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Fluvial geomorphologists use close to a 100 different terms to describe the landforms that make up riverscapes. We identified 68 of these existing terms that describe truly distinctive landforms, in which form is maintained under characteristic conditions and fluvial processes. Clear topographic definitions for these landforms to consistently identify and map them are lacking. With the explosion of continuous, high-resolution topography and digital elevation models, we have plenty of new basemaps in which these landforms are clearly visible, but very few examples of manual or automated classification of fluvial landforms. Fluvial landforms are the building blocks of a river and are variously referred to as geomorphic units, morphological units, habitat units, and channel units. We present a tiered framework for describing geomorphic units, with tier 1 differentiating units on the basis of their stage, tier 2 separating shape (e.g., concave, convex, or planar), tier 3 using particular key attributes to narrow in on the likely specific geomorphic unit type, and tier 4 differentiating those types on the basis of vegetative or roughness modifiers. Information on the assemblage and configuration of geomorphic units can be used to inform process-based interpretations of the range of river behavior. The accuracy and transferability of such analyses is fundamentally tied to the taxonomy we assign to these discrete building blocks. In this paper we clarify the terminology and definitions relating to the identification and delineation of geomorphic units, margins, and structural elements. We establish a set of procedures that can be used to manually map and identify these features. The proposed framework provides a rigorous and repeatable approach to identification of topographically defined features of riverscapes. We demonstrate the application of these systematic yet flexible procedures with a series of maps from rivers in differing valley settings.
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Geomorphic mapping and taxonomy of uvial landforms
Joseph M. Wheaton
, Sara G. Bangen
, Nicolaas Bouwes
Gary O'Brien
Department of Watershed Sciences, Utah State University, 5210 Old Main Hill, Logan, UT 84332-5210, USA
Department of Environmental Sciences, Macquarie University, North Ryde, NSW, Australia
School of Environment, University of Auckland, Auckland, New Zealand
Eco Logical Research, Logan, UT, USA
abstractarticle info
Article history:
Received 25 December 2014
Received in revised form 2 July 2015
Accepted 3 July 2015
Available online xxxx
Geomorphic unit
Structural element
Physical habitat
River styles
Fluvial margin
Fluvial geomorphologists use close to a 100 different terms to describe the landforms that make up riverscapes.
We identied 68 of these existing terms that describe truly distinctive landforms, in which form is maintained
under characteristic conditions and uvial processes. Clear topographic denitions for these landforms to consis-
tently identify and map themare lacking. With theexplosion of continuous, high-resolutiontopography and dig-
ital elevation models,we have plenty of new basemaps in which these landforms are clearly visible, but very few
examplesof manual or automated classication of uvial landforms. Fluviallandforms are the building blocks of a
river and are variously referred to as geomorphic units, morphological units, habitatunits, and channel units. We
present a tiered framework for describing geomorphic units, with tier 1 differentiating units on the basis oftheir
stage, tier 2 separating shape (e.g., concave, convex, or planar), tier 3 using particular key attributes to narrow in
on the likely specic geomorphic unit type, and tier 4 differentiating those types on the basis of vegetative or
roughness modiers. Information on the assemblage and conguration of geomorphic units can be used to in-
form process-based interpretations of the range of river behavior. The accuracy and transferability of such anal-
yses is fundamentally tiedto the taxonomy we assign to thesediscrete buildingblocks. In this paper we clarify the
terminology and denitions relating to the identication and delineation of geomorphic units, margins, and
structural elements. We establish a set of procedures that can be used to manually map and identify these fea-
tures. The proposed framework provides a rigorous and repeatable approachto identication of topographically
dened features of riverscapes. We demonstrate the application of these systematic yet exible procedures with
a series of maps from rivers in differing valley settings.
© 2015 Elsevier B.V. All rights reserved.
1. Introduction
Fluvial geomorphologists have long mapped rivers to better under-
stand their form, looked for patterns in their organization, and made in-
ferences and interpretationsabout the processes producingand shaping
those forms. Such maps of rivers can be considered raw data describing
and/or quantifying a river. Maps also represent derivative products,
which reect syntheses and interpretations. In the modern era of ap-
plied geomorphic inquiry, emerging technologies provide enormous
opportunities to produce more accurate and detailed topographic
maps (Jones et al., 2007; Williams et al., 2013; Bangen et al., 2014),
automate mapping procedures, and quantitatively model river forms
and processes (e.g., Drăguţand Blaschke, 2006; Carbonneau et al.,
2011; Roering et al., 2013). Morphometric analyses and eld mapping
present a critical template for a range of toolkits for integrative river sci-
ence (e.g., Dollar et al., 2007; Thorp et al., 2013; Humphries et al., 2014;
Roux et al., 2014). Although morphometric analysis can yielda continu-
ous derivative output (e.g., a slope analysis), it is oftenused as classica-
tion exercise to help identify specic features, process zones, and
component parts of riverscapesfrom continuous data. While such
morphometric analyses are ultimately useful for helping us understand
the organization and processes shaping rivers, that is not the focus of
this paper. Instead, we seek to identify a taxonomy that could work
equally well for easy identication of features in the eld or to support
morphometric analyses for topography.
To the extent that geomorphic mapping and identifying the building
blocks of rivers relies on classication, we contend that the uvial geo-
morphic community lacks a broadly applicable framework for consis-
tent identication of such features. This is a problem that has equal
relevance in eld mapping/interpretation as well as interpretation of
remotely sensed data. All maps are products of the underlying concep-
tual models and available data from which they are constructed. Geo-
morphic maps in particular provide critical information on the nature,
patterns and conguration of landforms. When performed effectively
(e.g., Jones et al., 2007), geomorphic maps provide a platform to
Geomorphology 248 (2015) 273295
Corresponding author.
E-mail address: (J.M. Wheaton).
0169-555X 2015 Elsevier B.V. All rights reserved.
Contents lists available at ScienceDirect
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interpret and quantify process relationships and their controls, to eval-
uate river change and adjustment potential, and to assess evolutionary
trajectories (e.g., Brasington et al., 2003; Fuller et al., 2003; Beechie
et al., 2010; Roni et al., 2012; Carling et al., 2013; Wheaton et al.,
2013). More specically, such maps often simplify spatially continuous
information (e.g., topography) into a discrete interpretation of the key
features that comprise the riverscape.
To date, descriptions of uvial landforms have been notoriously
inconsistent, limiting our capacity to compare patterns of these features
across riverscapes even when using similar naming conventions
(e.g., Bisson et al., 1981; Montgomery and Bufngton, 1997). Terms
used to describe river landforms include geomorphic units (Brierley and
Hickin, 1991), channel geomorphic units (Hawkins et al., 1993), habitat
units (Bisson et al., 1981), architectural elements (Miall, 1985), morpho-
logic units (Wyrick et al., 2014), morphostratigraphic units (Brierley,
1991), and morphogenetic units (Brierley, 1996; Martínez García and
López Blanco, 2005). For simplicity, we refer to these features as geomor-
phic units (sensu Brierley and Fryirs, 2005; Fryirs and Brierley, 2013c).
A recent review of riverine geomorphic classication by Bufngton
and Montgomery (2013) highlighted the importance and pressing
need for a consistent set of geomorphic unit classication guidelines.
Fluvial geomorphology seems to have lagged behind other branches of
geomorphology in terms of clear denitions and classication of geo-
morphic units (cf., Finkl (2004) for coastal geomorphology; Pennock
et al. (1987) for hillslopes; and Bullard et al. (2011) foraeolian systems).
Instead uvial geomorphologists have focused on coarser-resolution
reach typing and channel planform classication (Rosgen, 1994;
Bufngton and Montgomery, 2013; Beechie and Imaki, 2014; Kasprak
et al., in review) or hierarchical frameworks of classication that recog-
nize where geomorphic units t, but do not focus on clarifying their
taxonomy (e.g., Brierley and Fryirs, 2005). Recently, one of the most
promising developments at this uvial landform scale was by Wyrick
and Pasternack (2014) who offered clear hydraulic denitions of what
they term morphological unitsfrom which automatic landform classi-
cation can be based. The Wyrick and Pasternack (2014) denitions are
based on combinations of velocity and depth. Where eld mapping of
hydraulics (e.g., depth from topography and velocity from ADCP) exists
or where multidimensional hydraulic models exist, this is a very useful
approach.Wyrick and Pasternack (2014) even showed that many of the
units persist with their hydraulic denitions at different ow stages,
with minimal adjustment of their boundaries. However useful such a
hydraulically dened framework is for in-channel and oodplain map-
ping, it cannot be applied to areas outside the valley bottom that do
not experience ows, and spatially distributed hydraulic data is no-
where near as common as topography. As such, we contend that an
even more generic, topography-centric landform mapping frame-
work for rivers would be more transferable and universally appli-
cable. This need raises signicant questions about the semantics
of how we classify these features (Richards and Clifford, 2011). A
diversity of perspectives and classication schemes that are used
for different purposes is perhaps inevitable. We applaud the efforts
of researchers like Wyrick and Pasternack (2014) who strive for
consistency and more rigorous denitions. However, collectively
the uvial geomorphic literature is inconsistent in its descriptions
of uvial landforms as we lack a exible taxonomy for geomorphic
units. This promotes confusion among the audiences geomorphol-
ogists target as consumers of our science (e.g., river managers,
restoration designers, civil and hydraulic engineers, sheries
biologists, lotic ecologists), and we do ourselves and those audi-
ences a disservice.
Fig. 1. Tiered uvial margins classication framework.
