Network width is a plot of the number of channels in the river network against distance from the catchment mouth. It is generally used to explain the flood response of a catchment. The patterns observed in a network width plot are often the result of the underlying geology of the river catchment.
The distance from the mouth can be a topological or geometric distance. RivEX implements two types of geometric distance only: mean polyline length and user defined constant.
The stepping distance mean polyline length is calculated from the whole network and not the individual catchment. If you wish to have the stepping distance to be a function of the drainage density of the catchment you will need to export the individual catchment to a separate Shapefile and process it separately.
RivEX calculates the network width by using the known distance from its upstream and downstream distance to the mouth. Then for each polyline it checks to see if the stepping distance falls within the length of the polyline. If it does, a counter increments for that specific distance. This method allows for very long polylines to be counted more than once as they will intersect more than one stepping distance. For example the stepping distance is set to 1Km and a polyline is 3Km long with its downstream end at 14.5Km away from the mouth. It will intersect stepping distances of 15, 16 and 17Km.
The output is a table of increasing distance from the catchment mouth and the number of channels identified at the specified distance.
The image below shows a river network, displaying the various types of nodes. Note the network contains a braiding section. The results of a network width analysis for this catchment are displayed to the right and plotted below.
Distance (Km)
# of channels
1
1
2
2
3
3
4
2
5
3
6
2
7
1
8
2
9
3
10
3
11
3
12
3
13
2
14
2
15
3
16
4
17
4
18
2
19
2
20
2
21
1
Both sides of a braid will be counted by RivEX if they intersect a stepping distance. If you wish to remove the influence of braids you will have to manually remove them from your river network. If you have processed the network for Shreve order you may take advantage of the fact that it only selects one route through a braid, leaving the other polylines coded as zero. Be aware the route taken by the Shreve order is based purely on the order of the polylines in the attribute table.
