SIST EN 18025:2026

SLOVENSKI STANDARD
01-marec-2026
Kakovost vode - Navodilo za strateški pristop k obnovi vodotokov
Water quality - Guidance standard on a strategic approach to river restoration
Wasserbeschaffenheit - Leitfaden für einen strategischen Ansatz zur Renaturierung von
Fließgewässern
Qualité de l'eau - Guide pour une approche stratégique de la restauration des rivières
Ta slovenski standard je istoveten z: EN 18025:2025
ICS:
13.020.70 Okoljevarstveni projekti Environmental projects
13.060.10 Voda iz naravnih virov Water of natural resources
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN 18025
EUROPEAN STANDARD
NORME EUROPÉENNE
September 2025
EUROPÄISCHE NORM
ICS 07.060; 13.060.99
English Version
Water quality - Guidance standard on a strategic approach
to river restoration
Qualité de l'eau - Guide pour une approche stratégique Wasserbeschaffenheit - Leitfaden für einen
de la restauration des rivières strategischen Ansatz zur Renaturierung von
Fließgewässern
This European Standard was approved by CEN on 20 July 2025.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this
European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references
concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN
member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by
translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management
Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
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United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2025 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN 18025:2025 E
worldwide for CEN national Members.

Contents Page
European foreword . 3
Introduction . 4
1 Scope . 5
2 Normative references . 5
3 Terms and definitions . 5
4 Principle . 12
5 Aims of river restoration . 12
6 Spatial context and scale . 14
7 Spectrum of intervention . 14
7.1 General . 14
7.2 Natural recovery . 16
7.3 Assisted natural recovery . 17
7.4 Designed restoration . 17
8 Opportunities and constraints . 18
8.1 Factors to consider when planning river restoration . 18
8.2 Ecological effects on morphology, and the risks of intervention . 19
8.3 Socio-economic development, legacy land use and river regulation (restoration
constraints) . 19
9 Planning and implementation . 20
9.1 Approach to restoration . 20
9.2 The restoration process . 20
9.2.1 General . 20
9.2.2 Understanding the catchment . 22
9.2.3 Prioritize and set objectives . 23
9.2.4 Design and delivery . 23
9.3 Monitoring and appraisal . 23
9.3.1 General . 23
9.3.2 Designing a monitoring programme to assess the impact of restoration on the indicator of
interest . 24
9.3.3 Survey timing . 28
9.3.4 Choice of indicator variables . 28
10 Quality assurance . 29
10.1 General . 29
10.2 Qualifications, experience and training . 29
Annex A (informative) Case studies of river restoration projects to illustrate a range of
approaches to river restoration . 31
Annex B (informative) Case studies of monitoring to illustrate the physical and ecological effects
of river restoration . 43
Bibliography . 47

European foreword
This document (EN 18025:2025) has been prepared by Technical Committee CEN/TC 230 “Water
analysis”, the secretariat of which is held by DIN.
This European Standard shall be given the status of a national standard, either by publication of an
identical text or by endorsement, at the latest by March 2026 of DOP, and conflicting national standards
shall be withdrawn at the latest by March 2026 of DOW.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
Any feedback and questions on this document should be directed to the users’ national standards body.
A complete listing of these bodies can be found on the CEN website.
According to the CEN-CENELEC Internal Regulations, the national standards organisations of the
following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria, Croatia,
Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland,
Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of North
Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and the United
Kingdom.
Introduction
Most European rivers and their catchments no longer function naturally. This loss of natural functioning
is the result of human modification undertaken over many centuries for (among other things) flood
defence, hydroelectric power generation, the provision of water for agricultural, industrial, and domestic
consumption, land use and land drainage. These activities have often resulted in disturbed river
functioning and led to degraded physical habitats and, as a consequence, to reductions in biodiversity,
reduced resilience to flooding, drought and temperature extremes, and a decline in ecosystem services
such as recreation. Climate change is now compounding the issues created by human modification, and
the need to restore rivers will become increasingly pressing to ensure the conservation of their naturally
occurring habitats and species and the sustainable provision of their ecosystem services. Accordingly,
river restoration following a nature-based approach is an imperative requirement to allow river
ecosystems to recover, a concept advocated by the International Union for Conservation of Nature (IUCN)
[1].
