EN 15843:2025

SLOVENSKI STANDARD
oSIST prEN 15843:2024
01-oktober-2024
Kakovost vode - Navodilo za določanje stopnje spreminjanja hidromorfoloških
značilnosti vodotokov
Water quality - Guidance standard on determining the degree of modification of river
hydromorphology
Wasserbeschaffenheit - Anleitung zur Beurteilung von Veränderungen der
hydromorphologischen Eigenschaften von Fließgewässern
Qualité de l'eau - Guide pour la détermination du degré de modification de
l'hydromorphologie des rivières
Ta slovenski standard je istoveten z: prEN 15843
ICS:
13.060.10 Voda iz naravnih virov Water of natural resources
13.060.45 Preiskava vode na splošno Examination of water in
general
oSIST prEN 15843:2024 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

oSIST prEN 15843:2024
oSIST prEN 15843:2024
DRAFT
EUROPEAN STANDARD
prEN 15843
NORME EUROPÉENNE
EUROPÄISCHE NORM
August 2024
ICS 13.060.45 Will supersede EN 15843:2010
English Version
Water quality - Guidance standard on determining the
degree of modification of river hydromorphology
Qualité de l'eau - Guide pour la détermination du degré Wasserbeschaffenheit - Anleitung zur Beurteilung von
de modification de l'hydromorphologie des rivières Veränderungen der hydromorphologischen
Eigenschaften von Fließgewässern
This draft European Standard is submitted to CEN members for enquiry. It has been drawn up by the Technical Committee
CEN/TC 230.
If this draft becomes a European Standard, 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.

This draft European Standard was established by CEN 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,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and
United Kingdom.
Recipients of this draft are invited to submit, with their comments, notification of any relevant patent rights of which they are
aware and to provide supporting documentation.

Warning : This document is not a European Standard. It is distributed for review and comments. It is subject to change without
notice and shall not be referred to as a European Standard.

EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2024 CEN All rights of exploitation in any form and by any means reserved Ref. No. prEN 15843:2024 E
worldwide for CEN national Members.

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prEN 15843:2024(E)
Contents Page
European foreword . 3
Introduction . 4
1 Scope . 5
2 Normative references . 5
3 Terms and definitions . 5
4 Principle . 9
5 Approach . 10
5.1 Spatial scales and delineating spatial units . 10
5.2 River and floodplain hydromorphological type . 10
5.3 Hydromorphological reference conditions . 10
5.4 Modification bands . 12
6 River valley segments . 12
6.1 General. 12
6.2 River flow regime . 13
6.3 Sediment delivery . 13
6.4 Longitudinal connectivity . 14
6.5 Lateral connectivity . 15
7 River reaches . 16
7.1 Longitudinal connectivity . 16
7.2 Lateral connectivity . 17
7.3 River channel long and cross profile and planform (evidence of direct human
interventions) . 18
7.4 River channel long and cross profile and planform (evidence of channel dynamics in
response to human interventions) . 19
7.5 River bed and bank character . 20
7.6 Instream vegetation . 21
7.7 Geomorphological features . 22
8 Interpreting and reporting hydromorphological modifications . 23
8.1 General. 23
8.2 Using bands assigned to individual properties to describe the degree of modification
of river hydromorphology . 23
8.3 Combining bands assigned to several properties to summarize the degree of
modification of river hydromorphology . 24
9 Quality assurance in obtaining and analysing data . 24
9.1 Qualifications and experience . 24
9.2 Training . 24
9.3 Certification, data entry and validation . 25
Bibliography . 26

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European foreword
This document (prEN 15843:2024) has been prepared by Technical Committee CEN/TC 230 “Water
analysis”, the secretariat of which is held by DIN.
This document is currently submitted to the CEN Enquiry.
This document will supersede EN 15843:2010.
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Introduction
This document will enable broad comparisons to be made of river hydromorphological modifications
throughout Europe (e.g. for reporting by the European Environment Agency). The assessment of river
‘quality’ in Europe has evolved over the past 30-40 years. From its original focus on organic pollution it
now relies on methods for analysing a range of chemical and biological attributes. More recently,
several European countries have developed systems for evaluating the hydromorphological features of
rivers. The EC Water Framework Directive (WFD) has reinforced the need for this broader view of river
‘quality’ through its requirement for determining ‘ecological status’ based on macrophytes,
phytobenthos, invertebrates and fish. The Directive also requires that hydromorphological and physico
chemical conditions should be suitable for supporting biological communities.
