Landcare ICM Report No.
200X-200Y/XX
Motueka Integrated Catchment Management Programme Report Series:
<insert report title here>
<insert date
here>
<Type report number here if applicable>
River bank styles and effects of vegetation on bank stability –
a pilot assessment
Prepared for
Stakeholders of the
Motueka Integrated Catchment Management Programme
June 2008
ii
Landcare ICM Report No.
200X-200Y/XX
Motueka Integrated Catchment Management Programme Report Series:
<insert report title here>
<insert date
here>
River bank styles and effects of vegetation on bank stability –
a pilot assessment
Motueka Integrated Catchment Management
(Motueka ICM) Programme Report Series
by
C.J. Phillips & M. Marden
Landcare Research
PO Box 40
Lincoln
NEW ZEALAND
Phone: 03 321 9775
Fax: 03 321 9998
Email: phillipsc@LandcareResearch.co.nz
Information contained in this report may not be used without the prior consent of the client
Cover Photo: Bank erosion in the Orinocco River, Motueka catchment.
iii
Landcare ICM Report No.
200X-200Y/XX
Motueka Integrated Catchment Management Programme Report Series:
<insert report title here>
<insert date
here>
PREFACE
An ongoing report series, covering components of the Motueka Integrated Catchment
Management (ICM) Programme, has been initiated in order to present preliminary research
findings directly to key stakeholders. The intention is that the data, with brief interpretation, can
be used by managers, environmental groups and users of resources to address specific questions
that may require urgent attentin or may fall outside the scope of ICM research objectives.
We anticipate that providing access to environmental data will foster a collaborative problemsolving approach through the sharing of both ICM and privately collected information. Where
appropriate, the information will also be presented to stakeholders through follow-up meetings
designed to encourage feedback, discussion and coordination of research objectives.
iv
Landcare ICM Report No.
200X-200Y/XX
Motueka Integrated Catchment Management Programme Report Series:
<insert report title here>
<insert date
here>
INTRODUCTION ............................................................................................................................................................ 1
METHODS ........................................................................................................................................................................ 2
RESULTS .......................................................................................................................................................................... 2
1. Literature Review ........................................................................................................................................................... 2
River classification .................................................................................................................................................... 2
Stream bank erosion and morphology....................................................................................................................... 3
Riparian vegetation and bank erosion ...................................................................................................................... 4
Field assessments ...................................................................................................................................................... 6
2. Field assessment and development of bank styles .......................................................................................................... 6
Implications for management .................................................................................................................................... 6
CONCLUSIONS & RECOMMENDATIONS ............................................................................................................... 7
ACKNOWLEDGEMENTS ............................................................................................................................................. 8
REFERENCES ................................................................................................................................................................. 8
Appendices ....................................................................................................................................................................... 11
Appendix 1 – Field data dictionary ......................................................................................................................... 11
Appendix 2 – Preliminary classification of bank types ............................................................................................. 1
v
Introduction
Catchment erosion, sediment transport and sediment effects on the freshwater and marine habitats
of the Motueka River catchment and Tasman Bay are some of the key issues that the ICM Motueka
research programme is addressing.
A number of strands of investigation have enabled us to build a picture of the current status of the
catchment and its contribution to the sediment issue (eg., sediment sources (Marden et al 2004),
sediment yield (Wild et al 2006), substrate character (Basher 2006; Basher & Young 2006), river
cross-sections (Henker & Basher 2006) and sediment modelling (Basher 2004).
A parallel stream of work has focussed on understanding riparian issues – condition (Phillips &
Marden 2004), classification (Langer & Rodgers 2003), vegetation enhancement (Langer et al
2008), native plant trials (Marden et al 2005, 2007) – largely because in a catchment management
sense, management within the riparian margins of rivers systems is often the place where
interventions take place and where the greatest gains for the least loss of productive land occur. It is
also where the terrestrial and freshwater ecosystems intersect.
