SIST EN 14614:2021
(Main)Water quality - Guidance standard for assessing the hydromorphological features of rivers
Water quality - Guidance standard for assessing the hydromorphological features of rivers
This document is focused on the structural features of rivers, on geomorphological and hydrological processes, and on river continuity. This document is focused on the structural features of rivers, on geomorphological and hydrological processes, and on river continuity. It provides guidance on the features and processes to be taken into account when characterizing and assessing the hydromorphology of rivers. The word ‘river’ is used as a generic term to describe flowing watercourses of all sizes, with the exception of artificial water bodies such as canals. The document is based on methods developed, tested, and compared in Europe, including the pan-European REFORM project (https://reformrivers.eu/). Its main aim is to improve the comparability of hydromorphological assessment methods, data processing and interpretation. It provides broad recommendations for the types of parameters that should be assessed, and the methods for doing this, within a framework that offers the flexibility to plan programmes of work that are affordable. Although this document does not constitute CIS guidance for the WFD, relevant references provided by the CIS expert group on hydromorphology have been included in the Bibliography.
Although it has particular importance for the WFD by providing guidance on assessing hydromorphological quality, this document has considerably wider scope for other applications. 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. In addition, while recognizing the important influence of hydromorphology on plant and animal ecology, no attempt is made to provide guidance in this area, but where the biota have an important influence on hydromorphology, these influences are included.
NOTE A case study illustrating the application of this document is given in Gurnell and Grabowski[1].
Wasserbeschaffenheit - Anleitung zur Beurteilung hydromorphologischer Eigenschaften von Fließgewässern
Der Schwerpunkt dieses Dokuments liegt auf den strukturellen Eigenschaften von Flüssen, auf geomorpholo¬gischen und hydrologischen Prozessen sowie auf der Durchgängigkeit von Flüssen. Dieses Dokument gibt eine Anleitung zu den bei der Charakterisierung und Beurteilung der Hydromorphologie von Fließgewässern zu berücksichtigenden Merkmalen und Prozessen. Das Wort „Fluss“ wird als Oberbegriff für fließende Wasserläufe aller Größen verwendet, mit Ausnahme künstlicher Gewässer wie Kanäle. Das Dokument beruht auf Verfahren, die in Europa entwickelt, geprüft und verglichen worden sind, einschließlich des europaweiten REFORM-Projekts (https://reformrivers.eu/). Das Hauptziel dieses Dokuments ist es, die Vergleichbarkeit der hydromorphologischen Beurteilungsmethoden, der Datenverarbeitung und der Interpretation zu verbessern. Es enthält umfassende Empfehlungen für die Arten von Parametern, die bewertet werden sollten, und die Methoden dafür in einem Rahmen, der die Flexibilität bietet, erschwingliche Arbeitsprogramme zu planen. Obwohl dieses Dokument keine CIS-Leitlinien für die WRRL darstellt, wurden relevante Referenzen der CIS-Expertengruppe für Hydromorphologie in die Literaturhinweise aufgenommen.
Obwohl es von besonderer Bedeutung für die WRRL ist, indem eine Anleitung zur Beurteilung der hydromorphologischen Beschaffenheit bereitgestellt wird, hat dieses Dokument einen erheblich größeren Geltungsbereich für andere Anwendungen. Es wird weder versucht, Methoden zur Definition eines hohen Status für die Hydromorphologie im Rahmen der WRRL zu beschreiben, noch eine breit angelegte hydromorphologische Klassifizierung mit Bewertungen des ökologischen Status zu verknüpfen. Obwohl der bedeutende Einfluss der Hydromorphologie auf die Pflanzen- und Tierökologie anerkannt wird, wurde darüber hinaus kein Versuch unternommen, in diesem Bereich eine Anleitung zur Verfügung zu stellen; die wichtigen Einflüsse der Biota auf die Hydromorphologie wurden jedoch einbezogen.
ANMERKUNG Eine Fallstudie, die die Anwendung dieses Dokuments veranschaulicht, ist in GURNELL und GRABOWSKI [1] enthalten.