274 J.M. Wheaton et al. / Geomorphology 248 (2015) 273295
This paper presents a coherent, repeatable, and generic framework
for mapping uvial landscapes. Our intent is not to interject a new
and confusing lexicon for naming these building blocks, but we do
seek to build off past denitions (e.g., Fryirs and Brierley, 2013c) and
clarify inconsistencies. Our proposed taxonomy contains many of the
same terms that geomorphologists have longused to describe the mor-
phology of rivers. However, we organize this inconsistently used termi-
nology into a tiered taxonomy that leads to more complete, universal,
and consistent identication and interpretation in theeld. For geomor-
phic units, at tiers 1 and 2 we focus on topographic denitions that will
facilitate development of tractable algorithms based on topography for
automating the derivation of these features (not reported here). Our ap-
proach also outlines procedures to identifystructuralelements (natural
or human-induced) and uvial margins, both of which can exert a crit-
ical control upon river character, behaviors and the assemblage of geo-
morphic units present. The proposed framework is demonstrated
through production of simple maps at reach-scale extents (in this in-
stance 10
m). Within each reach,geomorphic units and structural
elements were classied at a resolution of 10
m. In short, the clas-
sications proposed provide the legend labels of a good geomorphic
map, representing geomorphic units as polygons, structural elements
as discrete objects that occupy smaller extents (e.g., points), and mar-
gins as polylines. The relative simplicity or complexity of the map
then reects the degree of heterogeneity of that riverscape and provides
useful clues as to its histories and the processes that shape it.
2. A framework for producing a geomorphic map of a riverscape
Clear steps for drawing a geomorphic map can help ensure that the
outputs are consistent and rigorously arrived upon (Jones et al., 2007).
First, the scale (i.e., extent and resolution) of the required map must be de-
cided. How features are identied and mapped is dependent on the mini-
mum mapping unit (area and resolution) and the purposes for which the
map will be used (e.g., broad-scale description vs. detecting changes in
unit assemblage through time). Ideally, one framework could serve the
general needs and the more specic needs. Having a tiered taxonomy
(e.g., Linnaean taxonomy for biology) allows users to make general classi-
cations or more specic depending on their needs (e.g., kingdom phyla
classes orders families genera species).
One logical entry point to map construction is the identication and
drawing of margins. For a broader reach-scale extent mapof riverscapes
(e.g., 1:2000 to 1:10,000), the valley margin is often mapped rst (if it is
within the extent of the required map), followed by the valley bottom
margin and then the channel margin. Conning margins can then be
added based on where the channel margin abuts other margins that
constrain its ability to adjust laterally. These margins form the basis
for identication and coding of the out-of-channel geomorphic units.
For mapping that is intended to resolve ner scale features (e.g., 1:100
to 1:2000), discrete entities such as structural elements may be added. At
the resolution of mapping, if structural elements are rare and exert a sig-
nicant inuence on either channel morphology or geomorphic unit for-
mation, all features should be drawn. If, however, structural elements are
pervasive (e.g., hundreds of pieces of wood or boulders in a rapid), sym-
bology can be used to indicate their presence (e.g., hatch a region) rather
than drawing each individual structural element.
Finally, within the areas bounded by different margins, the geomor-
phic units that make up the in-channel and oodplain zones should be
delineated and symbolized accordingly. The scale of geomorphic units
considered needs to be explicitly considered with respect to the pur-
poses of the mapping and resolution. A minimum mapping unit size
Fig. 2. Illustration of howmapping the uvial margins and which areconning the channels lateral capacity for adjustment cansimply contrast the valley setting for different river styles.
275J.M. Wheaton et al. / Geomorphology 248 (2015) 273295
can help determine the degree of generalization versus splitting every
feature out. At the desired resolution, units can be identied by working
rst at identifying the center or focal point of the unit (e.g., the crest of a
rife or the deepest point of the pool) and then at working outward to
consider its boundaries, which may be gradual or abrupt. In the case
of the latter, edges can be blended or classied as transition zones.
From this, determinations can be made about how far out that unit ex-
tends, its shape, its position, its orientation and the ow and sediment
interactions required to form the unit.
2.1. Identifying margins
A margin represents a border or edge betweendistinct regions and is
used to dene the riverscape's valley setting. In a uvial context, several
types of margins may be evident. They may be an expression of river
form; alternatively, they may constrain river behavior. We differentiate
between margins of anthropogenic or natural origin (Fig. 1). Margins
of anthropogenic origin include: embankments,fences,hedgerows,
constructed levees,railroads,roads, and walls. Anthropogenic margins
Fig. 3. Denition diagram forhydraulic inuenceof structural elements. The primarystructural elementsin this example are boulders (labeled 1, 2, 3, and4), and their hydraulic impact at
low ow is shown above.
276 J.M. Wheaton et al. / Geomorphology 248 (2015) 273295
now occupy, ank, fragment, and dissect an alarming number of valley
bottoms (Tockner and Stanford, 2002; Lewin,2013). Margins of natural
origin include valley margins,valley bottom margins, andchannel margins
(Fig. 1).
We dene valley margins as the margin between a bedrock (or collu-
vial) hillslope and the alluvialsediment stores that make up the valley
oor (Fig. 2). With some minor exceptions, most rivers and streams
ow through valleys that are made up of some mix of active channels,
active oodplains,inactive oodplains (i.e. terraces), and fans (alluvial,
colluvial,anddebris)and sometimes lakes, reservoirs, or other
The valley bottom comprises the active channel and contempo-
rary oodplain. The valley bottom margin can abut against the valley
margin or other conning features such as terraces and alluvial fans
(e.g., Fig. 2C and D). The contemporary character and behavior of a
river are interpreted for the effective valley width that makes up
the valley bottom (Fryirs and Brierley, 2010). From this, conned,
partly conned, and laterally unconned valley settings can be dif-
ferentiated, as dened in the River Styles framework (Brierley and
Fryirs, 2005).
Aconning margin is dened as any section of channel bank that
abuts against a valley margin, valley bottom margin, or anthropogenic
margin (Fig. 2). Conning margins are those that currently or actively
constrain lateral adjustment of a channel (Nicoll and Hickin, 2010). In
rivers where the channel abuts a connement margin on either side
more or less continuously (e.g., along N90% of its length) the valley
setting is conned (e.g., Fig. 2B). When the channel abuts a conning
margin frequently but not continuously (e.g. along 1090% of its length)
the valley setting is partly conned (e.g., Fig. 2C and D). Within this
category, differentiation can be made between bedrock-controlled
(Fig. 2C) and planform-controlled variants (Fig. 2D). Bedrock-
controlled rivers will have channels that abut the valley margin along
5090% of its length, and the valley margin is the primary control on
river planform. Discontinuous pockets of oodplain occur on the valley
bottom. These rivers tend to have low sinuosity channels within a mod-
erate sinuosity valley. Planform-controlled rivers have channels that
abut a conning margin along 1050% of its length. Channel planform
has greater capacity to adjust on the valley bottom relative to
bedrock-controlled variants. These rivers tend to be formed in irregular-
ly shaped valleys and have irregular-shaped oodplain pockets. Not all
riverscapes have channels in contact with a conning margin. As
dened in the River Styles framework (Brierley and Fryirs, 2005), in riv-
ers and streams where the conning margin comes in contact with the
channel rarely (e.g., along b10% of its length), the valley setting is
described as laterally unconned (e.g., Fig. 2E).
From a mapping perspective, margins can be represented as lines
with a different line weight or color for each margin type. The margin
types and their relative positions help dene the natural capacity for
adjustment of a river. For example, measuring the relative proportion
of a channel that is abutting a valley margin versus a conning margin
Fig. 4. Tiered uvial structural element classication framework.
277J.M. Wheaton et al. / Geomorphology 248 (2015) 273295
may explain the relative extent of hillslope-channel coupling, the
relative resistance of channel banks to erosion, and the local sediment
composition of in-channel geomorphic units.
2.2. Structural elements
Despite the rich literature on specic structural elements such as
large woody debris (Abbe and Montgomery, 1996; Gurnell et al.,
2002), restoration structures (e.g., Thompson, 2005), and beaver dams
(Butler and Malanson, 1995; Pollock et al., 2014), there is no clear over-
arching denition for structural elements. The lack of a clear denition
limits our ability to consistently map these features and to interpret
their role in shaping rivers and habitat. We dene structural elements
of riverscapes as discrete objects that directly inuence hydraulics. We
use the term structuralbecause these features exert an inuence
upon the structure of streams, and their presence is a direct indication
of the degree of structural complexity or heterogeneity (i.e., patterns
and assemblages of geomorphic units). Subsequently, structural ele-
ments inuence the presence/absence, maintenance/destruction, or
the sculpting/accentuation of uvial geomorphic units. Based on this
denition, we limit our focus to those structural elements that have di-
rect contact with ow at some stage. Structural elements produce ow
separations, which lead to the forcing of shear zones (Manners et al.,
2013). In shear zones, lower owenergywakesoreddiesformonone
side of the ow seam while higher energy convergent jets form on the
other side of the ow seam (Fig. 3). These structural elements are criti-
cal because distinctive forcedgeomorphic units often form because of
the altered hydraulics. A geomorphic unit is structurally forcedif a
structural element forcesits creation or enhancement. Structural ele-
ments can include natural inorganic features (e.g., rock outcrops),
natural organic features (e.g., large woody debris; hereafter LWD), and
anthropogenic features (e.g., bridge piers,rip rap,etc.).
2.2.1. Distinguishing characteristics of structural elements
A tiered approach is used to identify, dene, and map structural ele-
ments (Fig. 4). At tier 1, we distinguish natural and anthropogenic fea-
tures. Functionally, there may be no difference in the hydraulic and
geomorphic impact of a natural or anthropogenic structural element
(e.g., an engineered LWD structure and a LWD jam may each produce
convergent ow jets around them and eddies or wakes in their lee).
