D.6 OVERVIEW OF FINAL PERFORMANCE
MEASURES (PMS) USED
BY AET SUBTEAMS
This section provides a brief
summary of the final subset of performance
measures that were used to evaluate Plans A-D and the
problem to be improved or
corrected by the alternative plans. While the subteam
reports presented in Section
D.8 include a far more detailed discussion of the
Performance Measures, the
subregion/topic problem(s) and evaluation results of
Plans A-D, the following list
and brief discussion of the final Performance Measures
was developed to provide a
quick and concise guide to what the Alternatives
Evaluation Team believed were
the most important and desirable hydrologic conditions
to be obtained within each
of the subregions. Likewise, this section does not
discuss the results of the
alternative plans because the results are summarized in
the tables in Section D.7.
Tables showing Plan Rankings, Letter Grades, and Colors,
along with a detailed
discussion can be found in Section D.8. The final
Performance Measures, by
subregion/topic are discussed in the following sections.
D.6.1 The Total System Matrix:
Continuity, Sheetflow, and Fragmentation
The total system matrix was
evaluated according to three attributes:
continuity, sheetflow, and fragmentation.
D.6.1.1 Continuity (expressed as Water
Surface Elevation Differences Across
Barriers)
Water surface elevations on
either side of the C&SF Project structures
(canals and levees) tend to be very different (i.e.
pooling upstream and too dry
downstream) from what they were originally. These
conditions adversely effect
aquatic organisms and their prey. Different species of
wading birds, for example,
rely on various depths of shallow marsh to capture prey.
Abrupt changes in depth,
from too deep and to too shallow, limit feeding
opportunities in these modified
areas.
Final performance measures (PMs) used were based on a
count of the number
of weeks where the difference in water surface
elevations across eight barriers
within the remaining Everglades exceed the difference
predicted by NSM 4.5F. The
eight barriers were L-39 (between Loxahatchee NWR and
WCA-2), L-38 (Between
WCA-2 and 3), Miami Canal South, Miami Canal North,
L-67, Tamiami Trail West
of L-67, Tamiami Trail East of L-67, and L-28.
D.6.1.2 Sheetflow (expressed as
Overland Flow Volume Transects)
Today’s Everglades have been
highly modified from a vast expanse of
sheetflow to a compartmentalized system. The C&SF
Project caused pooling on the
upstream side and excess drying on the downstream side
of hydrologic barriers.
Ponded systems favor some species while flowing systems
favor others. Differences
resulting from these two systems include: food types and
sources, migration of
macroinvertebrates, dispersion of nutrients, aeration
and diffusion of gases in
water, particulate suspension, and thermal
stratification. Sheetflow also helps
shape tree islands, supports microhabitats on the
upstream and downstream sides,
enhances the uptake of nutrients from the water column
and creates an
environment that precipitates phosphorus, along with
calcium carbonate, into the
substrate.
Final PMs used were flow volumes (wet season and dry
season average
overland flows) across 26 transects grouped into
categories representing their
general area: Big Cypress, Central Everglades, Central
Everglades, Southern
Everglades, Tamiami Trail, and L-67.
D.6.1.3 Fragmentation (expressed as
miles of canals and levees)
Levees block the flow of water
and thereby restrict the movement of aquatic
and semi-aquatic life forms. Land-based predators use
levees to invade the marsh
interior and prey upon animals that try to cross these
terrestrial habitats. Levees
also act as conduits by supporting invasion of
terrestrial plants into natural areas.
Canals act as corridors for non-native animals and
plants that extend their ranges
from points of introduction and move into wetlands where
they alter habitats and
affect food webs. Artificial, deep-water habitats
provide thermal and spatial refuge
to large numbers of both non-native and native aquatic
predators in the dry season,
enhancing their survival and ultimate population sizes.
During the dry season,
these predators feed heavily on small marsh fishes and
invertebrates that move into
the canals from adjacent wetlands.
Final PMs used were the number
of miles of canals and levees in the South
Florida Water Management Model bordering or bisecting
natural areas.
D.6.2 Lake Okeechobee
Lake Okeechobee is a valuable
regional as well as local natural resource.
