CWR4101: Hydrology

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CWR4101 Hydrology
Mr. Jeff Earhart earhart_at_bhiinc.com 407-426-8994 F
low Measurement http/classes.cecs.ucf.edu/cwr4101
/shagen
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Velocity Area Method
Flow gage at one or more depths
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Measurement of flow

• Velocity Area Method

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Mannings equation
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Weir
Weir
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Weir

• Apply Conservation of Energy, or, in this case

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Weir

• Let z1-z2 y
• Then

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Weir (looking upstream)
y
Weir
B
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Weir
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Weir Equation

• Let H equal the height above weir, then

Incorporating Cf friction loss over the weir
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Weir Equation

• Integrating

or
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Weir Equation

• Then

or
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Orifice Flow

• A. Derivation

Z1
Z2
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Orifice Flow

• Consider the velocity at center of orifice
• Applying Bernoullis equation

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Orifice Flow

• Let z1-z2 H

• Given the average velocity through the orifice we
  could state Q AV. Since we do not know this
  average velocity, V, or exact area, we
  incorporate a discharge coefficient

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Orifice Flow

• where
• Cd discharge coefficient (? 0.6)
• Ao orifice area
• H head above orifice center

note, with Cv coefficient of velocity Cc
coefficient of contraction
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Orifice Flow vs. Weir Flow

• 1.Weir Flow

H
Riser pipe
Riser pipe
Orifice Flow
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Orifice vs. Weir Flow

• What would be the minimum depth (H) for orifice
  flow?
• Area of flow over riser pipe APIPE