Qualité de l'eau - Guide pour l'évaluation des caractéristiques hydromorphologiques des rivières
Le présent document se concentre sur les caractéristiques structurelles des rivières, les processus physiques et géomorphologiques, ainsi que sur la continuité de la rivière. Il fournit des recommandations relatives aux caractéristiques et processus à prendre en considération lors d’une caractérisation et d’une évaluation de l’hydromorphologie d’une rivière. Le mot « rivière » est utilisé en tant que terme générique pour décrire les cours d’eau de toutes tailles, à l’exception des plans d’eau artificiels, tels que les canaux. Le présent document se fonde sur les méthodes développées, testées et comparées en Europe, y compris le projet REFORM paneuropéen (https://reformrivers.eu/). Il a pour objectif d’améliorer la comparabilité des méthodes d’évaluation hydromorphologique, du traitement et de l’interprétation des données. Il fournit des recommandations relatives aux types de paramètres qu’il convient d’évaluer ainsi qu’aux méthodes d’évaluation, dans un cadre qui propose suffisamment de flexibilité pour prévoir des programmes de travail qui sont abordables. Bien que le présent document ne constitue pas des recommandations CIS pour la WFD, les références pertinentes fournies par le groupe d’experts CIS concernant l’hydromorphologie ont été incluses dans la Bibliographie.
Bien qu’il soit d’une importance toute particulière pour la WFD du fait qu’il fournisse des recommandations relatives à l’évaluation de la qualité hydromorphologique, le présent document peut également s’appliquer à de nombreux autres domaines. Il n’a pas pour objectif de décrire des méthodes permettant de définir un très bon état pour l’hydromorphologie selon la WFD ni de faire le lien entre la classification hydromorphologique à grande échelle et les évaluations de l’état écologique. En outre, malgré l’influence importante de l’hydromorphologie sur l’écologie végétale et animale, aucune recommandation n’est faite dans le présent document. Cependant, ces influences sont mentionnées dans les cas où les biotes exercent une influence cruciale sur l’hydromorphologie.
NOTE Une étude de cas illustrant l’application du présent document est fournie par Gurnell et Grabowski[1].
Kakovost vode - Navodilo za ocenjevanje hidromorfoloških značilnosti vodotokov
General Information
Relations
Standards Content (Sample)
SLOVENSKI STANDARD
01-januar-2021
Nadomešča:
SIST EN 14614:2005
Kakovost vode - Navodilo za ocenjevanje hidromorfoloških značilnosti vodotokov
Water quality - Guidance standard for assessing the hydromorphological features of
rivers
Wasserbeschaffenheit - Anleitung zur Beurteilung hydromorphologischer Eigenschaften
von Fließgewässern
Qualité de l'eau - Guide pour l'évaluation des caractéristiques hydromorphologiques des
rivières
Ta slovenski standard je istoveten z: EN 14614:2020
ICS:
07.060 Geologija. Meteorologija. Geology. Meteorology.
Hidrologija Hydrology
13.060.10 Voda iz naravnih virov Water of natural resources
13.060.70 Preiskava bioloških lastnosti Examination of biological
vode properties of water
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
EN 14614
EUROPEAN STANDARD
NORME EUROPÉENNE
September 2020
EUROPÄISCHE NORM
ICS 07.060; 13.060.70 Supersedes EN 14614:2004
English Version
Water quality - Guidance standard for assessing the
hydromorphological features of rivers
Qualité de l'eau - Guide pour l'évaluation des Wasserbeschaffenheit - Anleitung zur Beurteilung
caractéristiques hydromorphologiques des rivières hydromorphologischer Eigenschaften von
Fließgewässern
This European Standard was approved by CEN on 17 May 2020.
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,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and
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
© 2020 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN 14614:2020 E
worldwide for CEN national Members.
