Surface Water Part II

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Surface Water(Part II)
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Stream Monitoring

• Pictured The Middlebury stream
• gauge and rain gauge.
• Tioga County is one of the most heavily gauged
  areas in the United States.
• Brian Guillaume and Jason Dunn's website for
  stream gauging in Tioga County.

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What is monitored?

• Stage
• elevation of the water above a
  reference datum
• usually measured in feet
• directly measured by the gauge
• uses
• bridge heights
• flood-prone area maps
• flood warnings
• speed of flood crest movement
• rafting / fishing

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Stage Hydrograph

• Hydrograph
• Stage vs Time
• Stream behavior
• Record of flow
• Tioga River

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Stream Gauge Operation

• Automatic stream monitoring
• Data transmitted by satellite and posted on the
  internet
• Continuous record of flow
• Rapid response in emergencies
• Tioga River at Mansfield

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More Important than Stage...

• Discharge
• volume of water passing a given point
  in a unit of time
• usually measured in cubic feet per
  second
• can not be measured by the gauge -
  estimated
• uses
• relates stream conditions to
  reservoir capacity
• better than stage for
  historical information
• predicted precipitation ---gt
  stream response
• contaminant dilution

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Discharge

• Volume of water passing a given point in a
  unit of time

Q width x depth x velocity
velocity (3 feet / sec
depth (2 feet)
Q 2' x 4' x 3'/sec
Q 24 cubic feet / sec
width (4 feet)
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You Calculate...

• What is the discharge?

velocity (2 feet / sec
depth (3 feet)
width (12 feet)
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Discharge is difficult to measure in the field

• Channel shape is irregular
• (not a simple rectangle)
• Velocity is variable
• (fast at the top / slow at bottom)
• (fast in middle / slow at banks)

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Calculating Discharge in the Field

• First Problem Irregular channel Geometry

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Calculating Discharge in the Field

• Solve by first dividing the channel into segments

• The segments are nearly rectangular in shape

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Calculating Discharge in the Field

• Measure the depth in the center of each segment
  . (it will be
  close to the average depth of the segment)

V

• Measure the width of each segment

• Measure the velocity of each at 6/10 of the
  depth
• (it will be close to the average velocity of
  that segment)
• Discharge of the stream is obtained by adding
  all
• of the segment discharges

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Measuring Discharge in the Field

• The only way to get accurate data
• Stream gauges can only measure stage
• Expensive, time-consuming, dangerous during
  floods