Relationship of Headwater Stream Geomorphology to Catchment Geomorphology in the Piedmont of North Carolina
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2007-11-04
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Abstract
Headwater streams serve as the connection between land and rivers. They are the places in the landscape where water first begins to accumulate into a flowing stream. These headwater streams directly drain more than half of the landscape, creating water flow and possibly pollution pathways to larger river systems. Ongoing studies in North Carolina of the characteristics of headwaters streams to support field identification and digital mapping initiatives have raised many questions about the relationships of catchment and stream geomorphology.
The objectives of this research were to 1) determine the differences among catchment geomorphologic parameters at the intermittent and perennial stream origins, 2) to describe the stream geomorphology as the headwater streams transition from intermittent to perennial and 3) to determine if significant relationships exist between stream geomorphology and the associated catchment geomorphology in the headwater stream reaches.
Large variation was found in drainage area, valley slope and catchment shape values at both the intermittent and perennial origins. Drainage area threshold has been proposed as an indicator of intermittent or perennial stream origin and the ArcHydro extension of ArcGIS uses a drainage area threshold value set by the user to begin modeling of the stream network. However, with catchment size at the intermittent origins ranging from 2.4 to 15.6 acres and at the perennial origins ranging from 10.1 to 25.8 acres among the 8 highly similar catchments, drainage area does not appear to be a simple predictor of stream origin location. Horton?s form factor and valley slope at the intermittent and perennial origins also varied greatly from stream to stream and are not simple threshold indicators of stream origin.
Stream geomorphology measures also varied greatly in their progression downstream. Sinuosity, which is a measure of stream pattern, increased in the downstream progression as a general trend. Within-reach channel slope, a measure of stream profile, decreased as the channels progressed from intermittent to perennial also with some minor variation. However, cross-sectional area, a measure of stream channel dimension, was highly variable throughout the headwater stream reaches. Channel cross sections varied from deeply entrenched, with relatively high cross-sectional area, to depositional fans having very little stream channel at all (very low cross-sectional area). This wide variation in channel cross-sectional area occurred not only among the 8 studied stream channels but within the same stream at different locations along a study reach.
Possible relationships found were between stream sinuosity and catchment drainage area, between Horton's form factor and catchment drainage area, between valley slope and catchment drainage area and channel slope and catchment drainage area. Relationships were not found in other comparisons, most notably in the cross-sectional area to catchment drainage area relationship and in the channel slope to cross-sectional area relationship. Further research is needed to quantify possible relationships found in this study.
Research in this area is complicated by the lack of undisturbed watersheds in the region. Variation in location, geology, soil characteristics, and land use complicates efforts to find comparable study sites. Highly detailed studies such as this involve a large time investment in data collection.
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catchment geomorphology, stream geomorphology
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MS
Discipline
Natural Resources
