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
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
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
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
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
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);
(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
(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
· 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
· earlier timing of colony formation by wading birds and wood storks,
· resumption of the return frequency of wading bird and white ibis super
· 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
· 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
· enhanced production and community composition of periphyton,
· accelerated accretion of marl substrate,
· increased nesting success and population size of Cape Sable seaside
· persistence and resilience of highly diverse macrophyte and tree island plant
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
· resumption of the return frequency of wading bird and white ibis super
· 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
· persistence and resilience of the mangrove, salt marsh and tidal creek
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-
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
(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
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
(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
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
(1) Crocodile Habitat Suitability and Wood Stork Nesting Patterns
(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
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