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2 Stage One, Step One: Regional and catchment setting analyses

2 Stage One, Step One: Regional and catchment setting analyses

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Stage One of the River Styles framework



Figure 9.1 The River Styles nested

hierarchy

The River Styles nested hierarchy is

arranged into five key scales at

which a range of analyses are

undertaken. At the coarsest scale,

catchment scale boundary

conditions are assessed. Nested

within the catchment are areas of

relatively homogeneous topography

that are called landscape units. The

configuration and connectivity of

the landscape at this scale provides

the key set of imposed boundary

conditions within which rivers are

formed and operate. They also

dictate the flux boundary conditions

that drive the character and behavior

of rivers by regulating the water and

sediment regimes of the catchment

and associated vegetation

composition. Interpreting controls

on river character and behavior

occurs at this scale. At finer scales of

resolution, hydraulic units are

assessed as the basis for habitat

assessment. These areas of

homogeneous flow and substrate

characteristics are nested within

geomorphic units which are the

building blocks or key landforms

that are formed along rivers. Each

River Style has a distinct assemblage

of geomorphic units that is used

to interpret river behavior. A

constructivist approach is used to

build river morphology and interpret

river behavior from its component

parts. These two sets of analyses

(top-down and bottom-up) are

manifest at the reach scale where

different River Styles are formed.

Modified from Brierley and Fryirs

(2000). Reprinted with permission

from Springer-Verlag GmbH & Co.

K.G. 2004.



255



256



Chapter 9





Figure 9.2 Approaches and scales of analysis adopted in the River Styles framework

The River Styles framework is arranged in a nested hierarchy of scales extending from catchments to geomorphic

units. The structure of this hierarchy allows for top-down explanations of controls on river character and behavior and

a bottom-up constructivist approach to interpretation of river character and behavior. These two sets of approaches

come together at the reach scale where River Styles are identified and interpreted.







Figure 9.3 Stage One of the River

Styles framework



catchments being assessed), or within an individual catchment. For example, drainage density and

catchment shape are not particularly useful for explaining the within-catchment variability of River

Styles, but the configuration and relative proportion of landscape units within differing subcatchments will provide useful guidance. In contrast,

the interpretation of downstream patterns of River

Styles across a region requires a broader focus, in

which drainage density, catchment shape, relief

factors, regional climate variability, etc., are key

factors in the interpretation of the region-wide distribution of River Styles and their downstream

patterns. Hence, in the text that follows, a review

is provided of the tools that can be molded to suit

the level and scale of analysis being undertaken. A

flow diagram depicting the procedures undertaken

in Stage One, Step One of the River Styles framework is presented in Figure 9.4. Analysis of these

various forms of data is used to assess the catch-



ment-scale boundary conditions and controls

within which rivers operate.

Skills in Geographic Information Systems (GIS)

assist in several components of this assessment,

especially relating to derivation of various catchment-scale attributes from manipulation of

Digital Elevation Model (DEM) data and associated mapping and graphic skills. Some experience

with manipulation of hydrological data aids

completion of rainfall-runoff analyses and derivation of associated catchment area–discharge

relationships.

These various sources of information are compiled as a Regional Setting chapter within a River

Styles report. These analyses should be completed

prior to going into the field, as relevant background

information can be incorporated into the River

Styles analysis, gaps in knowledge are identified,

and numerous short cuts may be provided for the

field work. Discussions with resource managers



Stage One of the River Styles framework



257















Figure 9.4 Stage One, Step One:

Procedures used to produce a

regional setting



who have compiled differing components of these

data sets, and with technical staff who work in the

catchment of concern, will enhance completion of

field and analytical tasks.

9.2.1 Background information and review of

literature to derive catchment maps

At the outset, background literature and maps of

catchment geology, soils, climate, vegetation, land

use and settlement history, etc. are compiled.

Many maps may already be available in a GIS

format from regional offices and local agencies. In

regional applications, distinctive catchment characteristics can be identified and compared across

the (eco)region. In many catchments, an extensive

amount of information can be derived from:

• academic literature including theses, referred

publications, books;

• government databases, including commissioned reports;

• consulting reports;

• land systems and topographic map sheets;

• regional resource maps and GIS databases (e.g.,

soils, geology, land use, etc.);

• local knowledge (historical society, local library,

etc.);

• meteorological office data and reports;

• flood history records and gauge station data, etc.