EN 14614:2020, Water Quality ― Guidance standard for assessing the hydromorphological features of
rivers describes a standard for field survey and feature recording, whereas this standard gives guidance
on assessing the modification of river hydromorphological features. It focuses especially on human
pressures that affect rivers; thus, it may be helpful for implementing the WFD by indicating the extent
to which these pressures might have caused a departure from hydromorphological reference
conditions. Although the procedure described in this standard enables the hydromorphological
characterization and assessment of rivers, it does not attempt either to describe methods for defining
high status for hydromorphology under the WFD or to link broadscale hydromorphological
classification to assessments of ecological status. However, the content of this standard has the
potential to contribute to both of these.
In addition to its relevance to the WFD, this standard has applications also for nature conservation,
meeting the goals of the Biodiversity Strategy (e.g. re-instating connectivity), environmental impact
assessment, river basin management, flood risk management (e.g. the EC Floods Directive) and setting
targets for river restoration work.
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1 Scope
This document provides guidance on characterizing the modifications of river hydromorphological
features described in EN 14614:2020. Both standards focus more on morphology than on hydrology
and continuity, and include a consideration of sediment and vegetation. This document will enable
consistent comparisons of hydromorphological forms and processes between rivers within a country
and between different countries in Europe, providing guidance for broad-based characterization across
a wide spectrum of hydromorphological modification of river channels, banks, riparian zones and
floodplains. Although of lesser focus, it considers the indirect effects of catchment-wide modifications to
these river and floodplain environments. Its primary aim is to assess ‘departure from naturalness’ as a
result of historical and modern human pressures on river hydromorphology, and it suggests suitable
sources of information (see EN 14614:2020, Table A.1) which may contribute to characterizing the
modification of hydromorphological properties. In doing so, it does not replace methods that have been
developed for local assessment and reporting.
Decisions on river management for individual reaches or catchments require expert local knowledge
and vary according to river type.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
EN 14614:2020, Water quality - Guidance standard for assessing the hydromorphological features of
rivers
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
aquatic vegetation morphotype
morphological character of aquatic vegetation, which combines the shape of the leaves, whether the
leaves are emergent, floating or submerged, and whether or not the vegetation is rooted in the river bed
3.2
armouring
where the river bed surface comprises coarser particles than the underlying river bed layers as a result
of removal (mobilization and transport) of the finer particles from the bed surface layer
[SOURCE: EN 14614:2020, 3.4]
3.3
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
[SOURCE: EN 14614:2020, 3.7]
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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.
3.4
bar
in-channel, elevated sediment deposit exposed during periods of low flow, which may 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]
3.5
bench
natural flat-topped shelf that evolves from a natural berm as further deposited sediment raises its
surface gradually to higher elevations within the river channel
[SOURCE: EN 14614:2020, 3.14]
3.6
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
[SOURCE: EN 14614:2020, 3.13]
Note 1 to entry: Natural berms are vegetated features composed of sediments deposited by the river to the
baseflow level.