However, intentional and unintentional hydraulic and geomorphic re-
sponses of man-made features are helpful to differentiate from those
that occur naturally (e.g., boulders are often found placed in reach-
types that they would not naturally occur because of the competence
of the stream).
In tier 2, we identify the broad type of structural element, andin the
case of natural structural elements we further differentiate between in-
organic (e.g., bedrock and boulders) and organic structural elements
(e.g., large woody debris). The list of names for tier 2 that is shown in
Fig. 4 is not exhaustive and is only intended to illustrate the basic and
most common types of structural elements.
Tier 3 entails identication of a variety of key attributes that help dif-
ferentiate types of structural elements. We identify ve key attributes of
structural elements: orientation, position, obstruction type, the ow
stages it inuences, and the shear zone it creates. Table 1 provides a
detailed description of each key attribute type. Not all key attributes
are necessary to identify a specic structural element. Rather, using
what information is readily available one can lter to a tier 3 denition
by process of elimination. Alternatively, in many cases the tier 3 identi-
cation can be made directly without explicit consideration of the key
Table 1
Key attributes that help differentiate tier 3 structural elements; abbreviations: SE (structural element).
Key Tier 3
Types Description
SE orientation The orientation refers to the relative alignment of the structural element's long axis with respect to the dominant
streamwise ow direction
Transverse Transverse SEs are oriented perpendicular to the ow (e.g. beaver dam)
Streamwise Streamwise SEs are oriented parallel to the ow (e.g. a piece of LWD aligned with the ow)
Diagonal Diagonal SEs intersect the ow at an angle
SE Position The position of the SE with respect to the channel(s); Note use consistency whether the channelrefers to the low ow
channel or bankfull channel.
Bank Attached Attached or connected to one side of the channel margin
Channel Spanning Spanning across the entire channel from channel margin to channel margin
Mid Channel Not attached or connected to either side of the channel margin
Side-Channel Located in a side or secondary channel
Floodplain Located on the oodplain
SE obstruction type Refers to the type and nature of ow obstruction the SE object creates
Complete Barrier When all ow is forced around or over top of the SE
Porous Barrier When most ow is forced around or over top of the SE, but some ow can ow through the SE itself (e.g. a debris jam)
Deformable Barrier When SE is non-rigid such that when subjected to ows it deforms in a streamwise fashion (e.g. grasses)
Sieve When most ow is forced through various pathways through SE, but some can ow over or around
Funnel When ow is funneled through the SE (e.g. a culvert)
Roughness When ow is not obstructed by SE, but instead SE simply exerts more drag on the ow at the boundary then the typical
Stages inuenced Refers to the ow/ood stage at which the SE exerts an inuence on the ow
Baseow The mean low ow stage (note, this may be zero for intermittent and ephemeral channels)
Bankfull Flow The discharge just before ow spreads out on to a oodplain (not present in all channels)
Typical Flood The discharge associated with oods that occur regularly (e.g. 1 to 5 year recurrence intervals)
Rare Flood The maximum probable or historically recorded ood
Shear zone type Refers to the type of hydraulic impact induced by the downstream typically just downstream or on the lee side of the SE; the
shear zone type is very stage dependent, but closely related to the obstruction type
Wake A wake is a zone of slower moving water in the lee of an obstruction to the ow but that is still generally owing in a
streamwise direction
Eddy An eddy is a ow recirculation cell downstream of a ow separation (often, but not always induced by SE) in which the ow
direction varies (including owing upstream) but generally makes a circular vortice
Hydraulic Jump Represents a transition from subcritical to supercritical (typically over the SE) and back to subcritical ow; such hydraulic
features can take various forms (e.g. wave trains, standing wave, submerged jump (i.e. drop))
278 J.M. Wheaton et al. / Geomorphology 248 (2015) 273295
attributes (e.g., it is not necessary to consider the orientation and ob-
struction type to know a beaver dam is a beaver dam). However,
once the identication is made, one can safely assume some of the
dening attributes identied in Table 1 are characteristic of the struc-
tural element. Table 2 highlights some examples of specic structural
elements and some of their common key attributes. Although roughly
40+ specic structural elements are listed in Table 2, others exist and
could be dened.
Structural elements have the potential tocreate hydraulic conditions
that are conducive to scour where they accelerate ow around the
obstructions they cause (e.g., carving a forced pool) and can create bar
deposits (e.g., eddy bar) in their shear zones. In some instances, the ab-
sence of structural elements may induce a river to revert to a largely
simplied, plane-bed-dominated geomorphic unit assemblage in
contrast to those instances in which wood induces a more diverse
assemblage of units dominated by various forcedpools and bars
(Montgomery and Bufngton, 1997; Polvi and Wohl, 2013).
2.3. Dening and identifying geomorphic units
A geomorphic unit is a landform that is a byproduct of the deposition
of sediment and/or erosion of sediment or bedrock. Fryirs and Brierley
(2013a, pp. 154) dene geomorphic units as the building blocks of riv-
ers, each with its own form-process association. Fluvial geomorphic
units are commonly differentiated on the basis of their position with re-
spect to the channel, and by differentiating instream, oodplain, inac-
tive oodplain, hillslope, and fan units.
Table 2
Structural elements (SE)at tier 3 and their key attributes: note, any key attribute listed as variesor NA(not applicable)is not useful in differentiating that SE from other SEs; this list is
complete at tiers 1 and potentially tier 2, but other specicSEsexistattier3.
Tier 1 Tier 2 Tier 3 Key attributes to differentiate specic structural elements
Origin Type Specic structural
element name
Geometry Nature of ow impact
SE orientation SE position SE obstruction
Shear zone type
Bank revetment Bioengineered, Gabions,
detroit rip rap, boulder
rip rap, erosion control
Streamwise Bank-attached Roughness Varies DS eddy
Beaver dam analogue Primary dam, secondary dam, reinforced existing
Channel-spanning Porous barrier All US backwater
Bridge abutments NA Bank-Attached Complete barrier Varies DS eddy
Bridge pier NA Mid-channel Complete barrier All DS eddy
Culvert Box, arch, pipe Streamwise Channel-spanning Funnel All US backwater
Diversion Irrigation, canal, pump
point of diversion
Transverse Bank-attached or
channel- spanning
Complete barrier Varies US backwater
ELWD Debris jam, bank
Varies Varies Porous barrier Varies Varies
LWD Post-assisted log
structure, constriction
structure, mid-channel
Varies Varies Porous barrier Varies US & DS eddies
Ford Concrete, native bed
Transverse Channel-spanning Complete barrier All US backwater
Restoration structure Many types Varies Varies Varies Varies Varies
Rock vein NA Diagonal Bank-attached Porous barrier All DS & US eddy
Vortex weir NA Transverse Channel-spanning Porous barrier All Varies
Natural inorganic
Bedrock ledge Varies Varies Complete barrier Varies DS eddy
Bedrock outcrop Varies Varies Complete barrier Varies DS eddy
Boulder cluster Varies Mid-channel Complete barrier All DS eddy
Boulder dam Transverse or diagonal Channel-spanning Porous barrier All US backwater
Boulder ribs Transverse or diagonal Mid-channel Porous barrier Varies DS eddy
Natural organic
Aquatic vegetation Many types Varies Varies Porous barrier All DS Wake (occ. DS eddy)
Beaver dam
Intact Dam Transverse Channel-Spanning Porous Barrier All US Backwater & DS
Breached dam Transverse Channel-spanning Porous barrier All US backwater and DS
Blown-out dam Transverse Channel-spanning or
Porous barrier All DS & US eddy
Individual root wad Varies Varies Porous barrier Varies DS Eddy or wake
Debris jam Transverse Channel-spanning Porous barrier All US backwater & DS
Channel spanning log Transverse or diagonal Channel-spanning Varies Varies Varies
Raft jams
Log Varies Varies Varies Varies Varies
Riparian vegetation Many types Varies Varies Porous barrier NFlood stage Varies
279J.M. Wheaton et al. / Geomorphology 248 (2015) 273295
From a mapping perspective, a geomorphic unit is a spatially contin-
uous area or region that can be topographically dened. From a GIS per-
spective, the most typical data representation of a geomorphic unit
would be in the form of a polygon. It is also possible, although less com-
mon, to represent a geomorphic unit in a raster data model where either
(i) the raster is a categorical raster and eachcell is assigned to a different
class (i.e. geomorphic unit type); or (ii) there is a separate raster for
each class or category and the raster cells have values from zero to
one where the values represent either the probability of belonging to
a class (probabilistic) or the membership in a class (e.g., fuzzy classica-
tion; Wood, 1996).
We propose a four-tiered, hierarchical taxonomy for geomorphic
units whereby units are differentiated on the basis of (i) vertical posi-
tion or ow stage relative to the channel bed, (ii) their shape, (iii) spe-
cic morphology type, and (iv) subcategories of sedimentological and
vegetative characteristics (Fig. 5). The order of this proposed hierarchy
is critical because itemphasizes a primary topographic denition of geo-
morphic units in tiers 1 and 2 that explicitly ties it to the ow regime
and relative magnitude of events responsible for creating, maintaining,
and/or sculpting these features. Secondarily, the rst tier is tied explic-
itly to broader scale controls on reach types, valley setting (e.g., Fig. 2)
and to the natural capacity for adjustment (see Brierley and Fryirs,
2005; Fryirs and Brierley, 2013c). The further into the tiered system a
specic geomorphic unit is classied, the more reliable a form-process
association or interpretation can be made about the uvial processes
that form and/or rework that feature.