River restoration is the act of returning natural functioning and form to a river that has been directly or
indirectly altered by human activity. Ideally it should result in uninterrupted lateral, longitudinal, and
vertical connectivity of hydraulic, sedimentary, chemical, thermal and biological processes, allowing
unhindered channel and floodplain evolution, and the associated mosaic of habitats that support a
characteristic array of flora and fauna. In many locations, physical and other constraints will affect what
restoration is practicable, but the ambition should be to achieve the greatest degree and spatial scale of
re-naturalization possible.
Rivers are restored for many reasons including to: re-establish natural patterns of water and sediment
movement and so remove the costs associated with managing modified channels; restore habitats and
biodiversity; manage flood risk through natural flood management; enhance the aesthetics of an area;
and create opportunities for recreation. Key policy and legal frameworks to drive river restoration within
the European context include the Water Framework Directive (WFD), Habitats Directive and the Floods
Directive. Furthermore, the EU Biodiversity Strategy 2030, and the UN Framework Convention on
Climate Change, for example, provide additional impetus for increased restoration efforts. Although the
motivation for restoring rivers and the extent to which rivers can be restored vary, a fundamental basis
common to all restoration projects should be the re-establishment of natural physical processes, leading
to the development of natural form and features, and the sustainable evolution of instream, riparian and
floodplain habitats. Activities such as adding gravel to construct specific spawning areas can be part of a
larger river restoration scheme, but are not by themselves considered to be river restoration unless they
are measures for restoring natural river processes.
Specifying the desired outcome of restoration is an essential element of any plan, and the meaningful
monitoring and appraisal of any project will depend upon the clarity in setting this goal.
1 Scope
This document gives guidelines for the restoration of rivers, including their channels, riparian zones and
floodplains. The word ‘river’ is used as a generic term to describe permanently flowing and intermittent
watercourses of all sizes, with the exception of artificial water bodies such as canals. Some aspects of
landscape restoration beyond the boundaries of what are often considered typical river processes are
also considered.
A clear framework of guiding principles to help inform the planning and implementation of river
restoration work is provided. These principles are applicable to individuals and organizations wishing to
restore rivers, and stress the importance of monitoring and appraisal. This document makes reference to
existing techniques and guidance, where these are appropriate and within the scope of this document.
This document gives guidelines on:
— the core principles of restoration;
— aims and overall outcomes of river restoration;
— the spectrum of typical approaches to river restoration with a focus on those that are nature-based
and restore both physical and ecological aspects;
— identifying opportunities for restoration and possible constraints, with a focus on physical and
natural rather than socio-economic aspects;
— different scales of restoration and how restoration works across different catchments and
landscapes;
— the importance of monitoring and appraising restoration work across the range of approaches and
scales.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https://www.iso.org/obp
— IEC Electropedia: available at https://www.electropedia.org/
3.1
bank
side of a river channel or island which extends above the normal (e.g. mean) water level and is only
completely submerged during periods of high river flow
Note 1 to entry: In the context of this document, the bank top is marked by the first major break in slope, above
which cultivation or development is possible.
[SOURCE: EN 14614:2020, 3.7]
3.2
bar
in-channel, elevated sediment deposit exposed during periods of low flow, which could be a side bar,
(including a point or counterpoint bar, located respectively along the convex or concave bank of a
meander bend) or a mid-channel bar
[SOURCE: EN 14614:2020, 3.9]
3.3
Before-After-Control-Impact
BACI
investigation of the effect of an Impact at a site by comparing the conditions ‘Before the Impact’ with
those ‘After the Impact’ while accounting for natural/background change through the use of a Control
site (see 3.11)
3.4
berm
natural or artificial, flat-topped shelf along the margin of a river channel that is exposed above water level
during low flows but is submerged during high flows
Note 1 to entry: Natural berms are vegetated features composed of sediments deposited by the river to the
baseflow level.