Fluctuation and timing of lake stages affect the distribution
of native and exotic
plant communities, and overall habitat quality (cover,
nesting sites, foraging
habitat) for fish, birds, and other wildlife. Extreme
low lake levels can result in loss
of the littoral zone as habitat for aquatic biota and
promote expansion of exotic
plants into pristine native-plant dominated regions of
the lake. Prolonged moderate
low lake levels also reduce areas of the littoral zone
available for wildlife habitat
and promote exotic plant expansion. Extreme high lake
levels can result in wind
and wave damage to shoreline plant communities, and
transport phosphorus-laden
pelagic water into pristine inner regions of the
littoral zone. Prolonged moderate
high lake levels limit light penetration to the lake
bottom (which results in loss of
benthic plants and algae that stabilize sediments and
provide habitat), and promote
greater circulation of phosphorus-rich waters from the
mid-lake to less eutrophic
near-littoral regions, where phosphorus inputs stimulate
algal blooms.
While extreme or prolonged
high and low lake levels are damaging to the
ecosystem, some variation within an intermediate range
has great benefits. In
particular, a spring recession of lake levels from near
15 feet to 12 feet NGVD has
been shown to favor nesting birds and other wildlife in
the marsh, allow for re-invigoration
of willow stands, and permit fires to burn away cattail
thatch. Yearly
recessions to 12 feet also facilitate the growth of
submerged plant communities,
which serve as habitat for commercially and
recreationally important fish. The goal
is to have a substantial number of these events.
Final performance measures
used were:
1. Frequency and duration of extreme low lake stages
(number of events <11 ft),
2. Prolonged moderate low lake stages (number of
prolonged [>12 months] events
<12 ft),
3. Number of extreme high lake stages (>17 ft),
4. Prolonged moderate high lake stages (number of
prolonged [>12 month] events
>15 ft), and
5. Spring recession patterns based on number of years
January through March lake
stages decline from near 15 ft to 12 ft. without
reversals >0.5 ft.
D.6.3 Lake Okeechobee Service Area
(LOSA)
Water supply effects the
frequency, duration, and severity of water supply
cutback events in the Lake Okeechobee Service Area (LOSA).
The service area
includes the Everglades Agricultural Area, the
Caloosahatchee, St. Lucie, S-4, and
L-8 Basins, and the Seminole Indian (Brighton and Big
Cypress) Reservations.
Performance measures were
developed to evaluate the frequency, duration
and severity of water supply cutback events in the Lake
Okeechobee Service Area.
Water restriction events vary as to how often they occur
(frequency), how long an
event lasts (duration), and how much of the water that
would normally be
demanded is not delivered (severity). Scores were
developed for each of these
characteristics.
The number of years with water
restrictions from the “Frequency of Water
Restrictions” graphic was used to identify water
shortages. The established
performance target is that there be no more than three
years during which cutbacks
occur over the 30-year period of performance available
from each simulation.
The “LOSA Supply Side
Management Report” was used to develop a
combined duration/severity score, for relative
comparisons of alternatives only.
D.6.4 Lower East Coast (LEC)
During the dry season
structural releases are periodically made from the
Water Conservation Areas (WCAs) and Lake Okeechobee to
maintain ground water
levels and to minimize the possibility of saltwater intrusion
along the Lower East
Coast. This water is required to recharge secondary
canal networks, wellfields and
other recharge areas, and lakes. When water stored in
the WCAs and Lake
Okeechobee is scarce, the urban water supply demands are
restricted (cut back) in
order to conserve the remaining supplies in the regional
system.
Several final PMs were used:
1. The ability to meet the 1-in-10 year water supply
planning goal: The planning
goal is to find a balance between ability of the
regional system to supplement
recharge of the aquifer and meet the public water supply
planning goal of a 1-in-10
year level of service in the lower east coast of
Florida. The planning goal is in terms
of the frequency of cutback events and is defined as no
more than three cutback
events, no more than seven months in duration over the
period of record.
2. Percentage of months not in a water supply cutback:
The duration of water
supply cutbacks was used as an indicator of the
reliability of water supplies.
3. Stage duration curves in south Miami-Dade canals:
saltwater intrusion criteria
do not exist for the major canals in southern Miami-Dade
County. However, water
levels in these canals were evaluated because
encroachment of the salt front into
the Biscayne aquifer has occurred previously in this
area. Also, major public water
supply wellfields are located in southern Miami-Dade
County. This area was
evaluated by using the stage duration curves for the
following structures: C-100A @
S-123, C-1 @ S-21, C-102 @ S-21A, and C-103 @ S-20F.