Much has been written on stream channel behaviour and how natural stream channels might be
classified. There is a complex set of interactions between the many processes that govern the shape
or form of a river and many researchers over the years have managed to dissect these complex
processes and have provided valuable dimensions to the discreet individual physical processes
associated with the natural functioning of the river and its catchment. In more recent times, there
have been attempts at arranging the results of this more detailed research into a form that can be
utilised to make a common statement about a river and several classification schemes have arisen
such as the River Styles Framework (Brierley and Fryirs 2005) and the Rosgen classification
(Rosgen 1996). Both of these go into significant depth on the interactions and complexity of the
processes that lead to the various physical river and bank morphologies we can observe.
There have also been a number of reports and papers on river bank erosion that deal with its
assessment (Thorne et al 1996), protection (Environment Agency 1999), and the use of vegetation
for stabilisation (Abernethy and Rutherfurd 1999, 2000, 2001).
Despite the recognition that riparian vegetation influences riverbank stability, many of the
mechanical and hydrological mechanisms involved are yet to be fully quantified. In particular,
although empirical research (e.g. Abernethy and Rutherfurd, 2001; Simon and Collison, 2002) has
advanced our knowledge of the relative importance of each of these mechanisms in certain
environments, results are not necessarily transferable. This is because vegetation influences bank
stability via a complex suite of process mechanisms that vary in effectiveness as a function of
environmental characteristics. The net effects on bank stability at an individual site are therefore
difficult to predict.
From our field observations of rivers and streams within the Motueka River and its tributaries, and
from looking at the role of vegetation and how it controls (or not) river bank erosion we posited that
it might be possible to develop a simple field-based assessment of a river bank’s stability based on
its morphology or form. Further, we suggested that it might be possible from such a simple
assessment of bank form, the likelihood that vegetation would stabilise that bank.
1
This report outlines a pilot assessment of stream bank form to determine if it would be possible to
devise a simple system – stream bank styles – that could be used to determine current bank stability
and the stabilisation potential by vegetation.
Methods
A review of the literature was carried out to determine if an existing classification of river bank
stability based on form was already available. In addition, related literature on river classification,
river bank stability and the use of vegetation to manage river bank erosion was also assessed.
The second part of the project was a field assessment of a selection of stream reaches within the
Motueka River catchment. The selection of stream reaches was based on those that were within the
managed part of the catchment rather than within the conservation estate. This was because the sites
in the conservation estate are not managed in order to retain their ‘naturalness and those in the
productive parts are generally where management interventions are made in order to protect or
maintain that productive use.
Reconnaissance-level stream bank assessments were made during the summers of 2005 and 2006.
In addition field work was also carried out in February 2006 and in 2007 as part of sediment source
and substrate characterisation work within the wider catchment.
Observations from assessments made as part of developing a riparian typology (Phillips & Marden
2004) for the catchment were also included. At each location, a range of information was collected
and the points were spatially referenced. Details of the characteristics assessed as part of this study
are listed in Appendix 1.
The third objective was to determine if a simple assessment of bank form could be used as a way to
assist in determining if banks were suitable or not for stabilising with vegetation.
Results
1. Literature Review
River classification
River classification schemes are now widely used by a range of government agencies, managers and
researchers to help reach an understanding of river form and process among the geomorphic
complexity found in river channels, as a basis for understanding ecosystem patch dynamics and
connections, and as means of organising and prioritising research and management activities
(Spencer et al 2007). Most existing schemas are generally qualitative, relying largely on expert
judgement to delineate “homogeneous geomorphic reaches” for a specific river, from field, GIS,
and/or remotely sensed data.
As outlined in the introduction, there has been much written about classifying rivers and the
processes that form them. Since streams in their stable form take on many various combinations of
dimension, pattern, profile, and materials within a wide range of valley slopes, sediment size,
sediment load, and streamflow, river classifications are used to stratify and describe various river
types (eg. Rosgen 1994, 1996; Brierley & Fryirs 1995). These river classifications integrate
individual variables into a morphological description that combines various forms of the existing as
well as "probable state" variables.
2
Two of the most common river classifications are those used and developed in the US (Rosgen
1994, 1996) and in Australia (Brierley & Fryirs 1995). Both have their advocates and detractors.
There is not one universally accepted system that is used and many variations exist and are often
adapted for local conditions. All approaches however, acknowledge the complex interaction
between form and process.
