Our preoccupation with flowing water and large lake impoundments leads our view away from an important dimension of water and the land. This dimension is the place of excess water on the land. Excess water is any water the stream system of the watershed is not yet ready to receive. This is water in excess of the immediate hydrologic and biological water budgets for a given area. In order for water to be effective within the watershed, it must move through the watershed at a rate that makes it accessible to the type of vegetation that prevails in the watershed. [The other side of this concept is that the type of vegetation that prevails is related to the amount of water available in the watershed.] If the water moved too quickly it would not be available for plants in the places or volume required by the plants for growth. Immediate runoff of rainwater without seepage or percolation would leave a landscape that dried quickly and which had very little water available for plant growth.
Immediate runoff can occur because of the configuration of the land itself: steep slopes and large amounts of exposed rock with little soil can generate rapid runoff. Rapid runoff can be triggered, along with subtle climatic changes, where there has been excessive removal of vegetation resulting in the loss of the capacity of the land to hold the rainwater that falls upon it. Climate changes resulting from locally reduced biomass are implicated in the shift from arable to arid land in the Indus River valley as well as across portions of northern Africa and the Middle East. Although the process is complicated and involves many local as well as global factors, land that begins to dry out may become ensnared in a deepening cycle of continued drying: less rain will fall and less water retained resulting in less plant growth as the cycle repeats.
Not all rain that falls is immediately needed by the land and the plants growing upon it. But if this water were immediately flushed from the land, there would be less long-term water available for the land. There are several ways that the land and the river systems store excess water in order to reduce the rate of removal and make the water available over longer periods of time than during rainfall. For instance, excess water in the watershed is stored by the river system itself in the capacity of the river to meander: a meander is a bend of the river that reflects the river's capacity to lengthen itself relative to its volume and thus contain more water. Another way that excess water is stored by a river system for subsequent withdrawal is in the system of natural levees that parallel the watercourse and temporarily trap some portion of stream load behind silt or mud dams that parallel the axis of the stream. These levees are important not only for their obvious function in flood control on natural streams but also because they slow down the waterflow and thus allow entrained silt to fall out of the river as bottom land soil deposits.
Other forms for the temporary containment of excess water are the natural bogs, marshes, ponds, and swamps that occur within the watershed. These low places in the local topography are capable of receiving excess water and holding it in place for local use or for slow seepage into the watershed during times of diminished rainfall or stream flow. These forms of water storage are characteristically rich in both wildlife and plants and in time of severe stress may represent reservoirs of brood stock for invertebrates, amphibians, and other forms of life in addition to serving as actual reservoirs of water for the watershed. During periods of violent alteration of the streambed of a watercourse during a flood, the food chain may be severed or destroyed. This effect could be observed on the Elk River immediately following the great solstice storm of December 1990. In the main river course the rock substratum of the riverbed was overturned and the main channel in some area swept almost completely free of invertebrates. The contiguous bogs and sloughs of the river along with the tributary streams acted as a nursery for replacing the lost populations at the base of the food chain in the main river.
A minor but locally important means of containing excess water especially along small streams is the beaver pond. Beavers were common animals throughout North America until the trapping industry exterminated them from many areas. With the passing of the fur industry, beaver populations have begun to recover and in some areas--such as around Sewanee--they have reappeared in sufficient numbers to constitute a nuisance as they fell trees and create new ponds. Although their dams often are destroyed by floods along the valley creeks, beavers persist in dam building and their work can now be observed on the Domain of the University, along Crow Creek toward Sherwood, and immediately beside Interstate 24 at the Martin Springs Exit. At Martin Springs, a colony of beavers have constructed a series of six dams creating small ponds. The uppermost of these ponds is visible from I-24 immediately beside the southbound ramp. Many people see this standing water but few can observe the hidden dam which creates it. This dam raised the water level of the little stream by about four feet at the dam.
Another important form of excess water storage is the flooded field. Such field conditions can be observed across the county in the springtime, particularly in the fields within the coves or in the valley areas nearest the lower edge of the plateau. Several such fields are usually visible along the Georgia Crossing Road between Cowan and Winchester. Near the point where the Georgia Crossing Road intersects the CSX railroad at the underpass one field often holds water three feet deep over several acres. This condition obviously impairs the capacity of the farmer to tend the field. The flooded condition may persist for several months and has inspired the farmers, the Corps of Engineers, and TVA to take steps to drain these areas and allow them to be farmed early in the growing season. Flooding is typically relieved, for instance, by a drainage ditch that leads excess water away from the field to a natural streamcourse.
We might note here an important side effect of the excess water in these flooded fields. Since most local field flooding occurs in the period from January to March, the appearance of these field ponds coincides with the return migration of waterfowl. Several species of ducks, Canada geese, and Sandhill cranes use the ponds directly or land nearby and feed and water around the pond edges. If the pond persists for a few months or if it contains fish that have been washed out from conventional farm ponds or nearby streams, herons will appear to feed along the edge of the pond. A significant cluster of flooded field ponds appears annually in the large triangle formed by the Franklin County airport, Route 64, and the CSX railroad. The ponds which form here create excellent opportunities for birders.