D.6.4.1 Performance Measure Used in
the Agricultural Area along the L-31N
Six cells in the western areas
of southern Miami-Dade County were
evaluated. End of the month stage duration curves for
1983-1993 were used to
compare an 11-year target stage duration curve to the
31-year stage duration
curves for the bases and alternatives.
D.6.5 Northern/Central Everglades
Modifications to hydropatterns
have resulted in adverse impacts on the flora
and fauna inhabiting portions of the Everglades that now
exist as Water
Conservation and other managed areas. The Performance
Measures identified for
use in the Restudy were developed to evaluate a plan’s
potential for:
· protection and accretion of
peat soils (indicated by a low predicted occurrence
of extreme low water [depths more than 1.0 ft below
ground surface]);
· persistence of tree island
communities (indicated by a low predicted
frequency of extreme high water); and
· an inundation pattern suitable
for an Everglades sawgrass or ridge-and-slough
marsh (indicated by a number and mean duration of
inundation events
that either closely matched the target for that
indicator region, or that fell
within the range of patterns predicted by the NSM for
that landscape type).
The final set of Performance
Measures used was:
(1) Inundation pattern (number
and mean duration of inundation periods);
(2) Extreme high water (number
and mean duration of high water events);
and
(3) Extreme low events (number
and mean duration of low water events).
Target variable values for the
performance measures were those predicted by
NSM 4.5, Final, with four exceptions:
(1) Indicator Region 17,
performance was evaluated by comparing values to
the average of NSM values for
Indicator Regions 14 and 18; this was because
the NSM depths in this
indicator region had been identified during
evaluation of alternatives 1-3
as being lower than desirable for this relatively
pristine marsh area;
(2) LNWR, the targets were
1995 Base values, in keeping with the refuge’s
current regulation schedule;
(3) High water extremes, the
performance target was that the number and
duration of events be less
than or equal to NSM values; and
(4) Low water extremes, the
performance target was for frequencies and
duration of events to be
minimized.
The final evaluation
classified the indicator regions into ten subregions that
correspond to areas with distinct hydrologic
performance. These are:
(1) Loxahatchee NWR (Indicator
Regions 26 & 27);
(2) Holey Land &
Rotenberger WMAs (Indicator Regions 28 & 29);
(3) WCA-2A (Indicator Regions
24 & 25);
(4) WCA-2B (Indicator Region
23);
(5) NW WCA-3A (N of Alligator
Alley & W of Miami Canal; Indicator
Regions 20 & 22);
(6) Northeastern WCA-3A (N of
Alligator Alley & E of Miami Canal;
Indicator Region 21);
(7) Eastern WCA-3A (S of
Alligator Alley, E of Miami Canal; Indicator
Region 19);
(8) Central & Southern
WCA-3A (S of A. Alley, W of Miami Canal; Indicator
Regions 14, 17 & 18);
(9) WCA-3B (Indicator Regions
15 & 16); and
(10) Pennsuco Wetlands
(Indicator Regions 52 & 53).
D.6.6 Southern Everglades
Southern Everglades were was
evaluated according to two regions: Shark
River Slough and Rockland Marl Marsh.
D.6.6.1 Shark River Slough
Ecological values and
indicators of restoration success in Shark River Slough
that are linked to the hydrologic performance measures
in the conceptual model
include:
· increased
nesting success and abundance of American alligators and a
corresponding increase in the number of occupied alligator holes
to serve
as drought refugia and to increase habitat heterogeneity,
· increased
population density of aquatic fauna,
· increased
abundance of wading birds and wood storks,
· re-establishment
of coastal nesting colonies of wading birds and wood
storks,
· earlier
timing of colony formation by wading birds and wood storks,
· resumption
of the return frequency of wading bird and white ibis super
colonies,
· enhanced
production and community composition of periphyton,
· accelerated
accretion of peat soils, and
· persistence
and resilience of macrophyte and tree island plant
communities including the cessation of sawgrass expansion into
wet
prairies and sloughs.
