6/9/2010
Stream classification: the Rosgen method
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Rosgen’s Classification of
Natural Rivers
Goals of Rosgen’s (1994) classification:
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Stream classification: the Rosgen method
Predict a river’s behavior from its appearance
Develop specific hydraulic and sediment relations for
a given morphological channel type and state
Provide a mechanism to extrapolate site-specific data
collected on a given stream reach to those of similar
character
Provide a consistent and reproducible frame of
reference of communication for those working with
river systems in a variety of professional disciplines
Stream classification: the Rosgen method
Preliminary assessment
using topo maps, air
photos, GIS
(Rosgen, 1994)
Stream classification: the Rosgen method
Level I: Geomorphic characterization channel slope
(Rosgen, 1989)
Stream classification: the Rosgen method
Level I: Geomorphic characterization channel shape
Type Aa  steep, frequent spaces, vertical drop/scour-pool bed features,
high debris transport systems
systems, waterfalls
Type A steep, step/pool bed features
Type B riffle-dominated with rapids, infrequently spaced scour-pools at
bends or areas of constriction
Types C, DA, E, & F gentle-gradient, riffle/pools
Type G gullies, step/pool channels
Type D braided channels
Type A narrow, deep, confined, entrenched
Type C wider, shallower, well-developed floodplain, broad valley
Type E narrow, deep, very wide & well-developed floodplain
Type F wide, shallow, entrenched meandering, little or no floodplain
Type G narrow, deep, entrenched, steeper, less sinuous than E
“Bed morphology can be predicted from stream type by using bed-slope
indices.”
(Rosgen, 1994)
(Rosgen, 1994)
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6/9/2010
Stream classification: the Rosgen method
Stream classification: the Rosgen method
Level I: Geomorphic characterization channel pattern
Level I: Geomorphic characterization
Type Aa and A straight
Type B low sinuosity
Type C meandering
Type E tortuously meandering
Type D braided
Type DA anastomosed
(Rosgen, 1994)
(Rosgen, 1994)
Stream classification: the Rosgen method
Stream classification: the Rosgen method
Start with A-G then stream types are broken into discreet slope ranges and
dominant channel-material particle sizes 42 major stream types
More detailed assessment
that requires some field
work to measure specific
channel dimensions e.g.,
slope and channel
materials
(Rosgen, 1989)
(Rosgen, 1989)
Stream classification: the Rosgen method
Stream classification: the Rosgen method
Level II: Morphological description
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Level II: Morphological description
Slope water surface slope

measure channel slope for broad-level delineations
using topo maps and air photos
(Rosgen, 1989)
Channel materials
D50 = size that 50%
of sample is of the
same size or finer
(Rosgen, 1989)
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Stream classification: the Rosgen method
Stream classification: the Rosgen method
Level II: Morphological description

Let’s talk about bankfull discharge…
 Bankfull Discharge—how is it defined?
 Channel-forming discharge aka dominant discharge
Entrenchment
ratio=
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“for a given alluvial channel geometry, there exists a
single discharge that given enough time would produce
width, depth, and slope equivalent to those produced
by the natural hydrograph. This discharge therefore
dominates channel form and process.”
Three approaches to determine Qcf effective Q,
Bankfull Q, and return interval Q. These are sometimes
assumed to be equal.
(Rosgen, 1989)
Stream classification: the Rosgen method
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Stream classification: the Rosgen method
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Bankfull Discharge—how is it defined?

