Middle St. Johns - Florida Department of Environmental Protection

38 Water Quality Assessment Report: Middle St. Johns
Karst
A type of topography that
is characterized by caves,
sinkholes, springs, and other
types of openings caused by
dissolution of limestone.
The Econlockhatchee River watershed drains 280 square miles of
the western edge of the watershed between Orlando and Bithlo and is
35.8 miles long. The second largest tributary of the St. Johns River, it
enters the St. Johns River south of Lake Harney. The headwaters for
this river include a large swamp drainage known as the Econlockhatchee
Swamp and a karst area with internal drainage. The channel in the
lower portion of this tributary is cut into the shallow water aquifer, which
provides baseflow at all times. The major tributary is the Little Econlockhatchee
River, which drains 71 square miles and is 14.8 miles long.
The Lake Jesup watershed drains 145 square miles. It has only
1 discharge point from Lake Jesup to the St. Johns River, consisting of a
narrow outlet channel by the State Road (S.R.) 46 bridge upstream of Lake
Monroe. Historically, the lake connected to the St. Johns by both river
channel and floodplain marshes. Eleven streams flow into Lake Jesup, of
which 4 are major tributary streams: Gee Creek, Howell Creek, Soldier
Creek, and Sixmile Creek. The largest by drainage area is Howell Creek,
which originates in Lake Maitland in Orlando and drains 52 square miles.
Lake Maitland receives the discharge from numerous lakes, which are
connected by channels or underground pipes. A fixed elevation control
structure controls Lake Maitland’s water level. Howell Creek then continues
northeasterly through Lake Howell. Most of the Howell Creek watershed
is highly urbanized, with extensive loss of wetlands and floods during
major storm events (Rao et al., 1994).
The Lake Kerr watershed drains about 188 square miles (Adamus
et al., 1997). The major waterbody, Lake Kerr, discharges to Lake George
through Salt Springs Run.
The Wekiva River watershed drains more than 376 square miles. The
river forms from the confluence of Wekiwa Springs Run and Rock Springs
Run and flows for approximately 14.2 miles before joining the St. Johns
River north of Lake Monroe. A large part of the river’s discharge is from
springs, on average 64 percent of the total measured flow. Its major tributary
is the Little Wekiva River. This urbanized tributary drains 42 square
miles of largely high-density development. Part of the Little Wekiva River
channel has been replaced by an underground pipe.
Lakes
The total surface area of lakes is 174.3 square miles, or about
9.17 percent, of the basin. Reservoirs occupy 12.53 square miles, or about
0.62 percent.
The largest lakes are the chains of lakes that comprise the St. Johns
River. Lake George, the second largest lake in the state, has a surface
area of 46,000 acres. It receives spring flow from Croaker Hole within
the Little Lake George and via spring runs from Salt Springs, Silver Glen
Springs, Juniper Springs, and Fern Hammock Springs. Lake Monroe
covers 9,406 acres, Lake Jesup, 10,011 acres, and Lake Harney, 6,058 acres;
these are the seventeenth, fifteenth, and twenty-sixth largest lakes, respectively,
by area within the state (Dickinson et al., 1982).
The chain of lakes (Harney, Monroe, and George) that forms the
St. Johns River is believed to have initially developed from natural