Contents Page
European foreword . 4
Introduction . 5
1 Scope . 6
2 Normative references . 6
3 Terms and definitions . 6
4 Principle . 14
5 Study context and requirements . 14
5.1 Investigating hydromorphology across both space and time . 14
5.2 Desk study . 15
5.3 Field survey . 16
5.4 Analysis and interpretation . 16
6 Delineation . 16
6.1 General . 16
6.2 Extent of delineation . 17
6.3 Catchments . 17
6.4 Landscape units . 17
6.5 Valley segments . 18
6.6 River reach units . 18
7 Characterization . 20
7.1 General . 20
7.2 Catchment to valley segment units . 20
7.3 River reach units . 22
8 Reference conditions . 31
8.1 Pristine reference conditions . 31
8.2 Near-natural reference conditions and processes . 32
9 Quality assurance in obtaining and analysing data . 33
9.1 Qualifications and experience . 33
9.2 Training . 33
9.3 Certification, data entry and validation . 34
Annex A (informative) Overview of some freely available pan-European data sets . 35
Annex B (informative) Explanations of the relevance of elements in this document . 38
B.1 Introduction . 38
B.2 Hydromorphological characteristics indicative of processes and human pressures at
spatial scales from catchment to valley segment (Table 1) . 38
B.3 Hydromorphological characteristics indicative of flow and sediment transport
processes (Table 2) . 39
B.4 Hydromorphological characteristics indicative of river channel size and type
(Table 3) . 40
B.5 Hydromorphological characteristics of the river bed (Table 4) . 41
B.6 Hydromorphological characteristics of the river channel (and large island) margins
(Table 5) . 42
B.7 Hydromorphological characteristics of floodplains (Table 6) . 43
Annex C (informative) River and related floodplain styles . 45
Bibliography . 50
European foreword
This document (EN 14614:2020) 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 2021, and conflicting national standards shall
be withdrawn at the latest by March 2021.
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.
This document supersedes EN 14614:2004.
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, Turkey and the
United Kingdom.
Introduction
In the past, many countries in Europe assessed river ‘quality’ simply in terms of water chemistry or
pollution within river channels. A more comprehensive understanding of rivers is needed, however, in
view of global issues such as climate change, to answer pressing ecological questions such as those
arising from the EC Water Framework Directive (WFD), the EC Habitats Directive and EC Floods
Directive, to underpin the International Convention on Biodiversity, or to assess proposed river
engineering work and to evaluate the effectiveness of restoration schemes and other catchment
developments.
River habitats and physical processes have suffered historically from a wide range of human impacts,
especially changes in land use since World War II. In most European countries there is now widespread
agreement among environment and conservation agencies to see modified rivers returned to a more
natural condition. This implies a need to evaluate areas deserving protection and those requiring
restoration, and to encourage sustainable management of river systems throughout Europe.
NOTE In this document, ‘assessment’ is used as a broad term referring to the general description of features
and the pressures affecting them. It is not used to imply the judgement of particular levels of ‘quality’ or ‘value’,
whether related to status under the WFD or more generally.
1 Scope
This document is focused on the structural features of rivers, on geomorphological and hydrological
processes, and on river continuity. It provides guidance on the features and processes to be taken into
account when characterizing and assessing the hydromorphology of rivers. The word ‘river’ is used as a
generic term to describe flowing watercourses of all sizes, with the exception of artificial water bodies
such as canals. The document is based on methods developed, tested, and compared in Europe,
including the pan-European REFORM project (https://reformrivers.eu/). Its main aim is to improve the
comparability of hydromorphological assessment methods, data processing and interpretation. It
provides broad recommendations for the types of parameters that should be assessed, and the methods
for doing this, within a framework that offers the flexibility to plan programmes of work that are
affordable. Although this document does not constitute CIS guidance for the WFD, relevant references
provided by the CIS expert group on hydromorphology have been included in the Bibliography.
Although it has particular importance for the WFD by providing guidance on assessing
hydromorphological quality, this document has considerably wider scope for other applications. 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. In addition,
while recognizing the important influence of hydromorphology on plant and animal ecology, no attempt
is made to provide guidance in this area, but where the biota have an important influence on
hydromorphology, these influences are included.
NOTE A case study illustrating the application of this document is given in Gurnell and Grabowski[1].
