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Water: WARSSS

Aggradation

The results of excess sediment deposition, sediment competence, and capacity reduction due to increases in width/depth ratios or slope changes are often responsible for aggradation. Direct disturbance to stream channels such as over-widening due to bridges, channelization projects, riparian vegetation changes, excessive hoof shear from poor grazing practices, "back water" from road crossings, and accelerated streambank erosion can all potentially lead to aggradation. Information needed to complete this potential risk assessment includes

a) Aerial photographs
b) Stream types
c) Depositional feature evaluation (Figure 79)
d) Bankfull width/depth ratio (Figure 97)
e) Hillslope processes sediment supply risk
including mass wasting
(Figures 80, 81, & Table 15),
surface erosion (Figures 75 & 76)
and roads (Figure 77)

Figure 97

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The overall risk rating is determined from a numerical ranking as completed in Worksheet 9 (xls, 29 kb). The first category used in the overall risk rating deals with sediment supply or introduced sediment from hillslope processes. The second category is associated with departure of width/depth ratio (over-wide channels). The third category used in the overall rating are potential aggradation indicators as shown in Worksheet 9. The next step is to summarize the category totals and make adjustments in the overall risk ratings due to depositional and/or aggradation indicators.

The results are again summarized individually by sub-watershed in Worksheets 5a & 5b and for multiple sites/sub-drainages in Worksheet 6.

Worksheet 5a: Printable PDF (10 kb, 1 p.) | Excel Spreadsheet (27 kb)
Worksheet 5b: Printable PDF (9 kb, 1 p.) | Excel Spreadsheet (35 kb)
Worksheet 6: Printable PDF (8 kb, 1 p.) | Excel Spreadsheet (21 kb)

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