Lake Seminole was produced by the construction of the Jim
Woodruff dam and is the result of the water flow coming in from the
Chattahoochee and Flint Rivers. Originally, the confluence of these
two rivers was about 1000 feet north of where the dam is now. The
construction of the dam and the resulting lake drastically changed
the geology of the surrounding area in southwest Georgia and north
Florida.
The impoundment or production of Lake Seminole reduced the
amount of ground water flowing from Florida to Georgia southeast of
the lake. Ground-water storage was increased by the impoundment, as
indicated by an increase of as much as 26 feet in the water level
in the Upper Floridan aquifer. The impoundment of Lake Seminole
caused changes to the components of the ground-water budget,
including reduced discharge from the Upper Floridan aquifer to
streams (315 million gallons per day); reduced recharge from or
increased discharge to regional ground-water flow at external
boundaries (totaling 183 million gallons per day); and reduced
recharge from or increased discharge to the undifferentiated
overburden (totaling 129 million gallons per day).
What this means is the lake interacts hydraulically with the
limestone bedrock by direct leakage through sinkholes, cavities,
and other dissolution features that were once exposed in the
karstic floodplains of the Chattahoochee and Flint Rivers, but
since impoundment are now part of the lake bed. The region is
underlain by karst limestone of Eocene and Oligocene age that
comprises the Upper Floridan aquifer. A relatively thin mantle of
chemically weathered limestone residuum and alluvium, collectively
termed undifferentiated overburden, overlies the aquifer and allows
indirect leakage to and from Lake Seminole where these sediments
are present in the lake bed. Many springs originate in the
limestone discharge into Lake Seminole along the lake bottom or
adjacent to the impoundment arms, flowing into the lake from small
channels or spring runs.
This Upper Floridan aquifer is also one of the most productive
aquifers in the United States, and in the Lake Seminole area is the
primary source of ground water for agriculture, industry, and
public supply. The impoundment or production of Lake Seminole by
the dam changed ground-water flow directions in the Upper Floridan
within about 20–30 miles of the lake. The largest change
occurred southeast of the lake, where, prior to impoundment, ground
water flowed from Florida into Georgia, discharging to the Flint
River downstream of Bainbridge, Ga. This water then flowed into the
Apalachicola River. Following impoundment, ground water southeast
of the lake flows from Lake Seminole to the Apalachicola River.
Also, discharge to the Upper Floridan aquifer from Lake Seminole
has created an increase in the amount of ground water that is
stored in this area. Aquifer water levels were increased by as much
as 26 ft near Jim Woodruff Lock and Dam; the area in which water
levels were increased at least 10 ft extends nearly 20 miles
upstream along the Chattahoochee and Flint Rivers, and several
miles downstream along the Apalachicola River.
The cause of all this change to the geology of the local area
was the construction of this dam. With construction having begun in
1947, the Jim Woodruff Lock and Dam was completed in 1957 by the
U.S. Army Corps of Engineers. It is a hydroelectric dam about 1,000
feet (300 m) south of what was the original headwaters of the
Apalachicola River. The confluence of the two rivers that formed it
is now submerged under the lake that the dam formed. The dam is
named in honor of James W. Woodruff, Sr., a Georgia businessman who
spearheaded the development of the Apalachicola-Chattahoochee-Flint
Project. The Jim Woodruff Lock and Dam impounds Lake Seminole,
produces hydroelectric power and allows navigation of the
Chattahoochee River. It is the southernmost dam on that river and
is located on the downstream end of Lake Seminole. Lake Seminole is
produced by the confluence of the Chattahoochee and Flint Rivers.
On the downstream side of the dam is the Apalachicola River, which
flows south and empties into the Gulf of Mexico.
The dam is located entirely within the state of Florida, but all
except the extreme southern part of Lake Seminole right at the dam
is located in Georgia and in the part of the Florida panhandle that
wraps around the southwest corner of Georgia. In fact, as you drive
onto the dam from the east you cross over into Georgia for about a
mile and then cross back over the Florida state line as you
approach the dam.
Lake Seminole
You can just make out the Chattahoochee River to the northwest
and Flint River to the northeast from here.