Priority performance measures
for the ecological restoration of Shark River
Slough are identified in the Everglades Sloughs
Conceptual Model. Those
measures, in order of priority, are:
(1) duration of uninterrupted
flooding,
(2) drought severity as
measured by the duration of dry conditions,
(3) water depth during periods
of flooding,
(4) total annual flow volume,
and
(5) seasonal distribution of
flow in mid Shark River Slough.
NSM4.5 Final (NSM4.5F) characterized
Shark River Slough as a
predominantly aquatic system that was continually
flooded and flowing during wet
and dry seasons and during wet years and all but the
most extreme dry years.
NSM4.5F indicated that Shark River Slough would have
dried only two, three and
six times during the 31-year period of record in the NE,
Mid and SW indicator
regions, yielding uninterrupted periods of inundation
that averaged 535, 401 and
226 weeks. Water depths averaged 1.8, 1.6 and 1.2 feet
during periods of flooding in
the three respective indicator regions. Dry conditions
lasted for an average of four,
three and six weeks respectively.
D.6.6.2 Rockland Marl Marsh
Ecological values and
indicators of restoration success in the Rockland Marl
Marsh that are linked to the hydrologic performance
measures in the Conceptual
Model include:
· re-colonization
and population resurgence by American alligators and a
subsequent increase in the number of occupied alligator holes to
serve as dry
season refugia for aquatic fauna and to increase habitat
heterogeneity,
· increased
population density of aquatic fauna,
· increased
seasonal abundance and foraging activity of wading birds and wood
storks,
· enhanced
production and community composition of periphyton,
· accelerated
accretion of marl substrate,
· increased
nesting success and population size of Cape Sable seaside
sparrows, and,
· persistence
and resilience of highly diverse macrophyte and tree island plant
communities.
Priority hydrologic
performance measures for the ecological restoration of the
Rockland Marl Marsh are identified in the Marl
Prairie/Rocky Glades Conceptual
Model. Those measures, in order of priority, are:
(1) duration of uninterrupted
flooding,
(2) drought severity as
measured by the duration of dry conditions, and
(3) number of wet season water
level reversals when the depth drops to less
than 0.2 feet during a period of flooding.
NSM4.5F characterized the
Rockland Marl Marsh as a seasonally flooded
system where water levels typically dropped below the
ground surface during most
years, except during prolonged high rainfall periods
when the marsh remained
flooded for multiple years. NSM4.5F indicated that
uninterrupted periods of
inundation averaged 44 weeks. Only two wet season water
level reversals occurred
during 31 years. Dry conditions lasted for an average of
26 weeks.
D.6.7 Florida Bay
Ecological values and
indicators of restoration success in the Florida Bay
mangrove estuary and coastal basins that are linked to
the hydrology/salinity
performance measures in the conceptual model include:
· increased
production of low-salinity mangrove fish and invertebrates,
· re-establishment
of coastal nesting colonies of wading birds and wood
storks and eastern Florida Bay colonies of roseate spoonbill,
· earlier
timing of coastal colony formation by wading birds and wood
storks,
· resumption
of the return frequency of wading bird and white ibis super
colonies,
· increased
growth and survival of juvenile American crocodiles,
· increased
cover of low-to-moderate salinity aquatic macrophyte
communities in coastal lakes and basins,
· return
of seasonal waterfowl aggregations to coastal lakes and basins,
· enhanced
nursery ground value for sport fishes and pink shrimp in coastal
basins, and
· persistence
and resilience of the mangrove, salt marsh and tidal creek
vegetation mosaic.
Priority performance measures
for the ecological restoration of the Florida
Bay coastal basins are identified in the Florida Bay
Mangrove Estuarine Transition
Conceptual Model. All performance measures are based on
relationships between
mean monthly salinity in five coastal basins, from Joe
Bay to North River Mouth, to
water stage at the P33 gage in mid Shark River Slough.
The final PMs used are:
(1) number of months during
the period of record when stages equal or
exceed 6.3 feet msl at P33,
(2) number of months during
the period of record when stages equal or
exceed 7.3 feet msl at the P33
gage,
(3) cumulative salinity
difference (ppt) from the undesirable high salinity
levels that were identified
for each basin, and
(4) cumulative salinity
difference (ppt) from desirable low salinity levels that
were identified for each basin
during the wet/dry season months of August-
October.
