Basic Hydrology
Water Quality:
Sediment production and transport
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
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
– 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
Grain size classes
size class
gravel
v. coarse sand
coarse sand
medium sand
fine sand
v. fine sand
coarse silt
silt
clay
diameter range (mm) microns
2.00 +
1.0 - 2.0
0.5 - 1.0
250 - 500
0.25 - 0.5
125 - 250
0.125 - 0.25
63 - 125
0.0625 - 0.125
31 - 63
0.031 - 0.0625
3.9 - 31
0.0039 - 0.031
< 0.0039
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
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
Suspended sediment pulse,
Russell Creek
300
30
200
20
100
10
0
0
11
/1
9
9/
1
11
/2
9
0/
1
11
/2
9
1/
1
11
/2
9
2/
1
11
/2
9
3/
1
11
/2
9
4/
1
Suspended Sediment (mg/l)
Discharge (m3/s)
40
SS concentration vs. discharge
Suspended Sediment (mg/l)
300
19 - 20 November 1991
Russell Creek
Supply limited
200
100
0
0
10
20
Discharge (m3/s)
30
40
Spray River near Banff, 1973
Supply limited
400
300
10
200
5
100
0
4/30/73
0
5/31/73
7/1/73
8/1/73
9/1/73
Suspended Sediment (mg/l)
Streamflow (m3/s)
15
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
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
Fraser River at Mission, 1983
400
8000
300
6000
200
4000
100
2000
0
3/31/83
0
4/30/83
5/30/83
6/29/83
7/29/83
Suspended Sediment (mg/l)
Streamflow (m3/s)
10000
Transport vs. supply limited
Fraser River 1983
transport limited
April
Suspended Sediment (mg/l)
400
supply limited
May - June
300
200
100
0
0
2000
4000
6000
Streamflow (m3/s)
8000
10000
Columbia River 1976
somewhere south of Golden
800
transport limited
event
600
2000
400
1000
200
0
3/31/76
0
4/30/76
5/30/76
6/29/76
7/29/76
8/28/76
Suspended Sediment (mg/l)
Streamflow (m3/s)
3000
May 1976 Columbia River
Suspended Sediment (mg/l)
400
300
200
100
0
200
400
600
Streamflow (m3/s)
800
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
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

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
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
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
Sediment Production at Russell Cr.
Total Sediment Yield
(kg/storm)
1000000
100000
10000
1000
100
10
Peak Suspended
Sediment Conc. (mg/l)
0
20
40
60
Maximum 12-hour Rain Intensity
1000
100
10
1
0
0
5
10
15
20
25
Maximum 3-hour Rain Intensity (mm)
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