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3 Stage One, Step Two: Definition and interpretation of River Styles

3 Stage One, Step Two: Definition and interpretation of River Styles

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Chapter 9

of river character and behavior may occur between


In the River Styles framework, three valley settings are differentiated: confined, partly-confined,

and laterally-unconfined, along which floodplains

are absent, discontinuous, or continuous respectively. In the latter category, differentiation is

made between rivers with continuous channels,

and those in which channels are discontinuous or

absent. In some instances, continuous floodplains

are relatively thin veneers with a bedrock-based

channel. Valley settings, in turn, are fashioned in

large part by the type of landscape unit within

which they lie. For example, confined valley settings are often found in the escarpment landscape

unit, partly-confined valleys in the rolling

foothills landscape unit, and laterally-unconfined

valley settings along lowland plains. Differences

in valley cross-sectional morphology, width, and

slope directly influence river character and behavior. Within each valley setting a range of River

Styles is evident.

While it may be appealing to derive quantitative

measures for the three valley setting classes, the

following should only be considered as a guide. In

the confined valley setting, bedrock or terraces are

observed along both channel banks. Over 90% of

the channel abuts directly against bedrock or terraces. The river course has either no floodplain,

or floodplains are restricted to isolated pockets

(< 10% of reach length). Channel planform is imposed by valley configuration. For example, if longterm landscape evolution has resulted in a deeply

incised and sinuous bedrock valley, the channel

must conform to this configuration producing a

gorge River Style. Elsewhere, gorges may be

straight, as they follow the geologic structure of

a region (e.g., along fault lines). In other instances,

the channel can be fully contained within terraces

or ancient, cemented alluvial deposits that line the

valley margin. In almost all cases, bedrock also

imposes a vertical control, as bedrock lines the

channel bed.

In the partly-confined valley setting, between

10 and 90% of the channel abuts directly against

bedrock or ancient, cohesive materials. Discrete

floodplain pockets occur along the reach, commonly in an alternating or semicontinuous manner. Partly-confined valleys commonly have a

sinuous or irregular planform that dictates

where floodplains can form (e.g., along the convex

banks of bends, or behind bedrock spurs). Along

most, but not all rivers found in this valley setting,

bedrock also imposes significant base level control, with bedrock outcrops common along the

channel bed.

In the laterally-unconfined valley setting, less

than 10% of the channel margin abuts against

bedrock or terrace features. Rivers are laterally unconstrained with continuous floodplains along

both channel banks. Banks are deformable, such

that the channel is able to mold and rework its

boundaries. However, some variants of laterallyunconfined rivers are vertically constrained by

bedrock or ancient lag deposits. Rivers found in the

laterally-unconfined valley setting are further

split on the basis of the continuity of the channel

along the valley floor. Reaches with a continuous

channel are differentiated from those where the

channel is discontinuous or absent. Geomorphic units

Analysis of channel and floodplain geomorphic

units provides the key tool to interpret reach character and behavior. Given their distinct set of

form–process associations, geomorphic units are

the key interpretative parameter in the River

Styles framework. A bottom-up constructivist

approach builds a picture of river character and

behavior for any reach, framed in terms of its

constituent channel and floodplain components

and their interactions. These features can be analyzed across the range of rivers found in different

landscape settings, regardless of whether they are

confined, partly-confined, or laterally-unconfined

variants. While individual types of geomorphic

units may be observed in reaches of differing River

Styles, a distinct assemblage of geomorphic units

occurs along each River Style. For example, pools

are evident in many River Styles, although the

nature of these pools may be quite variable.

Ultimately, it is the assemblage of geomorphic

units along a reach, their sedimentological composition, and their mutual association with channel

planform and channel geometry, that defines the

distinguishing attributes of each River Style.

Stage One of the River Styles framework


Assessment of channel planform in the River

Styles framework builds on conventional notions

described in Chapter 4. The following criteria are


1 The number of channels. Rivers are identified

on the basis of whether they have single channels,

up to three channels, more than three channels, or

discontinuous/absent channels.

2 Sinuosity. The cutoff between low sinuosity

and meandering rivers is considered to be 1.3.

