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Stream Ecology example

The author used 12 physical parameters grouped into 3 categories to describe 21 separate sections of 8 streams in a single drainage system!  Plenty of opportunities for confusion, so my main task was to maintain order among all those elements.

General Watershed Phase Trends
Aggradation Phase

    During this phase, channel cross-section width will narrow and cross-section area will decrease in response to increases in water and sediment discharge.  Seven of the 21 sites sampled exhibited the physical characteristics of the Aggradation phase over the observation period.  Four of these sites are located in the Red Run basin (F2, F3, F4 and F10) and their associated drainages were relatively undisturbed (less than 10% impervious) in the 1980s and urbanized over the observation period.  The watersheds of the remaining three sites (GF5, GF7, and SL2) were already disturbed in 1987 (greater than 14% impervious) and urbanization activities continued in the upstream reaches over the observation period.  The channel at all three existing urban Aggradation phase sites has been altered (channelization, bridge crossings, etc).  The Aggradation phase characteristics exhibited by these sites over the observation period may be the result of such alterations.

    In 1987, the cross-section area and width of the urbanizing (Red Run) sites were small relative to the existing urban sites in the Aggradation phase and other phase (Early and Late Erosion phase sites) (Table 1).  Conversely, the cross-section area and width of the existing urban Aggradation phase sites (GF5, GF7, and SL2) were among the largest observed in part due to the relative size of their drainage area (Table 1).   Reach average cross-section area decreased or did not change at 6 of 7 sites and the largest reductions occur at existing urban sites (Figure 10, Table 1).  Site SL2 increased slightly in cross-section area from 34.7 to 40.6 square feet, although large bars characteristic of the Aggradation phase are present.  In addition, channel width decreased at most sites (4 of 7) with the largest reductions again occurring at existing urban sites (Figure 11, Table 1).  Channel width at F4 and F10 increased slightly (0.7 and 1.62 feet, respectively) over the observation period.  GF7 channel width increased 11.3 feet, while the cross-section area decreased.  New bridge construction near SL2 and GF7 has influenced local channel geometry by providing lateral and longitudinal controls.  While these changes were observed, the urbanizing Aggradation phase sites remain small in terms of cross-section area and narrow when compared to the existing urban Aggradation phase sites and Erosion phase sites (Table 1).  The existing urban Aggradation phase sites remain among the largest channels measured in 2000 (Table 1).

My revision:

General Watershed Phase Trends
Aggradation Phase

     During the aggradation phase, channel cross-section widths become more narrow and cross-section areas decrease in response to increases in water and sediment discharge.  Of the 21 sites sampled, 7 exhibited the physical characteristics of aggradation phase sites in both 1987 and 2000.  Four of the sites are located in the Red Run sub-basin (F2, F3, F4 and F10).  In the 1980s, their associated drainages were relatively undisturbed (less than 10% impervious surfaces), but they became increasingly urbanized in the ensuing 13 years.  The remaining sites (GF5, GF7, and SL2) were already urbanized by 1987 (more than 14% impervious surfaces), and urbanization activities continued along their upstream reaches throughout much of the 1990s.  Alterations were noted at all three existing urban aggradation phase sites (e.g., channelization or bridge construction); chances are the aggradation phase characteristics observed at these sites were the result of those alterations.

     In 1987, the cross-section areas and widths of urbanizing sites in the Red Run sub-watershed were small relative to those measured at existing urban sites, regardless of the then-current developmental phase (Table 1).  However, it was noted that cross-section areas and widths at existing urban aggradation phase sites (GF5, GF7, and SL2) were among the largest, in part due to the size of their drainage areas.  On average, cross-section areas decreased or did not change between 1987 and 2000 at 6 of the 7 Red Run aggradation phase sites, with the largest reductions found at existing urban sites (Fig. 10).  The cross-section area of site SL2 increased slightly, from 34.7 to 40.6 sq ft; the site also contained large bars characteristic of aggradation phase sites.  Furthermore, channel width decreased at 4 of the 7 sites, with the largest reductions again being observed at existing urban sites (Fig. 11).  Channel width at F4 and F10 increased slightly (0.7 and 1.62 ft, respectively) between 1987 and 2000.  GF7 channel width increased to 11.3 ft, but its cross-section area decreased.  Bridge construction near SL2 and GF7 appears to have influenced local channel geometry by adding lateral and longitudinal controls.  This may partly explain why the urbanizing aggradation phase sites remained small in terms of cross-section area and channel width compared to existing urban aggradation sites as well as to either early or late erosion phase sites.  In 2000, the channels at existing urban aggradation phase sites were among the largest measured (Table 1).


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