[SOURCE: EN 14614:2020, 3.13]
3.5
biodiversity
biological diversity
variability among living organisms from all sources including, inter alia, terrestrial, marine and other
aquatic ecosystems and the ecological complexes of which they are part; this includes diversity within
species, between species and of ecosystems
[SOURCE: Convention on Biological Diversity, Article 2 Use of Terms — Convention Text]
3.6
channel
main landform within river systems, conveying water
3.7
characterization
selection of properties or special features of a spatial unit that are uniquely relevant to identifying its
hydromorphological processes, forms and pressures
[SOURCE: EN 14614:2020, 3.19]
3.8
coarse sediment
sediment of grain size at or larger than very fine gravel (diameter ≥2 mm, ≤ −1 phi)
EXAMPLE Gravels, cobbles, boulders.
Note 1 to entry: The phi scale defines sediment grain size as the negative logarithm to the base 2 of the grain
diameter in millimetres.
[SOURCE: EN 14614:2020, 3.20]
3.9
confirmatory appraisal
process of confirming the expectations following a restoration intervention through simple observation
(cf. investigative appraisal)
3.10
control site
site representing (ideally identical) conditions to that of the Impact site except for the restoration
intervention
3.11
culvert
arched, enclosed or piped structure constructed to carry water under roads, railways and buildings
[SOURCE: EN 14614:2020, 3.25]
3.12
ecosystem services
benefits people derive from ecosystems
3.13
embankment
artificial levée
artificial bank built to raise the natural bank level thereby reducing the frequency of flooding of adjacent
land
[SOURCE: EN 14614:2020, 3.27, modified — the secondary term ‘artificial levee’ has been added]
3.14
equilibrium form
morphological condition of a river that represents physical balance (stable but not necessarily static)
3.15
fine sediment
sediment of grain sizes equal to or smaller than very coarse sand (diameter ≤2 mm, ≥2 phi), i.e. sands,
silt, clay
Note 1 to entry: The phi scale defines sediment grain size as the negative logarithm to the base 2 of the grain
diameter in millimetres.
[SOURCE: EN 14614:2020, 3.28, modified — Note 1 to entry added]
3.16
floodplain
valley floor adjacent to a river that is (or was historically) inundated periodically by flood waters and is
formed of sediments deposited by the river
[SOURCE: EN 14614:2020, 3.29]
3.17
fluvial audit
method for assessing the condition of a river and its associated human pressures, using information from
field survey, remote sensing, historical and recent maps, scientific literature and other sources
[EN 16859:2017, 3.18]
3.18
fluvial geomorphology
scientific study of the physical processes, form and functioning of rivers and streams and their physical
interactions with the surrounding landscape
[SOURCE: EN 14614:2020, 3.31]
3.19
hydrodynamic modelling
numerical tool or methodology used to predict hydraulic patterns in rivers
3.20
hydrology
study of the distribution and movement of water both on and below the Earth’s surface
3.21
hydromorphology
morphological and hydrological characteristics of rivers including the underlying processes from which
they result
[SOURCE: EN 14614:2020, 3.36]
3.22
hyporheic zone
spatio-temporally dynamic ecotone between the surficial benthic substrate and the underlying aquifer
[EN 16772:2016, 2.13]
3.23
impact site
site at which restoration intervention effects are measured
3.24
investigative appraisal
process of investigating the outcomes of a restoration intervention through an experimental approach
(cf. confirmatory appraisal)
3.25
large wood
piece of wood that is more than 1 m long and 10 cm in diameter
Note 1 to entry: ‘Wood’ refers to natural wood (e.g. tree branches)
[SOURCE: EN 14614:2020, 3.37, modified — Note 1 to entry added]
3.26
lateral connectivity
lateral continuity
freedom for water, sediments and biota to move between the channel and the floodplain/hillslopes
[SOURCE: EN 14614:2020, 3.39]
3.27
longitudinal connectivity
longitudinal continuity
freedom for water, sediments and biota to move along the river channel
[SOURCE: EN 14614:2020, 3.41]
3.28
meander
one of a series of regular, sinuous curves along the course of a stream
[SOURCE: EN 14614:2020, 3.42]
3.29
morphology
physical form and structure of a river
3.30
natural flood management
working with nature to reduce and control the impacts of flooding
3.31
nature-based solutions
actions to protect, sustainably manage and restore natural or modified ecosystems that address societal
challenges effectively and adaptively, simultaneously providing human well-being and biodiversity
benefits
Note 1 to entry: See IUCN Nature-based Solutions to address global societal challenges [21].