3 Lateral stability. This describes the degree to

which the channel is able to adjust its position

across the valley floor, through mechanisms such

as lateral migration, thalweg shift, or avulsion.

These behavioral attributes are differentiated into

differing rates of change, reflecting the likelihood

that adjustment will occur. This is dependent, in

large part, on bed material texture and available

flow energy.

In general terms, direct relationships can be discerned among the attributes used to assess channel

planform and the diversity and pattern of geomorphic units along a reach. For example, a laterally

migrating meandering channel comprises pool–

riffle sequences and point bars, and potentially has

a distinct array of geomorphic units on its floodplain (e.g., ridge and swale topography, cutoffs or

billabongs, levees, crevasse splays, abandoned

channels, etc.).

grained suspended load deposits. Rivers in the laterally-unconfined valley setting cover the full

suite of textures, with bedrock only locally significant. In these various settings, bed material texture, and its relation to bank composition, is a key

determinant of river character and behavior.

The relationship between bed material size

and the prevailing flow regime not only shapes the

assemblage of instream and floodplain geomorphic units, it also influences the capacity of the

channel to adjust its form, in terms of both its

geometry and planform. Textural differentiation

of channel and floodplain compartments, or the

bed and banks, may exert a significant influence on

the behavioral regime of a river. This is typically

reflected in the character and pattern of geomorphic units. For example, a gravel-bed meandering

River Style has a different package of geomorphic

units to a fine-grained meandering River Style.

Fine-grained systems generally have cohesive

banks, are laterally stable, and have floodplains

dominated by vertical accretion of suspended load

materials on the floodplain. In contrast, sand and

gravel dominated systems tend to be bedload dominated, have less stable banks, and are prone to lateral accretion and recurrent floodplain reworking.

Analysis of bed material texture provides a finer

level of resolution in the identification of River

Styles. The importance of bed material texture as a

defining characteristic varies for differing valley

settings. Bed material texture

9.3.2 The River Styles tree

In the River Styles framework, bed material

texture is differentiated on the basis of the dominant caliber of material found along the channel

bed. Five key classes are used: bedrock, boulder

(b-axis > 256 mm), gravel (2–256 mm), sand

(0.0625–2 mm), and silt/clay (termed fine-grained)

(< 0.0625 mm). In general terms, bed material size

reflects regional geology (lithology), flow energy,

and sediment influx from upstream. Confined-valley settings tend to be dominated by bedrock, with

occasional boulder and coarse-textured geomorphic units. Bedrock continues to be a major attribute of rivers in partly-confined valleys. In these

settings, bed material size may be locally very

variable, with gravels and coarser materials prominent. Floodplain pockets may comprise fine-

Associations between geomorphic units and channel planform, framed in context of valley setting

and differentiated on the basis of bed material texture, are the core criteria used to define River

Styles. Because river behavior varies in differing

valley settings, different mixes of these parameters

are used to classify rivers in different settings. In

other words, differentiation of River Styles is not

always made on the basis of the same criteria,

though geomorphic units are included in ALL interpretations. For example, floodplain considerations provide little insight into the character and

behavior of rivers found in a confined valley setting, while various channel planform attributes

are irrelevant in nonchannelized settings.

Similarly, while the number of channels and their Channel planform


Chapter 9

Figure 9.6 The River Styles procedural tree

Each River Style is identified on the basis of its planform, assemblage of geomorphic units, and bed material texture.

Depending on the valley setting, different sequences of procedures are applied to identify the River Style. Modified

from Brierley et al. (2002). Reproduced with permission from Elsevier, 2003.

stability are dominant attributes of a braided River

Style in a laterally-unconfined valley setting, key

attributes for other rivers may be, say, bedrock control, or the presence of a discontinuous channel.

Analysis of geomorphic units provides a basis to

interpret river character AND behavior. The presence/absence of individual units, and/or packages

of these features, provides a meaningful basis to determine boundaries between reaches with differing form–process associations. Placement of these

boundaries may range from clear and distinct

breaks to gradual and diffuse transitions.

