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Why Manage Stormwater?

Why Manage Stormwater?. Physical problems associated with stormwater include: 1. Flooding 2. Soil Erosion 3. Sedimentation 4. Water Quality 5. Pollution on Land What is particularly troublesome about the above problems is that they are dynamic and influenced by urban development .

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Why Manage Stormwater?

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  1. Why Manage Stormwater? • Physical problems associated with stormwater include: • 1. Flooding2. Soil Erosion 3. Sedimentation4. Water Quality 5. Pollution on Land • What is particularly troublesome about the above problems is that they are dynamic and influenced by urban development. • Further complicating the above is rising standards for protection from floods, minimization of soil impacts, and treatment of stormwater.

  2. Key Stormwater Terminology/Concepts I • Drainage Basin (Watershed) • Runoff • Coefficient of Runoff • Time of Concentration • Determining Amount of Runoff: What factors affect the amount of runoff? • The Rational Equation Method for Estimating RunoffQ = C*I*A • where Q = Quantity, C = Runoff Coefficient, I = Intensity, and A = Area --Size/shape of watershed --Amount/intensity of rain --Topography --Impervious surfaces --Soils --Condition of soil --Amount/Types of Vegetation

  3. Key Stormwater Terminology/Concepts II • Channel Flow versus Sheet Flow • Typical System Elements 1) Natural channels 4) Storm sewers 2) Excavated drainage ditches 5) Man-made ponds 3) Street gutters 6) Natural water bodies • The Typical Urban Stormwater Systems --Large system (Major and Minor System Linkages) --Localized system (Stand Alone Minor Systems) • Types of Man-made Stormwater Ponds • 1) Retention basins (water all the time)2) Detention basins (usually dry)3) Recharge basins (percolation for groundwater recharge) • Pipe sizes and materials • Design Storm --Local LOS Standard (“25 year” storm)

  4. There have been two major shifts in the American approach to managing stormwater in the last two decades: • 1) A shift in Stormwater Control from • Collect and Dispose QuicklyCollect, Store, and Dispose Slowly(Stormwater Riddance) (Stormwater Detention/Retention) (Through 1970s) (Since 1980s) • The failure of the pre 1980s strategy was evident from the high degree of flooding in downstream urban areas. • 2) A concurrent shift from: • Health/Safety Environment Sustainability • 1. Stormwater is now viewed as something that can be cleaned up • 2. It is also viewed as a resource for recreation, drinking, recharging groundwater, etc. Changes in Stormwater Management

  5. Stormwater Management Philosophy 1. The Drainage System is part of a larger environmental system 2. Wetlands are natural storage areas 3. Stormwater requires space 4. Stormwaters have potential uses 5. Water pollution control measures must be part of the process 6. Preventative measures are less costly than remedial measures

  6. Stormwater Detention Advantages Immediate Advantages of Stormwater Detention --Reduced peak runoff rates --Reduction of severity and frequency of flooding --Reduced soil erosion and stream sedimentation --Protection of surface water quality --Can be used for groundwater aquifer recharge Other Advantages: 1) Lessened Environmental Impact --More “natural” transportation systems for stormwater are being used. --Fewer underground pipes and more grass lined swales and natural streams. --Greater use of “wetlands” or low-lying areas to manage stormwater. --Treatment of runoff prior to release into water bodies. 2) Work Towards Goal of Sustainability --Use of stormwater management elements as recreational or environmental features (Lake Ella).

  7. Development and Stormwater • Development has two types of stormwater impacts: • Site Level, Short Term (During Construction) --Increased runoff amount --Faster runoff --Increased soil erosion --Downstream impacts (flooding, sedimentation, etc.) • Macro-Level, Longer Term Impacts due to Infilling & Sprawling--Decreased infiltration/Increased runoff amount --Time of concentration decreases/Faster runoff --Increased pollution (other than soil) --Increased downstream effects (flooding, pollution)

  8. On-Site Stormwater Control Principles • Keep Disturbed Areas Small • Stabilize and Protect Disturbed Areas • Keep Runoff Velocities Low • Protect Disturbed Areas from Runoff • Retain Sediment within Site Area Images from EPA’s Urban Storm Water Management.

