Adam Migliore Meyer
GEOG 591
January 27, 2012
Exercise 1: NHD Plus
Question 1: Describe areas in New Hope area that fall into the stream classes.
All Streams
Urban Stream
Urban streams occur in catchments classified as greater than 20 percent urban according to the NCLD values. Specifically, the NCLD values of 21 (developed, open space), 22 (developed, low intensity), and 23 (developed, medium density) are summed to determine how urban the catchment is.
These areas are concentrated north of Jordan Lake around the City of Durham and Towns of Chapel Hill, Carrboro, and Hillsborough. Generally these areas tend to have more impervious surfaces, which are reflected in the higher NCLD values.
Cumulative Urban
Cumulative Urban Streams are those streams that drain urban catchments, but are not necessarily located in an urban catchment themselves. A good example is the section of New Hope Creek flowing into Jordan Lake.
New Hope Creek drains catchments that are urban, but the catchments immediately north of the lake are not urban. These streams are still significant to nutrient loading because they carry with them the nutrients contributed by impervious surfaces found in the urban catchments upstream.
Cumulative Urban / Local non-Urban
This classification of stream is a subset of the Cumulative Urban Stream. The subset is a “clipping” of cumulative urban stream from catchments that are not urban. Following from the New Hope Creek example, the section of New Hope immediately north of Jordan Lake is featured in this class because it runs through catchments that are not urban.
By definition these streams are not found inside urban catchments, but adjacent to them. These sections of stream are significant because while they may not be draining as many nutrients from their own catchments, they are still carrying nutrients from urban catchments upstream.
Cumurban_nourban_stream is connected to Jordan Lake. In conclusion, New Hope area, one of the main drainage areas of Jordan Lake can be characterized as urbanized area when considering the whole upstream area of New Hope creek.
Question 2: Compare urban areas to sections of stream with high discharge (>30 cfs).
Using the figure on page 1 featuring all stream classes, streams with high discharge tend to drain the urban areas north of Jordan Lake. New Hope Creek and Morgan Creek are among these streams. In terms of the significance for water quality, more nutrients are able to make their way into Jordan Lake because the greater capacity of these streams enables them to deliver a larger quantity of the nutrients originating in the urban catchments. This degrades water quality. High stream discharge areas are overlapped mostly with urban and cum_urban stream. Since runoff from urban is characterized by surface runoff, which is direct, fast and wash-off the contaminants in impervious area, it threatens water quality problem to Jordan Lake (-0.5).
The higher capacity streams also increase the quantity of water flowing into the lake by their very definition of high discharge. These streams naturally have high discharges given their morphology and topography. However the increased impervious surfaces in the urban areas amplify the stream discharge, as more water runs off into these streams instead of being absorbed into the ground.
(24.5/25)
Next time, please use your ONYEN for naming your report.
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