The entry point into the River Styles procedural

tree is through identification of the valley setting

in which a river is found (i.e., confined, partly-confined, laterally-unconfined; Figure 9.6). Finer levels of differentiation are based on combinations of

channel planform, the assemblage of geomorphic

units, and bed material texture. Differing procedures are used because differing constraints are imposed on river character and behavior in different

valley settings. Hence, distinguishing attributes

of River Styles vary depending on the valley setting

in which the river occurs. However, a consistent

set of procedures is applied to derive a series

of generic labels within each valley setting.

Differentiation of River Styles becomes progressively more complex as the influence that bedrock

exerts on river morphology decreases and the capacity for river adjustment increases (i.e., from

confined through partly-confined to laterallyunconfined valley settings).

Each River Style has a discrete set of distinguishing attributes. In many cases, there may be an

overlap in the range of attributes. For example,

pool–riffle sequences are a common attribute for

many River Styles. However, each River Style has

unique identifying attributes, or combinations of

attributes. Practical application of the River Styles

framework and derivation of River Styles trees is a

catchment- or region-specific exercise. Examples

of a River Styles tree developed for rivers in coastal

valleys of New South Wales, and schematic representations of these River Styles, are presented in

Figures 9.7 and 9.8.

The first criterion used in analysis of rivers in

the confined valley setting is whether reaches are

completely bedrock-confined (i.e., no floodplain is

evident) or whether occasional floodplain pockets

are observed. These rivers are then differentiated

on the basis of the type and range of erosional/

sculpted geomorphic units found along the channel. Valley slope exerts a primary influence on

these features. Channel planform is irrelevant in

the differentiation of River Styles in these settings.

All three defining parameters are used to differentiate among River Styles in the partly-confined

valley setting. In the first instance, channel planform characterizes the distribution of floodplain

pockets based on the relationship between valley


Stage One of the River Styles framework



Figure 9.7 River Styles tree for a range of River Styles found in coastal NSW. Modified from Brierley et al. (2002).

Reproduced with permission from Elsevier, 2003

configuration and channel alignment. Valley configuration and the ability of the channel to laterally adjust determine channel sinuosity and the

degree to which discontinuous or alternating

pockets of floodplain occur. This is used to differentiate between bedrock-controlled and planformcontrolled discontinuous floodplain sequences.

Assemblages of erosional and depositional instream and floodplain geomorphic units, and bed

material texture, are assessed to further differentiate among River Styles.

In the laterally-unconfined valley setting, initial

identification of River Style is based on the presence or absence of a channel. Reaches with discontinuous channels are analyzed separately based on

the assemblage of geomorphic units and the texture of valley floor materials. Differentiation of

laterally-unconfined River Styles with continuous

channels is made on the basis of conventional

channel planform attributes, namely the number

of channels, sinuosity, and lateral stability. In the

instream zone, erosional, or depositional forms

and bank-attached and midchannel features are

differentiated. Bed material texture is then used for

finer level differentiation, highlighting differences

between boulder, gravel, sand, and fine-grained

variants. In some instances, laterally-unconfined

rivers may be bedrock-based.

For highly modified rivers, such as urban

streams or regulated rivers (irrigation channels),

where river character and behavior are largely

imposed, analyses are framed in terms of the

“natural” setting of the river. The River Style is

then noted as modified (M) and separate layers of

Chapter 9

(Discontinuous channel)


Figure 9.8 Examples of River Styles

identified in coastal valleys of NSW.

Reproduced from Brierley et al. (2002).

Reproduced with permission from

Elsevier, 2003

Stage One of the River Styles framework


Figure 9.9 Stage One, Step Two:

Definition and interpretation of

River Styles

analysis are undertaken that consider the types of

imposed configurations and associated behavioral

traits of the river.

laterally-unconfined valley settings (Figure 9.6).

Bed material texture provides a finer level differentiation which is often completed in the field.

9.3.3 Procedures used to identify and interpret

River Styles Designation of River Styles using

air photographs and production of

a River Styles tree

The definition and interpretation of River Styles

is initially undertaken as a desk top exercise.