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 terminological databases for use in standardization at the following addresses:
— IEC Electropedia: available at http://www.electropedia.org/
— ISO Online browsing platform: available at https://www.iso.org/obp
3.1
aluvium
sediment deposited by rivers
3.2
anabranching river
river with more than one channel separated by vegetated islands
3.3
aquifer
underground layer of water-bearing permeable rock, rock fractures or unconsolidated materials
(gravels, sands) from which groundwater can be extracted
3.4
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
3.5
attribute
specific recorded element of a hydromorphological feature
EXAMPLE ‘Boulders’ and ‘silt’ are substrate attributes; ‘sheet piling’ and ‘gabions’ are attributes of
engineered banks.
3.6
backswamp
low-lying marshy area that lies between the valley margin and the natural levée of an alluvial channel
3.7
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.
3.8
bankfull
level at which water begins to spill out of the channel onto the floodplain
3.9
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
3.10
baseflow
sustained component of streamflow, usually resulting from drainage of groundwater, but also from
drainage of large lakes, swamps, soils, snow and ice packs
3.11
baseflow index
measurement of the ratio of the long-term baseflow to total stream flow, often representing the slow,
continuous contribution of groundwater to river flow
3.12
baseflow channel width, depth and slope
the width, depth and water surface slope of the part of the channel that conveys the baseflow
3.13
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.
3.14
bench
natural flat-topped shelf along the margin of a river channel that evolves from a natural berm as further
deposited sediment raises its surface gradually to higher elevations within the river channel
3.15
boulder step
accumulation of boulders (> 256 mm) transverse to and crossing the river channel creating a step in the
river’s long profile
3.16
braiding
river whose bankfull channel is naturally divided by mid-channel bars into at least two separate flowing
threads at baseflow
Note 1 to entry: See also ‘bar’.
3.17
burial
accretion of fine sediment over coarser bed material
Note 1 to entry: Burial is the opposite of armouring.
3.18
cascade
stream bed covered with disorganized boulders in steep confined channels
3.19
characterization
selection of properties or special features of a spatial unit that are uniquely relevant to identifying its
hydromorphological processes, forms and pressures
3.20
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.
3.21
confinement
degree to which the lateral movement of a river channel is confined by the presence of valley sides or
terraces
3.22
counterpoint bar
side bar type that develops in the flow separation zone along the concave bank of tight river bends
3.23
crevasse
breach in natural levée
3.24
crevasse-splay
local accumulation of sand or gravel, deposited by water escaping from the river channel through a
crevasse
3.25
culvert
arched, enclosed or piped structure constructed to carry water under roads, railways and buildings
[SOURCE: EN 15843:2010, 3.8]
3.26
dune
usually fine sediment (sand–silt) river bed feature typical of low-gradient, alluvial sand-bed rivers that
is linear in plan, aligned perpendicular to the flow, with a gentle upstream and steep downstream cross
profile
−1 1
Note 1 to entry: Dunes can be distinguished from ripples by their larger height (10 m / 10 m) and wavelength
(proportional to the water depth).
3.27
embankment
artificial bank built to raise the natural bank level thereby reducing the frequency of flooding of
adjacent land
3.28
fine sediment
sediment of grain sizes equal to or smaller than ‘very coarse sand’ (≤ 2 mm diameter, ≥ 2 mm −1 phi),
i.e. sands, silt, clay
Note 1 to entry: The phi scale defines sediment grain size scale as the negative logarithm to the base 2 of the
grain diameter in millimetres.
3.29
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
3.30
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 could be present
3.31
fluvial geomorphology
scientific study of the physical processes, form and functioning of rivers and streams and their physical
interactions with the surrounding landscape
3.32
forced bar
non-mobile bar whose position is forced by the presence of natural (e.g. large wood) or artificial
structures
Note 1 to entry: See also ‘bar’.
3.33
forced pool
non-mobile pool whose position is forced by the presence of natural (e.g. large wood) or artificial
structures
Note 1 to entry: See also ‘pool’.