D.6.8 Model Lands / C-111
The Model Lands Alternatives
Evaluation Matrix consists of the following
performance indices, which are applied to each of the
four indicator regions in the
Model Lands area: 4, 5, 6, and 47:
(1) High water index: The
proportion of time that water levels are below the
high water threshold which has
been specified for the indicator region. The
target is 1.00, however
proportions down to 0.90 are acceptable to allow for
interannual variation. This
index quantifies the period of time that water
levels are so high that they
may stress the vegetation communities naturally
characteristic of these areas.
(2) Low water index: The
proportion of time that water levels are above the
specified low water threshold.
The target is 1.00. This criterion seeks to
minimize the period of time
that water levels are below a specified low water
level.
(3) Extreme low water index:
The proportion of time that water levels less
than 1 ft below the specified
low water threshold. Target is 1.00. Values
near 1 indicate that dry
season levels are above the extreme low water level
almost all of the time. Values
closer to 0 indicate that dry season water
levels typically fall at least
another foot below the specified low water level.
(4) Relative dry period slope
index: Relative measure of the steepness of the
slope of the stage duration curve
during dry periods. The index can vary
from almost 0 (very steep
slope; water levels drop dramatically during dry
periods) to approximately 1.0
(slope shallow; water levels relatively stable
throughout the dry season).
Values closer to one are preferred.
(5) Wet season inundation
pattern index: Proportional measure of how many
times during the 31-yr
simulation that water levels drop below surface
elevation during the
July-October portion of the wet season. The best
alternative received a score
of 1.0 and the worst received a score of 0.0. This
criterion gives a relative
ranking for how many times the aquatic habitat is
disrupted by dry-downs during
the core months of the wet season. The
months June and November were
omitted from the analysis to allow for
variation early and late in
the season.
(6) Late wet season inundation
index: Proportional measure of how many
times during the 31-yr
simulation that autumn periods of inundation ended
during the months of November
and December. This index was applied only
to Indicator Region 5 (Model
Lands South), which includes habitat critical for
Roseate Spoonbill feeding. A
good year for wading bird feeding would be
characterized by standing
water in this indicator region well into January.
Premature drydowns in the
early dry season in this region may severely
reduce available food to
support Roseate Spoonbill nesting. The best
alternative received a score
of 1.0 and the worst received a score of 0.0.
D.6.9 Big Cypress
The Big Cypress area was
evaluated as three areas, North Big Cypress,
South Big Cypress, and Southeast Big Cypress. The
following is a summary
description of the PMs and problems by subarea:
D.6.9.1 North Big Cypress National
Preserve.
Impacts in north Big Cypress
are due primarily to agricultural development
and its associated canals upstream (north) of this area.
However, the results were
suspect because there are model boundary problems with
hydrologic model output
in this area since the area to the north is included in
the Natural System Model, but
not the South Florida Water Management Model. PMs used
were:
(1) Percent of North Big Cypress National Preserve that
matches NSM (mean NSM
hydroperiod matches)/100. This PM provides a spatial
measure of one of the more
impacted portions of the Big Cypress that lies along its
northern border.
(2) Reduction in percent of time inundated from NSM
condition based on indicator
regions 42-43. This PM provides a measure of deviation
from NSM hydroperiod for
these indicator regions.
(3) Maximum deviation from NSM stage duration curve
using indicator regions 42-
43. This PM used normalized weekly stage duration curves
to provide a measure of
how much water levels have been altered from NSM
conditions as a function of the
NSM range of fluctuation for these indicator regions.
(4) Average flood duration for indicator regions 42-43.
This PM provides a measure
of deviation from NSM for average duration of individual
flooding events for
indicator regions 42-43.
D.6.9.2 South Big Cypress National
Preserve.
Final PMs used for the
southern portion of the Preserve:
(1) Percent of South Big
Cypress National Preserve that matches NSM (mean
NSM hydroperiod matches)/100.
This PM provides a spatial measure of the
relatively unimpacted portion
of the Big Cypress.
(2) Reduction in percent of
time inundated from NSM condition based on
indicator regions 31, and
36-40. This performance measure provides a
measure of deviation from NSM
hydroperiod for an indicator region.