Fieldwork is then undertaken to collect relevant

information on river character and behavior for

each River Style and ratify boundaries between

them. Procedures undertaken in Stage One, Step

Two of the River Styles framework are depicted in

Figure 9.9. Analysis of the catchment-wide

distribution of River Styles

Appraisal of topographic maps in conjunction with

the latest set of aerial photographs is undertaken to

gain an initial “feel” for the range and distribution

of River Styles in the area. The distribution of

floodplains along the primary trunk streams in

each subcatchment is used to determine the range

and pattern of valley settings. Within each valley

setting, River Styles are identified using the procedural trees for confined, partly-confined, or

A catchment- or region-specific River Styles tree is

constructed, outlining the distinguishing attributes of each River Style. Each River Style is given a

diagnostic name that synthesizes river character

and behavior, and a schematic representation is

presented. An example of a catchment-specific

River Styles tree is presented in Figure 9.10. The

distinguishing attributes of River Styles in Bega

catchment are presented in Table 9.4.

Boundaries of River Styles are mapped throughout the catchment. The boundaries between River

Styles are defined by a change in the diagnostic geomorphic structure of a river. These boundaries can

be distinct or gradual. Distinct changes often coincide with tributary–trunk stream confluences,

changes in valley gradient (e.g., at bedrock steps) or

sudden changes in valley width or morphology associated with lithological or structural changes.

Gradual changes are less easily pinpointed. For example, a change from occasional to discontinuous


Chapter 9

Figure 9.10 The Bega catchment River Styles tree (from Fryirs, 2001)

floodplain pockets may occur over several kilometers. A pragmatic decision needs to be made about

the placement of the boundary. In these cases, the

boundary is generally placed in the middle of this

transition zone and a gradual boundary noted. In all

instances, however, whether the boundary is distinct or gradual, the distinguishing attributes

should be discernible for River Styles upstream

and downstream of each boundary. Things to note

while identifying and ratifying boundaries between River Styles are downstream changes in:

• valley morphology (width, slope, and alignment);

• channel alignment on the valley floor and the

presence/continuity of floodplain pockets;

• channel planform (i.e., number of channels, sinuosity, indicators of lateral stability);

• floodplain character (flat, leveed, proximaldistal changes, evidence of reworking/scour);

• the presence/absence of geomorphic units and

packages of genetically-related assemblages;

• channel geometry (e.g., symmetrical, asymmetrical, compound, irregular);

• bed material texture and associated geomorphic

units if visible.

There is no definitive range of River Styles.

Using a flexible, open-ended approach to the assessment of river character and behavior retains as

much information as possible. It is much easier to

clump reaches together in production of the final

Table 9.4 Distinguishing attributes of River Styles in Bega catchment.

River Style

Valley setting/



River character

Channel planform

Geomorphic units



Single channel,

highly stable


Discontinuous floodplain,

pools, riffles, glides,

runs, vegetated islands




Single channel,

straight, highly

stable channel

No floodplain, bedrock

steps, pools and

riffles, cascades

Confined valley

with occasional






Single, straight,

channel, highly


Discontinuous pockets of

floodplain, extensive

bedrock outcrops, sand

sheets, pools


valley with




PartlySingle channel.


Sinuous valley



foothills and

moderately stable

base of


Discontinuous floodplain,

point bars, point

benches and sand

sheets, midchannel

bars, pools and riffles,

bedrock outcrops

Low sinuosity

boulder bed


Base of


Fans extend to valley

margins. Channel

consists of boulder

islands, cascades, runs,

pools, bedrock steps

Single channel trench

consisting of

multiple low

flow threads

around boulder

islands, highly


Bed material


Boulder-bedrock- Bedrock channel with a heterogeneous assemblage


of geomorphic units. Acts to flush sediments

through a confined valley. Limited ability for

lateral adjustment.

Boulder-bedrock Steep, bedrock controlled river with an alternating

sequence of bedrock steps and pool–riffle–

cascade sequences. Efficiently flushes all

available sediments. Channel cannot adjust

within the confined valley setting.


Found in narrow valleys, these rivers move

sediment along the channel bed via downstream

propagation of sand sheets. Bedrock induced

pools and riffles, and island development occur

where sediment availability is limited and the

bedrock channel is exposed.


These rivers are found in sinuous valleys. They

progressively transfer sediment from point bar to

point bar. Sediment accumulation and floodplain

formation is confined largely to the insides of

bends. Sediment removal occurs along concave

banks. Over time sediment inputs and outputs

are balanced in these reaches. Floodplains are

formed from suspended load deposition behind

bedrock spurs.