As Fig. 5 outlines, the entry point to the tiered geomorphic unit clas-
sication scheme is to identify therelative topographic stage position of
the geomorphic unit of interest (e.g., in-channel or out-of-channel;
i.e., tier 1). Then, from the perspective of the center of that geomorphic
Fig. 5. Tiered uvial geomorphic unit classication framework.
280 J.M. Wheaton et al. / Geomorphology 248 (2015) 273295
unit (e.g., the deepest part of a pool, the crestof a rife), not focusing too
much on the precise boundaries of the unit, we proceed as far as desired
through thenext three tiers using a series of questions to arrive at a pro-
gressively more specic name or taxonomic description.For example, in
Fig. 6 approximate unit boundaries are drawn in the eld and up to tier
3 units have been identied. Note that some of the boundaries are
abrupt, and some are more gradual transitions. Correct identication
within each progressive tier of detail increases theaccuracyof the infer-
ences one can make about the processes that shaped that unit and the
associations with neighboring units.
The real value in a tiered system is, as a user progresses from a rst
tier into lower tiers, they are ltering the range of possible choices to
a much smaller list of possible units. For example, while there may be
75+ tier 3 geomorphic units to choose from initially (analogous to a
Fig. 6. Annotated site photo looking upstream at upper portion of Bear Valley Creek study site. Visible tier 3 geomorphic units are delineated.
Table 3
Key attributes that help differentiate tier 3 out of channel geomorphic units.
Types Description
GU Forcing Occurs when a non uniform hydraulic ow pattern creates a ow environment conducive to forcing the formation,
maintenance or accentuation of a geomorphic unit.
Flow concentration When the oodplain GU is the result of convergent ow being concentrated onto a portion of the oodplain
Flow expansion When the oodplain GU is the result of ow spreading out and diverging across a oodplain
Flow short circuiting Where the ow path of ood-stage ows short-circuits its regular path in the channel
Grade control Where ood ows are backed up from an obstruction downstream and the backwater extends on the oodplain
GU orientation relative to valley bottom channel The orientation is dened by the longest axis of the geomorphic unit and relative to the main channel ow
Perpendicular GU is oriented perpendicular to the ow across the oodplain
Streamwise GU is oriented with the ow parallel to the main channel
Radial perpendicular GU has a radial orientation
GU position relative to valley bottom channel Denes the position of the GU relative to the main channel
Proximal When the GU is positioned close to the main channel
Distal When the GU is positioned far away from the main channel
Proximal to distal A GU that originates close to the main channel and extends perpendicular across the oodplain away from the channel
Distal to proximal A GU that originates far away from the main channel but extends toward the channel
Surface morphology Refers to the planform outline or trace of the GU feature (different than its tier 2 shape)
Elongate A GU that is elongate is stretched out such that it is thinner in the cross stream direction and longer in the streamwise
Arcuate A GU that is arcuate has a curved trace or surface expression like that of a bow
Longitudinal continuity of feature Refers to whether the GU is spatially continuous longitudinally along the oodplain and channel, or just a discrete feature
Continuous A GU that extends longitudinally along the channel for some distance along an entire reach (e.g. N20 bankfull widths)
Discrete A GU that occurs at discrete or isolated location on the oodplain
281J.M. Wheaton et al. / Geomorphology 248 (2015) 273295
Table 4
List of known tier 3 geomorphic units (specic morphology) for oodplain out-of-channel geomorphic units and their denitions (i.e. tiers 12 and key attributes); see also Table 9.1 in Fryirs and Brierley (2013b); abbreviations: GU (geomorphic unit).
Tier 1 Tier 2 Tier 3 Key attributes to differentiate specic morphologies
Stage height Shape/type Specic morphology
GU forcing GU orientation
relative to
valley bottom
GU position
relative to
valley bottom
of feature
Also known as Similar to or confused with
Active oodplain
Anabranch* Flow concentration Streamwise Varies Varies Continuous Secondary channel Side channel, but separated by oodplain instead of bars
Beaver canal NA Perpendicular Proximal to distal Elongate Discrete NA Confused with beaver overow channels, but these are dug
by beaver and tend to extend laterally away from ponds.
Beaver overow channel* Grade control Streamwise Proximal Elongate Continuous NA Confused with beaver canals, but these tend to be overow
channels around the side of a dam
Backswamp Varies Varies Distal Round Discrete Distal oodplain,
oodplain wetland,
Swamp, but positioned along valley margins on distal edges
of oodplain
Back channel* Grade control Varies Distal Elongate Continuous NA Secondary channel, but lower sinuosity then main channel.
AKA oodchannel
Chute cutoff* Flow concentration,
Diagonal Proximal Arcuate Discrete NA Meander cutoff, but straighter and process of
Flood channel* Flow concentration Streamwise Varies Elongate Varies NA Secondary channel, but lower sinuosity then main channel
Flood runner* Flow concentration,
Diagonal Varies Elongate Varies NA Chute, but atop oodplain instead of bar top
Meander cutoff Planform Diagonal Proximal Arcuate Discrete Oxbow Lake, Billabong Formed by a neck cutoff
Paleo channel* Varies Streamwise Varies Varies Varies NA Billabongs and oxbows; similar to oodchannels and
secondary channels but not actively ooded; AKA abandon
channel or ancestral channel
Secondary channel* Flow concentration Streamwise Varies Varies Varies NA Anabranch, but more generic
Swale Flow concentration Streamwise Varies Arcuate Continuous NA Paleo channels, oodchannels and secondary channels, but
less well dened
Crevasse splay Flow width expansion Radial DS Proximal Arcuate Discrete Splay Lobate bar, but located DS of levee breach instead of chute &
on oodplain
Floodout Flow width expansion Radial DS Varies Arcuate Discrete NA Lobate bars and Crevasse Splays, but more extensive
Island Often GU forced (growth of
Varies Proximal Elongate Discrete NA Any exposed in-channel bar, except that surface elevation is
Levee Flow width expansion Streamwise Proximal Elongate Continuous Natural levee Ridges and scroll bars, except that surface elevation is N
Ridge Flow width expansion
(during overbank oods)
Streamwise Varies Elongate Varies NA Scroll Bars, but found on oodplains instead of point bars
and often associated with swales.
Beaver meadow Grade control Streamwise Proximal Varies Discrete NA Regular oodplain, but longitudinally discontinuous &
Beaver wetland Grade control Varies Proximal Varies Discrete NA Backswamp, but not necessarily a depression, just forced
wetland by elevated water table associated with beaver dam
Floodplain Flow width expansion Streamwise Varies Varies Continuous Alluvial at, braidplain,
meander belt
Sheet Flow width expansion Varies Varies Varies Varies Floodplain sheet Sand Sheet or Gravel Sheet, but not-specic to grain size
(applies at Tier 4)
Valley ll Flow width expansion NA NA NA Continuous NA
Note that depending on the scale of mapping and the minimum mapping unit size, any channelcan also have its in-channelgeomorphic units differentiated. For most oodplains and fans, these are lumped instead.
282 J.M. Wheaton et al. / Geomorphology 248 (2015) 273295
species distinction in biology), by ltering through tier 2 there may be
only 612 to choose from and with two or more key attributes (tier
3) the list can be ltered either to a unique unit or a choice between 2
and 3 units. In tier 1 the vertical position differentiates geomorphic
units topographically on the basis of stage. From a uvial perspective
this highlights critical differences in process regimes (e.g., low ow,
bankfull, overbank, probable ood, historic ood, above plausible
ood stage). In reality the boundaries between these stage breaks are
blurry. However, from a classication perspective these boundariespro-
vide a convenient distinction between a mutually exclusive classica-
tion of categories that lead to differentiation between components
that make up the valley.In tier 2, surface shape is a fundamental charac-
teristic of geomorphic units that can be dened topographically
(Pennock et al., 1987) in terms of surfaces that curve inward (concave),
or outward (convex), or generally lack curvature (planar). At the begin-
ning of tier 3, the procedure splits depending on whether the unit is lo-
cated out-of-channel or in-channel. In tier 3 there are a host of key
attributes, some combination of which help identify a specicgeomor-
phic unit's morphology. In tier 4, these specic morphologies can be fur-
ther described with optional adjective prexes, which discriminate
units based on their specic vegetative and/or sedimentological charac-
teristics. Below we elaborate on these tiers.
2.3.1. Tier 1 stage height
Geomorphic units in a uvial setting vary in large part based on the
ows responsible for their formation. The simplestway to conceptualize
this is with respect to a vertical ood stage height. Using the channel
itself as a datum, we can differentiate in-channel units from active ood-
plain,fromterrace or fan units, from hillslopes. If making this distinction
on a DEM, the DEM can be detrended by valley slope and used to iden-
tify these approximate stage breaks (Roux et al., 2014). The precise
stage height thresholds for these breaks would vary by location and
ow regime, but would roughly be:
abankfullow for separating in-channel from active oodplain,
a maximum probable contemporary ood for separating active ood-
plains from terraces that are no longer inundated, and
a maximum upper historical ood stage for separating terraces and
fans from hillslopes.
Fans are likely the most unreliable features to differentiate on the
basis of stage, as the proximal portion of the fan will often be higher
than terraces or any point in the valley and the distal portion may
extend well out down into the oodplain or channel. In any speciccon-
text, these stage bands not only differentiate ood stage levels but will
correspond to progressively rarer ow events as stage is increased to
the point that you leave the plausible range of ows for that setting
and enter into the hillslope realm. Transitions exist at the interface be-
tween all geomorphic units. Sometimes these transitions are abrupt
(e.g., between a pool and a bank) and sometimes they are gradual
(e.g., between a pool and rife). A specic type of abrupt transition at
the interface between in-channel units and any other tier 1 geomorphic
Table 5
Examplesof tier 3 geomorphic units(GU) for terrace, fan,and hillslope out-of-channel geomorphic units(non-exhaustivelist for hillslopesand uplands) and theirdenitions (i.e. tiers12
and key attributes).