3.7
biogeographical region
extended area, usually distinguished by its global position, climate and topography, within which
species live under broadly similar environmental conditions
3.8
confinement
degree to which the lateral movement of a river channel is confined by the presence of valley sides or
terraces
[SOURCE: EN 14614:2020, 3.21]
3.9
culvert
arched, enclosed or piped structure constructed to carry water under roads, railways and buildings
[SOURCE: EN 14614:2020, 3.25]
3.10
embankment
artificial bank built to raise the natural bank level thereby reducing the frequency of flooding of
adjacent land
[SOURCE: EN 14614:2020, 3.27]
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3.11
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]
3.12
flow regime
typical magnitude, frequency, timing, and duration of river flows that drive physical and some
ecological processes and so, within the constraints of valley slope and confinement, influence the sizes
and types of river channel that may be present
[SOURCE: EN 14614:2020, 3.30]
3.13
hydromorphology
morphological and hydrological characteristics of rivers including the underlying processes from which
they result
[SOURCE: EN 14614:2020, 3.36]
3.14
hydro-peaking
rapid and frequent fluctuations in flow resulting from hydropower generation to meet peak demands in
electricity
3.15
hyporheic zone
spatio-temporally dynamic ecotone between the surficial benthic substrate and the underlying aquifer
[SOURCE: EN 16772:2016, 2.13]
3.16
large wood
piece of wood that is more than 1 m long and 10 cm in diameter
[SOURCE: EN 14614:2020, 3.37]
3.17
lateral connectivity
freedom for water, sediments and biota to move between the channel and the floodplain/hillslopes
[SOURCE: EN 14614:2020, 3.39]
3.18
longitudinal connectivity
freedom for water, sediments and biota to move along the river channel
[SOURCE: EN 14614:2020, 3.41]
3.19
planform
geometric form of a river channel viewed from above
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EXAMPLE sinuous, straight
[SOURCE: EN 14614:2020, 3.43]
3.20
reach
section of river along which boundary conditions are sufficiently uniform that the river maintains a
near consistent internal set of process–form interactions
[SOURCE: EN 14614:2020, 3.47]
Note 1 to entry: In some situations, chemical changes along the length of a river, as well as physical and
hydrological ones, may also be important in defining river reaches.
3.21
reinforcement
strengthening of river beds and banks for various purposes (e.g. ford construction, erosion control)
using materials such as boulders, sheet piling, geotextiles, etc
[SOURCE: EN 14614:2020, 3.48]
3.22
ridge and swale
arcuate, alternating floodplain features, where the ridge is a rising, elongated deposit and the swale is a
depression, which develop from scrolls as they are incorporated into the floodplain
[SOURCE: EN 14614:2020, 3.49]
3.23
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)
[SOURCE: EN 14614:2020, 3.51]
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.
3.24
river channel cross profile
two-dimensional representation of river channel morphology perpendicular to the flow
[SOURCE: EN 14614:2020, 3.54]
3.25
river hydromorphological type
group of river channels displaying similar morphological and hydrological characteristics and their
associated processes
[SOURCE: EN 14614:2020, 3.55]
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3.26
river long profile
two-dimensional representation of river bed topography, where bed elevation is plotted against
longitudinal distance downstream along the channel
[SOURCE: EN 14614:2020, 3.56]
3.27
river morphodynamics
combination of the form and dynamics of a river
3.28
scroll
linear ridge deposit formed on point and counterpoint bars of meandering rivers, which, when
incorporated into the floodplain develop into ridges and swales
[SOURCE: EN 14614:2020, 3.60]
3.29
sluice
structure installed in a water course for controlling the flow of water
3.30
sediment transport
movement of sediment particles of a range of sizes by flowing water, which may include mobilization
and deposition
[SOURCE: EN 14614:2020, 3.61]
3.31
valley segment
section of river subject to similar valley-scale influences and energy conditions
[SOURCE: EN 14614:2020, 3.67]
3.32
weir
artificial structure across a river for controlling flow and upstream surface level, or for measuring
discharge
[SOURCE: EN 14614:2020, 3.70]
4 Principle
This document provides guidance for assessing the extent to which the hydromorphological features of
river channels, banks, riparian zones and floodplains or adjacent land (collectively river corridors) are
modified as a result of human actions.
This document recognizes that river corridors are dynamic and vary widely in their natural character. It
is applicable to all river types including those with only temporary flows. Although some modifications
such as channel straightening, bank and bed reinforcement and the imposition of other artificial
features by humans can be assessed regardless of the type of river under consideration, any thorough,
robust assessment needs to be set in the context of the hydromorphological type of river and floodplain
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under consideration and to consider driving processes as well as physical structure. Wherever possible,
assessment should take account of historical as well as contemporary information.
The document builds on EN 14614:2020, which provides guidance on assessing the
hydromorphological features of rivers. The information on hydromorphological features shall be
assembled according to EN 14614:2020 to provide the basis for assessing the degree of modification.
Following from EN 14614:2020, the present document is also not prescriptive but outlines a broad
approach to determining the degree of modification of river hydromorphology for two main reasons:
1) The natural driving processes of river-floodplain form and dynamics include not only physical
processes associated with flowing water and transported sediment but also the character and
vigour of local riparian and aquatic vegetation. As a result, the standard needs to be interpreted and
applied, recognizing the biogeographical region within which the river is located.
