Mitigation for the Construction and Operation of Libby Dam

Table 7. Mean cross sectional area, bankfull width, depth, maximum bankfull depth, and width to depth ratio measured for 4 riffles in
the existing stream channel and 10 riffles in the stream channel shortly after construction in the fall of 2003 (as built) for the Young
Creek State Lands Stream Restoration Project. Variance estimates for annual mean values are presented in parentheses. Mean values
between treatments were compared using a t-test, and the one tailed p-value for each comparison is presented. The percent change for
each parameter between treatments is also presented.
Riffle Cross
Sections
Cross
Sectional Area
(ft 2 )
Mean Bankfull
Width (ft)
Mean Bankfull
Depth (ft)
Maximum Bankfull
Depth (ft)
Width to Depth
Ratio
Existing 16.75 (1.58) 27.88 (22.73) 0.60 (0.008) 1.05 (0.017) 48.3 (239.6)
As Built (2003) 21.99 (10.07) 16.3 (9.18) 1.24 (0.05) 1.985 (0.09) 13.7 (21.2)
Percent Change 31.3% -41.5% 107.5% 89.0% -71.6%
t-test P Value 0.004 6.6*10-5 7.5*10 -5 3.6*10 -5 1.1*10 -5
Table 8. Mean cross sectional area, bankfull width, depth, maximum bankfull depth, and width to depth ratio measured for 2 pools in
the existing stream channel and 8 pools in the stream channel shortly after construction in the fall of 2003 (as built) for the Young
Creek State Lands Stream Restoration Project. Variance estimates for annual mean values are presented in parentheses. Mean values
between treatments were compared using a t-test, and the one tailed p-value for each comparison is presented. The percent change for
each parameter between treatments is also presented.
Pool Cross
Sections
Cross
Sectional Area
(ft 2 )
Mean Bankfull
Width (ft)
Mean Bankfull
Depth (ft)
Maximum Bankfull
Depth (ft)
Width to Depth
Ratio
Existing 19.25 (3.13) 23.5 (24.5) 0.79 (0.005) 2.35 (0.13) 30.14 (80.15)
As Built (2003) 37.68 (65.09) 21.8 (18.0) 1.73 (0.084) 3.23 (0.42) 12.99 (12.78)
Percent Change 95.7%
t-test P Value 0.0076
-7.18% 119.0% 0.318 37.77% -56.9%
0.0012 0.053 0.0008
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