905R90112
                    United States
                    Environmental Protection
                    Agency
                     Watershed Management Unit
                     Water Division, Region V
                     Chicago, IL
December 1990
vvEPA
Facts About Stormwater
Management  Programs  in
the  State  of Florida
 The Stormwater Problem
           tormwater is that surface and ground
           water resulting from precipitation. In
           developed areas, surface water
           runoff is the major component of
           sewer and stream flows. The
           percentage of impervious areas that
           are directly connected to a sewer or
           other water conveyance system
 determine the major portion of the volume and rate
 of discharge.
    As an area becomes more urbanized, the peak
 rate of discharge, volume of discharge, and
 pollutant mass discharge increases. These effects
 are caused in part by modifications to surface
 drainage patterns, increased impervious areas
 (less infiltration and depression storage), and
 increased human and vehicle traffic. Human
                     activities add pesticides, fertilizers, animal wastes,
                     oil, grease, solids, heavy metals, and other
                     potential pollutants to the stormwaters.
                        The increased urbanization and many existing
                     drainage practices in rural lands have caused
                     flooding, erosion, and water quality degradation. In
                     Florida, Stormwater is the largest source of
                     pollutants to lakes, rivers, and estuaries. In many
                     lakes, it is the only major source of pollutants. On
                     a statewide basis, Stormwater as compared to
                     regulated discharges (sewage and industrial
                     treatment facilities) is the source of: (1) 80 to 95
                     percent of heavy metals; (2) 99 percent of all
                     sediment; (3) 90 percent of oxygen demanding
                     substances; and (4) 50 percent of the nutrients.
                     Thus, severe environmental and economic
                     impacts result when stormwaters are not managed.
 Stormwater  Management  Defined
           tormwater management is a
           comprehensive, interdisciplinary
           body of knowledge required to
           design and operate Stormwater
           programs to prevent flooding, reduce
           land loss due to erosion, maintain
           water quality, increase water
           availability, and provide funding
                     sources. A Stormwater program must have goals
                     and objectives that are implemented using a
                     Stormwater rule that specifies levels of
                     performance. The minimum levels of performance
                     in Florida are based on pre- versus post-peak
                     discharge and 80 percent removal of pollutants.
                     Stormwater management practices have been
                     developed to meet these performance standards.

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Stormwater  Management  Practices
           or a stormwater management
           practice to be successful, it must
           satisfy water quality and quantity
           considerations and have the
           necessary funding to be constructed
           and operated. There are at least five
stormwater management practices that are now
used in the State of Florida, namely (1) off-line
retention by infiltration ponds and exfiltration
trenches; (2) wet-detention ponds; (3) swales that
both infiltrate and transport; (4) porous parking
areas; and (5) alum injection.
Retention  Using Infiltration  Ponds
            n infiltration pond is one that retains
            stormwater on-site in a surface
            pond. The soils beneath the pond
            must be capable of percolating the
            infiltrated water, and as such, the
            water table is usually below the
            bottom of the pond. The pond is
            designed to store a specific runoff
volume. This volume is determined from an
analysis of storm events with
their rainfall volume
(Wanielista, 1990). In the
State of Florida, these rainfall
analyses have defined the
design criteria for pond
volume as the runoff from the
first inch of rainfall with a
minimum of 1/2 inch over the
watershed. The objective for
sizing is to remove 80 percent
of the runoff mass. The
practice incorporates both
pollution control and ground water recharge;
however, the impact of soluble pollutants on
ground water must be carefully considered. The
practice  is used throughout the State where soils
permit infiltration rates of at least 3-5 inches an
hour. The infiltration pond is sized for the runoff
from the first inch of rainfall; thus, additional runoff
is diverted to direct surface water discharge or into
a detention pond for peak discharge control.