2) The quantity, quality and types of data available to support analysis and assessment may vary from
one location to another and so may influence the precise way in which the standard can be applied.
While the main aim of the document is to determine the degree of modification, it is based on separate
assessments of the nature as well as the degree of modification of hydromorphological properties of
river corridors. This information highlights the location, type and severity of modification and so
provides information relevant to river management (e.g. the design of river rehabilitation or restoration
efforts, improving biodiversity, resilience to the effects of climate change).
5 Approach
5.1 Spatial scales and delineating spatial units
Following the hierarchy of spatial units defined in EN 14614:2020 that govern the processes affecting
the hydromorphology of rivers, this guidance focuses mainly on the ‘segment’ to ‘reach’ scales.
(EN 14614:2020, Figure 1).
Thus, the first stage in preparing to undertake any assessment of the degree of modification of river
hydromorphology is to delineate the river reach(es) containing the section(s) of river to be assessed
and, in turn, the river segment(s) within which the reach(es) are located as well as those upstream. The
procedures for delineation of segments and reaches are provided, respectively, in EN 14614:2020
Clauses 6.5 and 6.6.
5.2 River and floodplain hydromorphological type
Having delineated river reach(es), the river hydromorphological type needs to be determined for each
reach. EN 14614:2020, Table C1 lists and describes 22 widely occurring river hydromorphological
types and their associated floodplain types based on the river channel’s planform and bed material size
and the degree to which the river segment containing the reach is confined by its valley. The list of river
hydromorphological types presented in EN 14614:2020, Table C1, is not exhaustive and so additional
types (e.g. postglacial) can be added to suit local environmental conditions.
The current river hydromorphological type and its evolution of planform is used to guide assessment of
the potential river and associated valley bottom or floodplain character in the absence of human
modification. Where the planform has been extensively modified by humans over an extended period, it
could be helpful to consult historical maps or find nearby less modified reaches with similar valley
confinement, valley gradient and bed material to establish an appropriate river hydromorphological
type for a particular site.
5.3 Hydromorphological reference conditions
EN 14614:2020 (Table 7) describes reference conditions for hydromorphological properties of a river
and its corridor. These properties are listed and described in Table 1 along with the spatial scale(s) at
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which each is assessed. The outcome of applying the standard described herein is an assessment of the
degree to which each of these properties fails to reach reference conditions at a particular site and thus
the degree of modification that is apparent.
Table 1 — Hydromorphological properties to be assessed at segment and reach scales and their
reference conditions
Hydromorphological
Reference
Spatial Scale for
Property (process or
Assessment
Conditions
form)
Segment and Reach Longitudinal Lacking any artificial instream structural
connectivity: modifications that affect the natural
Longitudinal flow of movement of water, sediment, other
water, sediment and materials and biota within the reach, the
other materials and upstream catchment, and downstream
organisms reaches that could have an upstream
influence
Segment and Reach Lateral connectivity: Lacking any artificial modifications that
Lateral flow of water, modify the flow of water, sediment, other
sediment and other materials and biota between the channel and
materials and adjacent floodplain and/or valley bottom or
organisms, and freedom prevent the lateral movement of the river
for lateral movement of channel
channel
Segment Hydrological and Having a flow regime and sediment delivery
sediment regime appropriate to the geographical location and
natural land cover of the catchment
Reach Vegetation Having undisturbed, fully natural riparian
and aquatic vegetation with a structure and
spatial distribution appropriate to the river
hydromorphological type and geographical
location
Reach River long profile Long profile not modified by human activities
such as steepening resulting from planform
straightening
Reach River channel cross Cross profile not modified by human
profile activities such as reprofiling, widening,
deepening
Reach River channel planform Planform not modified by human activities
such as straightening or blocking of side
channels
Reach River bed and bank Lacking any artificial instream and bank
character structures that disrupt natural
hydromorphological processes, including
exchanges with the hyporheic zone; bed and
banks composed of natural materials
Reach Geomorphological Having in-channel, bank or marginal and
features floodplain geomorphological features
appropriate to the river hydromorphological
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Hydromorphological
Reference
Spatial Scale for
Property (process or
Assessment
Conditions
form)
type
5.4 Modification bands
EN 14614:2020, Tables 1 to 6 provides lists of hydromorphological properties and their characteristics
that describe relevant processes and features at segment and reach scales and suggests data sources
and measurement units for each characteristic. The properties are grouped here in Table 1 to assess the
degree of modification of the properties listed. A comprehensive assessment of each property would
attempt to quantify and assess all of the relevant characteristics, but in practice this will rarely be
possible. Therefore, EN 14614:2020, Tables 1 to 6 should act as a guide to supporting the most robust
assessment of the degree of modification of a river corridor that is feasible at any specific site.