Available GIS data are used to produce a catchment base map showing the river courses under

investigation and subcatchment boundaries.

Various locational identifiers, such as towns and

prominent local landmarks are added to the map,

and each primary subcatchment is labeled. If GIS

data are not available, 1 : 100,000, 1 : 50,000, or

1 : 25,000 maps (or local equivalents) are used.

This provides the catchment template onto which

River Styles are subsequently added in Stage One,

Step Two of the framework.

9.2.2 Designation of landscape units

In many instances, profound differences in river

character and behavior may be evident in differing

landscape units. In the River Styles framework,

the designation of landscape units builds on the

CSIRO Land Systems Unit approach (e.g., Gunn

et al., 1969). Various landscape and environmental

factors are combined, such as relief, rainfall, elevation, geology, and vegetation coverage. In each

land systems unit, environmental factors are sufficiently consistent that a characteristic array of

landscape-forming processes occurs, producing

distinctive sets of soil, vegetation, and landforms

(i.e., ridges, spurs, fans, valley floor, etc.). Hence,

landscape units are readily identifiable topographic features with a characteristic pattern



258



Chapter 9



Table 9.1 Parameters used to identify landscape units.

Identifying characteristics



Significance



Physiographic character or

landscape morphology



Characteristic pattern of landforms (e.g., shape and size of ridges, shape and smoothness of

mountains and hills) can be related to long-term controls on landscape evolution, such as

the tectonic setting, structural geology and lithology, rate and extent of escarpment

retreat, sea-level adjustments, hydrological and climatic conditions. These in turn dictate

the character of the valley setting in which River Styles operate.

Landscape position is important as it dictates the process zone distribution (i.e., whether it

acts as a source, transfer or accumulation zone for water and sediment). Characteristic

within-catchment patterns of landscape units may be discerned. For example, uplands are

commonly found upstream of rounded foothills, which are found upstream of the lowland

plain.

Geological controls on landscape morphology, and hence river character and behavior, are

manifest through structural and lithological controls. Structural controls dictate the

alignment and configuration of valleys, induced by patterns of folding, faulting, etc., and

associated factors that determine the degree and patterns of landscape dissection.

Lithological controls determine the availability and caliber of material, dictated in part by

the weathering regime. These factors not only influence the structure of a river, but also

affect its capacity to adjust (i.e., its sensitivity to change).

Gross differences in relief provide some indication of the degree to which the landscape is

dissected (i.e., a measure of drainage density). This in turn affects the delivery of sediment

and water into the river system. As such, the peakedness, geomorphic effectiveness and

lagged effects of flow can be determined and inference made about how that may dictate or

impact on river morphology.



Landscape position



Geology



Relief



of landforms. Identification and mapping of landscape units is undertaken on the basis of physiographic character, landscape position, geology, and

relief (Table 9.1). Examples of landscape units

include: tablelands, uplands, mountains, escarpment, rounded foothills, low-lying hillslopes, and

lowland plain. A map showing the distribution of

landscape units in the catchment is produced (e.g.,

Plate 9.1). Elevation, longitudinal valley slope, and

valley width are tabulated to characterize each

landscape unit (Table 9.2). These descriptors represent fundamental controls on river character

and behavior. In many instances, landscape unit

boundaries are demarcated by distinct breaks in

slope along longitudinal profiles, indicating downstream changes in valley width and elevation that

result in a transition in River Style. An example of

the summary table of landscape unit attributes for

Bega catchment is presented in Table 9.3. These

considerations form a basis for assessing controls

on the character and behavior of River Styles, as

discussed in Stage One, Step Three of the frame-



work, wherein each River Style is viewed in context of its landscape unit setting.

9.2.3 Longitudinal profiles and contributing area

Longitudinal profiles record downstream changes

in elevation, and hence slope, along a river. Given

that slope is a primary control on river character

and behavior, changes in slope along a longitudinal

profile often coincide with landscape unit and/or

River Styles boundaries. Overlaying longitudinal

profiles from different subcatchments can be used

to compare downstream changes in slope and

assess tributary–trunk relationships. Superimposition of River Styles boundaries onto longitudinal profiles enables analysis and interpretation of

controls on the downstream patterns of River

Styles in Stage One, Step Three.

In the River Styles framework, longitudinal

profiles are constructed using DEM data. Contributing area plots are superimposed onto the longitudinal profiles. This defines the area draining



Stage One of the River Styles framework



259



Table 9.2 Descriptors used to characterize landscape units.