3.32
oxbow lake
small lake located in an abandoned meander loop of a river channel
3.33
palaeochannel
remnant floodplain feature indicating location of a previously active channel
3.34
planform
geometric form of a river channel viewed from above
EXAMPLE Sinuous, straight.
[SOURCE: EN 14614:2020, 3.43]
3.35
quantitative sampling
process of collecting measured information (e.g. flow measured in m s-1)
3.36
qualitative sampling
process of collecting information that is subjectively assessed
3.37
reach
section of river along which boundary conditions are sufficiently uniform that the river maintains a near
consistent internal set of process–form interactions
Note 1 to entry: In some situations, chemical changes along the length of a river, as well as physical and
hydrological ones, could also be important in defining river reaches.
[SOURCE: EN 14614:2020, 3.47]
3.38
restoration
establishment of natural physical processes (e.g. variation of flow and sediment movement), features (e.g.
sediment sizes and river shape) and physical habitats of a river system (including submerged, bank and
floodplain areas)
[SOURCE: EN 14614:2020, 3.57]
3.39
riparian zone
transitional, semi-terrestrial area of land adjoining a river channel (including the river bank) that is
regularly inundated and influenced by fresh water and can influence the condition of the aquatic
ecosystem (e.g. by shading and leaf litter input and through biogeochemical exchanges)
Note 1 to entry: Riparian corridor is the linear extension of this concept along a channel or reach length; in this
document, the term riparian zone does not include the wider floodplain.
[SOURCE: EN 14614:2020, 3.51]
3.40
river bed incision
process where a river has cut vertically to lower its bed
[SOURCE: EN 14614:2020, 3.53]
3.41
runoff
net discharge of water into the stream from surface-water and groundwater sources with losses
occurring from evapotranspiration and other consumptive uses
[SOURCE: EN 14614:2020, 3.58]
3.42
sediment transport
movement of sediment particles of a range of sizes by flowing water, which could include mobilization
and deposition
[SOURCE: EN 14614:2020, 3.61]
3.43
sinuosity
distance from upstream to downstream along the channel centre line between two points, divided by the
distance along the valley course between the same points
[SOURCE: EN 14614:2020, 3.63]
3.44
spatial unit
subdivision of a catchment at various geographical scales
EXAMPLE Catchment, landscape unit, valley segment, reach.
[SOURCE: EN 14614:2020, 3.64]
3.45
stream power
rate of energy dissipation against the bed and banks of a river per unit downstream length, which when
divided by channel width gives the specific stream power
[SOURCE: EN 14614:2020, 3.65]
3.46
substrate
material making up the bed of a river
[SOURCE: EN 14614:2020, 3.66]
3.47
vertical connectivity
freedom for water, biota and nutrients to move between the benthic substrate and the underlying aquifer
3.48
weir
artificial structure across a river for controlling flow and upstream surface level, or for measuring
discharge
[SOURCE: EN 14614:2020, 3.70]
3.49
wetland
habitat occupying the transitional zone between permanently inundated, and generally dry,
environments
EXAMPLE Marsh, fen, shallow temporary water.
[SOURCE: EN 14614:2020, 3.71]
3.50
WFD water body
length of river defined and delineated according to criteria outlined in the European Water Framework
Directive
3.51
xylophagous insect
adult or larva of insects that feed on or bore into wood
4 Principle
A standard protocol is described for planning, implementing, and monitoring river restoration and draws
on experience from around Europe and elsewhere to provide a common framework that can be applied
across a wide geographical range. This document, focused on nature-based solutions, gives guidance on
how to apply a strategic approach to practical restoration, but does not attempt to describe the detailed
methods used to restore rivers. It emphasizes that restoration should explicitly take account of the
dynamic nature of rivers and should be set within a catchment context, even when the scale of restoration
is relatively limited. This document recognizes that river restoration is carried out for many reasons, but
focuses especially on the importance of restoring hydromorphology for the benefit of biodiversity.