The outcome of an assessment is to recognize the degree to which a reach and its surrounding segment
have been degraded by human actions and to be able to identify the level and nature of degradation of
different hydromorphological properties. In this way reaches and segments can receive an overall
‘grading’ (see Clause 8) according to the integrated level of human modification and, at the same time, a
sound assessment of where and how improvements could be achieved to reinstate a more natural form
and function to the river corridor. At each stage of assessment, the level of human modification or
natural functioning/condition of the properties listed in Table 1 should use a five band scale:
1) negligible modification / near-natural functioning or condition;
2) slight modification / close to natural functioning or condition;
3) moderate modification / moderate degree of natural functioning or condition;
4) extensive modification / limited natural functioning or condition;
5) extreme modification / negligible natural functioning or condition.
Definitions of these modification bands are needed for each hydromorphological property listed in
Table 1. Where appropriate, these definitions can be adapted to local environmental conditions.
Furthermore, the bands can be assigned subjectively using expert judgement, or (semi)quantitatively
using available data sets. However, the unifying principle is that one of five bands should be assigned to
each hydromorphological property to represent the level of modification at an assessed reach and this
should be supported by information on the condition of the river corridor characteristics (listed in
Tables 1 to 6 EN 14614:2020) that are relevant to that property. To flag a completely unmodified
hydromorphological property, a band of 1* should be assigned.
6 River valley segments
6.1 General
Prior to conducting an assessment of human modifications, it is necessary to delineate the relevant
river valley segment(s) within which each assessed reach is located as well as those segments
upstream. A methodology for delineating river valley segments is outlined in EN 14614:2020 Clause 6.5.
Broad indicators of natural function and human constraints on natural function are assessed at the
segment scale as indicated in EN 14614:2020, Table 1.
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6.2 River flow regime
Where a river flow gauging station is present within or close to the segment, the current flow regime
can be quantified. A list of flow indicators is provided in EN 14614:2020, Table 2. Indicators can be
selected from this list to fit local circumstances. Where the gauging station record is sufficiently long,
past flow regimes can be similarly quantified. Where flow records are short, data from nearby segments
that are relatively free of human modification can be used to indicate the likely properties of the
contemporary natural flow regime. In all of these cases the aim is to estimate the degree and type of
change in river flows with the aim of finding critical changes that may have affected the river’s ability to
mobilize, transport and deposit sediment and also to support native riparian and aquatic plants.
Changes in flow indicators estimated by these means can be interpreted qualitatively and assigned to
modification bands (Table 2). Formal methods to estimate flow regime change are also available that
could aid in assessing the degree of flow modification.
Where flow records are not available, human influences on the flow regime can be qualitatively
assessed by synthesizing information on land cover and management, the number and size of
impoundments, diversions, hydro-peaking, abstractions and major discharges that influence flows into
the segment, using the information collected on longitudinal connectivity at the segment (Clause 6.3)
and reach (Clause 7.1) scales. Even where flow records are available, assessing the likely severity of
such human influences on the flow regime to the segment will support interpretation of quantitative
changes estimated from the flow records. Based on this evidence the degree of human modification of
flows delivered to the segment can be assigned to a band (Table 2).