Descriptors of landscape units

Elevation



Valley slope



Valley width



Significance

Elevation can be used as an explanatory descriptor for landscape position. For example,

tablelands in coastal catchments of NSW are generally found in headwater regions at

elevations above 1000 m. In contrast, lowland plains are generally observed at elevations

below 50 m. Elevation may be a primary control on climate patterns. It must also be noted

that elevation can be highly variable for each landscape unit.

Slope is a primary control on the nature and rate of geomorphic processes, whether viewed in

terms of the movement of water and sediment on slopes, on the valley floor, or the

connection between the two. Breaks in slope along the longitudinal profile often fall at the

boundaries of the landscape units. In addition, the slope of the longitudinal profile is one of

the key controls on river character and behavior in each landscape unit.

Significant changes in valley width commonly define the boundary between landscape units.

Valley width is a significant control on the character and behavior of each River Style found

in each landscape unit. Although general trends can be discerned, valley widths are often

highly variable within landscape units and between subcatchments. Valley width is a key

determinant of the valley setting within which a river operates.



into each section of the river (i.e., a surrogate for

discharge), providing a visual summary of changes

in catchment area along the river. It is often instructive to note (and explain) whether the character and behavior of the trunk stream changes

downstream of tributaries. Examples of the products derived from the use of longitudinal profiles

are presented in Figure 9.5.

9.2.4 Analysis of catchment

morphometric parameters

Geomorphologists have developed a wide range of

morphometric parameters with which to characterize landscape morphology. Examples include

drainage pattern, drainage density, catchment

shape (elongation ratio), stream power, etc. While

it is not essential to measure all these parameters

in every River Styles assessment, these descriptors

may later be used to highlight differences between

subcatchments (and assess downstream patterns

of River Styles).

9.2.5 Analysis of discharge and

hydrological regimes

The timing and frequency of flows influence

the capacity of a river to adjust its morphology,

while the sequencing of floods affects the geomor-



phic effectiveness of any given event (i.e., its

capacity to perform geomorphic work). To assist

in the analysis of flow regimes as controls on

the range and downstream pattern of River

Styles, a series of graphs and tables are produced

including:

• regional catchment area-discharge plots for a

range of flood recurrence intervals (2, 5, 10, 50, 100

years);

• catchment-specific flood history plots, with an

assessment of within catchment variability (if

available);

• flow duration curves;

• log Pearson III plots from the most reliable gauge

records in the catchment;

• calculation of various flood magnitude indices

(e.g., Q10/Q2).

Hydrological analyses undertaken in applications of the River Styles framework provide an

appreciation of what scale of event is the dominant

control on river morphology, and how frequently that type of flood occurs. Estimates of

stream power are plotted on longitudinal profiles

and inundation frequencies are indicated on

River Styles cross-sections. From this, triggers

for geomorphic changes are assessed at differing

positions within the catchment and at differing

stages of evolutionary adjustment (Stages Two

and Three).



260



Chapter 9



Table 9.3 Parameters used to identify and describe landscape units in Bega catchment.

Parameter/

Landscape unit



Uplands



Escarpment



Dissected

plateau with

relatively

deep incised

valleys



Steep face incised

with deep

gorges



Tongue shaped

or elongate

deep valleys

that form

downstream

from the

escarpment



Landscape

position



Atop the

escarpment



Between uplands

and central

catchment



Geology

Relief



Largely granites

~ up to 400 m

> 600 m reaches

a maximum

of 1070 m

Flat to < 3

Up to 60 m



Identifiers

Physiographic

character or

landscape

morphology



Descriptors

Elevation (asl)



Longitudinal valley

slope (degrees)

Valley width



Base of

escarpment



Rounded

foothills



Lowland plain



Flay, low lying plain

with low lying

adjacent

hillslopes



At the base of the

escarpment,

where valley

exists from a

gorge



Rounded hills that

form ridges

dividing each

subcatchment.

These ridges

extend from the

base of the

escarpment in

many cases

Between the base

of the

escarpment

and the

lowlands



Largely granites

400–600 m



Largely granites

~ 250 m



Largely granites

~ 180 m



Downstream of the

rounded foothills

where valleys

widen

significantly.

