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2 Stage Three, Step One: Determine the trajectory of change
Figure 11.3 Stage Three, Step One:
Determining the trajectory of
Reaches on the creation trajectory are adjusting to
altered ﬂux boundary conditions.
The future recovery trajectory is dependent on
the history of change (i.e., whether irreversible
geomorphic change has occurred), present reach
conditions, and prevailing ﬂux boundary conditions. The further down the degradation scale a
reach sits, the less likely it is that it will recover
along the restoration pathway, and creation is the
most likely future scenario. Reaches that have experienced reversible geomorphic change have the
potential to recover along the restoration pathway.
These reaches are generally in good or moderate
geomorphic condition and sit higher on the degradation pathway. However, if ﬂux boundary conditions have been severely altered, creation is
underway. These reaches tend to be in poor condition and sit low on the degradation pathway.
Ultimately, both the restoration and creation pathways reﬂect the operation of self-healing processes
that improve river condition. By deﬁnition, reaches that have experienced irreversible geomorphic
change are unable to recover along the restoration
pathway. As such, they recover along a creation
pathway irrespective of their contemporary geomorphic condition.
Since effective rehabilitation strategies work
with the contemporary condition and trajectory of
river changes, the position of each reach on the recovery diagram must be determined (Figure 11.1).
The procedure used to assess the trajectory of
change in the River Styles framework is outlined
in Figure 11.3. With the evolutionary framework
of river changes in-hand (Stage Two, Step Two), the
position of each reach on the recovery diagram is
determined using a decision tree. Based on this
analysis, stages of adjustment for each reach and
trajectory of change are interpreted.
11.2.1 Position each reach on the evolutionary
sequence of the River Style
The ﬁrst step in determining the trajectory of
change is to apply ergodic reasoning and position
the reach under investigation on the evolutionary
sequence for each River Style constructed in Stage
Two, Step Two.
11.2.2 Translate each evolutionary timeslice
onto the recovery diagram using the
The second step towards assessing the trajectory of
change involves translating the entire evolutionary sequence of the River Style onto the recovery
diagram. The position of each timeslice relates directly to its geomorphic condition and past evolutionary adjustments. Figure 11.4 summarizes the
decision-making process that is applied for each
reach in the catchment.
18.104.22.168 Is the reach intact?
The ﬁrst decision involves evaluating whether
the reach has developed a range of attributes such
that contemporary river condition does not
differ from an intact (predisturbance) state. Intact
reaches operate within the natural capacity for
adjustment of a River Style in the absence of
human disturbance. A comparison is made between the character and behavior of the intact version of a River Style and the contemporary reach.
Stage Three of the River Styles framework
Figure 11.4 Decision tree for
determining the trajectory of
change of a reach. Modiﬁed from
Fryirs and Brierley (2000) with
permission from © V.H. Winston &
Son, Inc., All rights reserved
If the geomorphic character and behavior of the
reach are not signiﬁcantly different from the predisturbance condition, the reach is considered to
22.214.171.124 Has the reach started to recover?
A reach that is recovering has moved to the righthand side of Figure 11.1. Assessment of whether
geomorphic recovery is underway is determined
through interpretation of historical information
and knowledge about system structure and function derived in Stages One and Two of the River
Styles framework. In particular, analysis of
changes to the assemblage of geomorphic units
within a reach provides a key indicator of whether
recovery is underway. For example, the formation
of benches that narrow enlarged channels are
an initial recovery mechanism. Similarly, the
reemergence of pools and the redeﬁnition of a low
ﬂow channel following the passage of a sediment
slug are indicative of geomorphic recovery.
Reaches that show initial signs of recovery are considered to be at the turning point (Figure 11.1).
These reaches are generally in moderate geomorphic condition.
If the reach has been altered, and is experiencing
progressive deterioration in its geomorphic condition, it is placed in the degraded category. These
reaches are generally in poor or moderate geomorphic condition. In degrading reaches, the range of
geomorphic units is inappropriate for the environ-
mental setting. For example, sand sheets that have
inﬁlled pools or cover the ﬂoodplain indicate that
there is an oversupply of sediment to that reach.
Such reaches are adjusting their character and behavior to this change in sediment regime. Speciﬁc
indicators of degradation or modiﬁed rates of geomorphic change may be detected, without any indication that processes of geomorphic recovery are
126.96.36.199 Is restoration possible?
The ﬁnal two steps in the decision tree shown
in Figure 11.4 determine whether a reach is adjusting along a restoration or creation pathway. The
recovery trajectory is dependent on the history of
change (i.e., whether irreversible geomorphic
change has occurred), the present reach condition,
and the ﬂux boundary conditions under which the
reach operates (i.e., altered or unaltered). If ﬂux
boundary conditions have not been signiﬁcantly
altered along reaches that have experienced reversible geomorphic change, there is potential for
restoration to occur. These reaches are generally in
good geomorphic condition and sit high on the
degradation pathway. Restoration is underway
when the geomorphic unit assemblage of a reach
approximates the intact, predisturbance character
and behavior. For example, the reinstigation of
swamps and discontinuous watercourses are indicative of geomorphic restoration along cut-andﬁll rivers.