Some, such as River Styles® (Brierley & Fryirs 1995), outline four stages that move beyond just
the geomorphic approach for examining river character, behaviour, condition and recovery potential
and into the realm of providing a physical template for river management. This approach has also
been used in New Zealand in Auckland (Reid et al 2007).
Stream bank erosion and morphology
Stream bank morphology records the balance of erosional and depositional processes induced by
the alignment and energy of flow at differing flow stages. It is also a function of bank composition
and texture (Brierley and Fryirs 1995). Stream bank erosion is a natural geomorphic process which
occurs in all channels as adjustments of channel size and shape are made to convey the discharge
and sediment supplied from the stream catchment. However, increases in sediment supply due to
accelerated stream bank erosion are often linked to land-use change and are a major contributor to
sediment yield in rivers. The cause of local bank instability can be difficult to isolate and identify.
Regardless of the wider geomorphological context, the nature and extent of local bank erosion at
some specific point along a riverbank are controlled by:
1. local discharge;
2. channel shape (cross-section and planform);
3. location of eroding bank section (i.e. inner or outer bank);
4. bank geometry;
5. bank geotechnical properties;
6. bank hydrological properties; and
7. vegetation (Abernethy and Rutherfurd 1999).
With the exception of vegetation, each of the above factors is dependent on local conditions.
However, generalised descriptions usefully identify the broad interactions of vegetation with each
of the three erosion process groups: mass failure, fluvial scour, and subaerial preparation.
In a review of bank erosion assessment, measurement and modelling Watson & Basher (2005)
concluded that in New Zealand there is little data on the contribution of bank erosion to measured
river sediment yields and it has been a poorly studied process. The following section is taken from
their report where more detailed descriptions can be found.
Bank erosion includes two main groups of processes:
 hydraulic processes at or below the water surface entrain sediment and directly contribute to
erosion, particularly of non cohesive banks, by processes of bank undercutting, bed
degradation, and basal cleanout.
 gravitational mass failure processes (including shallow and rotational slides, slab and
cantilever failures, earthflows and dry granular flows) detach sediment primarily from
cohesive banks and make it available for fluvial transport.
Bank erosion process can be classified into two basic groups, those dominated by gravitational or
mechanical failures and those where hydraulic-induced failure mechanisms (fluvial erosion)
dominate. The circumstances under which these processes occur are determined by bank material
characteristics and local soil moisture conditions. Table 1 summarises seven main bank erosion
3
mechanisms and indicates typical sediment and moisture conditions associated with each of these
process.
Mechanisms
Classification
Wedge
failure
Popout
failure
Gravitational
Typical flow
conditions
Low
Sediment
characteristics
Fine-grained
cohesive
Fine-grained
cohesive
Bank
moisture
Varies
Gravitational
Low
Preferential
flow induced
failure
Hydraulic/
gravitational
Low
Interbedded
fine/coarse
Saturated
Cantilever
failure
Gravitational
Low
Composite
fine/coarse
Varies
Undercutting
Fluvial
High
Generally
Non-cohesive
N/A
Bed
degradation
Fluvial
High
Relatively
erodable bed
N/A
Basal
cleanout
Fluvial
Varies
N/A
N/A
Saturated
Description
Tension
cracks
formed
behind bank
Small blocks forced out of
bank due to excessive pore
pressure and overburden
Selective removal of coarse
material due to preferential
flow. Removal of support
during rapid drop in stage
Tension cracks form near
base of cantilever. Linked to
under cutting
Shear stress applied to lower
bank. In general
rate
increases with discharge.
Shear stress applied to
channel bed. Banks failure
due
to
gravitational
mechanisms
Banks made unstable by
removal of material at base.
Table 1
Bank erosion mechanisms (after O’Neill and Kuhns 1994, Thorne 1998,
Environment Agency 1999)
Bank height and slope are critical factors when assessing stream bank erosion potential. Failures
take place when the erosion of the bank and the channel bed adjacent to the bank, have increased
the bank’s height and steepness (slope) to a point where it reaches a condition of limiting stability.
The mechanics of failure then depends on the properties of the bank material and the geometry of
the bank at the point of collapse.
