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4 Stage One, Step Three: Assess controls on the character, behavior, and downstream patterns of River Styles
• can discernible changes in imposed boundary
conditions be isolated in the transitional zones between River Styles? Do transition zones coincide
with tributary–trunk stream boundaries as noted
by changes in contributing area, breaks in slope,
and base level controls along the longitudinal
proﬁle, or geological (lithologic and/or structural)
changes? Do certain River Styles occur in certain landscape units at certain positions in the
• can underlying factors that result in changes to
ﬂux boundary conditions be expressed in terms
of changes to the ﬂow and sediment ﬂuxes? Do
cumulative responses reﬂect a change in stream
power? Can these relationships be quantiﬁed?
What has fashioned patterns of sediment transport
and storage along river courses, and their relationships to geomorphic process zones?
Interpretation of controls on river character and
behavior may result in assessments that are catchment (or region) speciﬁc. As many factors may conspire to create an opportunity for any given type of
river to be generated, it is considered to be overly
simplistic to quantify controls on the distribution
of individual River Styles in a prescriptive manner.
River character and behavior do not reﬂect variability along a single continuum in, say, slope,
grain size or valley width. Rather, they reﬂect a
multivariate continuum with an inﬁnite complexity of associations. Any given set of boundary conditions may result in an array of River Styles, and it
is unlikely that any particular River Style will only
be observed under a “unique” set of conditions
such as a speciﬁc lithology on a characteristic
slope set within a particular range of stream power
conditions. Hence, there will be overlap among the
circumstances under which any River Style is observed and associated “typical” patterns in space
The best way to assess controls on river character and behavior is to determine the conditions
under which all examples of a particular River
Style operate. Differences, similarities, and overlaps in controls among River Styles are analyzed
and interpreted. Just as differing parameters deﬁne
the character and behavior of River Styles, so the
relative inﬂuence of differing controls condition
the presence/absence and distribution of River
Styles. To interpret the dominant controls on the
character and behavior of each River Style, a comparison is made between River Styles to determine
which controlling parameters are signiﬁcantly
different. Obviously, depending on the scale of
analysis (e.g., regional versus catchment versus
subcatchment), and the nature of the environmental setting, other measures may be required, such
Figure 9.14 Stage One, Step Three:
Assessment of controls on the
character, behavior and downstream
patterns of River Styles
Stage One of the River Styles framework
as structural geology, drainage density, stream
order, catchment shape, vegetation cover, forms of
human disturbance (e.g., urban attributes, irrigation schemes), etc. Beyond this, an assessment is
made of how various controls interact to dictate
the character and behavior of the River Style.
Finally, any anomalies are explained. Procedures
used to assess controls on the character, behavior,
and downstream patterns of River Styles in a
catchment are summarized in Figure 9.14.
patterns, from those that are distinct. Alternating
patterns of River Styles can be synthesized in this
assessment. This analysis provides a basis to assess the similarity in downstream controls on
River Styles and helps explain river character and
behavior in different subcatchments. A tree-like
diagram is produced showing the tributary patterns of River Styles and how they connect to the
trunk stream (Figure 9.15). The pattern is noted on
the catchment River Styles map (see Plate 9.2).
9.4.1 Determine downstream patterns
of River Styles
9.4.2 Determine imposed boundary condition
controls on river character and behavior along
Downstream patterns of River Styles are determined for all river courses in the catchment, differentiating those that have similar downstream
River Styles boundaries are placed atop the longitudinal proﬁle-contributing area plots, noting
Figure 9.15 Downstream patterns of River Styles in Bega catchment
Four primary downstream patterns of River Styles were identiﬁed from 16 subcatchments in Bega catchment:
• those in which headwaters are transitional to long, elongate, bedrock-controlled valleys downstream of the
escarpment (Pattern 1);
• those which have large accommodation spaces at the base of the escarpment in which extensive Holocene ﬁlls have
formed (Pattern 2 rivers have channelized ﬁlls, Pattern 3 rivers have intact valley ﬁlls);
• those in which boulder fans at the base of the escarpment are transitional to bedrock-controlled valleys and the
lowland plain (Pattern 4).
Representative examples of each were chosen to explain the controls on the character, behavior, and downstream
pattern of River Styles in the catchment.
Figure 9.16 Controls on the downstream pattern of River Styles along the Bega River
Signiﬁcant catchment areas drain from the uplands landscape unit where the steep headwater River Style occurs. The
longitudinal proﬁle has a distinct step in the escarpment zone where the gorge River Style is formed. Beyond the
escarpment, the longitudinal proﬁle has a relatively smooth, concave-upwards form. Associated with this progressive
downstream change in slope, there is progressive downstream widening of both the channel and the valley through
the base of the escarpment, the rounded foothills and the lowland plain landscape units. At the base of the escarpment,
the low sinuosity boulder bed River Style occurs. This occurs where slopes are high and ﬂow exits from the
escarpment zone. Large boulder fans have been deposited. There is a lack of a valley constriction along the
downstream margin of the base of escarpment landscape unit. This prevents the accumulation of valley ﬁlls at the
base of the escarpment along these valleys. Instead bedload materials are transferred through the system, until they
reach the lowland plain where they accumulate.