(3) Maximum Deviation from NSM
stage duration curve based on indicator
regions 31, 36-40. Normalized
weekly stage duration Curves were used to
measure how much water levels
have been altered from NSM conditions as a
function of the NSM range of
fluctuation for the indicator regions.
(4) Average flood duration for
indicator regions 31, 36-40. This PM provides
a measure of deviation from
NSM for average duration of individual flooding
events for indicator regions
31, 36-40.
(5) Percent change in flow
from NSM condition/100. Total flows during the
wet and dry season for a flow
cross section (“Eastern Big Cypress”) were used
to express hydrologic
conditions and how they changed in response to
proposed alternatives.
D.6.9.3 Southeast Big Cypress.
Final PMs used for the
southeast Big Cypress were:
(1) Reduction in percent of
time inundated from NSM condition. This PM
provides a measure of
deviation from NSM hydroperiod for indicator region
13.
(2) Maximum deviation from NSM
stage duration curve. This PM used
normalized weekly stage
duration curves to provide a measure of how much
water levels have been altered
from NSM conditions as a function of the NSM
range of fluctuation for
indicator region 13.
(3) Average flood duration for
indicator region 13. This PM provides a
measure of deviation from NSM
for average duration of individual flooding
events for indicator region
13.
(4) Percent change in flow
from NSM condition/100. Total flows during the
wet and dry season for a flow
cross section (“Lostman’s Slough”) were used to
express hydrologic conditions
and how they changed in response to proposed
alternatives.
D.6.10 Caloosahatchee Estuary
Caloosahatchee Estuary has been adversely impacted by
extreme water
delivery events from Lake Okeechobee and local drainage
basins. These events
cause extreme ranges in salinity as well as severe
physical alterations within the
estuary. The following are the final performance
measures used:
1. Minimum mean monthly flows less than 300 cfs. This PM
is based on the
number of times the minimum mean monthly flows from the
lake and watershed
fall below 300 cfs at S-79. Insufficient fresh water
discharges had direct effects on
estuarine seagrasses, fish and invertebrates, including
critical indicator species (e.g.
Vallisneria) by enabling the estuary to become too
saline.
2. Mean monthly freshwater discharges exceeding 2,800
cfs. This PM is based on
the number of times mean monthly flow exceeds 2,800 cfs
as measured at S-79.
High volume discharges to the estuary contribute to poor
estuarine water quality
conditions including increased turbidity, color and
violation of favorable salinity
envelopes. These conditions have direct effects on
estuarine seagrasses by reducing
light penetration necessary for photosynthesis,
destroying fish and invertebrate
habitat, and contributing to unfavorable salinities for
aquatic vegetation, fish and
invertebrates, including critical indicator species
(e.g., the American oyster, turtle
grass, and Vallisneria).
3. Fresh water discharges exceeding 4,500 cfs. This
performance measure is based
on the number of times mean monthly flows exceed 4,500
cfs at S-79. Mean
monthly flows above 4,500 cfs results in freshwater
conditions throughout the entire
estuary causing impacts to estuarine biota. This volume
of flow also begins to
reduce water quality and adversely impact biota in San
Carlos Bay.
4. Zone A discharges from Lake Okeechobee. This PM is
based on the number of
days of Zone A discharges from the lake, measured as
7,800 cfs per day at S-79.
Zone A discharges have rapid and serious effects on
estuarine seagrasses in the
Caloosahatchee River Estuary and San Carlos Bay by
reducing light penetration
necessary for photosynthesis destroying fish and
invertebrate habitat, and
contributing to unfavorable salinities for estuarine
biota.
D.6.11 St. Lucie Estuary
The St. Lucie Estuary receives freshwater inputs both
through interbasin
transfer from Lake Okeechobee and from local watershed
contributions. The
maintenance of flows to the estuary to achieve the
appropriate salinity regime
therefore must manage both watershed runoff and
regulatory flows from Lake
Okeechobee. Final PMs used were:
1. Minimum flows (mean monthly flows <350 cfs). This PM is based on the
number
of months the mean monthly flows fall below 350 cfs. The
target is to have no more
than 50 months with mean monthly flow less than 350 cfs.
Insufficient freshwater
discharges during the dry season contribute to reduced
estuarine productivity.
