Table 2.2. Adjustment Factors for the Determination of n Values.
Conditions
n Value
Remarks
n1
Smooth
0
Smoothest Channel
Minor
0.001-0.005
Slightly Eroded Side Slopes
Moderate
0.006-0.010
Moderately Rough Bed and Banks
Severe
0.011-0.020
Badly Sloughed & Scalloped Banks
n2
Gradual
0
Gradual Changes
Alternating
0.001-0.005
Occasional Shifts From
Occasionally
Large to Small Sections
Alternating
0.010-0.015
Frequent Changes in
Frequently
Cross-Sectional Shape
n3
Negligible
0-0004
Obstructions < 5% of
Cross-Section Area
Minor
0.005-0.015
Obstructions < 15% of
Cross-Section Area
Moderate
0.020-0.030
Obstructions 15-50% of
Cross-Section Area
Severe
0.040-0.060
Obstructions > 50% of
Cross-Section Area
n4
Small
0.002-0.010
Flow Depth > 2 x Vegetation Height
Medium
0.010-0.025
Flow Depth > Vegetation Height
Large
0.025-0.050
Flow Depth < Vegetation Height
Very Large
0.050-0.100
Flow Depth < 0.5 Vegetation Height
m5
Minor
1.00
Sinuosity < 1.2
Moderate
1.15
1.2 < Sinuosity < 1.5
Severe
1.30
Sinuosity > 1.5
2.25
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