  9. Longer Term Stormwater Impacts Macro-Level, Longer Term ImpactsWith increasing urbanization comes a number of problems, many experienced here in Tallahassee. --Decreased infiltration and resultant increased runoff --Time of concentration decreases --Increased pollution and declining water quality --Increased downstream flooding Why do these impacts result? --More impervious surface --Cumulative impacts of single-site decisions --Runoff from urban uses and roadways hurts water quality --Greater runoff leads to greater downstream effects Two Broad Approaches to Addressing these Problems 1) Structural 2) Regulatory

  10. Stormwater Management Goals • The Basic Goals of Stormwater Management Agencies 1. Solve existing runoff problem 2. Prevent new problems from developing • Advanced Goals might include --Stormwater treatment and disposal --Protection and development of water supplies --Develop recreational opportunities --Conservation efforts

  11. Tallahassee’s Stormwater Division • Mission Statement • To assist the community with defining its priority stormwater management objectives, in the context of physical, environmental, and socio-economic concerns, and to develop and implement strategies to address the same, as expeditiously and to the fullest extent possible, within the resources the community chooses to allocate to these efforts. • Areas of Effort • Major Capital Improvements • Small Projects Initiatives • Floodplain Management • Lake Management and Water Quality • Funding Sources • Stormwater Fee (Residential: $75 per year; Other Uses: Based upon amount of impervious surface) • Other City Funds • Special Allocations (Blueprint 2000) • http://talgov.com/citytlh/stormwater_man/index.html

  12. Floods, Floodplains, and Flood Control • Flood: A general and temporary condition of partial or complete inundation of normally dry land areas from overflow of inland or tidal waters or from the unusual and rapid accumulation or runoff of surface waters from any source. • Floodplains: The area of land covered by a 100 year flood (the usual standard), also called the “flood hazard area”. • What is a “100 year flood event”? • Flooding can be a natural event, as when the Mississippi River spills over its banks, or can be human-generated, as when upstream development causes downstream flooding. • Annual damages to flooding ranged from $760 million to over $16 billion during the 1990s. The “Great Flood” of 1993 killed 48 people and has been estimated to have caused $16.37 billion in damages.

  13. Mitigating Floods • There are two broad approaches to Flood Control: • Structural (Physical): Storage Reservoirs, Channelization, Levees, and Dikes “mitigate flood events by changing floodwater distribution in time and space” • Nonstructural: Land treatment, Flood-proofing, Land use controls, Design standards for runoff control“mitigate the effects of a flood” by using ‘nature’s easements’, floodplains”

  14. Stormwater/Flood Policy Options Local/Regional Federal -Stormwater Systems-Combined Sewer Systems-Detention/Retention Basins-Regional Stormwater Treatment Facilities -Pumping Facilities Structural/ Physical -Dams-Dikes-Levees-Channelization -Land Use Regulations (e.g.Zoning, Development Restrictions)-Building Codes-Subdivision Ordinances-Construction Regulations-Information Dissemination-State Regulations-Wetlands Preservation -National Flood Insurance Program (NFIP)-Purchase of Floodplains-Information Dissemination-Water Pollution Control Regulations, Section 208 of Clean Water Act (1972)-Soil Conservation Acts -Wetlands Preservation Non-Struct/ Regulatory

  15. Why Manage Floodplains in Florida? • The Magnitude of the Problem • Flooding can occur in either: 1) Floodplains (low-lying lands around rivers, streams, lakes, and wetlands), or 2) In other low-lying, poorly drained areas (like my old neighborhood) • The Federal Emergency Management Association (FEMA) estimates that about 14.25 million acres of Florida (41 percent) is flood-prone, the highest percentage of all fifty states. • The Department of Community Affairs (DCA) estimates that about 1.3 million Floridians live in areas routinely subject to flooding. • State Planning Requirements • Florida’s growth management laws require local governments to address floodplain and stormwater management in their Comprehensive Plans.