Minimum levels of inflow and nutrients usually occur at
the end of the dry season
(April and May). It is during these months that numerous
species of juvenile fish
depend on an abundant food supply of phytoplankton and
zooplankton which requires
a minimum level of fresh water and nutrients.
2. Moderately high flows (mean monthly flows
>1,600cfs). This PM is based on the
number of months with mean monthly flows > 1,600 cfs.
The acceptable violations
(target) allowing for natural variation is nine. As
flows exceed this limit, salinity is
reduced below desirable levels for some estuarine
resources. High volume discharges
to the estuary contribute to poor estuarine water
quality including increased
turbidity, and violation of the favorable salinity
envelope. These events have direct
effects on submerged aquatic (SAV) by reducing light
penetration necessary for
photosynthesis, degrading fish and invertebrate habitat,
and contributing to
unfavorable salinity concentrations for aquatic
vegetation, fish and invertebrates,
including the indicator species (American oyster and
SAV).
3. High flows (mean monthly flows>2,500 cfs). This PM
measures the number of
times mean monthly flows from the lake and watershed
exceeds 2,500 cfs. The target
is no more than three months with mean monthly flows
> 2,500 cfs. Mean monthly
flows above 2,500 cfs result in freshwater conditions
throughout the entire estuary
causing severe impacts to estuarine biota. This volume
of flow begins to impact the
Indian River Lagoon to the north and south of the St.
Lucie Inlet.
4. Zone A discharges. This PM is based on the number of
days of Zone A discharges
from Lake Okeechobee (7,200 cfs per day at S-80). The
target is zero (0) violations.
Zone A discharges transport large amounts of sediment
and results in freshwater
conditions within the entire estuary. These events can
have rapid and serious effects
on estuarine SAV by reducing light penetration necessary
for photosynthesis,
destroying fish and invertebrate habitat and contribute
to unfavorable salinity
concentrations for most aquatic life. Zone A discharges
cause adverse effects on large
areas of the Indian River Lagoon surrounding the St.
Lucie Inlet and possibly
influence nearshore ocean habitats adjacent to the
Inlet.
D.6.12 Lake Worth
Lake Worth has been adversely impacted by altered
salinity. The
performance measure used in this analysis for the Lake
Worth Lagoon was
“Wet/Dry season average flows discharged to Lake Worth
Lagoon through S-40, S-41,
and S-155 for the 31 year simulation.” The restoration
target is to create
estuarine conditions, to the extent possible, in the
Lake Worth Lagoon. An
estuarine salinity envelope of 23 ppt to 35 ppt has been
chosen as the target salinity
range. This is a viable salinity range for a number of
organisms, many which are
commercially and recreationally important. To attain
this salinity a maximum flow
needed to be developed. Previous hydrodynamic modeling
indicated that 500 cfs
creates a steady state salinity of 23 ppt. For the low
flow part of the salinity
envelope, 0 cfs is the target. Enough ground water
occurs that should still allow
estuarine conditions. Based on past modeling, this flow
range of 0-500 cfs should
create the salinity range of 23 ppt - 35 ppt.
Performance Measure: Wet/Dry Season Average Flows
Discharged to Lake
Worth through S-40, S-41 & S-155 for the 31-year
simulation.
D.6.13 Biscayne Bay
Operation of coastal water
control structures results in rapid changes in
salinity gradients within Biscayne Bay that may occur on
a daily basis and over
several months, particularly during the rainy season.
During the dry season,
hypersalinity has been observed as a result of
evaporation, retention of canal flow,
and bay circulation. The presence and operation of the
canals and construction of
permanent oceanic inlets has resulted in a loss of
estuarine function and shifted
Biscayne Bay to more of a lagoon, adversely impacted
from freshwater pulses and
highly variable salinities. These conditions have been
at least partly responsible for
the loss of historically abundant estuarine species,
such as red drum, black drum,
and eastern oyster, the loss of juvenile fish habitat,
and the significant increase in
stress-tolerant fish species such as the gulf toadfish.
Performance measures were
developed based on the potential effect of water
management alternatives on surface water reaching
Biscayne Bay. Canal
discharges from gauged structures on canals that
discharge into the bay were used.
