Many factors contribute to the story of SIWR, but to me, the French Broad River and the ridges that transect the site are the standout characters. The topography of the site is very typical of the East Tennessee Ridge and Valley Province, but there's something about the way the river perpendicularly transects the ridges, and about the vast floodplain and islands that begins to distill the ancient processes that formed this part of the continent. If you look closely, it's as though the site is inviting you to have a conversation about its past.
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| SIWR 2011 Aerial Photo |
The next question then, is how can design help translate this story to park users?
A transect is a path along which one records and counts occurrences of
the phenomena of study. The transect is an important geographic tool for
revealing physical changes from one place to another. I am performing my site inventory and analysis along two transects, one along the river, the other along a ridge.
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| Key Plan |
The Ridge Transect trails the northern end of Bays Mountain and a remnant of this ridge that has been separated by the French Broad River and its floodplain. The Ridge Transect is accessible adjacent from the parking area. To begin this walk, one first ascends the steep, northwestern facing slope. The transect then turns southwest following the ridge top. The topography is less steep along the crest of the ridge, and large stands of Beech, Hickory, Maple, Pine, and Oak are abundant. There are many uprooted trees, evidence of strong winds. About 150’ from the southwestern bend in the path, there is a level, circular clearing in the trees about fifty feet in diameter. The clearing frames a view of the sky. Views to the southeast show the river valley and rural development with the Appalachian Mountains and foothills in the distance. Looking northwest there are views of the parallel meadow valley and adjacent ridge. Near the highest point of the ridge small outcrops of Rome Formation are numerous. Formed during the Cambrian Period, Rome Formation is the oldest subsurface geologic material on the SIWR site. Rome Formation, as well as the other geologic parent material at SIWR, is sedimentary and was formed during the Cambrian and Ordovician Periods between 550 and 435 million years ago. During these periods, present day East Tennessee was under a shallow, epicontinental sea. Calcium deposits that precipitated out of this ancient sea formed layers on the continental crust, and over the ages became lithified into the limestones, shales, and sandstones that are typical of the Valley and Ridge Province we see today. The northwest exposure and upward angle of the sedimentary outcrop strata reveal the intense forces that shaped the Ridge and Valley Province during a series of orogenies, or mountain building events. Beginning with the Grenville Orogen (about 1bya) repeated forces from colliding continental plates, subsequent rifting, and uplift from subducting oceanic plates off the eastern coast have produced the “rumpled carpet” that is known as the Ridge and Valley Province. The ridge tops are generally composed of sandstone, a major component of Rome Formation, which is less prone to erosion. The valleys are composed of the newer, Ordovician Period limestones and shales, which typically erode much faster than sandstone and produce rich, fertile soils. The Rome Formation outcrop is evidence of these ancient and powerful tectonic events, that thrusted the older Cambrian Period strata over the younger Ordovician Period strata. The entire site, with its parallel steep, rocky ridges, and rolling, fertile valleys tells the story of its own formation.
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| Experience of the Ridge Transect |
The River Transect parallels the French Broad and intersects the Ridge Transect about midway. The southernmost end of the transect lies at the tip of peninsula, where young forests are replacing fallow agricultural fields. This area is in the floodway, as evidenced by the dark, productive, alluvial soils. Freshly tilled earth reveals pebbles of metamorphic rock. These pebbles speak to the origin of the French Broad River and tell us about the topography of the Appalachian Mountains. The French Broad River presently flows 213 miles from Transylvania County, North Carolina, westward across the Appalachian Mountains to the state of Tennessee. Because the river flows across the mountains, instead of draining east toward the coast, we know that the topography of the mountains must have risen after the river formed its westward drainage. The stories of the French Broad River and the Valley and Ridge Province are closely intertwined, with the river slowly and steadily eroding its course through a rising topography. The metamorphic pebbles in the soil have been carried to SIWR by the French Broad from the Appalachian Mountains, where metamorphic rock is the geologic parent material. SIWR’s namesake islands are composed of accumulations of these pebbles, but several relatively recent factors have changed the islands, and the floodplain, drastically. The French Broad Corridor has a long history of human use. The floodplains have served as seasonal encampments for Native Americans as far back as 12,000 B.C.and within the last 150 years as permanent agricultural settlements. Agricultural practices in the past 150 years, such as clear-cutting the alluvial forests and tilling the soil, have contributed to increased erosion rates, resulting in more sediment in the river. This sediment is changing the morphology of the river channel, as well as the islands at SIWR. Deposits of silt and clay sediment have led to seven small islands coagulating into two large islands. This is a physical, directly visible effect of the sediment, but its effects on aquatic wildlife, while not as visible, are still strongly felt. Another recent character in the story is the Douglas Hydroelectric Dam. Built in the early 1940’s, the dam now regulates the flow of the French Broad, preventing the seasonal floods that replenished the floodplains with layers of alluvium. The dam also acts as a barrier, preventing metamorphic mountain rock from entering the river below the dam. The combination of increased sediment from agricultural practices and the regulatory control of the dam, have changed the geography of SIWR in the past 150 years at a vastly accelerated rate.
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| Experience of the River Transect |