Table 2 — Bands for describing the degree of human modification of the river flow regime
Band Description Comment
1 Near-natural flow regime No modifications to flow that have any notable
impact on the seasonal flow regime or the
magnitude-duration-timing of flow extremes
2 Slightly modified flow Modifications are small and have a very limited
regime impact on the seasonal pattern of flows and the
magnitude-duration-timing of flow extremes
3 Moderately modified flow Modifications have a notable impact on either the
regime natural seasonal pattern of flows or the magnitude-
duration-timing of flow extremes
4 Extensively modified flow Modifications have a notable impact on both the
regime natural seasonal pattern of flows and the magnitude-
duration-timing of flow extremes
5 Extremely modified flow Modifications have heavily modified the natural
regime seasonal pattern of flows and the magnitude-
duration-timing of flow extremes
6.3 Sediment delivery
A list of quantitative sediment delivery and transport regime indicators are provided in EN 14614:2020,
Table 2. Direct observations of sediment transport are rarely available but indirect quantitative
indicators can be assembled using simple modelling approaches. Therefore, this clause focuses on
sediment delivery or supply, rather than the sediment transport regime, which is the product of flow
regime and the supplied sediment. Any available data or modelled estimates describing sediment
delivery and transport are invaluable in informing the assessment of sediment delivery. However, as
flow regime alteration, which governs sediment mobilization, transport and deposition, has already
been assessed (Clause 6.1), the focus here is on human activities that affect the volume and grain size of
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sediment delivered to the river channel. Such human activities need to be located on or be well-
connected to the river margins. Land cover or management activities such as arable or overgrazed
pasture fields, forestry activities, land drainage, irrigation return waters, open-cast mining, waste
disposal sites and unsurfaced tracks can increase total sediment delivery. This may also increase the
amount of fine sediment that can smother, infiltrate and clog the river bed and reduce hyporheic
exchanges. Sealed urban and road surfaces may reduce sediment delivery but also degrade the quality
of delivered sediments
Table 3— Bands for describing the degree of human modification of sediment delivery and
transport
Band Description Comment
1 Near-natural sediment No notable human modifications to sediment
delivery delivery to the segment
2 Slightly modified sediment Some small human modifications (increases or
delivery decreases) to sediment delivery into and along the
segment but not sufficient to significantly change
sediment and landform dynamics within the
segment.
3 Moderately modified Human modifications sufficient to have a notable
sediment delivery impact on the volume and grain size of sediment
delivery (e.g. increased delivery of sand and finer
sediment to a gravel or coarser bed river), which
could lead to local changes in the character of the
river bed and its landforms.
4 Extensively modified Human modifications sufficient to change the
sediment delivery sediment supply and lead to widespread changes in
the grain size and elevation of the bed, bank erosion
or advance, channel size and position, and floodplain
aggradation or degradation.
5 Extremely modified Human modifications sufficient to change the
sediment delivery sediment supply and lead to spatially continuous
changes in the grain size and elevation of the bed,
bank erosion or advance, channel size and position,
and floodplain aggradation or degradation.
6.4 Longitudinal connectivity
Three types of major disruption of longitudinal connectivity are listed in EN 14614:2020 Table 1:
— major structures in the river channel (e.g. major dams, large weirs);
— major sites of sediment removal from the river bed;
— major discharges, abstractions and diversions.
These need to be investigated within segments extending as far upstream and downstream as
necessary to assess their likely impact on the longitudinal connectivity of water, sediment, organic
material and ‘physical engineer’ organisms (particularly plants) to the reaches under consideration. In
relation to the presence of major structures in the river channel, it is also necessary to search
downstream to identify structures that may be having a backwater effect of on any investigated reaches.
The term ‘major’ needs to be interpreted in relation to local environmental conditions. For example, in a
low gradient, lowland setting, a 5 m high weir could be considered ‘large’ because of its extremely large
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backwater extent, but in a steep mountain setting it would not have a sufficient hydromorphological
impact to be relevant at the segment scale. As the distance of each segment from the investigated
reaches increases, so the threshold size of a feature likely to cause disruption to the reaches also needs
to increase. Information regarding these three characteristics can be integrated (qualitatively or
quantitatively) to assign an appropriate descriptive band for modification of longitudinal connectivity
(Table 4).
Table 4— Bands for describing the degree of human modification of longitudinal connectivity at
the segment scale
Band Description Comment
1 Near-natural longitudinal No notable disruptions to downstream transfer of
connectivity water or sediment through the segment
2 Slightly disrupted Some disruptions to downstream transfer of water
longitudinal connectivity or sediment but these are small in the context of the
size and environmental setting of the river
3 Moderately disrupted Disruptions present with notable local effects on
longitudinal connectivity connectivity through the segment
4 Extensively disrupted Disruptions sufficient to affect connectivity to a
longitudinal connectivity significant degree through the segment.