3.34
gabion
wire basket containing stones, used for river-bed or bank protection
3.35
hyporheic zone
spatio-temporally dynamic ecotone between the surficial benthic substrate and the underlying aquifer
[SOURCE: EN 16772:2016, 2.13]
3.36
hydromorphology
morphological and hydrological characteristics of rivers including the underlying processes from which
they result
3.37
large wood
piece of wood that is more than 1 m long and 10 cm in diameter
3.38
landscape unit
area displaying distinctive combination of environmental attributes such as altitude, topography and
geology
3.39
lateral connectivity
lateral continuity
freedom for water, sediments and biota to move between the channel and the floodplain/hillslopes
3.40
lateral movement
freedom for a river channel to move across a floodplain
3.41
longitudinal connectivity
longitudinal continuity
freedom for water, sediments and biota to move along the river channel
3.42
meander
one of a series of regular, sinuous curves along the course of a stream
3.43
planform
the geometric form of a river channel viewed from above
EXAMPLE Sinuous, straight.
3.44
pool
distinctly deeper part of a river bed that is usually no longer than one to three times the channel’s
bankfull width, and where the hollowed river bed profile is sustained by scouring
3.45
pseudo-meandering
river with a meandering, baseflow channel, defined by alternate side bars within a less sinuous bankfull
channel
3.46
rapid
area of steep confined river bed composed of boulders and large cobbles, often organized into irregular
lines approximately perpendicular to the channel and partially or completely crossing the channel
width that are only exposed at low flow
3.47
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.
3.48
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 15843:2010, 3.21]
3.49
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
3.50
riffle
fast-flowing shallow water area of a river bed with a distinctly broken or disturbed water surface over a
gravel/pebble or cobble substrate
3.51
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.
3.52
ripple
small fine sediment (sand-silt) river-bed features of a few centimetres high, linear in plan, with a long
crest perpendicular to the flow
Note 1 to entry: See also ‘dune’.
3.53
river bed incision
process where a river has cut vertically to lower its bed
3.54
river channel cross profile
two-dimensional representation of river channel morphology perpendicular to the flow
3.55
river hydromorphological type
group of river channels displaying similar morphological and hydrological characteristics and their
associated processes
3.56
river long profile
two-dimensional representation of river bed topography, where bed elevation is plotted against
longitudinal distance downstream along the channel
3.57
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)
3.58
runoff
net discharge of water into the stream from surface-water and groundwater sources with losses
occurring from evapotranspiration and other consumptive uses
3.59
scour hole
scour pool
local, often deep, scouring of the river bed, exploiting weakness in bedrock or downstream of roughness
elements such as rock, boulder or wood steps
3.60
scroll
linear ridge deposit formed on point and counterpoint bars of meandering rivers, which, when
incorporated into the floodplain develop into ridges and swales
3.61
sediment transport
movement of sediment particles of a range of sizes by flowing water, which could include mobilization
and deposition
3.62
sheet piling
material used for vertical bank protection
EXAMPLE Corrugated metal sheets.
3.63
sinuosity
distance from upstream to downstream along the channel centre line between two point, divided by the
distance along the valley course between the same points
Note 1 to entry: The two points need to span a sufficient distance to differentiate river channel from valley
curvature.
3.64
spatial unit
subdivision of a catchment at various geographical scales
EXAMPLE Catchment, landscape unit, valley segment, reach
3.65
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
3.66
substrate
material making up the bed of a river
3.67
valley segment
section of river subject to similar valley-scale influences and energy conditions
3.68
wandering
transitional river planform between single-thread and multi-thread (braiding, anabranching),
displaying a single flowing thread within the bankfull channel that splits locally into two or more
threads separated by bars, or channels separated by permanently vegetated areas (islands)
3.69
watershed
line delimiting the outer topographic boundary of a catchment or drainage basin
3.70
weir
artificial structure across a river for controlling flow and upstream surface level, or for measuring
discharge
3.71
wetland
habitat occupying the transitional zone between permanently inundated, and generally dry,
environments
EXAMPLE Marsh, fen, shallow temporary water.
