P1253296570pzcvs - PowerPoint PPT Presentation

Title: P1253296570pzcvs


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
  Runoff Q CIA
• 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) --Locali
  zed 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
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 EPAs 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
Tallahassees 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.ht
  ml

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 natures 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
• Floridas 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