Littoral shelf with wetland plants

• Limited open water

• Mean depth three to ten feet

• Separation of inlets and outlets for biological contact

Wet Detention Pond

Wet Detention – How Not to Do It

Wet Detention – Site Constraints Considered

Control Box/Structure

Exfiltration

• Temporarily hold water in perforated pipes• Allow water to percolate and filter through

surrounding soils• Typically installed in parking lots, under garages

and other buildings (access for maintenance)• Not appropriate for poorly drained soils or high

groundwater conditions• Heavy reliance in a concentrated area can alter

groundwater conditions and cause damage

Exfiltration System

Exfiltration

Why Retrofit?

• It may be the only way to achieve further water quality improvements

• It may be the only cost-effective way to recover diminished capacity in existing stormwater conveyance systems

• It’s the right thing to do!

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Rainfall Probability Histogram

Example #1

• treat runoff from 1 inch of rainfall over treat runoff from 1 inch of rainfall over project area (100 acres)project area (100 acres)

• 1,000 lbs of pollutants generated1,000 lbs of pollutants generated

• 894 lbs of pollutants are removed894 lbs of pollutants are removed

• 106 lbs are not removed106 lbs are not removed

• an adjacent identical 100-acre tract an adjacent identical 100-acre tract generates an additional 1,000 lbs of generates an additional 1,000 lbs of pollutants, for a total of 1,106 lbspollutants, for a total of 1,106 lbs

Example #2

• treat half the runoff over twice the areatreat half the runoff over twice the area

• 2,000 lbs of pollutants generated2,000 lbs of pollutants generated

• 1,530 lbs of pollutants are removed1,530 lbs of pollutants are removed

• 470 lbs are not removed470 lbs are not removed

Technology Transfer

Lake Rowena Screening Facility

• Basin 1 area – 539 acres

• Pipe Length – 3.45 miles

• 75% of pollution to lake is from this one area

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Colonial Drive

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Concord Street

Virginia DriveMills

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FestivalPark

Lake Druid

Lake Cay Dee

Lake Estelle

Lake Formosa

ColonialPlazaMall

LeuGardens

LakeRowena

SubBasin

1

Periphyton Water Garden

Regional Stormwater Management SystemsWhen a Regional Approach is Best

• Multiple use objectives

• Multi-use can mean multi-funding

• Economies of scale

• Improve the chance of success

Southeast Lakes BasinCharacteristics

• Intensely developed, 3.5 sq mile area

• Lowest elevation 58 feet

• Much of the basin 65-75 feet

• Lowest point on basin rim 103 feet

• 18 lakes

• Over 60 drainage wells

• No outfall to any surface receiving water

Southeast Lakes BasinStrategies to Solve Flooding

• Gravity diversion of stormwater away from basin rim

• Creation of additional impoundments

• Increased storage through lowered regulation schedules

• Transfer of surface water from lakes that flood to those requiring augmentation

Greenwood Urban Wetland

• Over 75 homes flooded for 3 weeks in 1960

• 2-acre lake expanded to 13 acres

• New parkland created

• Stormwater re-use employed for irrigating park as well as adjacent cemetery

Greenwood Urban Wetland

Karst Geology in the Southeast Lakes Basin

Lake Lancaster Augmentation Well

• Cannot be used if lake is above 68 feet above sea level

• Must be turned off once lake reaches 69 feet above sea level

• Limited to 114,000,000 gallons per year

• Use is prohibited during water emergencies

• Has more nutrients than surface water

Lake Lurna-Lake Lancaster Interconnection

• Protects Lake Lurna from flooding

• Moves excess water to Lake Lancaster for augmentation

• Is a cleaner source than groundwater

• Mimics natural processes in a landlocked basin

• Postpones or eliminates the need for more drainage wells or surface outfall from a large, intensely developed landlocked basin

• No guarantee that there will always be enough water for augmentation!

Use of Re-Use Water (Highly Treated Effluent)

• Regulatory concerns about impact to surface waters

• Other, greater demands for a new resource that cannot meet all demands

• The good news: we will be drinking our own wastewater in the future.

• The bad news: there won’t be enough to go around!

Lake Fran Area, 1890

Lake Fran Area, 1965

100-Year Flood Plain, Prior to Lake Fran

100-Flood Plain, After Construction

Lake Fran Flood Control Project

• Nearly 2,000 homes removed from 100-year flood plain

• 47 acres of wetland preservation

• 38 acres of wetland creation

• Another 200 acres of wetland mitigation for nearby road project

• New school site

• Future environmental center

• Hub of new park and trail system

Flood Control Impoundments

• Potential for catastrophic failure• Higher level of protection

– Greater return frequency

– Longer storm duration

• Freeboard (factor of safety)• Plan for controlled failure

– Berm elevations set to direct flows that exceed design

– Erodible plugs

Regional Stormwater Management Lessons Learned

• Science and engineering – not politics - must lead design development

• Proper location (mimic nature)

• Apply sufficient resources (land, money, manpower)

• Ease of maintenance increases chance of success

• Still the most cost-effective way to recover capacity in an over-capacity system

• Can be an engine of redevelopment and revitalization

Don’t forget the little things – like pedestrian circulation

Future Challenges

• Numeric Nutrient Criteria

• State-wide Stormwater Rule

• Water Body Classification & Use Determination

Lake Baldwin Outfall Canal

Questions?