Jackson Henderson
Leigh, D., Price, K. 2005. Morphological and sedimentological responses of streams to human
impact in the southern Blue Ridge Mountains, USA. Geomorphology 78 142-160
The article, Morphological and sedimentological responses of streams to human impact
in the southern Blue Ridge Mountains, USA, was prepared and written by Katie Price from the
University of Wisconsin’s Geography department and David Leigh from the University of
Georgia’s Geography department. Katie Price, a graduate of the University of Wisconsin, is
currently working for the Environmental Protection Agency conducting scale analyses of
watershed hydrologic models and input sources of meteorological data, determining which
models and data types are most appropriate for use at varied and temporal scales. David Leigh is
a Professor and Associate Department Head at the University of Georgia, and is interested in
research concerning quaternary studies, geomorphology, geoarcheology, environmental, and
soils.
The overarching question asked repeatedly throughout the article was whether or not
human impact in the southern Blue Ridge Mountains had an impact of streams and river basins,
and if so, what were the measureable results. The researchers were looking primarily at
anthropogenic development in highland stream regions in the upper Little Tennessee River basin,
which mostly falls within the Nantahala and Chattahoochee National Forests where development
and timber harvest have been restricted since the 1930s. Another question that the researchers
were interested in was: how local topographical relief and terrain, as well as forest cover and
developed-land cover play relate specifically to water and soil quality along the impacted
waterways.
The hypothesis presented by the researchers asked simply if highland land use, involving
modest changes in forest cover at the basin-scale, causes significant the sedimentology of stream
beds in the four streams of the study area in the Little Tennessee watershed. The four creeks
were Coweeta Creek, Skeenah Creek, Keener Creek and Rocky Branch. Leigh and Price
presented this hypothesis in the context of past methodologies of studying highly developed
areas, but how there was need to study less anthropogenically affected regions of the southern
Appalachians.
The researchers used a variety of methods to conduct their study, but the majority of their
operations were classification studies conducted within GIS and satellite imagery analysis
software, using remotely sensed data, as well as in-situ verification and original biological and
sedimentological data. Leigh and Price chose two pairs of lightly and moderately impacted
basins on the basis of percentage of forested land in the drainage basins. This percentage of nonforested land was treated as an estimator of the percentage of land experiencing human impact.
Forest cover in the basins was measured using ArcView and Erdas Imagine software for each
year of available data for land cover derived from Landsat satellite imagery and aerial
photographs. To isolate human impacts from natural variation, characteristics were established
within each pair based on well-documented linkages to channel morphology and sedimentology.
A topographic survey of each stream was conducted with at least a 35 meter transect on
either side. Each of these extended transects was surveyed using an electronic total station. A
Giddings hydraulic coring rig was used to extract 7.5cm diameter cores from key landforms
along the extended transect. Soil cores were described according to USDA terminology.
Dimensions of the channels were measured at each transect. The height of the channel was
defined by measuring the lowest prominent alluvial surface characterized by vertical accretion
facies and noted as either a floodplain or a terrace for each side of the stream. Width of the
channel was measured at the level of the top of the bank from the lowest alluvial surface, which
in in most cases was the floodplain.
Baseflow discharge was measured at an optimal transect across each stream on three
occasions in October 2003, January 2004, and February 2005. Measurements of flow were
limited to frontal, widespread precipitation events in fall/winter months to avoid potential
complications arising from the highly localized summer precipitation characteristic of this
region.
The results of Leigh and Price’s study emphasized consistent, statistically significant
differences in both stream pairs. The lightly and moderately impacted streams in this study
exhibited significant differences in Baseflow wetted width, baseflow width/depth ratio, dominant
particle size in the entire channel bed and riffle (short, relatively shallow and coarse-bedded
length of stream) particle size. These conclusions indicate that highland land use, involving
modest changes in forest cover at the basin-scale, may cause significant differences in the
sedimentology of stream beds. Particle size and embeddedness on riffles have been shown to be
linked with the biotic integrity of streams and to be highly sensitive to external disturbance in the
southern Appalachians.
This paper is important because it reveals and highlights environmental issues of a region
of the southern Appalachians not often studied. It discusses human impacts in a place not often
thought to have much of an anthropogenic influence. The study shows that human development
and impact in these basins has resulted in an overall fining of bed texture but few conclusions
can be drawn regarding morphological responses of the streams to the levels of impact affecting
the upper Little Tennessee River basin. Widening of channels in response to intensive
agriculture and urbanization has been well documented throughout the world, and the modest
differences in forest covers between these lightly and moderately impacted basins yield
statistically significant differences in morphological parameters. With these concepts and their
methods, Leigh and Price showed that the moderately impacted streams are narrower than the
lightly impacted streams.