As indicated above, the bank morphology or form reflects a range of imposed conditions and the
balance between erosion and deposition processes along a river channel. Similarity of form may
reflect a range of different processes and history of formative events
Riparian vegetation and bank erosion
Riparian vegetation has different impacts on stream processes depending upon its position in a
catchment. Riparian vegetation interacts with a range of geomorphological, geotechnical,
hydrological and hydraulic factors to affect the type and extent of riverbank erosion (Thorne 1990;
Abernethy and Rutherfurd 1999). Increasingly in New Zealand and elsewhere, native vegetation is
becoming the favoured stream management tool to meet a range of needs relating to catchment
health. Vegetation may provide a range of services depending on its type and density. These
services include provision of bank stabilisation, contaminant filtering, enhancing terrestrial habitat
for improved biodiversity, creating ecological connections between habitats and so on.
While riparian vegetation has been cast in a positive light in terms of the services that it provides, it
is worth remembering that bank erosion is a natural process and that given enough time, even fully
vegetated natural streams will erode over their flood plains. A healthy, vegetated riparian zone
4
should not be expected to provide absolute stability to a stream. Further, in many degraded streams,
there are many situations in which vegetation alone will not stabilise streams or their banks, and it is
important to recognise such situations. On vegetated banks, factors such as the type and density of
vegetation, its age and health are also important because they directly control the vegetations’
influence, which may be either to enhance or reduce bank stability (Thorne 1990).
Bank erosion processes and failure mechanisms act in different ways to produce bank retreat.
Vegetation also plays a central role in bank accretion and berm building. These effects have
important implications for the use of vegetation in schemes to protect and stabilise riverbanks.
Reinforcement of the bank sediment by roots, transpiration and improved bank drainage all act to
enhance river bank stability. On the other hand, wind loading and the additional weight of riparian
trees have often been implicated in the failure processes of bank sections within vegetated reaches.
Possibly the most important way that trees affect bank stability is by increasing the strength of bank
material with their roots. Ground cover species do not generally contribute to the mass stability of
banks because of their limited root depth. Bank material strength is a function of its internal angle
of friction, and cohesion. The effect of small roots is to increase the effective cohesion of the
sediment. The literature suggests that small roots of Northern Hemisphere species can increase
cohesion by about 20% on average but in some cases by as much as 50% (Greenway 1987; Coppin
and Richards 1990). Abernethy and Rutherfurd (1999) suggest from Australian studies that the
effects of tree roots may be even greater than this, with perhaps up to a ten-fold increase in cohesion
close to the trunks of riparian trees, falling to about a two-fold increase under the dripline. Longer
and more firmly anchored roots provide greater reinforcement than do their shorter and loosely
anchored counterparts. Mature trees thus provide more reinforcement than younger trees.
The extra weight or surcharge of trees on a river bank is often thought to encourage the banks to
collapse (Gray and Sotir 1996). Tree surcharge on the top of a bank is especially pronounced when
the trees lean over the channel as a result of growth asymmetry, grazing of the bankward side only,
or wind loading (Thorne 1990). However work by Abernethy (1999) showed that the effect of tree
surcharge on bank stability, even those that appeared to be detrimental was marginal.
Bank vegetation increases the flow resistance and reduces the forces of drag and lift acting on the
bank surface thus reducing scour. However, the degree to which this happens is very dependent on
many factors, including the type of vegetation. While grasses and shrubs are effective at low
velocities, their impact decreases as velocities increase, and is all but eliminated once the stems are
prone. Conversely, the stems of woody vegetation continue retarding the flow up to very high
velocities, but may generate scour through the local acceleration of flow around their trunks.
Vegetation density and plant (tree) spacing are also important as they can also affect patterns of
scour and turbulence. On the other hand, vegetation provides a level of erosion resistance to the soil
itself by protecting the soil surface directly and introducing additional cohesion over and above the
intrinsic cohesion the bank material may have. Further vegetation also affects the local soil moisture
and in general terms, vegetated banks are better drained and drier than unvegetated ones. For a
vegetation cover to provide effective protection, it must cover the bank down to the low water level.
Otherwise, erosion at low flows will undercut the bank below the root zone, reducing the overall
stability. Uniformity of cover is also important if localised eddying and scour are to be avoided.