Along the majority of the Bega trunk stream, the conﬁned valley with occasional ﬂoodplain pockets River Style
occurs. As catchment area increases and discharges increase with the inputs from numerous tributaries, gross stream
power along this River Style progressively increases. Peaks occur where bedrock steps occur in the longitudinal proﬁle
(e.g., at ~ 60 km where Kanooka knickpoint is located). It is not until the valley widens and slope decreases
signiﬁcantly around the Wolumla Creek conﬂuence that the transition to a low sinuosity sand bed River Style occurs.
This transition coincides with the start of the lowland plain landscape unit and a drop in the gross stream power. No
partly-conﬁned valleys are found along this pattern of River Styles in Bega catchment.
Stage One of the River Styles framework
Figure 9.17 Controls on the downstream pattern of River Styles along Wolumla Creek
Most subcatchments in Bega catchment drain directly from the escarpment and have smooth concave-upward
longitudinal proﬁles, with a gentle break in slope at the base of the escarpment. In these tributaries, where the uplands
landscape unit is absent, the channelized ﬁll River Style is formed at the base of the escarpment. These laterallyunconﬁned valley settings are formed under a particular set of catchment boundary conditions. Broad, asymmetrical
valleys are formed downstream of a gentle break in slope. The downstream margin of these valleys is characterized by
either a signiﬁcant narrowing of the valley or a bedrock step which gives the valley a funnel shape. Large
accommodation spaces store material behind these constrictions. The formation of these laterally-unconﬁned valley
settings at the base of the escarpment is a direct result of interactions between escarpment retreat and valley-sidewall
expansion (Fryirs, 2002). When inﬁlling, these valleys are characterized by the intact valley ﬁll River Style. When
cutting, these valleys are characterized by the channelized ﬁll River Style. In 8 of the 10 subcatchments that display
this downstream pattern of River Styles, only two remain intact (i.e., contain the Intact valley ﬁll River Style at the
base of the escarpment).
In the rounded foothills of these subcatchments, the conﬁned valley with occasional ﬂoodplain pockets and the
partly-conﬁned valley with bedrock-controlled discontinuous ﬂoodplain River Styles extend to the trunk stream.
Unlike the classical downstream sequence of channel geometries and process zones along long proﬁles, streams along
this pattern of River Styles have large, laterally-unconﬁned valleys with wide, deep channels at the base of the
escarpment. These channels are mixed load in composition, with sands and muds accumulating on the channel bed.
These are transitional to narrower, shallower channels in the conﬁned and partly-conﬁned valley settings in the
middle and lower sections of the catchment which act to effectively transfer bedload materials through to the lowland
their relation to each valley setting and landscape
unit (see Figures 9.16 and 9.17). These imposed
boundary condition controls deﬁne the potential
range of variability of a River Style. For each River
Style, the range of valley widths, valley slope, and
contributing areas are determined, and presented
as part of a “controls” table. The transition zone
between River Styles is related to catchment-scale
boundary conditions (e.g., geological boundaries),
associated landscape units, and the catchment
position (and contributing area). By deﬁnition,
shifts in River Styles are evident whenever
changes in valley setting occur. These transitions,
in turn, are commonly associated with downstream changes in landscape units, reﬂecting landscape history. Considerable overlap may exist in
these imposed boundary conditions, as a range of
River Styles can be formed under similar sets of
tion zones) and associated sediment transport
regime (i.e., bedload, mixed load, or suspended
load system) are plotted beneath these curves. An
estimate is made as to whether each reach is sediment supply- or transport-limited. In general,
rivers in conﬁned and partly-conﬁned valley
settings act as sediment transfer reaches, as sediments are readily ﬂushed. Rivers in laterallyunconﬁned valley settings tend to be accumulation zones, unless the reach responds to disturbance by reworking its sediment stores, thereby
acting as a sediment source zone.
This analysis provides the basis to interpret
process responses of each reach to imposed and
ﬂux boundary condition controls, which are major
determinants of river character and behavior. A
summary representation of the range of controls
for all River Styles in Bega catchment is presented
in Figure 9.18.
9.4.3 Determine the ﬂux boundary condition
controls on river character and behavior along
9.5 Overview of Stage One of the River
Stream power provides a guide to the energy
regime at differing positions along a river. Outputs
required to generate stream power include contributing area and a running average of slope.
