Basic Hydrology

1
Basic Hydrology

• Water Quality
• Sediment production and transport

2
Sediment in streams

• The significance of sediment in streams has two
  aspects
• the water quality aspect is related to suspended
  sediment
• unwanted suspended sediment can cause domestic
  water quality problems, and can cause physical
  damage to fish
• supply and movement of coarse sediment in
  streams is a channel morphology issue
• excessive coarse sediment in streams can
  adversely affect fish habitat and fill in water
  control structures

3
Sediment movement in streams

• Sediment movement in stream channels can be
  categorized by grain size or by the process that
  transports it
• suspended sediment consists of fine particles of
  silt and clay that are carried by the water
  column
• suspended sediment movement is independent of
  flow rate
• wash load is a term that refers to sediment that
  is carried by the water column, that has grain
  size distribution smaller than the channel bed

4

• saltating bed load
• consists of fine to medium sand
• movement is dependent on the velocity of flow at
  low flow it may not move, but at high flow it may
  bounce high up into the water column
• behaviour may be similar to suspended sediment
  for fine sand at high flow
• bed load consists of coarse sand, gravel and
  larger sized particles that are transported by
  rolling along the channel bed.
• bed load transport is also dependent on flow rate
• there is a threshold flow velocity needed to get
  it moving

5
Grain size classes
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Sediment production vs. transport

• Sediment production refers to the addition of new
  sediment to the channel system
• landslides
• surface erosion
• channel bank erosion
• Sediment transport refers to the movement of
  sediment that is already in the channel system

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Types of sediment transport systems

• Supply limited
• most rivers are supply limited in terms of
  sediment production
• the stream has the ability to move all the
  sediment that is supplied to it, hence sediment
  transport is limited by the supply
• sediment transport tends to exhibit pulse
  behaviour, sediment movement occurs mostly on the
  hydrograph rising limb
• hysteresis occurs where sediment concentration
  for a given flow is greater for rising than
  falling streamflow

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Suspended sediment pulse, Russell Creek
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SS concentration vs. discharge
19 - 20 November 1991 Russell Creek Supply limited
Rising
Falling
10
Spray River near Banff, 1973
Supply limited
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Sediment transport types

• Transport limited
• transport limited sediment transport is far less
  common than supply limited
• occurs when the sediment supply to the stream is
  in excess of the ability of the stream to
  transport it
• occurs in braided and anastamosed rivers where
  sediment supply is high
• as a result, more sediment moves on the falling
  limb than the rising limb of the hydrograph
• hysteresis occurs where sediment concentration
  for a given flow is greater for falling than
  rising streamflow
• large rivers can exhibit both types of transport
  behaviour

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Dual behaviour of large rivers

• Large rivers tend to be transport limited during
  freshet periods
• sediment concentrations tend to be high during
  spring freshet because
• flow is low - sediment is concentrated
• sediment production occurs as a result of supply
  of sediment accumulated over winter that enters
  the system all at once
• As flows increase, they become supply limited
• sediment transport capability increases

13
Fraser River at Mission, 1983
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Transport vs. supply limitedFraser River 1983
transport limited April
supply limited May - June
rising
falling
falling
rising
15
Columbia River 1976somewhere south of Golden
transport limited event
16
May 1976 Columbia River
Falling
Rising
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Measurement of suspended sed.

• Direct method sample analysis
• a sample of stream water is collected using a
  manual DH48 depth integrated sampler or an
  automatic sampler such as ISCO 3700
• the sample is filtered through a 2 mm filter to
  determine sediment concentration in mg/l
• Indirect method turbidity is measured and
  interpreted as SS conc. by field and lab
  calibration

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Sediment production processes

• rain splash erosion
• sheet wash erosion - surface runoff
• freeze-thaw erosion
• expansion and contraction of erodible rock
  surfaces
• frost expansion
• needle ice development
• animal movement
• ravelling of loose sediment surfaces
• undercutting and slumping of loose surfaces
• mass wasting

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Factors controlling sediment production

• Cause of runoff
• rainfall produces more sediment than an
  equivalent volume of snowmelt
• rain erosion on exposed sediment sources vs.
  water yield from snowpack that blankets the
  exposed sed.
• rainfall produces larger peaks than streamflow,
  hence greater sediment transport and channel
  scour
• Size of storm
• larger storms generally produce more sediment
• larger yield, and greater peak concentration

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Controlling factors

• Watershed morphology
• lithology softer more erodible bedrock (e.g.,
  basalt - Catherine Cr.) produces more sediment
  than harder more resistant bedrock (e.g., granite
  - Russell Creek)
• type and connectivity of sediment sources
• debris flow deposits are big producers
• hillside sediment sources
• landslide scars, road cuts
• slope stability

21
Controlling factors

• Land use, e.g. logging and related activities
• related to other factors such as slope stability
  and surface erosion from road surfaces and cut
  and fill slopes
• increase in mass wasting processes following
  logging
• yarding disturbance
• potential increase in streamflow after logging
• increase in sediment transport capability
• increase in stream channel and bank erosion

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Sediment Production at Russell Cr.
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How does logging affect sediment production?

• Studies show that increased sediment after
  logging is related to logging roads
• surface erosion from road surfaces
• road related landslides
• Open slope failures increase after logging
• If soil disturbance is minimized, clear-cuts are
  not sediment sources
• burning
• ground skidding