Abernethy and Rutherfurd (1999) concluded that to understand the role of vegetation in stream bank
erosion and stability, one must:
1. understand the processes of bank erosion;
2. appreciate that different processes may dominate at different points within the catchment;
3. consider the influence of vegetation on each of the processes;
5
4. determine those properties of vegetation that effect each of the processes; and
5. quantify the effect of vegetation on the processes acting in different parts of the river
system.
Field assessments
Any field assessment of bank erosion requires an assessment of the current conditions and needs to
be both simple and comprehensive. A number of methods have been devised (e.g. Thorne 1996,
Environment Agency 1999; etc) and although there are minor differences in the parameters assessed
at each site they generally collect similar information for either a point in a reach, a reach, one bank
or both banks.
2. Field assessment and development of bank styles
It has been difficult to determine a simple morphologically-based classification that might have
more universal application outside of the situations we have observed. While it has not been
possible to devise a strict classification system the pilot field assessment indicated that there are a
number of morphological characteristics that are relevant to the question of using vegetation to
stabilise stream banks.
In terms of treatment with vegetation, there were 3 main factors - bank geometry, bank height, and
bank composition which in various combinations can describe different types of banks. Of these
bank height is the major factor for determining if vegetation can be used to assist with stabilising
the banks. This is supported from both the literature and from our observations that bank heights
that are greater than 3m and perhaps some where between 2 and 3m are the maximum heights that
vegetation will have an active part in control of the banks stability (assuming plants are planted on
the top of the bank).This is dependent on the current erosion status i.e. active or passive. In the
active situation base planting and/or rip rap is likely to be a more successful treatment as top of
bank plantings will likely be undermined by fluvial activity
Secondly the slope of the bank is another key criterion where steep near vertical slopes are less
likely to be stabilised. However this largely depends on the activity of bank erosion high or low.
Thirdly the material composition plays an important part of whether vegetation can control banks –
layered sediments versus fine grained alluvium.
However based on the combinations of the factors outlined above it is possible to separate banks
into different “types”. These preliminary types are listed in Appendix 2 together with photographs
illustrating these differences.
In summary, there are a limited number of styles within the Motueka because of the narrow range of
bank materials which is largely influenced by the significant widespread nature of the Moutere
Gravels, and recent alluvium, much of which is derived from these materials. In comparison to
other regions, there is not the thick accumulation of overbank silts and sands found in soft-rock hill
country nor are there the slump-dominated bank profiles associated with deeply weathered bedrock.
Implications for management
In developing a strategy for the management of riverbank erosion problems, four guiding principles
have been established that set out a framework for appropriate, multi-functional responses to
perceived problems (Thorne et al 1996):
 Identify the cause of the bank erosion problem
 Seek a solution through active bank management
6


If active management is justified, match the scope, strength and length of bank covered by
the solution with the cause, severity and extent of the problem
Bear in mind the responsibility to balance conflicting goals in river management.
Frameworks and solutions for managing rivers have subsequently been developed in a number of
publications (Abernethy and Rutherfurd 1998; Environment Agency 1999; River Styles etc).
In assessing a range of stream and river banks in this pilot project it is clear that vegetation can help
stabilise river banks and prevent erosion but that it is unrealistic to expect revegetation to eliminate
all erosion (Abernethy & Rutherfurd 1999).
Soft or hard solutions?
Where a structural solution that involves physically protecting the bank is appropriate there is now a
wide range of designs and products that can be used including hard engineering materials like
concrete and steel through to softer materials such as geotextiles. Increasingly vegetation is
promoted in many situations as an integral component of bank stabilisation solutions either to hide
the hard structures or to actually be a part of the stabilising solution.
Many of the techniques and plants currently being employed and used in various parts of the world
have been rediscovered as many were in widespread use several centuries ago and pre-date the use
of concrete and steel. However, while some feel that vegetative solutions are innovative, it is
important to recognise that soft solutions are not appropriate in every situation.
Despite the recognition that riparian vegetation influences bank stability, many of the mechanisms
involved are yet to be fully quantified. In particular, although empirical research (e.g. Abernethy
and Rutherfurd, 2001; Simon and Collison, 2002) has advanced our knowledge of the relative
importance of both mechanical and hydrological mechanisms in certain environments, results are
not necessarily transferable. This is because vegetation influences bank stability via a complex suite
of process mechanisms that vary in effectiveness as a function of environmental characteristics. The
net effects on bank stability at an individual site are therefore difficult to predict.