(Shields et al., 2003)
Bankfull Discharge—how is it defined?
Effective Q (Qeff) = discharge that transports the largest sediment
load over a period of years; links flow with sediment transport
Bankfull Q (Qbf) = discharge that fills the entire channel of a
stable stream to the top of the banks (i.e., just up to the
floodplain)
Return interval Q (Qri) = discharge that occurs at a particular time
interval; in a stable channel bankfull discharge occurs, on
average, approximately every 1.5 years (range = 1-2.5 years)
(Shields et al., 2003)
Stream classification: the Rosgen method
(Shields et al., 2003)
Stream classification: the Rosgen method
Level II: Morphological description
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Bankfull indicators:
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Uppermost scour line
Back of a point bar
Upper break in slope of the bank
Occasionally the top of the bank
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Width/depth ratio dimension & shape factor
bankfull channel width/bankfull channel depth
bankfull discharge = “maximum peak flow; often
related to the 1.5 year RI”
low w/d ratio = <12 (narrow & deep)
moderate or high w/d ratios >12 (wide & shallow)
(Rosgen, 1989)
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Stream classification: the Rosgen method
Stream classification: the Rosgen method
Level II: Morphological description
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Sinuosity meandering vs. straight
stream length/valley length
Morphological descriptions
& calculations are linked
to channel stability and
sensitivity to disturbance,
sediment supply, etc. to
make predictions
(Rosgen, 1989)
Stream classification: the Rosgen method
(Rosgen, 1989)
Stream classification: the Rosgen method
Level III: Stream “state” or condition
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Level III: Stream “state” or condition
Detailed description of existing conditions
and “associated prediction/interpretation”
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Measurements in select reaches are compared to
a reference reach of the same stream type,
y
which has to be stable.
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Stream channel condition (morphological
descriptions)
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Stability defined as, “the ability of a stream, over time, in
the present climate, to transport the sediment and flows
produced by its watershed in such a manner that the
stream maintains its dimension, pattern, and profile
without either aggrading nor degrading.”
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Riparian vegetation (e.g., composition, density)
Sediment deposition patterns (8 patterns)
Debris occurrence (e.g., LWD)
Meander pattern (8 patterns)
Stream size/stream order
Flow regime (e.g., perennial, ephemeral, intermittent)
Altered state due to direct disturbance
(Rosgen, 1996 cited in Rosgen,1989)
Stream classification: the Rosgen method
(Rosgen, 1989)
Stream classification: the Rosgen method
Level III: Stream “state” or condition
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Level III: Stream “state” or condition
Vertical stability/degradation/aggradation
Bank height ratio = lowest bank height of the cross-section/maximum bankfull depth
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Lateral stability
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Meander width ratio is calculated to determine
degree of lateral confinement
meander belt width/bankfull channel width
meander belt width (amplitude) is the lateral containment of the channel within its valley
Also considers entrenchment ratio (<1.4 ±0.2 stream is entrenched), change in the
w/d ratio, observation of excessive bank erosion or bed/floodplain aggradation
(Rosgen, 1989)
(figure from Charlton, 2008)
(Rosgen, 1989)
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Stream classification: the Rosgen method
Stream classification: the Rosgen method
Level III: Stream “state” or condition
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Level III: Stream “state” or condition
Lateral stability, continued
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Calculation of the Streambank Erosion Hazard
Index (BEHI) and Near-Bank Stress (NBS)
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BEHI considers bank height, root depth, root density,
bank angle, surface protection
NBS
Channel pattern
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Measures meander width ratio, ratio of radius of
curvature/bankfull width, sinuosity, etc.
Dimensionless ratios are used for comparison
purposes.
River profile and bed features

Measures river slope, valley slope, pool/riffle
spacing, ratio of maximum depth of pools/mean
depth of channel, ratio of maximum depth of
riffles/mean depth of channel
(Rosgen, 1989)
Stream classification: the Rosgen method
(Rosgen, 1989)
Stream classification: the Rosgen method
Level III: Stream “state” or condition
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Level III: Stream “state” or condition
Channel dimension relations
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Determine changes in the bankfull width and
mean bankfull depth ratio (w/d ratio)
Stability Rating
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Ratio of W/D Increase
Very stable
1.0
Stable
1.0 – 1.2
Moderately unstable
1.21 – 1.4
Unstable
Stream channel scour/deposition potential
(stream competence)
Calculate critical dimensionless shear stress to
determine the size of the sediment particle that
can be moved. Determine d50 in a riffle and from
a core sample of bar material.
> 1.4
(Rosgen, 1989)
Stream classification: the Rosgen method
(Rosgen, 1989)
Stream classification: the Rosgen method
Level III: Stream “state” or condition
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Level III: Stream “state” or condition
Stream channel stability rating
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Evaluates the upper and lower banks and streambed
for evidence of excessive erosion/deposition
Dimensionless ratio sediment rating curves
bed load and suspended sediment values
the same units of sediment values at
bankfull discharge
corresponding discharge
bankfull discharge
(Rosgen, 1989)
(Rosgen, 1989)
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Stream classification: the Rosgen method
Stream classification: the Rosgen method
Level III: Stream “state” or condition
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Stream type evolutionary
scenarios
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Determine the current
state and evolutionary
y
sequences as show in
Figure 1
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Stream type and location in
evolution sequence must
be determined
Validation of predictions
(Rosgen, 1989)
Stream classification: the Rosgen method
(Rosgen, 1989)
Stream classification: the Rosgen method
Level IV: Validation level
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Vertical stability/degradation/aggradation
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Channel dimension relations
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Stream channel scour/deposition potential (stream
competence)
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Toe pins
T
i installed
i t ll d and
d cross sections
ti
surveyed
d tto measure
streambank erosion rates/lateral accretion
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Channel pattern
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Permanently monumented profiles and cross section
surveyed annually
Lateral stability
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Level IV: Validation level
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Air photo time trends & cross section surveys showing
down-valley meander migration
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River profile and bed features
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Measured bedload size distribution at bankfull stage
stage,
corresponding slope and depth measurements
Channel surveys and scour chains
Annual replicates of the bar core samples taken at the
same locations to show any changes in sediment size
Stream channel stability rating
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Channel survey
Channel survey
Measured sediment rating curves, surveyed cross
sections, channel material size distributions
(Rosgen, 1989)
Stream classification: the Rosgen method
Level IV: Validation level
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Stream classification: the Rosgen method
Application: Evolution of stream types
Dimensionless ratio sediment rating curves
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(Rosgen, 1989)
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Sediment and discharge measurements
Stream type evolutionary scenarios
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Sensitivity to
disturbance
Recovery
potential
Streambank
erosion
potential
Vegetation
controlling
influence
(Rosgen, 1989)
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