Sediment Yield and Channel Processes

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Sediment Yield and Channel Processes
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Definitions

• Suspend Sediment sediment (orgranic or
  inorganic) which remains in suspension in water
  for a considerable period of time without content
  to the bottom.
• Bed Load soil, rock particles, or other debris
  rolled along the bottom of a channel by the
  movement of water.
• Saltation is the process by which sediment is
  skipped along the channel bottom by the movement
  of water.
• Total Sediment Load (Sediment Yield) all the
  orgranic and inorganic material carried past a
  sampling station for a given period of time.

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Suspend Sediment and Bed Load
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Sampling

• Depth Integrated Sample across a vertical
  profile. Best to take multiple samples across
  the stream. Sampler type is the function of
  discharge. The best method for describing total
  load.

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Sampling

• Surface Grab Sample no effort is made to make
  an integrated sample. Used as an index of
  sediment condition.
• Point sample made at a given point in the water
  column, usually integrated over time. Many
  automated samples are point samplers. May be
  stage dependent.
• Acoustic Measurements of Suspended Sediments
• Turbidity measurements have be used as a
  substitute for sediment measurements due to cost.
  

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Stage suspended sediment sampler You will need
to be recording stage
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Sampling Procedures

• A suspend sediment sample provides you an
  estimate of concentration (m/l3). You need
  discharge to estimate load (m/t m/l3 l3/t).
• Sediment transport is function of velocity which
  changes with depth and width. You need to take
  depth integrated samples across the stream to get
  a good estimate. Sediment concentration is
  highly variable. Always take two samples or more.
  You can also loss samples in the lab.
• Always get an estimate of discharge so you can
  compute load and develop a sediment rating curve.

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Lab Work

• Dry and weight the filter paper before use.
• Filter the sample and then dry the filter paper.
• Weight the filter paper with sediment, subtract
  the paper weight. The result is mass from
  sediment (mg).
• Measure the liters of water in sample.
• Divide the mass by the sample volume. The result
  is the sediment concentration in mg/l or ppm.

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Turbidity

• Is the optical property of a fluid that causes
  light to be scattered and absorbed rather than to
  be transmitted. Used to describe murky or cloudy
  appearance in water.
• Light is beams into a water volume the intensity
  of light transmitted through the sample is
  recorded. Less light more turbid.
• Turbidity has been used as a water quality
  standard as the criterion for judging the level
  of suspend material permitted in streams.
• Cheap and Easy
• Errors in measurement.
• Measurements vary between instruments.
• Correlation between suspend sediment and
  turbidity not constant or without error. Other
  factors can increase turbidity (i.e. algae).
• U.S. EPA (and most states) is moving away from
  turbidity as a standard, but it has created a
  void in data series to assessing potential
  impairment.

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Sampling

• Bed Load Harder to do.
• Hand samples
• Cable
• Traps (portable and instream)
• The above samplers all change the local
  hydraulics and have issues with opening size.
• Barrier (dams)

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Lanes Equation (SL SS) a (Slope Q)
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Transport Capacity vs. Sediment Source