Tier 1 Tier 2 Tier 3 Key attributes to differentiate specic morphologies
Shape/type Specic
GU orientation
relative to
valley bottom
GU position
relative to
valley bottom
continuity of
Similar to or confused with
Inactive oodplain (terrace)
Paleo channel* NA Streamwise Varies Elongate Continuous NA Fan cutbank or hillslope cutbank,
except river carving into terrace
Alluvial terrace Planform Streamwise Varies Elongate Varies NA The terrace consists of both the
terrace tread (at top) and riser
Strath terrace By SE (bedrock) Streamwise Varies Elongate Varies NA
Fans Debris fan, except deposits are
alluvial from tributaries
Alluvial fan Grade control Radial DS Perpendicular Arcuate Discrete NA Alluvial fan, except deposits are
colluvial from mass wasting
Debris fan Grade control Radial DS Perpendicular Arcuate Discrete NA Terrace Cutbank or Hillslope
Cutbank, except river carving
into fan
Talus slope Grade control Varies Perpendicular Elongate Continuous Scree Slope
Fan channel* NA Streamwise Perpendicular Elongate Continuous NA
Concavities Concave slope NA Varies Varies Elongate Continuous NA Other hillslopes, but collects
surface runoff
Convexities Convex slope NA Radial DS Varies Elongate Continuous NA Other hillslopes, but sheds
surface runoff
Planar Planar slope NA Varies Varies Elongate Continuous NA
Note that depending on the scale of mapping and the minimum mapping unit size, any channelcan also have its in-channelgeomorphic units differentiated. For most oodplains and
fans, these are lumped instead.
283J.M. Wheaton et al. / Geomorphology 248 (2015) 273295
unit is a bank. Such transitions are characterized by steep slopes or
distinct breaks in slope. Through analysis of stage height, the differenti-
ation of margins that dene the valley setting of a river fall out automat-
ically (see Section 2.1). While the above stage distinctions may be
readily identiable in the eld, if adequate resolution topographic data
exists (e.g., LiDAR) they can also be identied using hydraulic models
or reasonably approximated from detrended digital elevation models
(McKean et al., 2009; Roux et al., 2014).
2.3.2. Tier 2 shape
We dene the shape of a geomorphic unit in terms of whether or not
it exhibits topographic curvature (i.e. a departure from a plane). This is
convenient, becausecurvature is a direct derivative of topography, such
that it is the second derivative of elevation with respect to distance
(slope is the rst derivative). Using curvature, a geomorphic unit's
shape can be dened as predominantly concave (curving inwards), con-
vex (curving outwards), or planar (lacking curvature). Curvature has
long been used as a key dening feature of hillslope landforms
(e.g., Pennock et al., 1987).
2.3.3. Tier 3 morphology
Tier 3 includes the plethora of geomorphic unitnames (e.g., we iden-
tify at least 68 in Tables 4, 5, 7, and 8) that many geomorphologists use
(often inconsistently) and non geomorphologists nd highly confusing.
We deliberately do not arrive at these specic morphologies until tier 3.
Unlike tiers 1 and 2, there is no dichotomous key that uniquely deter-
mines the geomorphic unit. In reality, some geomorphic units have
very simple histories and can be unambiguously categorized as a specif-
ic tier 3 geomorphic unit (e.g., unit bars). However, many geomorphic
units have more complicated histories and exist on a continuum of dif-
ferent unit types. Thus, we may think of our goal in tier 3 as not
identifying the absolute tier 3 answer, but rather the short-list of two
or three tier 3 geomorphic units that a feature might be classied as
and their relative probabilities.
In practice, a trained geomorphologist familiar with the 68 + geo-
morphic units and their denitions may be able to immediately iden-
tify a specic geomorphic unit's tier 3 type. Upon doing so, many
of its non-variedkey attributes are implicitly dened. Camp and
Wheaton (2014) cleanly implemented the logic underlying Tables 38
as a series of lters through a relational database eld App that allows
a user to map units and identify their types.
The scale at which geomorphic units are mapped varies depending
on the purpose of mapping. More detailed mapping of instream geo-
morphic units at tier 3 may be warranted to differentiate features that
make up a broader scale geomorphic unit. For example, in some cases,
when mapping a macroscale feature like a large bar that is fundamental-
ly a mid-channel bar but has a number of unit bars and smaller bank-
attached bars pasted on to it, it may be simplest to denote the bar as a
bar complex or to map individual geomorphic units that make up com-
pound features, e.g., ramps,ridges,chute channels,bar platforms,etc.
More detailed mapping of oodplain geomorphic units at tier 3 may
be warranted to differentiate oodplain units that make up a broader
scale geomorphic unit, or sometimes these can be simply clumped. For
example paleochannels (abandoned channels on a oodplain) versus
anabranches (channels separated by or carved into oodplain) may be
identied. Both are specic examples of concave oodplain features
that may be useful to map. However, both could be broken up into
their respective pools,thalwegs,plane beds,andbars that make up
these channels. We are not dictating absolute guidelines with respect
to mapping scale or resolution for this proposed geomorphic unit classi-
cation. Instead, we recognize that a different tier 3 assemblage arises
depending on the mapping resolution chosen and resolution of
Table 6
Denition of key attributes for differentiating tier 3 in-channel geomorphic units; abbreviations: GU (geomorphic unit), DS (downstream).
Key Tier 3
Types Description
GU Forcing Occurs when a non uniform hydraulic ow pattern creates a ow environment conducive to forcing the formation,
maintenance or accentuation of a geomorphic unit
Not forced The GU forms on its own (e.g. free bars)
By structural
Forcing can be caused by structural elements (e.g. large woody debris causing a plunge pool or an eddy bar)
By geomorphic unit Forcing can be caused by another geomorphic unit (e.g. a pool can be forced by a bar)
By planform Forcing can be induced by sinuosity (e.g. ow separation on inside bends leading to point bars)
By ow width Forcing is often associated with ow width expansion for depositional units and ow with constriction for erosional
GU orientation The orientation is dened by the longest axis of the geomorphic unit and relative to dominant ow direction.
Transverse Transverse units are oriented perpendicular to the ow (e.g. rifes)
Streamwise Streamwise units are oriented parallel to the ow (e.g. forced pools are elongated in a streamwise fashion associated with
the convergent ow jet)
Diagonal Diagonal units intersect the channel at an angle and ow is shunted diagonally over them at high ows.
Radial DS Some units have lobate shapes (e.g. lobate bars) which
GU position Denes the position of the GU within the low-ow channel
Bank-attached Many units are appended to the channel margins (e.g. point bars); Note bank-attachedis common terminology in the
uvial literature even though the entire length of all channels are bound by true banks. Channel margins is a more
generic term, but less common.
Channel spanning Some units are bank-attached on both sides and span the entire low ow channel (e.g. rifes)
Mid-channel Some units are not attached to a channel margin and occur in the center of a channel (e.g. longitudinal bar)
Side-channel For some mapping purposes, it is helpful to differentiate units that only occur in side and/or secondary channels
Low ow water surface
Especially for in-channel, planar units, low ow water surface slope is a helpful way of differentiating across the
spectrum from low-slope glides, through intermediate slope runs and rifes, through high slope rapids, up to very high
slope cascades.
Flat Water surface slope = 0
Shallow Water surface slope b0.005
Moderate Water surface slope N0.005 & b0.03
Steep Water surface slope N0.03
Low ow relative roughness Relative roughness is dened as the ratio of roughness height to ow depth (z
Low Relative roughness b0.5 (i.e. majority of ow depth not obstructed by substrate)
Moderate Relative roughness between 0.5 and 1 (i.e. majority of ow depth obstructed by substrate, but substrate not protruding
from water surface)
High Relative roughness N1 (i.e. particles protruding from water surface)
Very high Relative roughness 1 (i.e. ow depth is negligible relative to massive boulders protruding from water surface)
284 J.M. Wheaton et al. / Geomorphology 248 (2015) 273295
available data. However, the tier 2 assemblage should be consistent. We
advocate that users consciously and consistently choose a resolution
that is appropriate to their questions and the purposes for which the
map is being derived.
2.4. Out-of-channel geomorphic units
To identify out-of-channel geomorphic units we suggest ve key attri-
bute categories that are relatively easy to identify in the eld and can help
by process of elimination to arrive at the most likely units. The key attri-
butes for out-of-channel geomorphic units are dened in Table 3 and in-
clude unit forcing, orientation, position, surface morphology, and
longitudinal continuity. As with structural elements, the key attributes
of geomorphic units need not all be identied to recognize a specicgeo-
morphic unit. In fact, any of the key attributes in Table 4 (for oodplain
units) or Table 5 (for fan and terrace units) that are listed as variesfor
aspecic unit is not a helpful attribute for distinguishing that unit.
