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vertical bulkheads/seawalls. Shoreline mangroves are also nearly non-existent |
within this area, with the exception of shoreline mangroves within Oleta River |
State Park. |
Northern Biscayne Bay |
Immediately south of the Snake Creek/Oleta River sub-region, Northern |
Biscayne Bay (Figure 3) extends approximately 7.8 miles from the Oleta |
River/Haulover Beach Park area south to the northern edge of the Venetian |
Causeway area. The Bay widens considerably in this sub-region when compared |
with the Snake Creek/Oleta River area, varying in width from approximately |
one-half mile to 2.5 miles. Seagrasses are present throughout much of this area, |
which also includes one inlet, Baker’s Haulover. Shoreline mangroves are nearly |
non-existent within this sub-region. |
Miami River/Government Cut |
Located immediately south of the Northern Biscayne Bay sub-region, the Miami |
River/Government Cut sub-region (Figure 4) extends southward approximately |
3.2 miles south to the south side of the Rickenbacker Causeway. Natural |
conditions in this portion of the Bay are limited, with nearly all of the substrate |
having been dredged or filled. Seagrass and shoreline mangrove communities |
are largely absent from this sub-region except in its most southerly reaches, and |
water quality is heavily influenced by both tidal action through Government Cut |
and Bear Cut, and freshwater discharges from the highly modified Miami River. |
Central Biscayne Bay |
Immediately south of the Miami River/Government Cut sub-region, the Central |
Biscayne Bay sub-region (Figure 5) extends approximately 9.5 miles southward |
to the Cutler area. Two major canals (i.e., C-3 and C-2) empty into the Bay within |
this sub-region, which varies from approximately 1.5 miles to over 7 miles in |
width. Seagrasses are a prominent component of the sediment surface in this |
Biscayne Bay Characteristics |
Freshwater Flow and Ecological Relationships in Biscayne Bay 2-11 |
area, and mangroves are present sporadically along the shoreline. South of the |
barrier island of Key Biscayne, there is a direct connection with marine waters |
along the majority of the eastern portion of the Bay. |
South-Central Biscayne Bay |
Immediately south of the Central Biscayne Bay sub-region, the South-central subregion (Figure 6) extends approximately 15.8 miles southward to the Turkey |
Point/Cutter Banks area. Five major canals (i.e., C-100, C-1, C-102, Military Canal |
and C-103) empty into the Bay within this sub-region, which varies in width |
from approximately seven miles in the north to approximately five miles in the |
south. The substrate in this area is largely hardbottom interspersed with |
seagrasses and the western shoreline is primarily mangrove-lined. |
Southern Biscayne Bay |
Immediately south of the South-central sub-region, the Southern Biscayne Bay |
sub-region (Figure 7) extends approximately 17.2 miles southward from the |
Turkey Point area to the U.S. Highway 1 bridge that serves as the project’s |
southern boundary. There is one major canal (C-111) that discharges into the Bay |
in this sub-region. Seagrasses are a prominent feature in this sub-region, |
mangroves line the majority of the western shoreline, and direct tidal connection |
with marine waters is reduced by the natural obstructions of the offshore barrier |
island of North Key Largo, which is approximately five miles from the mainland |
shoreline. |
FRESHWATER FLOWS AND SALINITY CONDITIONS |
Freshwater flows and salinity conditions are described in detail in the SFWMD |
1995 Biscayne Bay SWIM Plan (Alleman et al. 1995) and the 1999 Issue Paper on |
Freshwater Flows into Biscayne Bay by Bellmund, et. al. (1999). The following |
provides some background taken from these references. During 2004, the |
District will be evaluating these freshwater flow and salinity relationships as part |
of MFL development for Biscayne Bay. |
Biscayne Bay is the largest estuary on the coast of southeast Florida and is |
contiguous with the southern Everglades and Florida Bay system. Historically, |
the Everglades, Biscayne Bay, and Florida Bay were part of a larger |
hydrologically connected natural system of coastal lagoons and wetlands. |
Biscayne Bay served as the eastern outlet of the Everglades (Davis, 1943; Parker |
et al., 1955). Historically, freshwater flowed overland to the Bay through natural |
sloughs and rivers, and as groundwater through the Biscayne Aquifer (Buchanan |
and Klein, 1976; Kohout and Kolipinski, 1967; Parker et al., 1955). This pattern |
Biscayne Bay Characteristics |
Freshwater Flow and Ecological Relationships in Biscayne Bay 2-12 |
has been altered by regional drainage, canal construction and operation, urban |
development, as well as construction of roads, levees, and other hydrologic |
barriers to surface flow. The Bay currently receives freshwater inflow as canal |
flow, minor overland flow, and groundwater (Alleman et al., 1995, Kohout and |
Kolipinski 1967, Buchanan and Klein 1976. |
Biscayne Bay is a shallow generally well mixed system in which circulation is |
primarily controlled by tidal action, proximity to inlets, water depth, salinity and |
wind speed and direction. Salinity is maintained by the amount of freshwater |
inflow and rainfall, tidal movements of sea water, and evaporation. Changes to |
physical features of the bay have occurred over time, resulting in changes in |
circulation and flushing patterns, salinity structure and the creation of different |
habitats. Much of the upper bay has been modified and dredged, so that depths |
now average six to 10 feet and include some dredged areas and channels up to 40 |
feet deep. Construction of inlets, channels, islands, causeways and deep holes |
(as sources of fill) have altered the natural circulation patterns of the bay |
resulting in areas that are stagnant and have poor water quality or high salinities |
and bottom conditions that will not support stable, viable or desirable benthic |
communities. |
A basin of about 840 square miles drains to the bay. Drainage of surface waters |
from eastern Miami-Dade County into Biscayne Bay is primarily controlled by |
the system of canals, levees, and control structures constructed as part of the |
Central and Southern Florida Flood Control Project (C&SF Project). C&SF Project |
control structures regulate the flow of water in the canals, facilitate the discharge |
of excess water during flooding and control water levels during drought periods. |
Historically, during wet periods, large amounts of water entered the bay as |
surface water that flowed across adjacent freshwater marshes. Today, the |
construction and operation of canals has accelerated the rate at which ground |
water levels recede at the end of the wet season, because surface water now |
discharges from the canals at a much faster rate than under natural conditions. |
Seventeen canals in eastern Miami-Dade County operated by the SFWMD |
provide most of the surface flows of freshwater into the bay. |
Changes made by man have altered the timing of flows to the bay increasing the |
amount and rate of runoff that occurs. Generally, more water now flows to the |
bay during the wet season and less water flows to the bay during the dry season, |
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