TROY

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GEM 4409HydrologyFall 2005

• TROY
• UNIVERSITY

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Hydraulically Most Remote Point
Time of Concentration (tc)

• Size
• Shape
• Slope
• Flow
• Cover

Point of Concentration
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Time of Concentration (tc)

• Given
• Slope 0.02 ft/ft 2.0
• L 300 ft
• H 6 ft
• A 20 acres 0.03125 sq mi
• C 0.85
• n 0.011 (Mannings)
• N Retardance Roughness 0.02 (Kerby)
• c Retardance Coefficient 0.012 (Izzard)

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Time of Concentration (tc)
Kirpich Method tc 0.0078 (L1.5/H
0.5)0.770 FAA Method tc 1.8 (1.1
C) L0.5 s1/3 Note s Average
Surface Slope
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Time of Concentration (tc)
Kerby Method tc 0.83 (L N
s-0.5)0.467 Bransby Williams Method
tc 21.3 L 5280 A0.1 S0.2
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Time of Concentration (tc)
Must Solve By T E
Kinematic Wave Method tc 0.94 (L0.6
n0.6) i0.4 s0.3 Izzard
Method tc 41.025(0.0007i c) L
1/3 s 1/3 i 2/3
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Time of Concentration (tc)
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Pre vs. Post-Development

• Pre-Development
• 20 acres Sandy Loam
• 5 acres Pasture
• 15 acres Woodland

• Post-Development
• 20 acres
• 10 acres Light Indust.
• 10 acres Woodland

C 0.23
C 0.45
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Intensity-Duration Curve for Montgomery
tc I