Presentation on theme: "State of Stormwater Management Practice in Florida Inter-American Development Bank User Charge Based Funding Mechanisms for Stormwater Management James."— Presentation transcript:
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, Florida Division Manager, Streets & Stormwater Services Division
The Stormwater Balancing Act cost of stormwater improvements probability of damage occurring
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.
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
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
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
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
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!
Example #1 treat runoff from 1 inch of rainfall over project area (100 acres)treat runoff from 1 inch of rainfall over 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 generates an additional 1,000 lbs of pollutants, for a total of 1,106 lbsan adjacent identical 100-acre tract generates an additional 1,000 lbs of pollutants, 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
Regional Stormwater Management Systems When a Regional Approach is Best Multiple use objectives Multi-use can mean multi-funding Economies of scale Improve the chance of success
Southeast Lakes Basin Characteristics 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 Basin Strategies 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
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 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