5 Aims of river restoration
River restoration is not simply engineering the physical form. It aims to understand and address the
modification and damage to river functioning, features and habitats, in the context of the river floodplain
corridor and its catchment, and to return the conditions that allow natural processes to operate
unhindered. At their simplest, such reference conditions refer to an absence of human interventions and
pressures, but these are not necessarily the desired conditions for the system or the river reach after
restoration. Reference conditions represent a benchmark against which to assess the degree of impact on
the present state of the river from human influence, and upon which restoration targets can be assessed
objectively. By restoring river processes, the movement of water and material (sediment and wood) from
the land (catchment area) to the mouth (estuary or inland lake) can shape and sustain a dynamic,
complex, physical environment and the characteristic flora, fauna and their habitats.
The restoration of physical processes, rather than simply recreating physical form:
— results in rivers that are more sustainable with the re-establishment of characteristic natural habitat;
— provides a focus on tackling the causes of degradation rather than its symptoms;
— creates conditions naturally more appropriate for specific sections of rivers that support
characteristic biodiversity;
— incorporates implicitly the dynamic physical processes that are a fundamental characteristic of a
naturally functioning river and essential to the evolution of diverse habitats;
— results in dynamic river environments that are more resilient and sustainable than an engineered
channel, particularly in the face of climate change;
— reduces construction and maintenance costs, by initiating or working with dynamic physical
processes that result in channel and floodplain evolution and associated habitat diversity;
— increases the likelihood of achieving wider ecosystem and societal benefits (i.e. ecosystem services)
(see Figure 1).
Figure 1 — Benefits to society provided by naturally functioning rivers and floodplains
The water quality and quantity necessary to sustain the expected biodiversity of a naturally functioning
river system also enables more cost-effective provision of drinking water (i.e. less treatment required)
and a sustainable supply of food and materials. A well-functioning system is able to cope better with
societal and economic demands, where those demands recognize the requirement for balance (e.g. water
companies investing in upstream catchment management to improve water quality and reduce water
supply costs).
Rivers that are fully connected to their floodplains (as opposed to those that have historically been
deepened and embanked) help to regulate flood risk by slowing and spreading flood waters, and by
reducing the height and delaying the peak of a flood. Restoring the floodplain’s hydrology in this way can
work with, or perhaps replace, more traditional flood protection measures and help to adapt to climate
change. Floodplains are important for fine sediment storage and for nutrient deposition and cycling,
through uptake by wetland/floodplain meadow/wet woodland communities. Reinstating these
processes has great potential benefit for carbon storage within the floodplain [2].
Many towns and cities were founded on the banks of rivers, thus benefiting from water supply, transport,
food resources and security. A restored clean, healthy, river rich in wildlife offers a focal open space in
often densely urbanized areas. River corridors provide routes for paths and cycleways, encouraging
exercise and access to nature, which promotes physical and mental health. Direct uses include fishing,
water sports, and wild swimming. Use and visual amenity promotes better awareness and social
understanding of the pressures and impacts on water and habitat quality, with pollution and other
deterioration being noticed rapidly and becoming more integrated in local policy and planning.
6 Spatial context and scale
River restoration work is often undertaken opportunistically – for example, when funding becomes
available or landowner agreement is secured. As a result, relatively small, reach scale interventions have
been most common to date. However, to address the fundamental impacts on natural processes (i.e. the
supply, transport and deposition of water, sediment and wood) that influence the physical and ecological
condition of the river environment, more ambitious and spatially extensive initiatives should be
promoted. To obtain the greatest sustainable improvements in river condition, restoration should be
applied at the largest spatial scale practicable. This should consider a catchment-scale strategy for
implementing specific restoration measures that can themselves be applied at the reach scale. Catchment
restoration measures applied beyond the river (e.g. planting native trees, increasing the amount of
wetland) can have indirect benefits for river corridors. The measures chosen should be assigned
priorities to optimize the cumulative benefit to the entire river system. Note that reach-scale
interventions can often have significant downstream benefits to physical processes and, therefore, to
ecological condition.
The importance of ensuring that the spatial context of any restoration is included at the planning stage is
now widely acknowledged. Whatever the scale of restoration, the work should take into account its
relative position within the catchment to ensure that any measures proposed are appropriate for the
physical conditions of that area that will subsequently affect the evolution of the restored section.
A detailed description of how to delineate and characterize spatial units (catchment, landscape, valley
segment, and river reach) is given in EN 14614:2020. This delineation and characterization identifies the
influences and controls on spatial units and will help to establish the most appropriate approach to
restoration.