188.8.131.52 Is the reach adopting a new condition?
Reaches that have experienced irreversible geomorphic change recover along the creation
pathway irrespective of their contemporary geomorphic condition. These reaches do not have the
capacity to return to a predisturbance character
and behavior under prevailing boundary conditions, and restoration is no longer a viable option.
In this case, a “new” condition is deﬁned, and
reaches recover towards the best attainable condition for the contemporary River Style. Reaches
that have experienced irreversible geomorphic
change were identiﬁed in Stage Two, Step Two of
the River Styles framework. If irreversible change
led to a shift in River Style such that the reach now
displays geomorphic structures that were not present at any stage in the evolutionary sequence, a
solid line is placed across the degradation pathway
of the recovery diagram. This depicts the irreversible nature of change and adjustment along the
creation trajectory (Figures 11.5 and 11.7).
Reaches that have experienced reversible geomorphic change can recover along either a restoration or creation pathway, depending on the
geomorphic condition of the reach and the degree
to which human disturbance has altered the ﬂux
boundary conditions under which the reach operates (Figure 11.6). Reaches that are in poor geomorphic condition, and which operate under altered
catchment boundary conditions, sit lower on the
degradation scale and are less likely to recover
along a restoration pathway. Under these conditions, creation is the most likely future scenario.
The further down the degradation scale a reach
sits, the less likely it is that it will recover along a
11.2.3 Determine the trajectory of change
of each reach in the catchment (i.e., either
degradation, restoration, or creation)
Using the recovery diagram for each River Style, a
direct assessment is made of the trajectory of
change of each reach in the catchment. The position of each reach in the evolutionary sequence for
that River Style determines where it sits on the recovery diagram. In turn, the position of the reach
on the recovery diagram determines its trajectory
of change. If the reach sits on the degradation path-
way it shows signs of continued deterioration. If
the reach sits at the turning point, the nature of
future ﬂow and sediment regimes will dictate
whether the reach continues to deteriorate or
moves onto a recovery pathway. If the reach shows
signs of recovery, it sits on either a creation or
restoration pathway. Examples of the resultant
diagrams are presented in Figures 11.5–11.7.
11.3 Stage Three, Step Two: Assess river recovery
potential: Place reaches in their catchment context
and assess limiting factors to recovery
The effectiveness and extent of river recovery
processes reﬂect a wide range of catchmentspeciﬁc considerations. Reaches of different River
Styles are at different phases of degradation and recovery. The character and mechanisms of recovery
differ from system to system conditioned by the
type of river, the extent of disturbance, reach position relative to off-site or lagged disturbance responses, and a range of physical issues related to
limiting factors operating within the catchment.
Assessment of limiting factors and pressures that
constrain the recovery of landscapes and their associated ecosystems enables the adoption of management strategies that minimize the impacts of
these constraints. Such practices address underlying causes of change, rather than their symptoms.
These factors must be assessed on a catchment-bycatchment and reach-by-reach basis. In the River
Styles framework, the changing nature of withincatchment linkages of physical processes is
examined, relating disturbances in one part of a
catchment to off-site impacts and lagged responses
Given that rivers are evolving, adjusting entities, a reach can sit at any position on the degradation pathway and, given favorable conditions, may
move onto a recovery pathway at any point.
However, even though a reach may sit on a recovery trajectory, the river may not have the “potential” to move along that pathway. Recovery
potential is deﬁned as the capacity for improvement in the geomorphic condition of a reach in the
next 50–100 years. Under the same set of environmental conditions, a reach may potentially adjust
along multiple recovery trajectories. Analysis
of the pathway of adjustment, and prediction of
Stage Three of the River Styles framework
Figure 11.5 Trajectories of change for reaches of the channelized ﬁll River Style in Bega catchment (from Fryirs, 2001).
The letters equate to the evolutionary stage in Figure 10.5
In Bega catchment, reaches that are sensitive to change have experienced irreversible change in River Style
(represented by the black lines on the degradation pathway). In this case, the river has changed from an intact valley
ﬁll River Style to a channelized ﬁll River Style. Reaches of the latter now operate under altered catchment boundary
conditions. These reaches are unlikely to recover along a restoration pathway over the next 50–100 years. Hence,
creation of a new condition is underway along these reaches.