Boulder-bedrock Lobes of boulder and gravel material have been

deposited over the valley floor. The primary

incised channel has a heterogeneous

assemblage of bedrock and boulder induced

geomorphic units that are only reworked in large

flood events.

Stage One of the River Styles framework

Steep headwater

River behavior



Table 9.4 Continued.

River Style

Valley setting/



River character

Channel planform

Geomorphic units

River behavior

Bed material



Base of


No channel

Continuous, intact swamp


Channelized fill


Base of


Single, straight

channel, unstable

Continuous valley fill,

terraces, inset features,

sand sheets, sand bars






No channel

Continuous intact swamp

with floodout


Low sinuosity

sand bed




Single macrochannel

consisting of an


channel network.

Potentially avulsive

and unstable

Continuous floodplain with

backswamps, levees.

Benches, midchannel

islands and sand bars


Intact swamps are formed from dissipation of flow

and sediment over a wide valley floor as the

channel exits from the escarpment zone.

Suspended and bedload materials are

deposited as sheets or floodout lobes.

Incised channel has cut into the swamp deposits of

the intact valley fill River Style. Large volumes of

sediment are released and reworked on the

channel bed. The channel has a stepped cross section with a series of inset features and bar

forms. These are a function of cut-and-fill

processes within the incised channel. Channel

infilling, lateral low flow channel movement and

subsequent reincision produce the stepped


Formed downstream of an incised channel, this

river contains a swamp over which materials

supplied from upstream are splayed over the

valley floor in a number of lobes.

Found in a broad, low slope valley, the river

accumulates sediments in wide, continuous

floodplains. These floodplains contain levees and

backswamps formed by flow and sediment

dispersion over the floodplain. In other sections,

floodchannels short circuit floodplain segments

at high flow stage. The channel zone is

characterized by extensive sand sheets and sand

bars. Where these are colonized by vegetation,

islands are formed. Where sediments are

obliquely accreted against the channel margin,

benches are formed.

Chapter 9

Intact valley fill


Stage One of the River Styles framework

map, once field analyses are completed, rather

than split reaches at a later stage. In the latter instance, the designation of boundaries is likely to be

biased by field observations, which are inevitably

constrained by selected field investigations and are

not representative of the catchment as a whole.

Once the boundaries between River Styles have

been identified, a draft catchment-wide map showing the distribution of River Styles is produced (see

Plate 9.2). River Styles boundaries are also plotted

onto the longitudinal profiles produced in Stage

One, Step One.

• vegetation cover and character, including any

woody debris;

• discernible hillslope sediment sources, such as


• infrastructure and associated fixed points

(bridges, buildings, fencelines, etc.).

Using this analysis, detailed drafts of River

Styles proformas are produced. This standard data

sheet provides a consistent platform with which to

document the character, behavior, and controls

on each River Style (Table 9.5). In general, one proTable 9.5 The River Styles proforma. Select representative reaches of

each River Style and draft proformas

and planform maps using air

photograph interpretation

The next stage of analysis involves detailed mapping of the geomorphic structure of representative

reaches of each River Style. Pragmatic concerns

such as accessibility are considered when choosing

representative reaches. Representative field reaches must encompass the full range of river character

and behavior for the River Style (i.e., a full range of

geomorphic units, and any alternation of patterns

that occur within the reach). If the reach is characterized by an alternating pattern, two (or more) representative reaches are required. Hence, the length

of reach to be analyzed is dictated by its character

and behavior.

Detailed geomorphic base maps are produced for

each representative example of a River Style in the

catchment. If possible, air photograph mapping of

each representative reach is undertaken at a scale

of around 1 : 6,000 or smaller. Even at this scale, the

resolution of analysis may be too coarse to identify

some geomorphic units. In many instances, vegetation cover may impede analyses. Alternatively,

differences in vegetation character and cover may

aid the identification of some geomorphic units

(e.g., wetland vegetation). Geomorphic base maps

can be stand-alone products or superimposed on

air photographs or topographic contour maps.