Jim Woodruff Lock and Dam is constructed in the Lower Miocene
Tampa Limestone, an earthy-to-crystalline limestone that provides
about 160 feet of local relief adjacent to the Apalachicola River
at the lock and dam (U.S. Army Corps of Engineers, 1948). Several
hundred feet of thickness of soluble and easily degraded limestone
of Eocene and Oligocene age in the Upper Floridan aquifer underlies
the Tampa Limestone near the dam. Solution features and caverns in
the karst limestone provide the mechanism for springflow to enter
Lake Seminole along the impoundment arms, and conversely, for water
to leak vertically out of the lake into the Upper Floridan aquifer
beneath the dam. Irregular and undulating topography containing an
abundance of sinks and depressions, typical of karst terrane,
dominated the pre-impoundment landscape of the Lake Seminole area.
Deeply incised remnants of former river channels contained water at
levels that fluctuated independently of the river, and shallow,
small depressions drained rapidly into the subsurface. These
features align in a general upstream-to-downstream direction,
indicating possible solutioning along a joint or fault system in
the underlying limestone. Drilling and exploration prior to
construction of Jim Woodruff Lock and Dam indicated the presence of
cavernous and deeply weathered bedrock. Most of the solution
cavities encountered during drilling were filled, although open,
water-bearing cavities were encountered in some of the borings
(U.S. Army Corps of Engineers, 1948). Water from in-lake sinkholes
acting as reverse-flowing springs, and from unknown leakage sites
in Lake Seminole, upwells or “boils up” in the
streambed of the Apalachicola River at a sink-hole or ledge-like
structure termed the “River Boil,” about 900 ft
downstream from Jim Woodruff Dam. Dye tracing performed by the
Corps of Engineers indicated that part of this lake leakage first
emerged from Polk Lake Spring, on the western flood plain of the
Apalachicola River and about 800 feet downstream from the dam. The
Polk Lake Spring is an artesian well located at approximately N 30,
42.267, W 84, 52.112. Flow from Polk Lake Spring combines with
other springflow from the south and enters a sinkhole on the flood
plain. The resulting subterranean flow in the Upper Floridan
aquifer discharges at the River Boil. (It is not recommended that
you actually attempt to visit this site, although it is possible.
However, due to the river boil and sinkholes in the area, visiting
the site of this artesian spring could be dangerous.)
The river boil caused by leakage from the lake through the
limestone aquifer
The Chattahoochee River is one of Georgia's 14 major watersheds.
It is a part of the Apalachicola-Chattahoochee-Flint River system
that drains an area of 19,600 square miles in Georgia, Alabama, and
Florida. Beginning in Union County, Georgia, with its headwaters in
the Blue Ridge Mountains, 200 feet from the Appalachian Trail, the
Chattahoochee flows 430 miles through Georgia. The lower portion of
the river is the boundary between Georgia and Alabama and between
Georgia and a small portion of Florida. It joins the Flint River at
Lake Seminole and forms the Apalachicola River here at the dam. The
Apalachicola River then flows 106 miles through Florida to the Gulf
of Mexico. The largest Georgia cities in the Chattahoochee
watershed are Atlanta and Columbus. The Chattahoochee is the
primary source of water for over half of Georgia’s
population.
The Chattahoochee River got its name from the Creek word for
“flowered stones.” It comes from the words chatto,
meaning stone, plus hooche, meaning marked, flowered or with
designs like flowers. A Creek settlement, Chattahoochee Old Town,
at today’s Franklin transferred its name to the river. The
first mention of the “Chattahoochee” by that name
occurs in Indian agent Benjamin Hawkins travel log of the
Chattahoochee River and the Creek country in the years
1798-1799.
Looking toward the NW
Seminole State Park, which is just to the north of this dam, is
on Lake Seminole, the 37,500-acre reservoir and is known for its
sport fishing. The lake is shallow, but natural lime sink ponds
have left areas of cool, clear water with a variety of fish. The
threatened gopher tortoise, the only tortoise native to Georgia,
makes its home along a 2.2-mile nature trail designed to interpret
the wiregrass community habitat. The park is located near one of
Georgia’s largest wildlife management areas, providing great
duck hunting and deer hunting.
The Dam Entrance
The listed coordinates will bring you to this location. From
here you can overlook Lake Seminole.
