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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