5 Extremely disrupted Disruptions have almost completely removed
longitudinal connectivity longitudinal connectivity through the segment
6.5 Lateral connectivity
Lateral connectivity between the river and its corridor at the segment scale is indicated by four
characteristics listed in EN 14614:2020, Table 1:
— % floodplain accessible by flood water (e.g. absence of embankments or deepening of the river
bed);
— average riparian corridor width (i.e. that part of the river corridor that encloses all patches of true
riparian vegetation);
— % river bank length under riparian vegetation;
— % river bank length bordered by trees.
Information regarding these four characteristics can be integrated (qualitatively or quantitatively) to
assign an appropriate descriptive band for modification of lateral connectivity (Table 5). Where rivers
are naturally confined, lateral connectivity is a more local process but it can be disrupted by
construction of infrastructure along the river or valley margins, and should be assessed in relation to its
effect on downstream transfer of sediment and wood.
Table 5 — Bands for describing the degree of human modification of lateral connectivity
between the river and its valley bottom or floodplain at the segment scale
Band Description Comment
1 Near-natural lateral Valley bottom and/or floodplain fully accessible by
connectivity floodwaters and mainly covered by riparian
vegetation
2 Slightly disrupted lateral Valley bottom and/or floodplain almost entirely
oSIST prEN 15843:2024
prEN 15843:2024(E)
connectivity accessible by floodwaters with widespread patches
of riparian vegetation that are near-continuous
along the river margins
3 Moderately disrupted A large proportion of the valley bottom and/or
lateral connectivity floodplain is accessible by floodwaters and riparian
vegetation is present in places with extended
patches along the river margins.
4 Extensively disrupted Access to the valley bottom and/or floodplain by
lateral connectivity floodwaters is limited and riparian vegetation is
extremely restricted in area and is patchy
5 Extremely disrupted lateral Access to the valley bottom and/or floodplain by
connectivity floodwaters is negligible or absent and the cover of
riparian vegetation is negligible.
7 River reaches
7.1 Longitudinal connectivity
Major disruptions to longitudinal connectivity were considered at the segment scale and reaches would
normally be defined so that such major disruptions are not included within a reach. Indeed, any major
structures in the river channel (e.g. large dams, large weirs) would normally be used to demarcate an
end of a reach. Reach-scale assessments need to focus on smaller barriers and management
interventions that are present within the reach. Five types of reach-scale human modifications that
disrupt longitudinal connectivity are listed in EN 14614:2020, Tables 4 and 5:
— bed reinforcement (including artificially introduced boulders or rubble),
— artificial barriers crossing the channel (weirs, sluices, culverts, bridges),
— artificial barriers encroaching from the banks into the channel (bridge piers, deflectors, jetties),
— sediment removal,
— vegetation management (aquatic vegetation, in-channel large wood).
The first three are human modifications that reduce the transfer of water or sediment downstream. The
last two are human activities that reduce the natural regulation of water and sediment transfer through
the reach. All five need to be investigated within the reach in question and then integrated to assign an
appropriate descriptive band for modification of longitudinal connectivity (Table 6).
Table 6 — Bands for describing the degree of human modification of longitudinal connectivity at
the reach scale
Band Description Comment
1 Near-natural longitudinal No notable disruptions to downstream transfer of
connectivity water or sediment through the reach
2 Slightly disrupted Some disruptions to downstream transfer of water
longitudinal connectivity or sediment but these are small in the context of the
size and environmental context of the river
3 Moderately disrupted Disruptions present with notable local effects on
longitudinal connectivity connectivity through the reach
oSIST prEN 15843:2024
prEN 15843:2024 (E)
4 Extensively disrupted Disruptions are sufficient to significantly modify
longitudinal connectivity connectivity through the reach
5 Extremely disrupted Disruptions have drastically reduced longitudinal
longitudinal connectivity connectivity through the reach
7.2 Lateral connectivity
Lateral connectivity between the river and its corridor at the reach scale is indicated by nine
characteristics of the river channel and its margins and/or floodplain that are listed in EN 14614:2020,
Tables 5 and 6.
Three characteristics represent direct human disruptions to connectivity:
— embankments,
— bank reinforcement,
— other measures designed to prevent floodplain inundation and erosion (e.g. land drainage and river
bed lowering).
Six characteristics represent the level of connectivity and river floodplain functioning that is pre
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