The large differences between species (either exotic or native) in terms of their ability to increase
riverbank stability, means that revegetation strategies with this objective in mind should consider
carefully the species to be planted. Using sound ecological practice suggests that a mix of species is
preferable, not only for the benefit of other organisms that may inhabit the environment but also for
the health of the vegetation itself; single species plantings may well be more prone to attack by pest
and disease. Employing the use of a single species based simply on the fact that it may have greater
soil reinforcement potential, may in fact undermine the perceived benefits by compromising the
overall health of the plantings.
Conclusions & recommendations
Bank erosion is not a single process. It encompasses a wide variety of hydraulic and gravitational
mass failure processes. The two process groups are often linked with hydraulic processes causing
gravitational failures. Identification of bank erosion processes is important for determining suitable
measurement techniques and for choosing appropriate remedial options.
Bank erosion assessment provides an alternative to detailed measurement, which in practice can
only be carried out in a few selected locations. A minimum bank assessment data set for
determining the contribution of bank erosion to an overall sediment budget, identifying
7
representative sites for detailed measurement and determining controls on bank erosion would
include: location (GPS, toe, slope or bank top, left or right bank), extent (length of feature, height of
bank), type of sediment (cohesive or non-cohesive, particle size, stratification), type of failure and
contributing processes (e.g., freeze/thaw, water drawdown), toe sediment accumulation, general
evidence (e.g., exposed roots, undercut banks), severity of erosion/bank stability, geometry of the
bank (height, slope, profile shape), evidence of cracking, vegetation, channel geomorphic unit,
protection status.
The pilot assessment carried out in the Motueka catchment suggests that it might be possible to
develop a generic set of bank styles that could be used to aid in the design of treatment options for
bank stabilisation using vegetation. However, the lack of variation seen across the catchment limits
its development in this situation. However there is still scope to expand the concepts beyond the
Motueka to include different regions and thus develop a system based on observations from places
where there is more variability in the factors that control the form of river banks.
Acknowledgements
Alex Watson is thanked for assisting with initial field work. Landowners of the Motueka River
catchment and its tributaries are thanked for granting access across their land.
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Thorne, C.R. 1998: Stream Reconnaissance Handbook. John Wiley and Sons Ltd, Chichester,
England, 133 pp.
Thorne, C.R., Reed, S., Doornkamp, J.C. 1996: A procedure for assessing river bank erosion
problems and solutions. University of Nottingham R&D Report 28, National Rivers Authority,
Bristol,UK.
Wild M, Hicks DM, Merrilees R 2006. Suspended sediment monitoring in the Motueka catchment:
data report to 1 May 2006. NIWA Client Report: CHC2006-087 July 2006.
http://icm.landcareresearch.co.nz/knowledgebase/publications/public/NIWA_data_report_chc2006_
087.pdf
10
Appendices
Appendix 1 – Field data dictionary
River Character Data Dictionary
River or stream name,
GPS position 1
Left bank
Right bank
Centre of river
GPS position 2
Upstream
Downstream
Centre of feature
Feature location
Left bank
Right bank
Both
Length (m)
Height (m)
Land-use top of bank, Within 10m of bank top/edge
Pasture
Horticulture
Plantation
Conservation
Mixed
Other
Can't tell
Veg top of bank
None
Sparse
Dense
Can't tell
Veg on bank
None
Sparse
Dense
Veg toe of bank
None
Sparse
Dense
Veg type, Woody and non-woody
Exotic
Native
Mixed
Veg age
Young
Mature
Old
Mixed
Can't tell
11
Exotic Woody Type, Mostly about willows
Willows
Gorse
Poplars
Other
Don't know
Weed-OMB infested, OMB, blackberry etc
Yes
No
Vegetation comments
Bank stability signs
Current activity
Low
Low-medium
Medium
Medium-high
High
Past activity, Evidence of past erosion
Yes
No
blank
Bank protection type
Bio-engineering
Hard engineering
Combination
None
Landform affected, Type affected by erosion
Floodplain
Low terrace
Intermediate terrace
High terrace
Hillslope colluvium
Hillslope rock
Protection condition
Good
Fair
Poor
Can't tell
BP Veg type
Brush layering
Poles
Single spaced trees
Flax or reeds
Combination
Control with veg?, None now but possible in future i.e. <2m
Yes
No
Maybe
Can't tell
Control veg type
Toe
12
Bank
Toe & bank
Channel
Not sure
BP comments
Biod enhancement?