These maps should show:

• the valley margin;

• the channel(s);

• discernible floodplain pockets and associated

geomorphic units;

• discernible instream geomorphic units;

River Style name

Catchment specific river name and reach name

Defining attributes of River Style (from River Styles tree)

Subcatchments in which River Style is observed:

(catchment specific)

Justification of River Styles boundary


Representative reach:

Map sheet(s) air photographs used



Upstream grid reference

Downstream grid reference


Valley setting

Channel planform

Bed material texture

Channel geometry

(size and shape)

Geomorphic units

(geometry, sedimentology)

Vegetation associations

Instream – bedrock

Instream – alluvial


Instream geomorphic units

Floodplain geomorphic units


Low flow stage

Bankfull stage

Overbank stage


Upstream catchment area

Landscape unit and within-catchment position

Process zone

Valley morphology (size and shape)

Valley slope

Stream power


Chapter 9

forma is presented for each River Style in the

catchment, summarizing the range of data recorded for any given attribute of the River Style.

Obviously this range is limited by the site selected

for detailed field or air photograph observations.

The River Styles proforma comprises four key


• Details of analysis. This summarizes resources and personnel used to complete the analysis, when the assessment was undertaken, and the

location of the reach.

• River character. A range of attributes is used

to identify and characterize the River Style, including valley setting, channel planform, bed material texture, and the assemblage of geomorphic

units. Various characteristics of geomorphic units,

such as their geometry and sedimentology, provide the basis to interpret river behavior.

Cross-sectional channel geometry is noted and

vegetation character is assessed for each geomorphic surface, aiding interpretation of its role in the

formation and reworking of geomorphic units, and

associated river behavior.

• River behavior. Form–process associations

of geomorphic units are used to interpret river

behavior at low flow, bankfull, and overbank


• Controls. The boundary conditions within

which the River Style operates are summarized.

This includes documentation of the landscape

unit and catchment-scale controls within which

each reach of the River Style is observed. Many of

the details presented in this section are analyzed

from resources compiled in Stage One, Step One

and Stage One, Step Three of the River Styles


9.3.4 Ratify River Styles boundaries

in the field

Field analysis is an integral component of the River

Styles framework. It is at this stage that the assemblage of geomorphic units and other geomorphic

parameters are assessed at finer resolution along

representative reaches of each River Style. Prior to

going into the field, the following data should be


• pertinent regional setting data compiled in

Stage One, Step One;

• landscape units map and longitudinal profiles;

• draft catchment map showing the distribution

of River Styles;

• draft versions of planform maps for representative reaches of each River Style, showing geomorphic units wherever discernible;

• draft versions of River Styles proformas for each

River Style.

The first task to be undertaken in the field is the

ratification of River Styles boundaries. Only conjectural boundaries are visited. This involves

locating the boundary on the ground and assessing

the distinction between river character and

behavior in upstream and downstream reaches

to validate the placement of the boundary.

Statements justifying the position of the boundaries are noted in the River Styles report and on the

River Styles proformas. Once this analysis has

been completed, the River Styles map is modified

as required.

9.3.5 Complete field analyses to finalize

proformas and amend planform maps

at each representative field reach

Data on each River Style are recorded in a systematic manner to aid the appraisal and communication of river character and behavior. Proformas are

finalized in the field, filling in details on geomorphic units, bed material texture, and river behavior. Annotated photographs, cross-sections, and

planform maps accompany these proformas in the

final presentation. Dependent on the nature of the

exercise, additional data may be required. In all

instances, adopted procedures should be clearly

articulated and rigorously applied, using standard

(accredited) sources whenever possible (e.g.,

Newbury and Gaboury, 1993; Harrelson et al.,

1994; Rosgen, 1996; Thorne, 1999; Rutherfurd

et al., 2000).

Depending on the goals of the exercise and the

complexity of the reach, field analysis can take up

to half a day for each site. A range of attributes is

measured (see Table 9.6). Due emphasis is placed

on analysis of distinguishing attributes of each

River Style, including key characteristics of

instream and floodplain geomorphic units.

Examples of representative River Styles proformas

derived for three types of river in Bega catchment

are presented in Tables 9.7–9.9 and Figures


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3 Stage One, Step Two: Definition and interpretation of River Styles

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