2.5. In-channel geomorphic units
As with before, we suggest ve key attribute categories that can
be identied on aerial imagery or in the eld and that by process of
elimination can be used to arrive at the most likely geomorphic
unit(s). The key attributes for in-channel geomorphic units are de-
ned in Table 6 and include unit position, orientation, forcing, low-
ow relative roughness, and low-ow water surface slope. Position
is most helpful for differentiating bar types (e.g., point bars are
bank attached whereas rifes are channel spanning). Forcing can be
caused by structural elements (e.g., LWD causing a plunge pool or
an eddy bar), planform (e.g., point bars on inside bends in sinuous plan-
forms), grade control (e.g., a channel-spanning structural elementbacks
up water, creates a shallower water surface slopes and promotes depo-
sition of a forced rife), and ow width (e.g., changes in the ow width
lead to convergent ow and carving of a pool). Relative roughness and
low-ow water surface slope are particularly useful for differentiating
plane-bed geomorphic units that exist along a continuum of relative
roughness and slope. At the lower end of that spectrum, glides exhibit
very low relative roughness; runs slightly higher (but still b1); rapids
have high relative roughness (close to or just above 1), and cascades
are dened by low ow relative roughness N1 (i.e. roughness elements
protrude above water surface) that results in tumblingows and jet
and wake(Montgomery and Bufngton, 1997).
We have attempted to include how the vast majority of geomorphic
units found in the literature in Table 4, Tables 5, 7, and 8. In total, we
Table 7
List ofall known tier 3 geomorphic units(specic morphology) for convexin-channelgeomorphic units(i.e., bars)and their denitions(i.e. tiers 12 andkey attributes);see also Tables 8.2
to 8.4 in Fryirs and Brierley (2013a); GU (geomorphic unit), DS (downstream).
Tier 1 Tier 2 Tier 3
Stage height Shape/type Specific morphology
GU forcing Low flow relative
GU orientation GU position Low flow water
surface slope
L Convexity (e.g. bar)
L Backwater bar Grade control Varies Varies Side channel Varies Slackwater deposit
Similar to other bars but found
in disconnected side channels
or secondary channels
L Boulder bar Flow width Varies Streamwise
or mid–channel Varies Boulder berm
Similar to other bars, but in
much higher gradient systems.
L Compound bar Varies Varies Varies Varies Varies Bar complex
An amalgamation of multiple
unit bars and other bar types
(complex history)
L Confluence bar Grade control Varies
Radial DS &
streamwise Bank–attached Varies NA
Expansion bar, except in
response to gradient drop
from tributary to mainstem.
L Diagonal bar
Planform & flow width
expansion Varies Diagonal Mid–channel Varies Mid–channel bar
Point bar, but no longer bank–
attached (separated by chute)
L Eddy bar
Planform, SE, and/or
flow width constriction Varies Streamwise
or mid–channel Varies Separation bar
L Expansion bar Flow Width Varies Transverse Mid–channel Varies NA
Transverse bar, but in response
to slope lowering, and does not
span channel
L Forced bar Varies Varies Streamwise
or mid–channel Varies NA Eddy Bar
L Forced riffle Channel spanning SE Moderate (< 1) Transverse Channel spanning Shallow NA
Riffle, but forced by channel
spanning structural element
buried in bed
L Lateral bar
By planform or by flow
width Varies Streamwise Bank–attached Varies Alternate bar
Point bars, but can be in bends
with lower curvature or
channels with lower sinuosity
or straight
L Lobate bar Grade Control Varies Radial DS Mid–channel Varies Mid–channel bar
Similar to other mid–channel
bars but distinctive in DS
tear–dropped shape and
avalanche faces
L Longitudinal bar Flow Width Varies Moderate (< 1) Mid–channel Varies Mid–channel bar
Similar to other mid–channel
bars but distinctive in
elongated streamwise
orientation and upstream
convexity at bar head
L Point bar Planform forced Varies Streamwise Bank–attached Varies Bank–attached bar
Alternate bars, but in bends
with higher curvature
L Reattachment bar Varies Varies Streamwise Bank–attached Varies NA
Eddy Bar, but occurs DS of
both flow separation and
reattachment point
L Ridge
Forced by SE and flow
separation Varies Streamwise Bank–attached Varies NA
Scroll bar or levee; generally
straighter, more linear feature
L Riffle Flow width expansion Moderate (< 1) Transverse Channel spanning Moderate Transverse bar Sometimes confused with runs
L Scroll bar
Planform & flow
width expansion Varies Streamwise Bank–attached Varies NA
Ridge, but positioned on point
bar and generally curved
L Unit bar Flow width expansion Varies Varies Varies Varies NA
The fundamental building
block of all bars
Key attributes to differentiate specific morphologies
Also known as Similar to or confused with
285J.M. Wheaton et al. / Geomorphology 248 (2015) 273295
identied 94 geomorphic unit names of which 68 are distinctive units
(26 are alternative names). We translated the most comprehensive
readily available list developed by Fryirs and Brierley (2013b) into this
framework for convexities (i.e. bars; Table 7) and for concavities and
planar features (Table 8). Any key attribute in Table 7 or Table 8 that
has variesfor a specic geomorphic unit, is an example of a key attri-
bute not helpful for differentiating that specic geomorphic unit from
others. By contrast, those key attributes that have only one type listed
are very useful for isolating what geomorphic unit it might be and con-
tinuing to lter the list down an attribute at a time by a process of
In some instances, uvial geomorphologists may discover, propose
or split out newgeomorphic units. For example, in the maps demon-
strated in the next section we dene a shallow thalweg as a new geo-
morphic unit for a frequently occurring morphologic feature for which
we found no clear denition in the geomorphic or in-channel habitat
literature. All channels have a thalweg the line along a channel that
represents the lowest elevation and often contains the highest velocity
lament. All channels at some level have a concave cross section; and
those that have pools, the thalweg runs through the deepest part of it.
Pools are concave in cross section and streamwise directions, such that
a residual pool (puddle) is left over if the channel is drained of water.
Other types of in-channel concavities that are intersected by thalwegs
include: chutes, which represent a generally steeper concavity that
short-circuits a ow path (e.g., across a bar,acrossaoodplain,or
along an inside channel margin in the case of diagonal bar), is relatively
steep, and generally lacks streamwise concavity; andramps, which rep-
resent cross-sectionally shallow concavities that ramp-up(i.e., have a
negative bed slope) onto a bar surface or glide. We dene a shallow
thalweg as an elongate geomorphic unit that is characterized by a
streamwise orientation, follows the thalweg, is typically located along
the outer bend along the axis of ow (i.e., bank-attached position),
but lacks a longitudinal concavity to produce a residual pool (Fig. 7).
Shallow thalwegs are commonly found in channels with mildly asym-
metric cross sections adjacent to a run, glide, or even broad shallow
point-bars that spans most of the channel and pushes the thalweg up
Table 8
List of all known tier 3 geomorphic units (specic morphology) for planarand concave in-channel geomorphic units (non exhaustive) and their denitions (i.e. tiers 12 and key attri-
butes); this is a non-exhaustive list; see also Table 8.1 in Fryirs and Brierley (2013a); GU (geomorphic unit), DS (downstream).
Tier 1 Tier 2 Tier 3
Stage height Shape/type Specific morphology
GU forcing Low flow relative
GU orientation GU position Low flow water
surface slope
L Planar
L Bench Not forced Varies Streamwise Bank–attached Varies Inset floodplain
Ledge, but depositional feature;
Terrace, but within active
bankfull channel
L Ledge Not forced Varies Streamwise Bank–attached Varies Inset floodplain
Bench, but erosional feature;
Terrace, but within active
bankfull channel
L Glide Not forced Low (< 0.5) Streamwise Varies Shallow NA
Run, but much lower gradient
water surface and low relative
L Run Not forced Moderate (< 1) Streamwise Varies
Shallow to
moderate NA
Sometimes confused with
riffles or glides
L Rapid Varies High (> 1) Streamwise Varies Moderate to
steep NA
Cascade, but less relative
roughness and lacking vertical
L Cascade Varies Very high (>>1) Streamwise Varies Steep NA
Rapid, but more relative
roughness, steeper water
surface, and vertical drops;
Sometimes confused with
L Concavity (e.g. Pool)
L Backwater Grade control Low (< 0.5) Varies Side channel Flat Slackwater
Similar to other pools but
found in disconnected side
channels or secondary channels
L Bar–forced pool By bar Low (< 0.5) Streamwise Bank–attached Shallow NA
Structurally forced pool, but
forced by bar shunting flow
against resistant boundary
L Beaver pond
Grade control from
beaver dam SE Low (< 0.5) Streamwise
spanning Flat Beaver pool
A specific example of a
dammed pool
L Chute Planform Varies Streamwise
or mid–channel Moderate NA
Shallow thalweg, but generally
steeper and dissecting bar;
Also confused with flood
channels, but these are in–
channel short–circuiting forms
L Confluence pool Planform Low (< 0.5) Streamwise Varies Shallow Scour pool
L Dammed pool DS grade control from SE Low (< 0.5) Streamwise
spanning Shallow NA
Beaver pond, but forcing SE
can be any channel spanning
obstruction. Also confused
with the upstream pool in a
step pool
L Plunge pool US grade control from SE Low (< 0.5) Transverse Varies Flat Scour pool
L Ramp Planform Varies Varies NA
L Return channel Forced by Eddy Bar Varies Streamwise Bank–attached Varies NA
Chute, but flow is upstream in
association with eddy
L Shallow thalweg
Forced by planar GU or
occasionally bars Varies Streamwise Bank–attached Moderate NA
Chute, but does not dissect a
bar surface
L Secondary channel Planform Varies Streamwise
channel Varies NA
Anabranch or secondary
channel, except that area
separating secondary and
primary channel is < bankfull
L Structurally–forced pool
Flow width constriction
forced by SE Low (< 0.5) Streamwise
Bank–attached or
mid–channel Varies NA Sometimes called 'scour pool'
Key attributes to differentiate specific morphologies
Also Known As Similar to or Confused With
286 J.M. Wheaton et al. / Geomorphology 248 (2015) 273295
against the outside bend. These are often positioned along relatively
shallow portions of the channel where you expect to nd a bar-forced
pool on the outside bend, but the pool is absent. If new geomorphic
units are proposed,we think their key tier 3 attributes should be dened
(i.e., Table 7) and ideally a reference card like that of Fig. 7 is created.
