Attribute your river network

RivEX can process topologically correct networks that have their node information stored within the attribute table of the dataset.  The current version of RivEX can compute the following network attributes:

• Strahler order

• Shreve order

• The sum of all upstream lengths

• Polyline link type

• A common ID to all polylines within the same catchment

• Main channel polylines

• Distance from network mouth

RivEX can handle braided/multi-threaded networks and the output is typically a new field containing the computed value.

RivEX will generate metadata for any of the above processes which you can read in ArcCatalog.  Remember the style sheet filters what you see, so you will need to swap between different style sheets to see specific information generated by RivEX.

Strahler stream order

Below is an image showing an unprocessed network and the same network processed for strahler stream order.  This information was calculated and stored in a new field called Strahler.  Note that RivEX can process braided river networks.

Unprocessed network displaying nodes	Strahler stream ordered network

Shreve stream order

In the image below the same network has been processed for Shreve stream order. 

Note the 3 grey polylines, these have not been given an order value.  Shreve stream order works only for non-braided networks. 

When RivEX encounters a braid, it uses only a single route.  This route is determined simply by the order of polylines in your dataset.  If they were digitised in another order, then the route will be different to the one shown below.  The chosen route may not be the main course of the river, remember all you have supplied to RivEX is a network of connected polylines, you have given no information on what each polyline represents.

Shreve stream ordered network

Summing Upstream Lengths

The sum of upstream river lengths flowing into a polyline can be calculated and attached to each polyline of your river network.  The value written back to the file includes the length of the polyline itself.  In the image below, red numbers indicate the length of the polyline and black numbers are the accumulated lengths.

Link type

The type of link the polyline represents can be identified and stored as field in the attribute table.  The 3 types of link identified are Interior, Exterior and Outlet and are encoded as I, E and O.

This output is heavily influenced by the network topology.  Pseudo nodes will alter the number of interior links and should be removed before processing a network for this attribute.  An exterior link will not be the same as what is defined in the literature if there are pseudo nodes present in the section of network that is the headwater stream.  Refer to the manual for extra guidance on the implications of pseudo nodes when calculating link type.

Catchment ID

All polylines within a single catchment can be given a catchment ID.  This ID can be an incremental number or the ID number of the node that represents the mouth of the network.  A catchment is defined as all polylines that flow to a mouth in a network.  A single polyline representing a stream would be treated as a catchment of one polyline. The image below demonstrates 3 catchments and the numbering used.

Main Channel

In RivEX, the main channel is defined as the route taken to reach the furthest point upstream from the mouth of the network.  Technically the algorithm works the other way around in that it traverses downstream from each source to the mouth of the network and chooses the longest.  When a braid or multi-threaded section of river is reached the algorithm takes a single route.  This route is based upon the order of the polylines stored in your dataset.  Therefore, the route through these sections as identified by RivEX may not actually be the main channel.  Remember all you have done is supplied a network to RivEX and no further information.  The output is a new field that codes the polylines and a Shapefile with only the polylines that are the main channel.

Distance from network mouth

The distance from the network mouth can be calculated and attached to each polyline of your river network.  The value written back to the file includes the length of the polyline itself.  In the image below, red numbers indicate the length of the polyline and black numbers are the distances from the network mouth.