Bridges are the result of our encounter with the seasonal variations of a watershed. If rivers were always shallow and of good bottom and if streams never flooded during thunderstorms or if there were no need for travel we would need no bridges. In the earliest days of American settlement, of course, there were no bridges except the occasional natural bridge which occurred here and there where a large tree fell across a stream. The great multiplicity of branched streams reaching from the Atlantic and Gulf coasts into the most interior parts of the coves and onto the highlands behind these coves created the need for tens of thousands of stream crossing points. To deal with the variety of American waterways, two early means of crossing were developed.
In shallow water fords were discovered by the
trial and error of usage. At some points, fords were improved by the placement
of fitted stones which were shaped like truncated pyramids about one square
foot on the base, slightly smaller on the other end. They were carefully wedged
together in tight rows alternating base-up, base-down. This pattern made a smooth,
stable surface that could bear the heaviest loads in all but the most extreme
conditions of flood.
A second approach to river crossings was the provision of a ferry and ferry keeper at important crossings. Sometimes the colonial legislature funded the ferry and keeper; in some areas the ferry was privately operated. To overcome the drift effect of the flowing current, a heavy rope line was often used to span the river above the ferry route and the ferry used this line for a guide in crossing. If the river were not too wide, the rope could be attached to either end of the ferry and run through pulleys attached to stout trees on the river banks. In a some places boats rigged in this fashion were left unattended and functioned as a kind of self-service ferry. The boat could be summoned from the opposite bank merely by pulling the rope through the pulley.
Colonists and settlers quickly began to build bridges, however. The bridge provided a reliable dry platform for river crossing and did not cause wagon cargo to become wetted or lost in swift currents. Bridge construction could be simple or elaborate. For streams, a simple bridge could be built from two tree trunks laid parallel across the stream and then planked over with heavy boards. Later this kind of simple bridge would be improved and then lengthened for wider streams by using hewn or sawed timbers instead of logs. If the stream were wider than tree trunk length, mid-stream supports or pilings were sunk to support the middle sections of the bridge. In many parts of New England and in some parts of the South, bridges of this simple timber design had roof or roof and wall structures built over them to provide weather protection and an element of safety. These bridges became the classic "covered bridges" of American History.
Another kind of bridge relied upon the architectural principle of the stone arch. Stone arch bridges were built in many areas where stone building material was available and where the bridge height did not have to be great or where large boats did not have to pass the bridge. On a stream a single arch bridge could be constructed with the arch anchored in each bank. On rivers, several arches might be required and mid-stream pillars would have to be constructed to anchor the middle arches. The careful masonry of these bridges make them aesthetically attractive and very durable. We might call these bridges "estate" bridges because they were costly and were frequently found on estates and plantations where their aesthetic qualities were needed and where the spans involved were short.
As iron and steel fabrication advanced in the late nineteenth century, metal framed bridges began to be widely used. The open spans of metal bridges could be much greater than with wood or stone bridges. A local example of this kind of bridge architecture can be observed from the concrete I-24 bridge over Nickajack Reservoir looking upstream. The old pre-Interstate steel bridge is still in place and although quite narrow, continues to bear a heavy daily load of trucks and cars.
Around Franklin County, bridges are of a much smaller scale. A few small span, old steel bridges survive as important artifacts of a past era of bridge building. These old bridges are also artifacts of a different era of human interaction with flowing water. The last decade has seen the loss or disuse of most of these old bridges. Many of them had become weakened from decades of use and stress. At the same time, new building materials and new engineering and safety standards mandated the replacement of the old bridges. An efficient if unattractive recent bridge design for small streams and washes is the "box culvert" bridge--basically a square or rectangular cement box built or placed in the streambed with a road above it.
Bridge connoisseurs can find interesting samples of old bridges on Crow Creek below Sherwood, on the Paint Rock River east of Huntsville, Alabama, and on the Elk River near Mulberry, Tennessee. An old steel railroad bridge can be found across Battle Creek between Kimball and South Pittsburg. (This bridge is barely visible from the road during the summer.) Many of these old bridges are now closed and condemned; access to them is now sometimes across private land. Bridge connoisseurs might also want to view the new Tennessee River bridge at South Pittsburg, one of the most dramatic bridges along the Tennessee River.
Sampler of Local and Regional Bridges
