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== Definition ==

Section of river along which boundary conditions are sufficiently uniform that the river maintains a near consistent internal set of process-form interactions. (A river segment can contain one to several reaches). As a general rule, the length of a reach should not be smaller than 20 times the mean channel width, although shorter reaches can be defined where local circumstances are particularly complex.

== Delineation criteria ==
* Channel morphology (particularly planform)
* Floodplain features  
* Artificial discontinuities that affect longitudinal continuity (e.g. dams, major weirs / check dams that disrupt water and sediment transfer)
* River confinement

== Methods and data sources==
Segments are subdivided into reaches by visual interpretation of consistent river and floodplain (bio) geomorphic pattern using
* Google Earth
* Orthophotos
* Multi-spectral remotely-sensed data 
* Lidar data
(Field reconnaissance can provide useful confirmation / additional data)

&lt;gallery&gt;
File:Frome_reach_deline.jpg|The River Frome is delineated into 15 reaches based on valley confinement, river planform and the presence of major weirs.
File:Frome_reach_type.jpg|The River Frome has sinuous, meandering and anabranching reaches.
&lt;/gallery&gt;


 [[Category:River Characterisation]] [[Category:Reach]] [[Category:Reach]]</rev>
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      <page pageid="6545" ns="0" title="Reach characterisation">
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          <rev contentformat="text/x-wiki" contentmodel="wikitext" xml:space="preserve">= Reach =
== Aim ==
Characterisation of river energy, channel and floodplain dimensions, morphology /geomorphic units, sediments, vegetation and physical pressures, including:
* Quantification of channel dimensions
* Stream power
* Bed and bank sediment calibre
* Vegetation extent and structure / patchiness
* Pressures, particularly on lateral connectivity.


== Data layers and hydromorphologically relevant parameters==
Remotely-sensed data sets (including Google Earth) can provide much of the basic information on channel dimensions, hydromorphological and vegetation features (geomorphic units) and sometimes a crude indication of bed material size. Flow information is drawn from the segment scale.

DEMs provide reach slope estimates. 

Where available, Lidar surveys provide very accurate information on channel slope, channel-floodplain morphology and width, and riparian vegetation distribution, height and structure.


== Potential data sources ==
* Google Earth
* Orthophotos
* Multi-spectral remotely-sensed data
* Digital Elevation Models (e.g. [http://epp.eurostat.ec.europa.eu/portal/page/portal/gisco_Geographical_information_maps/geodata/digital_elevation_model EU-GDEM])
* Lidar data 
* Pan-European and National vegetation databases


== Characteristics ==
===Channel dimensions===
''Channel dimensions: '' (1) Average reach and channel gradients; (2) Bankfull and baseflow channel width; (3) Bankful and baseflow channel sinuosity index (4) Braiding index (5) Anabranching index

===River energy===
''River energy: '' (1) total stream power; (2) specific stream power; (3) average bed shear stress

===Bank and bed sediment===
''Sediment size: '' (1) Bedrock exposure; (2) Composition (&gt;64 mm); (3) Composition (&lt;64 mm)

===Riparian and aquatic vegetation===
''Riparian vegetation: '' (1) Age structure; (2) Lateral structure; (3) Patchiness; (4) Species

''Large wood: '' (1) Large wood presence and abundance

''Aquatic vegetation: '' (1) Extent; (2) Patchiness; (3) Species presence and abundance

===Physical pressures and impacts===
''River bed condition: '' (1) Bed armouring (gravel-bed rivers); (2) Bed clogging / burial (gravel-bed rivers); (3) extent of bed reinforcement; (4) number of channel blocking structures; (5) sediment, wood, vegetation removal
 
''River bank condition and lateral continuity: '' (1) hard bank reinforcement; (2) bank edge levées/embankments; (3) set-back levées/embankments;  (4) bank top infrastructure; (5) immobilised river margin; (6) actively eroding river margin; (7) width of erodible corridor; (8) number of channel-crossing /blocking structures
 
''Riparian corridor connectivity and condition: '' (1) floodplain accessible by flood water; (2) riparian corridor accessible by flood water; (3) riparian corridor affected by intense woodland management activities; (4) abundance of alien, invasive plant species; (5) extent of impervious cover, severe soil compaction, excavations / extractions / infilling


More details on the characterisation of reaches can be found in [[media:Deliverable2.1.pdf|chapter 5 of Deliverable 2.1]].</rev>
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