Yes
No
Can't tell
Riparian fencing?
None,
Left
Right
Both
Stock access
Yes
No,
Photo taken
Yes
No
Photo number/camera, text, 30
Style comments
Sediment type
Cohesive
Non cohesive
Mixed
Dom sediment size
Boulders
Pebbles/cobbles
Sand/silt
Rock
Stratification
Uniform
Stratified sand/silt
Stratified sand/grav
Bank profile
Straight
Concave
Convex
Stepped
Complex
Failure type
Gravitational
Hydraulic
Grav+Hydr
Grav failure type
dry granular flow
soil fall
wedge
cantilever
rotational
13
slide
earthflow
piping
popout
Hydr failure type
undercutting
bed degradation
basal cleanout
Contributing process
freeze-thaw
rilling
gullying
stock damage
WL drawdown
bank toe sediment
absent
boulders
pebbles/cobbles
sand/silt
CGU
pool
run
riffle
step pool
waterfall
multiple
bar
CGU comment
Stream curvature
Outside of bend
Inside of bend
Straight
Channel sinuosity
low
medium
high
General comments
14
Appendix 2 – Preliminary classification of bank types
Type
1
Description
Treatment option
Reason
Example
Vertical bank incised in Channel/ base planting and/or rip Rooting depth limited
bedrock
rap
by bedrock and no
soil
2
Vertical
bank
indurated gravels
in Channel/ base planting and/or rip Rooting depth limited
rap
by bedrock and no
soil
1
3
Vertical
bank
Holocene alluvium
in If <1m plant on top and /or Rooting depth ok for
Channel/ base planting and/or rip plants to get roots
rap else >1m Channel/ base planting down
and/or rip rap
4
Vertical bank in modern If <1m plant on top and /or Rooting depth ok for
alluvium
Channel/ base planting and/or rip plants to get roots
rap else >1m Channel/ base planting down
and/or rip rap
2
5
6
Vertical
bank
combinations
of
materials - alluvium over
bedrock
Vertical
bank
combinations
of
materials - alluvium over
indurated gravels
If <1m plant on top and /or
Channel/ base planting and/or rip
rap else >1m Channel/ base planting
and/or rip rap
If <1m plant on top and /or
Channel/ base planting and/or rip
rap else >1m Channel/ base planting
and/or rip rap
3
7
Non-Vertical
bank Channel/ base planting and/or rip
incised in bedrock
rap
8
Non-Vertical bank
indurated gravels
in Channel/ base planting and/or rip
rap
4
9
Non-Vertical bank
Holocene alluvium
in Height not relevant - plant on top
and/or on bank and /or Channel/
base planting and/or rip rap
10
Non-Vertical bank
modern alluvium
in Height not relevant - plant on top
and/or on bank and /or Channel/
base planting and/or rip rap
5
11
Non-Vertical
combinations
materials –
over bedrock
12
Non-Vertical
bank
combinations
of
materials – alluvium
over gravels
Stepped alluvium
13
bank If <1m plant on top and /or
of Channel/ base planting and/or rip
alluvium rap else >1m Channel/ base planting
and/or rip rap
If <1m plant on top and /or
Channel/ base planting and/or rip
rap else >1m Channel/ base planting
and/or rip rap
Height not relevant - plant on top
and/or on bank and /or Channel/
base planting and/or rip rap
Notes:
1. Bank Materials
 Bedrock
 Motueka gravels
 Alluvium over bedrock
Need 80% of bank face in substrate type to be classed as dominant
2. Bank Geometry
 Vertical
 Stepped
 Graded
3. Height
6


<1 m
>1 m
4. Assumed erosion active
7