The Flint River, northeast of this dam, is also part of the
Apalachicola-Chattahoochee-Flint River system. Of the total
drainage area of that system, 8,460 square miles lie along the
Flint. Of the remainder, 8,770 square miles are along the
Chattahoochee arm, and 2,808 square miles are along the
Apalachicola River in Florida. Beginning near the Atlanta
Hartsfield-Jackson International Airport, the upper reaches of the
Flint flow through the Georgia Piedmont, a plateau characterized by
rolling red hills. At the Fall Line, the river drops about 400 feet
over a distance of 50 miles. (In the Yellow Jacket Shoals area, a
section of the Fall Line between GA 36 and Po Biddy Road Bridge,
the Flint has slopes of 50 feet per mile). Below the Fall Line, the
Flint flows through the soft, sandy sediments and limestone that
make up the Coastal Plain. For 200 miles the Flint is a wild and
free-flowing river. It is one of only 42 U.S. rivers with 124 miles
or more of unimpeded flow. The Crisp County Power Dam on Lake
Blackshear, approximately 220 miles from the headwaters is the
first dam on the Flint and one of only three dams on the river
– the others being the Georgia Power Dam at Lake Chehaw and
this dam, the Jim Woodruff Dam.
The Flint River got its name from the Creek Indian name for the
Flint River, which was Thronateeska. That means "flint-picking-up
place." (The properties of flint made it ideal for chipping into
arrowheads or spear points. It was highly valued and traded
throughout the region.) The name derives from the Creek word
ronoto, meaning flint, and hachi, meaning creek stream. Some old
maps show the river as Hlonotiskahachi. Indian agent Benjamin
Hawkins wrote that the Indian name for the Flint River was
Lonatiskahatchee and that the word lonato meant flint; hachee was
the Creek word for stream or creek.
The dam from the SE
Downriver from the dam is the city of Apalachicola. Behind New
Orleans and Mobile, Apalachicola was the third busiest port on the
Gulf Coast in the early 1800s. Cotton and other agricultural
products from the Chattahoochee and Flint River Watersheds were
transported downriver to Apalachicola via paddleboats. More than
200 homes, commercial structures and historic sites are located in
the 2.5-mile National Historic District of Apalachicola. The
Trinity Episcopal Church-sponsored Tour of Homes takes place
annually the first Saturday of May. Unguided walking/driving tour
brochures are available. More information: Apalachicola Area
Historical Society, Apalachicola Bay Chamber of Commerce.
Apalachicola National Estuarine Research Reserve Staff members
conduct educational programs on estuarine ecosystems for large
audiences ranging from school groups and the general public to
environmental management professionals. Visitors experience
hands-on exhibits; guest lecture series; interpretive field trips
and hikes into the river, bay and barrier island habitats. Teacher
workshops, classroom curriculum materials, traveling displays and
publications are available through the Reserve.
There is also an abundant amount of recreation available here.
There are two state parks, the Three Rivers State Park on the
Florida side, the Seminole State Park on the Georgia side, and a
local city park, which is reachable either from U.S Highway 90 just
south of the dam or through the service road that wraps around the
southeast side of the dam property.
In order to log this cache, send the cache owner the answers to
these three questions: 1. What does a horn sounding mean and what
should you do if you hear one? (Go to N 30, 42.536, W 84, 51.720 to
find the answer to this question.) 2. When water enters the dam, it
emerges on the east side of the dam an hour later than it does on
the west side. Why? (For the answer to this question, go to N 30,
42.054, W 84, 51.600.) 3. At present the Corps of Engineers claims
that the rate of water leakage through the aquifer in and around
the dam is not enough to drain or cause the collapse of any of the
limestone bedrock. In addition, the existing sinkholes are
currently filled with water. Theorize what might happen if the dam
were not there now and the lake allowed to return to its original
depth and course. What would happen to all the sinkholes? What
about the now-saturated, soluble limestone? 4. Pictures of your
visit are requested but, in accordance with earthcache rules, not
required.
the southern boundary of Lake Seminole
Send your answers BEFORE you log the cache or your log will be
deleted without warning. If you have the time to log the cache, you
have the time to comply with its requirements.