  16. National Flood Insurance Program • Established in 1968 in response to the rising cost of taxpayer funded disaster relief relating to floods. The program makes Federally-backed flood insurance available in communities that agree to adopt and enforce floodplain management practices. • Managed by FEMA, the program is self-supporting for the “average year”. (Insurance premiums cover the cost of claims payouts.) • Estimates place the reduced flood damage from the program at up to $1 billion annually. • Updated in 1990 to provide further incentives to flood insurance through a “Community Rating System”. There are three goals for CRS: • 1) Reduce Flood Damages 2) Facilitate Accurate Insurance Ratings 3) Promote Awareness of Floods/Flood Insurance • Much more information available:http://www.fema.gov/fima/nfip.shtm

  17. The Regular NFIP Process • Typically a community is provided with a Flood Insurance Rate Map (FIRM) after a detailed engineering study, termed a Flood Insurance Study (FIS), is conducted. • FEMA authorizes the sale of additional flood insurance in the community up to the Regular Program limits. • Community implements adopted floodplain management measures. • FEMA arranges for periodic community assistance visits with local officials to provide technical assistance regarding complying with NFIP floodplain management requirements. • Local officials may request flood map updates as needed. FEMA evaluates requests, encourages cost-sharing, and issues revised maps as priorities dictate

  18. Community Rating System • Implemented in 1990 as a program for recognizing and encouraging community floodplain management activities that exceed the minimum NFIP standards. • Under the CRS, flood insurance premium rates are adjusted to reflect the reduced flood risk resulting from community activities that meet the three goals of the CRS: (1) reduce flood losses; (2) facilitate accurate insurance rating; and (3) promote the awareness of floods/flood insurance. • There are ten CRS classes: class 1 requires the most credit points and gives the largest premium reduction; class 10 receives no premium reduction. • The CRS recognizes 18 creditable activities, organized under four categories: Public Information, Mapping and Regulations, Flood Damage Reduction, and Flood Preparedness.

  19. Community Rating System Benefits Premium Reduction Credit Points Class SFHA* Non-SFHA** 4,500+ 1 45% 5% 4,000 – 4,499 2 40% 5% 3,500 – 3,999 3 35% 5% 3,000 – 3,499 4 30% 5% 2,500 – 2,999 5 25% 5% 2,000 – 2,499 6 20% 5% 1,500 – 1,999 7 15% 5% 1,000 – 1,499 8 10% 5% 500 – 999 9 5% 5% 0 – 499 10 0% 0% * Special Flood Hazard Area (A and V zones) ** Preferred Risk Policies are available only in B, C, and X Zones for properties that are shown to have a minimal risk of flood damage.

  20. Source: http://www.fema.gov/nfip/crs.shtm

  21. NFIP Continued • Tallahassee joined the NFIP in 1976. Currently their rating is a Class 7, with a 15% reduction for Special Flood Hazard Areas. Only a handful of communities in Florida had a better rating in 2002. • Activities that garner points towards more credits (which then improves your local rating) include: • -Public Information: Information dissemination on floodplains, flood insurance, etc. • -Mapping and Regulations: Mapping of flood areas, preserving open space, enforcing building standards, and managing stormwater. • -Flood Damage Reduction: Relocating or retrofitting structures, creating a floodplain management plan, and maintaining existing drainage systems. • -Flood Preparedness: Flood warning system, levee safety and dam safety programs.

  22. Stormwater Management: The Role of Planners • Regulatory Work • Working with the NFIP • Crafting land use and development regulations that minimize the exposure and vulnerability of areas to stormwater/flooding damage • GIS-Related Work • Mapping flood prone areas • Modeling stormwater flows and impacts • Working with the Community • Information dissemination • Working with community/neighborhood groups, major institutions to solve stormwater issues • Infrastructure and Capital Budgeting • Identifying and prioritizing infrastructure projects • Capital Budgeting (allocating scarce resources) • Identifying and implementing user fees and other funding mechanisms

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