2.5.1. Tier 4 morphology sub categories
Whereas tiers 1 through 3 are all based on topographic denitions
and geographic attributes, tier 4 are modiers based on vegetation. Sed-
imentological characteristics and vegetation associations (e.g., bare,
vegetating, forested) are additional attributes that are helpful for further
differentiating tier 3 geomorphic units into tier 4 subcategories. These
attributes are not readily identiable from most topographic data sets.
Determining sedimentological characteristics requires either eld mea-
surements (e.g., Wolman pebble counts) or very high resolution point
data of bare surfaces (Brasington et al., 2012). Determining vegetation
associations also requires additional data sources such as eld surveys
or classication from imagery (Hough-Snee et al., 2013, 2014). Unlike
the key attributes proposed for tier 3, these attributes do not dene
the geomorphic unit per se, but are sometimes helpful to further sepa-
rate out what are fundamentally the same morphologies but exist
under very different ow energy conditions and frequencies of inunda-
tion. Tier 4 names are simply the tier 3 names with one or more adjec-
tives inserted in front of them. For example, a point bar could become a
ne-grained point bar in a suspended load river or a gravel point bar in a
gravel-bed river.
For sedimentological characteristics, useful categories by which
to differentiate further attributes include the surface roughness
(i.e., possible adjectives include: smooth to rough), surface grain size
(e.g., possible adjectives include: bedrock,boulder,cobble,gravel, sand,
ne (silt and clay)), and grain size sorting (e.g., possible adjectives in-
clude: poorly sorted to well sorted). Surface roughness and grain-size
are indicative of ow competence and sediment supply, whereas
grain-size sorting maybe indicative of the variability of hydraulic condi-
tions to which the geomorphic unit is subjected. For vegetation associa-
tions, this can be indicative of how regularly a surface experiences
competent ows or ows that are able to rework that surface. Potential
adjectives range from bare (active) through vegetating to vegetated or
forested. For example, many exposed bars only remain unvegetated if
they experience turnover or reworking on an annual basis. Alternative-
ly, one could use the facies classication scheme as a modier
(e.g., Bufngton and Montgomery, 1999).
3. Examples of mapping riverscapes
To illustrate the application of the proposed framework to mapping
real riverscapes, we provide examples of manual delineation of geomor-
phic maps using this framework for three distinct reaches in the Lemhi
Fig. 7. Example of a denition diagram or playing cardfor a newly dened shallow thalweg geomorphic unit. Using the denitions of Table 7,similardiagramscanbecreatedasreferencesforall
tier 3 geomorphic units in Tables 68. The lefthand side (front) focuses on its topographic denition (i.e., stages 1 and 2) and distinguishing key attributes (tier 3) thatlead to the description of its
geomorphic form; whereas the righthand side (back) focuses on the unit's typical conguration and what can be inferred about the uvial processes that create, shape, and maintain such units.
287J.M. Wheaton et al. / Geomorphology 248 (2015) 273295
watershed of the Columbia River basin (Fig. 8). These three reaches are
representative of river types in conned (Wright Creek), partlyconned
(Bear Valley Creek), and laterally unconned valley settings (Lemhi
River), allowing us to test the framework across a range of river and val-
ley types. These sites are more thoroughly described in Bangen et al.
Tier 1 mapping of each of the three reaches was performed using a
combination of aerial imagery and nationally available 10-m DEMs in
Google Earth and ArcGIS. This scale of mapping is the most general
and can be done from broadly available data sets for which there are
generally national coverages. As shown in Fig. 2,rst the valley and val-
ley bottom margins are drawn, then the channel margin is drawn.
Where the channel margin abuts either the valley margin or valley bot-
tom margin or anthropogenic margin (e.g., a road), these margins are
secondarily symbolized as conning margins. The space between the
channel margins is identied as in-channel. The space between the
channel margin and valley bottom margin is identied as oodplain.
The space between the valley bottom margin and valley margin is iden-
tied as either fan or terrace. Finally, the area outside the valley margin
is identied as hillslopes. The resulting map reects the valley setting
(e.g., Fig. 2) and is one of the key entry points in stage 1 of the River
Styles framework of Brierley and Fryirs (2005).
Tiers 2 and 3 mapping of geomorphic units is generally not possible
for low-order, wadeable streams of this size from coarse, nationally
available imagery and topography (e.g., Google Earth). For these exam-
ples, we performed manual tiers 2 and 3 mapping of representative
subreaches from 10-cmresolution DEMs that were topographically sur-
veyed by Bangen et al. (2014) using total stations for the bathymetry
and near channel area and airborne LiDAR for the rest of the valley
from Watershed Sciences (2011). The resolution of DEM required scales
to the size of stream and for the scale of geomorphic units one needs
to identify. In this example, we used 15-cm resolution orthophotos
from Bangen et al. (2014), the DEM, and topographic derivatives
(e.g., water depth maps, 10-cm contours, slope analyses) to identify
geomorphic units as polygons. Using the uvial margins from tier 1,
those polygons were then identied by their shape as concavities,
convexities, or planar fea tures. We started by identifying concavities,
then convexities, and then differentiating remaining areas between
transitions and planar depending on whether the planar features
were longer in the streamwise direction than at least 1 to 2 bankfull
channel widths. Then using the same evidence and eld observa-
tions, we deduced the key attributes (Tables 3 and 6)tohoneinon
the most likely specic geomorphic unit type by a process of ltering
(see Tables 4, 5, 7 and 8).
3.1. Tier 1 mapping
Fig. 9 contrasts the tier 1 mapping results of three different reaches
of river in three very different valley settings. In Fig. 9Athe Wright
Creek study reach is characterized by a channel in a conned valley set-
ting, in which the channel abuts conning margins along N90% of its
length. Along its rightbank, the valley margin and valley bottom margin
are shared for the entire length of the reach. There, the channel is up
against the valley margin for its entire length, except for one small
oodplain pocket onriver right. By contrast, on theleft bank the channel
starts outagainst the valleymargin, but soon abuts a high-angle relic fan
surface, which replaces the valley margin as the conning margin; the
channel itself is conned by this fan feature for virtually itsentire length.
As a result the channel has no capacity to adjust laterally on left or right.
This reach has the characteristics of a conned valley with occasional
oodplain pockets River Style.
Farther downstream, Wright Creek joins Bear Valley Creek, which
has a slightly wider valley. As Fig. 9B illustrates, Bear Valley Creek
abuts the valley bottom margin along roughly 25% of its length; and
Fig. 8. Location map for three example sites used in this study within the Lemhi watershed.
288 J.M. Wheaton et al. / Geomorphology 248 (2015) 273295
oodplain pockets are discontinuous, conrming that this is a partly
conned valley setting. Occasionally, the conning margin is the valley
margin itself (i.e. hillslopes), but more often inactive alluvial fans act
as the conning margin and the channel is deected by these toward
the opposite side of the valley bottom. The channel has a moderately
sinuous planform, partly as a result of deecting between conning
margins and partly from its own meandering. The channel has limited
capacity to adjust laterally except where there is sufcient valley bot-
tom width. This reach has the characteristics of a partly conned valley
with moderate sinuosity, planform-controlled discontinuous oodplain
River Style.
Downstream in the mainstem Lemhi River we see a very differ-
ent channel pattern within a laterally unconned valley setting.
The out-of-channel zones are dominated by continuous, active
oodplains along both sides of the channel (Fig. 9C). The valley
also contains convex alluvial fans and hillslopes, but these are situ-
ated at a distance from the multichannel network. This conrms
that this site occurs in a laterally-unconned valley setting. The con-
ning margins occur along b10% of the channel length. The multi-
channel network has planform characteristics of wandering and
anabranching rivers and has several concave paleochannels occur-
ring on the oodplain.
Fig. 9. Maps ofexample study reaches in threecontrasting valley settings,reecting conned (A), partly conned (B), and laterallyunconned (C). Marginsare mapped with tier one geo-
morphic units. Flow is left to right in (A) and (B) and right to left in (C).
289J.M. Wheaton et al. / Geomorphology 248 (2015) 273295
3.2. Tiers 2 and 3 mapping of Wright Creek
For the Wright Creek conned reach, two dominant structural ele-
ments (wood and boulders)weremapped(Fig. 10). Given the conned
valley setting in steep, rugged terrain within a thick Spruce-dominated
forest, regular wood recruitment and colluvial inputs are the source of
the dominant structural elements. Tier 2 analysis reveals that for the
in-channel zone, around 22% of the reach comprises concavities,9%of
the reach comprises convexities, and 69% comprises planar features
(Fig. 11). Given the presence of plentiful large boulders, and large
wood, we nd a number of forced geomorphic units (e.g., structurally
forced pools,dammed pools,plunge pools,forced bars,andforced rifes).
The most effective forcing mechanism (i.e. structural element) for
these units are the large woody debris. Roughly one third of the reach
produces forced bars and pools and the rest of it is dominated by a
steep plane bed morphology. Tier 3 differentiation identied an assem-
blage of 13 different in-channel geomorphic units. Concavities include
six types of pool and shallow thalweg units (mainly forced). Convexities
include three types of bars and rifeunits (two forced). Planar features
include cascades,rapids, and some less frequent runs above grade-
controlled debris jams and forced rifes (Fig. 10BandFig. 11).