When combined with the catchment areadischarge relationships derived in Stage One, Step
One, discharge estimates can be extracted for the 2,
5, 10, 50, and 100 year events and plotted as a continuous data set along the longitudinal proﬁle.
When discharge is combined with slope, gross
stream power is generated (Reinfelds et al., 2004).
In the River Styles framework, the gross stream
power curve is superimposed onto the longitudinal proﬁle-contributing area plot for each
subcatchment. If possible, unit stream power estimates are derived for each River Style, recognizing
explicitly that the range of estimates may vary
markedly for differing reaches (reﬂecting variability in slope or upstream catchment area, or the geomorphic condition of the reach; see Chapter 10).
Generally, only one recurrence interval relationship (e.g., 1 in 2 year event) is depicted, but all values are presented in a summary table of controls on
the character, behavior and pattern of River Styles
(Table 9.10). The distribution of geomorphic
process zones (i.e., source, transfer, and accumula-
The baseline survey of River Styles integrates
catchment-scale controls on rivers with reachbased assessments of river character and behavior
through use of a nested hierarchical approach.
Classiﬁcation of River Styles is based initially on
valley setting. For differing settings, variable sets
of parameters including channel planform, the assemblage of geomorphic units, and bed material
texture are used to deﬁne River Styles, emphasizing distinguishing attributes in River Styles trees.
Proformas are completed for each River Style.
Analysis of catchment-scale linkages and boundary conditions aids determination of the controls
on river character and behavior for each River
The following products are produced in Stage
One of the River Styles framework:
• regional setting chapter;
• River Styles tree that is speciﬁc to the
• catchment-wide map showing the distribution
of River Styles;
• River Styles proformas, annotated crosssections, annotated geomorphic unit planform
map and photographs for each River Style in the
Table 9.10 Controls on river character and behavior in Bega catchment.
Unit stream power (Wm-2)
recurrence interval (years)
1 in 2
1 in 5
1 in 10
1 in 50
1 in 100
Gorges are found on high slopes in conﬁned settings that generate high stream powers. This acts to ﬂush materials efﬁciently through the escarpment zone of the catchment.
High stream powers are also generated along the conﬁned valley with occasional ﬂoodplain pockets and the partly-conﬁned valley with bedrock-controlled discontinuous
ﬂoodplain River Styles. While found on lower slopes, their position in the catchment ensures that large discharges are generated in these midcatchment locations. Given their
bedrock-controlled character they too act to efﬁciently ﬂush sediment to the lowland plain. The lowest stream powers in the catchment are generated in the intact valley ﬁll and
ﬂoodout River Styles which remain unchannelized and effectively dissipate energy over valley ﬁll surfaces. These River Styles act as large sediment sinks.
Stage One of the River Styles framework
Intact valley ﬁll
Low sinuosity boulder bed
Conﬁned with occasional
ﬂoodplain pockets (trunk)
Conﬁned valley with occasional
Partly-conﬁned valley with
Low sinuosity sand bed
Figure 9.18 Summary controls on the character and behavior of River Styles in Bega catchment
This ﬁgure summarizes controls on the character and behavior of River Styles in Bega catchment. These controls
include slope and valley conﬁnement. Each reach is placed within its landscape context through analysis of landscape
units. Reprinted from Brierley and Fryirs (2000) with permission from Springer-Verlag GmbH & Co. K.G. 2004.
Figure 9.18 Continued
• longitudinal proﬁle diagrams with associated
assessment of controls for a representative example of each downstream pattern of River Styles in
• table of controls for all River Styles in the
Baseline information derived from analysis of
catchment-wide river character and behavior pro-
vides a geomorphological baseline for comparing
like-with-like, ensuring that reaches of the same
River Style are used in analyses of river condition
and recovery potential, as outlined in Chapters 10
C H A PT E R 1 0
Stage Two of the River Styles framework:
Catchment-framed assessment of river
evolution and geomorphic condition
Many rivers no longer support valued native species or sustain healthy ecosystems that
provide important goods and services.
LeRoy Poff et al., 1997, p. 769
Completion of Stage One of the River Styles
framework produces a catchment-wide analysis of
differing geomorphic types of river. Inevitably,
reaches of any given type do not have a uniform
character and behavior. Inherent diversity in river
forms and processes may be evident at the local
scale, such that a mapped River Style represents a
summary sense of character and behavior at the
reach scale. In many instances, these differences
may reﬂect variability in the geomorphic condition of differing sections of a reach of a given River
Style, as induced by human disturbance (whether
direct or indirect, at-a-site or off-site). In this chapter, a set of procedures with which to appraise the
geomorphic condition of rivers is documented.