In the 1960's Franklin County was one of several areas targeted for a more radical means of removing excess water from the landscape. This project involved the cutting of many miles of drainage ditches through and along the valley fields and of connecting these drains to a series of natural streams that had been customized for rapid water transfer to the TVA lake system. The argument was that this project would remove water quickly from the land and allow for it to be managed within the flood control reservoirs of the TVA system. The natural streams were altered by the removal of bank-side vegetation and by the straightening of the streams bends and meanders in a process called "channelization." While channelization did have the intended effect of drying out low fields, it also destroyed the natural qualities of the channelized streams and resulted in increased erosion and waterway siltation. A nationally notorious example of channelization is Crow Creek which parallels the road and railroad through the valley between Sherwood, TN and Anderson, AL. The heavily eroded appearance of this stream and its bank caving are continuing consequences of the original channelization. Streams in the Alto area of the county were also channelized.
A similar "channelization" effect can be observed in the Abbo's Alley stream in Sewanee. Here the driving concerns have been horticultural and aesthetic instead of agricultural, but the final effect is the same: stream degradation, excessive bank caving, and loss of stream capacity to contain excess water or to serve as a buffer against erosion. The root structure of weeds, vines, shrubs and trees can protect riverbanks against the most violent forms of erosion occasioned not only by natural flooding but also by dumps of excess water from flood control reservoirs. In the desire to have a grassy, park-like appearance in Abbo's Alley well-intentioned people removed natural vegetation down to soil level throughout the upper stream course. The original root clumps were grubbed out and grass was sown to allow for mowing. The result has been a virtually entire de-stabilization of the streams banks and the introduction of tons of unnecessary siltation into the watershed.
Immediately following the 15+" rainfall of the solstice storm of December 1990, TVA immediately contained the massive runoff from the Elk River watershed in the Woods and then Tims Ford reservoirs. Within twenty-fours hours, however, the accumulating water threatened to overwhelm the dam, and TVA was forced to begin a spillway release into the river below the dam. This release through a concrete-lined channel amounted to about 36,000 cubic feet per second or about ten times the volume released in normal hydro-electric generation. The violent effect of this water was to sever the abutments of the concrete service bridge leading to the dam powerhouse and the dislodging of the entire protective rip-rap along the lower end of the spillway. Serious erosion also occurred beneath the west end of the Route 50 bridge about 75 yards opposite the entry of the spillway into the original river channel. This heavy flow was then directed downstream in a broadening flood that eventually flooded portions of Fayetteville, TN and other towns downstream.
Although this spillway release caused the Elk to rise some nine to fifteen feet above its banks and to deposit flotsam high into the branches of trees, there was surprisingly little bank-side erosive effect downstream of dam. The banks of the Elk and of the many tributary streams are lined with dense vegetation which served to slow the flow of water, dis-entrain some of its silt, and to protect the riverbanks against caving. One might have expected this release to have caused severe erosion and caving of the banks; actually very little occurred. In a few places surface soil was eroded exposing the web of underlying roots, but the interlaced root system proved effective to hold the vegetation in place and to protect the banks against collapse. Along the Elk the only places where bank caving is a serious problem is where bank-side trees--and the associated structure of roots and shrubs--have been removed. These sites are few in number but remain a problem even apart from flood control conditions. Elsewhere, the root of the natural vegetation protect the banks and allow the stream to deal with the effects of excess water.
A final type of excess water containment is the bog. Bogs naturally occur where the soil and vegetation or the underlying rock formations create a shallow "pan" effect and slow down the drainage of water from the land. Bogs may also occur as the result of artificial effects such as the raising of a roadbed for a highway or railway. [Pooled water on the land exhibits a successional sequence of form and vegetational development just as abandoned fields do. An excellent general account of the succession from bog to marsh to swamp can be found in William A. Niering's nature guide, The Life of the Marsh.] Bogs and swamps in different stages of development occur throughout the Franklin County area. Areas to search for incipient bogs are the edges of recently raised roadways such as along Route 108 in Grundy County near Altamont. The raising of the roadbed for Interstate 24 between Martin Springs and Kimball, TN generated several artificial swamps that can be observed in the winter when leaves are off the trees.
The normal sequence from bog to swamp note by Niering is the eventual covering of a bog or open wetland by a canopy of trees thus transforming the bog into a swamp. A kind of reverse loop occurs in this process when the origin of the wetland is artificial. A roadbed may block a normal drainage route in an area already covered in trees. Initially what is then created is a swamp--a wetland with trees. If the water persists, however, many of the trees may be killed thus opening the canopy and allowing the vegetative sequence of the bog to begin. A loose field distinction: if the wetland has living trees it is a swamp; if it has red-winged blackbirds it is a bog or marsh. A wonderful bog/swamp occurs near St. Andrews-Sewanee School about 300 yards from Route 41 just north of the road leading to the fire tower and to the Deep Woods road. Along Route 64 immediately north of Belvedere, TN the marshy edge of the large Mingo Swamp can be seen. Another excellent swamp occurs in Cowan immediately north east of the town in the depression behind Buck's Market.
Excess water on the land is contained temporarily or permanently in environmentally and ecologically critical areas known a wetlands. Whether a wetland is artificially caused and of brief duration or is a permanent feature of the land, it capacity to store excess water is important in the overall water budget of a watershed. The auxiliary features of these wetlands in the vegetation they sustain and in the wildlife they attract give them an urgent environmental importance.