Historical human influences on the natural evolution of rivers and the ecosystem services that they
provide means that restoration ambitions often need to be tempered to accommodate current land and
river management activities. Restoration planning should take such constraints into account to identify
and prioritize locations based on some assessment of the cost–benefit associated with undertaking a
range of appropriate measures. For example, if the impetus for restoration is to improve aquatic
biodiversity, focusing on headwaters or other smaller streams can in some instances lead to the greatest
return [3]. Any appraisal of restoration opportunities should include the scale of improvement that
restoration is likely to bring to physical and ecological conditions, and its effect on other uses of the river
environment; tools to assess ecosystem service provision are available. Not all locations warrant the
investment necessary to implement the appropriate restoration measures.
7 Spectrum of intervention
7.1 General
The river restoration spectrum covers a broad range of intervention approaches and styles that aim to
produce a more natural physical condition through degrees of reinstatement of active processes (i.e.
process restoration). At one end of the spectrum, measures to protect environments already in optimal
condition are important. Such locations can support restoration efforts elsewhere (i.e. support physical
and ecological connectivity between degraded sections of catchments) and they can act as analogues for
restoration reference conditions in nearby locations, and locations of the same hydromorphological type
under similar pressures. Mechanisms to protect these environments can include legal designations,
incentives and regulatory controls. However, natural recovery relies on the reinstatement of natural
physical processes to undertake most or all of the design work. At the other end of this continuum,
functional design does not require natural adjustment of physical form but ensures that appropriate
consideration of processes (i.e. that influence morphology) is incorporated into the design of the
restoration measure. In the middle, initial conditions design provides a starting point for the river in
which natural physical processes then adjust to an equilibrium form
This continuum provides a useful framework to categorize restoration techniques based on several
criteria, including potential costs, technical requirements and levels of expertise. It also recognizes the
different potential restoration outcomes likely to be achieved: for example, the naturalness,
sustainability, and the likely time scales to realize the benefits and the overall long-term effectiveness of
an approach.
At the catchment scale, effective restoration will inevitably incorporate approaches across the entire
spectrum of process reinstatement, working as a blended suite of interventions, and with site-specific
implementation measures reflecting differences in environments, constraints (physical and socio-
economic) and restoration aims.
The broad spectrum of intervention types of restoration included within this document (see Figure 2;
Table 1) are:
— natural recovery:
— assisted natural recovery:
— designed restoration:
— initial conditions design: and
— functional design.
Figure 2 — Spectrum of intervention
Table 1 — Key elements of the different restoration intervention approaches
Spectrum of intervention
Natural recovery Assisted natural recovery Designed restoration
Intervention No or minimal intervention Some intervention (removal Significant design and
type (e.g. fencing to prevent of constraints, e.g. engineering intervention (e.g.
excavation of a new channel
livestock access) redundant structures)
course)
Spatial scales Typically multi-reach or Typically reach or multi- Typically sub-reach to reach
catchment/sub-catchment. reach scale; can include scale; often in the channel and
Channel, floodplain and channel, floodplain and adjacent floodplain
adjacent landscape adjacent landscape
Time scales Multi-year to decadal with Annual to decadal scale with Sub-annual/annual to decadal
benefits accumulating over benefits accumulating over with benefits accumulating
time time over time, especially for initial
condition designs
Main benefits Naturally designed; focus on Initiated with lower levels of Tailored outcome with
processes and forms, intervention; natural designed criteria; benefits can
offering long-term processes and forms be established quickly; often
resilience; can adapt to restored; can adapt to future more predictable outcomes
future environmental change
change
Main risks Outcomes can be Outcomes can be Designs can be inflexible to
unpredictable; needs space unpredictable; initial efforts further changes; possible
and time to be effective can initiate unforeseen maintenance requirements
changes (e.g. channel
adjustment following weir
removal)
Costs Typically low capital and Moderate initial capital Design and engineering costs
continuing costs; low costs; low relative cost per incurred; moderate to high
relative cost per unit unit length/area relative cost per unit
length/area length/area; possible
maintenance costs
Continuing Often low maintenance Can require some initial Some continuing maintenance
maintenance needs as natural recovery intervention, although can be necessary, although
encourages self-maintaining longer-term maintenance good design options can
systems needs can diminish or minimize intervention
disappear
Suitability Where adequate energy, In areas where existing Where capacity for
space and time are available modifications can be geomorphological work is low
for recovery; less removed, potential for and/or constrained in areas
constrained environments geomorphological work to where possible risk to people
initiate restoration; low to or infrastructure
moderate constraints
7.2 Natural recovery
The focus of this restoration approach is to enable the river environment to adjust its physical condition
naturally and self-recover. In practical terms, the specific actions typically involve reducing or stopping
channel or floodplain maintenance, fencing off channel margins or palaeochannels and allowing the
colonization of native vegetation, all encouraging natural recovery. This approach can often require little
or no intrusive intervention or cessation of continuing maintenance. Over time, and undertaken in the
appropriate locations, channel naturalization will occur (e.g. the development of features such as bars,
berms, and side channels) that will tend to improve channel–floodplain connectivity and increase
physical complexity. The degree and rate of natural recovery depend on the level of disturbance (i.e.