4 Principle
A standard protocol is described for recording the physical features and assessing the processes of river
channels, banks, riparian zones and floodplains. The range of features and processes to be taken into
account, and the methods used for assessment, might vary according to river character and the
objectives of the study. This document provides a common framework for these different methods.
Guidance is given on the characteristics that should be used for defining river hydromorphological
‘types’ (see Clause 3) and for further assessment of hydromorphological integrity through comparisons
with reference conditions. The document recognizes that rivers are dynamic, and observing the way
that they have changed in the past helps in understanding their present condition, how they might look
in a less modified (reference) state, and how they could change in the future. The selection of features
and processes for survey and assessment will depend upon geographical scale and on the purpose of
the exercise, with some suitable for characterizing river hydromorphological types, some for
assessment, and some for both.
5 Study context and requirements
5.1 Investigating hydromorphology across both space and time
The hydromorphological features of particular lengths or ‘reaches’ of river reflect the biogeographical
region in which they are located. These features vary along a river and over time in response to local
gradient, river flows, sediment movements, and vegetation colonization and growth, as well as human
interventions and pressures that disrupt or alter processes in the channel and in the wider catchment.
A river could be responding to several factors operating over different timescales. Many of the features
observed today are strongly influenced by characteristics and processes beyond the river reach, notably
across the surface of the river’s catchment and its different landscape units and also within the valley
segment that contains the reach. Therefore, it is important not only to identify features and processes
found within a river reach but also to understand how these relate to processes in the catchment,
landscape and valley within which the reach is located (Figure 1). By understanding the catchment
setting of reaches and changes over time, it is possible to establish:
— why certain hydromorphological features are present within reaches;
— how they could have changed in the past and might change in the future;
— whether the features found within a particular river reach are responding to natural river
processes, human pressures and interventions, or a combination of both;
— whether a particular reach is suitable to serve as a reference state for river assessment purposes
and to inform restoration of other reaches within a particular landscape, catchment and
biogeographical setting.
Figure 1 — The spatial units that govern the processes affecting the hydromorphology of river
reaches, their typical size and the criteria that can be used to delineate them
5.2 Desk study
The first stage in a thorough investigation of the hydromorphology of rivers is a desk study. This
gathers information from a wide variety of contemporary and historical sources including maps,
remotely-sensed images, time series (e.g. river flow records) and other sources such as technical
records (e.g. structures in the river channel, bank/bed reinforcement, sediment mining/removal)
relating to particular locations, including previous hydromorphological survey work. When using aerial
imagery, it is useful to establish the flow at the time of image capture and the recent flow history (e.g.
3 to 5 years for dynamic rivers) to ensure a correct interpretation. In addition to local sources of
information, there are many freely available pan-European data sets (Annex A) that can complement
local data sources to support desk studies.
A desk study helps to delineate spatial units within a catchment (Figure 1) and to characterize them.
Such a desk study allows information to be compiled about the river catchment, its different landscape
units, valley segments and river reaches, including information about changes that could have occurred
in the past. Wherever possible, changes should be investigated over at least the last 100 years or the
period since major human impacts have occurred.
5.3 Field survey
Field surveys can provide complementary information (and for small rivers most of the information) for
further characterization of river reaches.
Field survey is time-consuming and expensive so maximum use should be made of any archived field
survey data. Furthermore, it is possible to undertake broad reconnaissance surveys at the reach scale or
to select portions of reaches (sub-reaches) where detailed field characterization can take place. There
are many ways in which such sub-reaches can be selected (7.3.2). Larger rivers and those where access
is difficult will need a different survey strategy, with aerial imagery forming an important component.
Cameras mounted on remotely-controlled drones have the potential to capture detailed
hydromorphological information during a field survey and are particularly valuable for surveying large
rivers.
By combining desk study and field survey information, a cost-effective programme of
hydromorphological investigations can be developed. It should also be possible to identify with
reasonable confidence those processes and pressures affecting reach hydromorphology and whether
they have changed in recent decades. In turn, this provides a good basis for assessing the degree of
natural functioning and the level of degradation of hydromorphological processes and forms within
river reaches.