Based on SFWMM hydrologic model output, the bay was
divided into five regions
from north to south, based on the mean monthly discharge
from water control
structures in these regions. The regions were:
· Snake Creek (S29),
· North Bay (G58, S28, S27),
· Miami River (S25, S25B, S26),
· Central Bay (G97, S22, S123),
and
· South Bay (S21, S21A, S20F,
S20G).
Model output for each
alternative provides results as the sum of discharge
from the structures in each region in terms of a mean
annual wet season and dry
season volume. To judge the performance of a water
management alternative in
meeting restoration targets, model results were compared
to surface water budget
targets that were considered appropriate to achieving
restoration of the Biscayne
Bay ecosystem. These targets consist primarily of the
existing average annual
inflow to Biscayne Bay as defined by the 1995 Base
hydrologic period, with a 2%
increase in total inflow budget to be applied in the dry
season to the Central and
South Bay regions. A separate target for Snake Creek
(S29) was also developed
based on canal discharge that would maintain salinity
suitable for oyster survival.
D.6.14 Keystone/Endangered
Species/ATLSS
Evaluation of Restudy Alternatives’ performance with
regard to threatened,
endangered and keystone species was accomplished through
a combination of
several methods. ATLSS modeling results provided
information on expected
biological responses of several species and species
groups. The nature and extent of
information available through ATLSS results varied among
species and species
groups depending on the progress of each model’s
development. For example,
highly sophisticated results were available for the Cape
Sable seaside sparrow’s
western population and for fish abundance because
development of these models
was nearly complete at the time of evaluations. Less
sophisticated foraging or
breeding conditions indices were available for the snail
kite, wading birds, and
others because these models were in an earlier stage of
development. ATLSS
results for each Alternative were compared with results
for other Alternatives as
available, 2050 Base conditions, and in most cases, with
1995 Base conditions.
When results indicated that the Alternative would
improve species’ biological
response as compared to other scenarios, the subteam
concluded that there was
evidence to suggest that the Alternative was beneficial
for those species as
compared to the other scenarios.
Additional sources of evidence were considered as they
were available. These
included:
(1) Crocodile Habitat
Suitability and Wood Stork Nesting Patterns
performance measures;
(2) information on known
hydrological responses of species gleaned from
Volume I of the Multi-species
Recovery Plan for the Threatened and
Endangered Species of South
Florida, Technical/Agency Draft; and
(3) discussions with research
biologists widely recognized as experts on
particular species.
These sources of information
were considered along with ATLSS modeling
results to form a “weight of the evidence” or
“consensus” conclusion by the subteam
members and species experts. Results of the analyses are
presented in Table 7.
D.6.15 Water Quality
The Water Quality Team
utilized two water quality models in their analyses:
the Lake Okeechobee Water Quality Model, which simulates
lake eutrophication
processes and the Everglades Water Quality Model, which
simulates phosphorus
transport in the Everglades Protection Area. In
addition, an evaluation of the effect
of Restudy alternative plans on hydraulic and phosphorus
loads into and predicted
performance of the Everglades Construction Project was
performed by William W.
Walker, Jr. (Walker, 1998) using hydrologic outputs of
the South Florida Water
Management Model. The Water Quality Team also utilized
hydrologic outputs from
the South Florida Water Management Model to evaluate the
extent of hydrologic
change and corresponding water quality impacts or
benefits resulting from the
implementation of the alternative plans in other
subregions of the study area.
The Water Quality Team’s
evaluation was conducted on a sub-regional basis
by dividing the study area up into subregions. The team
did not empirically
evaluate the effect of Restudy alternatives on water
quality conditions in the Big
Cypress basin or the Holey Land and Rotenberger Wildlife
Management Areas. For
those areas, a qualitative assessment was made based
upon the proposed operation
of the components contained in the alternatives. Results
of the water quality team
are presented in Table 8.
The Water Quality Team
considered in detail existing federal, state, and
Tribal water quality regulatory programs in the study
area. For each alternative
plan, the plan’s components were examined to identify
potential water quality
impacts or benefits resulting from the operation of that
component and the
regulatory or ecosystem management programs affecting
the future implementation
of the component. Specific issues which were considered
by the Water Quality
Team during evaluations of alternative plans include
numeric and narrative water
quality criteria, designated uses of source and
receiving water bodies, special
classifications (e.g., Outstanding Florida Waters), and
existing and projected
pollution loads.