typically, the level of artificial constraints to physical process) and the intensity of geomorphological
processes operating within that section of the catchment related to valley slope, hydrology, sediment
supply and large wood input. The full potential of such interventions will often not be realized for several
decades, depending on the controlling conditions of the site. This approach can work over large spatial
scales and provide a range of ecosystem service benefits. The specification of outcomes can be less certain
and the time taken to see improvements can be much longer than for more prescribed interventions. This
approach is more feasible in less constrained environments (e.g. without significant flood risk or without
transport networks).
7.3 Assisted natural recovery
This form of river restoration focuses on the removal of constraints that are acting to inhibit natural
physical processes, in conjunction with improvements to the riparian zone. (e.g. fencing to limit
overgrazing pressure). The constraints generally include engineering such as bank protection, flood
embankments and other instream structures (e.g. barriers, dams and culverts) and invasive non-native
species, which can affect bank stability. These actions provide the potential and space for natural
geomorphological processes to create greater physical heterogeneity and biodiversity. As with all
restoration initiatives, such activities require a clear understanding of how natural geomorphological
processes have been changed, both in the section of river of interest and in the upstream catchment.
Assisted natural recovery can be applied at the scale of multiple channel reaches, given the relatively low
levels of intervention required. This type of approach is perhaps particularly suited to locations where
moderate constraints to physical processes are associated with the potential for dynamic
geomorphological activity and with relatively low use of the river corridor by human activity (e.g.
farming, other infrastructure/services).
7.4 Designed restoration
This approach to restoration includes activities such as full channel realignment (e.g. re-meandering) or
channel/floodplain regrading following the removal of large structures such as dams and embankments.
It usually means that significant capital funding is required with specialist contractors employed to
design and implement the works, often in collaboration with stakeholder organizations. Lengths or areas
of restoration are typically classed as individual projects in their own right. These approaches commonly
focus on providing the river with a defined restoration form, determined through a detailed design
process, usually incorporating information from historical reconstruction, analogue sites,
geomorphological channel design theory, and hydrodynamic/sediment transport modelling. Depending
on the degree of practical constraints and the potential for geomorphological change within the area for
restoration, the design immediately after implementation will self-adjust to a dynamically stable
equilibrium form (i.e. initial conditions design). If not, the design should at least incorporate an explicit
consideration of processes that prescribes a form that is appropriate for the site (i.e. functional design).
These approaches are generally more suitable in less dynamic settings or where further physical changes
need to be controlled; for example, close to important infrastructure and common in urban settings. In
such heavily constrained urban environments, the restoration of physical processes and features might
not be possible or desirable. However, the restoration principles described above can offer opportunities
for some appreciable enhancements within these constrained settings. Urban development or
regeneration can provide opportunities to incorporate elements of initial condition and functional design.
8 Opportunities and constraints
8.1 Factors to consider when planning river restoration
Opportunities for active restoration of natural hydrological and morphological forms and processes
should be guided by a sound understanding of the capacity of the river environment to recover without
intervention, or very limited intervention. This can direct where intervention is likely to be most effective,
and whether a river can be left to restore itself by natural recovery. An assessment of the present and
potential future hydrological regime, morphological condition and dynamics should be carried out. This
should identify the degr
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