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Retention  Using  Exfiltration Trenches
            hile infiltration ponds are
            constructed on the surface,
            exfiltration trenches are
            subsurface holding areas.
            They are also referred to as
            exfiltration pipes or pits.
            Highly permeable rock (i.e.,
            limestone) or soils (sandy)
must be present. The most common
construction practice is an excavation
trench backfilled with coarse graded rock.
Runoff is diverted to the exfiltration
system. The system often  includes
perforated pipe surrounded by aggregate
and a filter cloth. The pipe will increase the storage
volume, since the rock aggregate has a porosity of
about one-half or less that of the pipe. The design
volume is calculated as the runoff from the first
inch of rainfall, and a diversion structure or inlet
control can be used to regulate runoff volumes
greater than the design volume.
   Exfiltration trenches with pipes, fabric wrap and
rock are being used in central Florida. From these
operating systems, it was concluded that the
treatment volume should not be placed in the
water table. In southern Florida, the pipe is
frequently not used; however, the systems must be
maintained to remove debris. Maintenance will
vary directly with the amount of debris.
Wet  Detention  Ponds
            et detention ponds are excavated
            areas with a pool of water that exists
            throughout the year (permanent
            pool), a debris storage volume, and
            a temporary storage area. The
            ponds are^jsed to attenuate
            (reduce) hydrograph peaks, pollutant
            loadings and concentrations of
pollutants, and to provide water for re-use
purposes. Downstream water quality is improved
because of sediment removal, plant uptake of
nutrients, chemical transformation, and runoff
water re-use. Temporary storage volume designs
vary depending on the use of storage volume;
however, the minimum size is calculated as one
inch over the entire watershed. The  total pond
volume if used for peak attenuation  is frequently
greater than the temporary storage volume. A
maximum depth for the permanent pool has been
specified as six feet to minimize recycling of
pollutants stored in the bottom muds. A vegetated
area that leaves no more than 70 percent of the

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permanent pool in open water is recommended.
Short-circuiting of flow should be minimized.
   These detention systems are found throughout
the State in areas where the water table is of
sufficient height to maintain the permanent pool.
Recycling for irrigation purposes is being used
more frequently to minimize the volume of
discharge and pollutant loadings. In all cases, the
invert elevation for the discharge structure should
be above the seasonal high water elevation.
                                              Surface Water Discharge Control —
                          Flood Control Volume
   Average Water
   Table Elevation
                              Reuse Volume or Temporary Storage
                                 Permanent Pool Volume
                                                                               • Shallow Slope

                           Sediment Storage Volume
                 Elevation For Maximum Storage Depletion Before
                 Replenishment From Other Sources (Groundwater)

                     Steep Slope
Swales
             wales are vegetated ditches that
             both infiltrate and transport runoff
             water. The top width to depth ratio
             must be equal to or exceed 6 to 1.
             Generally, the longitudinal slope is
             shallow to prevent erosion of the
             ditch. The design infiltration
             volume is based on a State
 rule that requires 80 percent of runoff from
 the three-year, one-hour design storm to
 be infiltrated over the length of the ditch
 (Livingston et al., 1988). Design equations
 are available and were developed by the
 Florida Department of Transportation
 (Wanielista, 1988).
   Since long swale lengths are
 necessary to infiltrate runoff waters, swale
 blocks (berms) have been used to hold
 the runoff water until infiltration has
 occurred. The infiltration rate is critical,
 and care in selecting the rate is important.
   Swales are used primarily along major
highways within the right-of-way areas. However,
some residential areas provide raised inlets to act
as swale blocks and have been widely used in low
ground water table areas.

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Porous  Parking  Area
            pplications included
            both total and
            partial coverage
            using pervious
            concrete surfaces.
            They are used to
            reduce peak runoff
            and infiltrate
rainwater. Pervious concrete has
a special formulated mixture of
uniform open graded aggregate.
Air entraining agents may be
used. Proper installation is
required. Partial coverage with a
concrete grid having regularly
interspersed void areas that are
filled with sand, gravel, or sod is
used in a few areas. Applications
are found statewide and have
been limited to parking and walkway areas.
Alum  Injection
            uffered alum, which is a combination
            of aluminum sulfate and calcium
            compounds, is very effective for the
reduction of phosphorus and some metals. The
injection is being used in Tallahassee and Orlando.
References
Livingston, E., E. McCarron, J. Cox, and P. Sanzone.
   1988. The Florida Development Manual: A Guide to
   Sound Land and Water Management, Florida
   Department of Environmental Regulation,
   Tallahassee, FL.
Wanielista, M.P., Y.A. Yousef, and E. Avellaneda. 1988.
   Infiltration Capacity of Roadside Swales,
   FL-ER-38-88. Florida Department of Transportation,
   Tallahassee, FL
Wanielista, M.P. 1990. Hydrology and Water Quantity
   Control, John Wiley and Sons, New York, NY.

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                            TERRENE
                                INSTITUTE
For further information contact Martin Wanielista, College of Engineering, University of Central
Florida, Orlando, FL 32816 or Eric Livingston, State Department of Environmental Regulation,
2600 Blairstone Road, Tallahassee, FL 32301. This project was funded by the U.S.  Environ-
mental Protection Agency Office of Water Enforcement and Permits-Water Permits Division
and managed by Region V Watershed Management Unit-Water  Division.  Prepared by
Dynamac Corporation, Martin Wanielista,  and JT&A, Inc.  For copies of this publication, con-
tact The Terrene Institute, 1000 Connecticut Avenue, NW, Suite 300, Washington,  DC 20036,
(202) 833-3380.
                                 Printed on Recycled Paper

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