5.4 Analysis and interpretation
It can be helpful to synthesize the collated information on delineation and characterization into a high
level, qualitative narrative. This can provide an overview of the catchment, landscape units, valley
segments or river reaches and highlight the type and condition of the hydromorphological forms and
features present. High-level inferences may then be made about possible management interventions
and how the system might respond. The spatial and temporal scale covered by an assessment should be
appropriate to the investigation and should be sufficiently broad to allow an explanation of how
changes instigated at a particular location have migrated through the catchment. The categories and
reference condition descriptions set out in Table 7 can be used to help ensure that analyses and
interpretations are systematic and thorough.
6 Delineation
6.1 General
A first step in gaining hydromorphological understanding is to determine the boundaries of the
catchment, landscape, valley and reach units that are to be characterized through desk-based analysis
(Clause 7). This section focuses on delineating the spatial units shown in Figure 1, from catchment to
reach. Whereas all spatial units from geographical region to valley segment are defined primarily by
natural conditions, the reach scale can incorporate human impacts and artificial alterations to the river.
The process of delineation aims to define the approximate boundaries of spatial units that enclose areas
of reasonably consistent character, reflecting the criteria listed in Figure 1. Since most catchments are
contained within a single geographical region and maps are already available that delineate these
regions, this topic is not considered further here. Very large catchments can cross more than one
geographical region and so could be subject to distinctly different climatic regimes that need to be
considered in the delineation.
6.2 Extent of delineation
The degree to which spatial units are delineated and then characterized depends both on the catchment
size and the intended assessment, reporting and management purposes:
— for whole-catchment hydromorphological assessment and management purposes, the aim should
be to subdivide the entire catchment into units at all spatial scales from catchment to reach;
— in large catchments, it should be possible to sub-divide the catchment at least to the level of the
valley segment. Thereafter, a sufficient number of reaches should be defined to allow
characterization of the area under study;
— if the purpose is to focus on a particular reach or valley segment and a complete catchment
characterization is not needed, then a minimum assessment needs to focus on spatial units that
contain and are immediately upstream of the river reach under consideration.
6.3 Catchments
The core information required to delineate a river catchment is a topographic map or digital elevation
(terrain) model (DEM), from which the watershed (catchment boundary) surrounding the area that
delivers water to any point on the river can be delineated. In groundwater-fed catchments, it is
necessary to take account of significant deviations between the area delivering groundwater and
surface water to the river system.
6.4 Landscape units
Landscape units are areas displaying distinctive combinations of environmental attributes such as
altitude, topography and geology. They can be identified at multiple spatial scales so they could be
larger or smaller than an investigated catchment. Some catchments will contain only a single type of
landscape unit whereas other catchments could include several, showing different combinations of
altitude, topography, geology and soils. In some countries, such units have already been mapped.
Landscape units can be delineated using information from catchment-wide databases, maps and
remotely sensed imagery. Appropriate data layers can be combined and analysed within a Geographic
Information System but delineation of landscape unit boundaries from such diverse information also
requires some expert judgement, since the boundaries are often ‘fuzzy’. It is recommended that as a
minimum the following factors should be considered in the delineation of landscape units:
Altitude and topography: elevation range and degree of dissection of the land surface.
Geology: rock-type categories that indicate the permeability of the land surface and
the likely erodibility of the rocks — e.g. siliceous, calcareous, mixed,
organic; the surface exposure of aquifers.
6.5 Valley segments
Water and sediment move through a catchment along a sequence of valley segments. These can contain
quite long lengths of river (tens of kilometres) that are affected by a particular natural river flow
regime, sediment transport and degree of valley confinement. Initial delineation of valley segments
incorporates three criteria based on natural controls:
Catchment area: Valley segments end at major tributaries that are large enough to provide
a major increase in river flow (either measured by gauged flow or
estimated from catchment area) and/or change in sediment supply to the
downstream river.