Feeds into the

estuary

Largely granites

~ 15 m



> 200 m



150–400 m



15–200 m



< 15 m



> 15



10–15



3–10



Flat to < 3



< 60 m



Up to 300 m



10–150 m



Up to 1500 m



Note:

Five landscape units have been identified in Bega catchment, namely uplands, escarpment, base of escarpment, rounded foothills, and

lowland plain. The upland landscape unit is characterized by steep slopes, reflecting dissection of the plateau. It is only prominent in

Bemboka, Tantawangalo, and Candelo subcatchments, as the headwaters of other subcatchments lie in the escarpment zone. This differing configuration of landscape units at the upstream end of the subcatchments plays a significant part in determining river morphology in

downstream landscape units, especially at the base of the escarpment. Although the base of the escarpment landscape unit is found in all

subcatchments, there is pronounced variability in River Style (and response to human disturbance) in this part of the catchment. The differing length of these base of escarpment tongues, and the extent of sediment accumulation in this landscape unit, account for many of

the differences in river character in differing subcatchments. In aerial terms, the rounded foothills are the most significant landscape unit

in Bega catchment. This landscape unit comprises valley sidewalls of 8–15°, and is dissected by a multitude of lower order channels. The

rounded foothills, and the lowland plain, have been almost entirely cleared of vegetation. The lowland plain extends to the Pacific Ocean,

although lower Bega River flows through a bedrock-confined reach (Bottleneck Reach) prior to its estuary.



9.2.6 Presentation of the regional

setting chapter

Typically, the regional setting chapter of a River

Styles report comprises a series of summary tables,

plots, and maps. Short paragraphs of text highlight

trends and characteristics, but there is little in the



way of interpretation. Emphasis is placed on summarizing information that is pertinent to assessment of catchment-scale controls on river

character and behavior in Stage One, Step Three.

The following format is suggested for this chapter:

• geology;

• soils;



Stage One of the River Styles framework



261



• land-use character (including vegetation coverage) and history (including clearance, invasion of

exotics, etc.);

• topography (including landscape units, long profiles, catchment morphometric parameters)

• climate;

• hydrological analysis;

• settlement history and population trends.



9.3 Stage One, Step Two: Definition and

interpretation of River Styles

9.3.1 Analysis of river character: Parameters

used to identify River Styles



Figure 9.5 Longitudinal profiles and contributing area

plots along two contrasting river courses in Bega

catchment

(a) All subcatchments that drain directly from the

escarpment (e.g., Wolumla Creek) have relatively

smooth concave-up forms with occasional bedrock

steps downstream of the escarpment zone. These steps

act as local base level controls, dictating the slope of

valley segments and hence the morphology of river

courses. At the base of the escarpment a gentle break in

slope is transitional to the rounded foothills landscape

unit. These tributary subcatchments tend to be short

with relatively small catchment areas. (b) All

subcatchments that drain from atop the escarpment are

characterized by a distinctly stepped profile in their

upper sections where river courses are dissected into the

plateau country. This stepped zone is transitional to a

concave-up profile downstream of the escarpment

zone. However, the break in slope at the base of the

escarpment is distinct along these river courses. Again

occasional bedrock steps occur along these river courses

downstream of the escarpment. These streams tend to

be long with significant catchment areas (e.g., Bega

River).



River Styles are identified on the basis of a mix

of three key parameters: channel planform, the

assemblage of geomorphic units that make

up a reach (both channel and floodplain components), and bed material texture. The mix

varies depending on the degree of insight each

parameter provides into river character and behavior in each valley setting. For example, analysis of

channel planform for an alluvial river provides the

key initial differentiation between River Styles,

whereas bed material texture is the key defining

characteristic of confined (bedrock-controlled)

rivers.

9.3.1.1 Valley setting

The entry point into identification of a River Style

is the valley setting. Valley settings are differentiated on the basis of the degree of lateral confinement, expressed by the presence/absence and

distribution of floodplains along river courses. The

confining medium can be either bedrock valley

margin and/or cemented materials preserved in

terraces (a form of antecedent control on contemporary river morphology). Valley confinement

controls the capacity of the channel to adjust

over the valley floor, determining patterns of sediment storage and reworking. Inevitably, the degree

to which river morphology reflects an imposed

condition extends along a continuum from 100

to 0%. As in all classification schemes, the spectrum of variability must be differentiated into

meaningful classes, recognizing that some overlap



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Chapter 9



of river character and behavior may occur between

classes.

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.

9.3.1.2 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.



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