This represents Stage Two of the River Styles
Measures of geomorphic river condition record
deviations from a natural or expected state in any
given reach (i.e., how human disturbance has altered river character and behavior). In this book,
river condition is deﬁned as a measure of the capacity of a river to perform functions that are expected for that river within the valley setting that
it occupies (Table 10.1). The further a reach sits
from its reference condition, the poorer its geomorphic condition. When appraised in terms of the
capacity for adjustment that is appropriate for the
given boundary conditions (i.e., the reference condition), each reach is placed into a good, moderate,
or poor condition category.
To frame the assessment of geomorphic river
condition, human-induced changes to river forms
and processes must be viewed in context of the inherent evolutionary tendencies of the system. In
applying a generic set of procedures in each ﬁeld
situation, elements of subjectivity are encountered. So long as limitations are recognized, they do
not present an insurmountable problem. Indeed,
much is to be gained by thinking through and discussing these issues. Regardless of the challenges
faced, assessments of river condition (or health)
constitute an integral part of the river management
process, providing a critical platform for environmental decision-making and associated actions.
Given that each River Style records the character and behavior of reaches that operate within an
equivalent set of boundary conditions, comparison of reaches of the same River Style provides an
ideal basis to assess river condition. Geomorphic
river condition is appraised in context of the capacity for adjustment of the River Style and the degree
to which contemporary measures of geomorphic
structure and function for the reach have moved
away from the reference condition. As geomorphic
structure and function, and associated adjustments, are predictable for each River Style, a platform is provided with which measures of river
condition can be evaluated in a consistent yet ﬂexible manner, ensuring that appropriate criteria
are measured to make this determination. River
condition is appraised in terms of channel planform, channel geometry, bed character, and the
geomorphic unit assemblage along a reach.
Table 10.1 Deﬁnition of terms used to describe the geomorphic condition of a reach.
Capacity for adjustment
Degrees of freedom
Natural river (Natural
Deﬁnition in the River Styles framework
A measure of the capacity of a river to perform functions that are expected for that river within the
valley setting that it occupies. The contemporary geomorphic state of a reach relative to a
“natural” or “expected” reference condition of the same type of river. Assessment of river
condition requires an understanding of:
• the spatial distribution of river types
• how those rivers behave
• river dynamics (i.e., river evolution), and
• forms, extent, and impact of human disturbance, including an appraisal of whether this change
has been irreversible.
Morphological adjustments brought about by the changing nature of biophysical ﬂuxes that do not
record a wholesale change in river type.
The ability of differing components of a river system to adjust, measured in terms of bed character,
channel attributes, and planform attributes.
Parameters used to interpret and explain system structure, function, and condition for each degree
of freedom. “Relevant geoindicators” provide a reliable and relevant signal about the condition
of a reach. The geoindicators measured are River Style speciﬁc.
Assessment of the appropriateness of each relevant geoindicator for each River Style. A question is
posed for each geoindicator to produce a set of desirability criteria to identify a reference
condition and assess the geomorphic condition of a reach.
A “natural” river is dynamically adjusted so that geomorphic structure and function operate within
a capacity for adjustment that is appropriate for that type of river, given the prevailing boundary
conditions. A “natural reference condition” is considered to be a river that is operating in the
absence of human disturbance. Changes to this “intact” or “predisturbance” condition are
considered to be reversible.
A prehuman disturbance reference condition is largely irrelevant for many river systems. Hence,
expected reference conditions are identiﬁed against which the geomorphic condition of a reach
is assessed. Three types of expected reference condition differentiate among situations in which
the reach has been:
• reversibly altered by human disturbance;
• irreversibly altered by indirect human disturbance;
• irreversibly altered by direct human disturbance.
A wholesale shift in the geomorphic unit structure, planform, and bed material texture, such that
the river operates in a fundamentally different manner to its former state with no prospect of
return over a 50–100 year timeframe. This transition in the behavioral regime marks the adoption
of a different type of river.
River character and behavior are appropriate for the River Style given the valley setting and withincatchment position. Geomorphic structures are in the right place and operating as expected for
the River Style. These reaches have a near-natural potential for ecological diversity and associated
Certain characteristics are out-of-balance or inappropriate for the River Style. Localized degradation
of river character and behavior is typically marked by modiﬁed patterns of geomorphic units. Key
geomorphic structures are in the wrong places. Locally anomalous processes are occurring. In
general, these reaches have poor vegetation associations and/or cover.
River character is divergent from the natural reference condition. Abnormal or accelerated
geomorphic behavior occurs. Key geomorphic units are located inappropriately along the reach,
and processes are out-of-balance or anomalous. These reaches generally have low levels of bank
vegetation and/or are weed infested. If fundamental threshold conditions are breached,
irreversible geomorphic change would transform the reach to a new River Style.