Valley confinement The degree to which the river is prevented naturally from migrating
(of the river): sideways by the valley sides. Three or more simple degrees of
confinement can be identified to suit local circumstances: for example,
Confined (more than 90 % of river banks are in contact with the valley
sides or other elevated areas); partly confined (between 10 % and 90 %
of river banks are separated from the valley sides or other elevated areas
by floodplain); unconfined (>90 % of river banks are separated from the
valley sides or other elevated areas by floodplain).
Valley Gradient: The average downstream gradient of the valley. This is an important factor
determining the energy available for the river to erode, transport and
deposit sediment and so modify its bed and banks. Gradient should be
expressed as the actual valley gradient or a gradient class that is
meaningful in the local context. Major changes in valley gradient can be
encountered, for example, in association with hanging valleys in glaciated
areas, the presence of a distinct rock outcrop or a natural lake.
The information required to delineate valley segments should be derived from maps, aerial images,
digital terrain models and other detailed topographic survey information that could be available.
Algorithms are becoming available for the automated extraction of such information and also for the
identification of points or areas of change along the valley network that can be used to delineate valley
segments. These algorithms can help to provide an initial delineation of the position of valley segment
boundaries, but local knowledge will be helpful to fine-tune the results.
There is usually quite a strong correspondence between valley confinement and valley gradient, so that
in many catchments only a few groups of valley segments are distinguished. In complex catchments
with different types of landscape (e.g. mountains, plains, foothills), groups of valley segments showing
particular confinement–gradient combinations are often found only in particular landscape units.
6.6 River reach units
The reach delineation process does not assess the naturalness of the present morphology or the degree
of human modification, but results in reaches that form suitable units for characterization, allowing the
causes of their consistent properties to be investigated subsequently and any changes in their
properties to be tracked through time.
In subclauses 5.2 to 5.4, only natural criteria have been used to delineate the spatial units that deliver
water and sediment to river reaches (i.e. catchment, landscape unit, valley segment). In a naturally
functioning setting, water and sediment drain from landscape units through river valleys within the
river’s catchment, interacting with vegetation to produce river channel and floodplain reaches of widely
varying morphology and stability. Because flows of water and sediment are the primary control on river
reach morphology and dynamics, human activities that have a major impact on water and sediment
flows through the river network, as well as notable tributaries not already used in segment delineation,
are both essential for delineating river reaches.
Water and sediment flow discontinuities: Major discontinuities of flow and sediment transport
(e.g. natural lakes, dams and related reservoirs,
major weirs, major water abstractions and
discharges) and locally important tributaries.
Reaches are further delineated in accordance with their planform morphology. An initial assessment of
reach plan morphology (single thread straight, sinuous or meandering; wandering; multi-thread
braided, island-braided, anabranching) can be made from a desk study of maps, aerial images, digital
terrain models, and pre-existing field surveys. These should allow reach units to be identified with an
acceptable level of confidence. When bed sediment information is available, reaches can be further
delineated according to the size class of the bed material. The information used in characterizing river
reaches includes some or all of the characteristics described below, depending on river
hydromorphological type:
Sinuosity: For single thread reaches (typically a single thread of flowing water
within the bankfull channel at low (e.g. mean) flow), how sinuous is the
river? This should be assessed using a sinuosity index (SI), which is the
ratio of the length along the centre line of the river channel divided by
the length of the broad river or river valley course within the reach unit.
For example, reach units may be delineated according to whether they
are straight (SI < 1,05), sinuous (1,05 < SI < 1,5), or meandering
(SI > 1,5).
Degree of braiding: Does the river typically show a single thread of flowing water within the
bankfull channel, occasionally more than one thread, or typically more
than one thread separated by bare or sparsely vegetated bars at low
flow? This should be assessed by calculating a braiding index (BI), which
is the average number of distinct flowing threads counted at 10 equally-
spaced cross-sections (typically spaced by at least the width of the braid
belt or bankfull river channel) under low (e.g. mean) flow conditions. For
example, reach units may be delineated according to whether they are
single thread (BI = 1), wandering (1 < BI < 1,5), or multi-thread (BI > 1,5).
Degree of anabranching: Does the river typically show more than one distinct channel containing
threads of flowing water and separated by fully vege
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