3.3. Tiers 2 and 3 mapping of Bear Valley Creek
For the Bear Valley Creek partly-conned reach, only two pieces of
LWD were mapped (Fig. 12; see one of them in bottom left of Fig. 6).
Thus we expect structural forcing to play less of a role in geomorphic
unit forming processes. Manual tier 2 analysis of geomorphic units re-
veals that for the in-channel zone, 9% of the reach comprises concavities,
35% of the reachcomprises convexities,9%comprisesplanar features and
37% of the reach is made up of transition zones (Fig. 10A). Larger pools
(concavities), more temporary storage of sediment in active bars
(convexities), a modest amount of planar units, and numerous transi-
tions between individual units is indicative of reasonably complex hab-
itat (Fig. 6).
Tier 3 differentiation of geomorphic units revealed anassemblage of
13 different in-channel geomorphic units (Fig. 12BandFig. 11). Concav-
ities were primarily comprised of bar-forced pools on outside bends, a
few shallow thalwegs on outside bends where pools didn't quite form,
one backwater, and a few chutes on inside bends that were detaching
former point bars from the inside bends. Convexities were comprised of
ve types of bars, rifes,aforced rife,abench, and two islands.The
most prominent (by area) bar type was a mid-channel diagonal bar,
which are bars that start out inside bends as point bars, and via a process
of chute cutoff disconnect the bar from the inside bank as the outer bank
continues to adjust laterally via bank erosion (Ferguson and Werritty,
1983). The only planar features were runs.
3.4. Tiers 2 and 3 mapping of Mainstem Lemhi River
For the mainstem Lemhi River, only two structural element types
(LWD large woody debris and an anthropogenic diversion weir) were
mapped (Fig. 13A). LWD loading and recruitment was very modest in
this reach with b5 pieces of LWD in the large reach found. Tier 2 analysis
Fig. 10. Tier 2 (A) and tier 3 (B) geomorphic unit maps for conned example on Wright Creek.
290 J.M. Wheaton et al. / Geomorphology 248 (2015) 273295
reveals that for the in-channel zone, 31% of the reach comprises concav-
ities, 22% of the reach comprises convexities, 14% comprises planar fea-
tures and 33% comprises transitions (Fig. 11). The mix of pools,bars,
and transitions, and relatively modest amount of planar in-channel fea-
tures are characteristic assemblages of in-channel geomorphic units for
an anastomosing river.
Tier 3 differentiation identied an assemblage of 20 different in-
channel geomorphic units (Fig. 13BandFig. 11). Concavities produced
seven types of pools (not including secondary channels)andchute,
ramp,secondary channel,andshallow thalweg units. Convexities were
comprised of eight types of bar,rife, and island. Planar features com-
prised runs and glides.
4. Discussion
There are two primary contributions from this paper. First, we have
offered a taxonomy that is generic and easy to apply for the uvial
landforms of any riverscape. The rst and second tiers of identifying
geomorphic units are clearly dened in terms of topographic denitions
for stage and shape, respectively. The third tier uses the same specic
morphology names that many investigators have previously used, but
we attempt to dene the key attributes that help differentiate different
types of geomorphic units. Of key importance in this lexicon is not the
specic name one ends up with (more can always be added), but in-
stead its lineage from parent tiers and its dening attributes. The end
result is more consistent, systematic, replicable, and rigorous analyt-
ical steps to dene and classify geomorphic units. These uvial land-
forms that are byproducts of erosion and deposition of sediment
provide a key analytical tool in landscape interpretation because of
their direct link to process (Brierley, 1996; Fryirs and Brierley,
2013c). The interpretative lens to analysis of geomorphic units
adopted in this paper ts elegantly within existing hierarchically
framed applications (e.g., Brierley and Fryirs, 2005; Thorp et al.,
2013), thereby supporting efforts to apply top-down and bottom-
Fig. 11. Contrasting assemblages of tiers 2 and 3 in-channel geomorphic units across the three example sites.
291J.M. Wheaton et al. / Geomorphology 248 (2015) 273295
up interpretations of landscapes (e.g., landscape lters Poff, 1997;
Hough-Snee et al., 2014) and can now be readily executed with
help of new GIS tools (e.g., Roux et al., 2014).
The second primary contribution is that the framework includes
specic provisions for mapping and identifying margins and structural
elements in uvial environments. The margins help better explain the
link between the valley setting and the assemblages of geomorphic
units one is likely to nd. The structural elements provide mapping of
discrete features that directly inuence hydraulics and result in specic
forced geomorphic units. Without either, the context and mechanistic
link between the assemblages and the broader controls in a spatially hi-
erarchical framework are missing. For example, the instream geomor-
phic unit map for Wright Creek (Fig. 10) shows how a structurally
forced pool is induced by naturally occurring wood structures, while
the map for Lemhi Creek (Fig. 13) shows how a diversion weir produced
a lateral bar. From a mapping perspective, structural elements are
vector objects, which can be represented as individual points
(e.g., location of wood features), polylines (e.g., levee, road, or beaver
dam), or polygons (e.g., bedrock outcrop, concrete bridge abutment,
rip-rapped area). The addition of structural elements that modify geo-
morphic unit patterns enables this approach to be applied in natural
and in anthropogenically disturbed settings, potentially having the
power to cover the full spectrum of river diversity.
The framework we describe provides a logical sequence of proce-
dures that is conceptually organized around the observations and deci-
sions a geomorphologist uses to draw a map. The decision-making trees
(tier diagrams of Figs. 1, 4, and 5) generate mutually exclusive typesof
geomorphic units that are placed in a landscape context set by margins/
connement and the impact of structural elements on river forms and
processes. Our tiered approach to classication of instream geomorphic
units is framed as a series of questions, starting with assessment of stage
height (tier 1) before moving on to appraisal of shape (concave/convex/
planar; tier 2), morphology (including position: bank-attached,
channel-spanning, mid-channel, side channel; tier 3), and various sub-
sets of features based upon sediment properties (roughness, grain-
size, and sorting) and vegetation associations (tier 4). By extension,
the approach could be linked seamlessly to analyses of instream hy-
draulic units (e.g., Brierley and Fryirs, 2005), and associated process in-
ferences and appraisal of habitat associations (among many
applications). In fact, the framework presented here has proved equally
useful and tractablein mapping small reaches in detail (e.g., Figs. 911)
and in rapid-assessment mapping covering 510 km/stream/day. For
example, Camp and Wheaton (2014) recently developed and reported
a mobile monitoring and restoration design application that employed
the mapping framework here to inventory and map all in-channel geo-
morphic units on over 66 km of streams in two different watersheds.
We hope that the clarity in nomenclature surrounding uvial
landforms we have provided here will lend itself directly to
geoprocessing steps that can be derived from topographic lines of
evidence. This will make the framework more relevant in an age of
rapidly expanding high resolution topographic surveys of rivers.
We are actively developing software to help users derive their own
topographic lines of evidence and combine them to map geomorphic
units from topography. Wyrick et al. (2014) argued convincingly
that hydraulic denitions of morphological units were necessary
because topographic denitions (primarily one-dimensional cross
section and long prole based) had not yet produced spatially con-
tinuous mappings (in a two-dimensional sense) of riverscapes. How-
ever, we believe that our new topographic denitions that explicitly
account for stage and shape provide the breakthrough that the
Fig. 12. Tier 2 (A) and tier 3 (B) geomorphic unit maps for partly conned example on Bear Valley Creek.
292 J.M. Wheaton et al. / Geomorphology 248 (2015) 273295
transect-based view of rivers fails to adequately lev erage from DEMs.
Either the hydraulic denitions of morphological units of Wyrick
et al. (2014) or our topographic denitions of geomorphic units
will produce a spatially continuous map of the building blocks of
riverscapes. Both are stage dependent, but our denitions are less
sensitive to changes in ow. Both can be used to look at the assem-
blage or composition of geomorphic units. Ultimately, clever new
ways of moving beyond distributions and looking at the congura-
tion or spatial arrangement of these building blocks (e.g., Wyrick
and Pasternack, 2014)willprovidethemostusefulinsightstopro-
cess and behavior. Similarly, leveraging DEM differencing of repeat
surveys to tie specic erosion and deposition patterns to changes in
geomorphic unit assemblage and conguration will allow direct
quantication (instead of just inference) of process (e.g., Wheaton
et al., 2013). Eventually , we may be able to test the efcacy of process
inferences made from snapshots of assemblages of geomorphic units
against empirical data from repeat surveys.
5. Conclusion
Our paper has claried issues relating to the identication and de-
nition of geomorphic units as the building blocks of riverscapes and
proposed a new taxonomy to aid in their consistent identication
from either eld observation, map interpretation, or morphometric
analysis. The taxonomy we proposed is tiered and based rst on topo-
graphic denitions of stage (tier 1) and shape (tier 2), but tier 3 uses
key attributes to help further lter the potential units from N68 choices
down to 13 possible units. We have not invented new terms for these
landforms, but instead provided a framework that leads to their
consistent identication. As new landforms are discovered, they can
be added to the framework, and we propose one such new landform
we nd frequently shallow thalweg, which we do not think has been
previously dened. We have added a key interpretative layer for
explaining the presence of structurally forced geomorphic unitsthrough
denition of structural elements (e.g., LWD, boulders, etc.). These forc-
ingfeatures are especially important in assessing the character and be-
havior of highly modied river systems. We also claried denitions of
uvial margins, which can be mapped as linear features in riverscapes
and exert a key control on the natural capacity for adjustment of rivers.
In our denitions of structural elements and uvial margins, we explic-
itly accounted for and emphasized the distinction between natural and
anthropogenic features, which can inuence the behavior of rivers and
We documented a suite of straightforward analytical procedures
that can be used to map rivers