Site Spacing

• RivEX can determine the distance between points located along a single channel.  These could be riffle-pool sequences, debris dams, physical structures or biological/chemical survey sites.

• Your points must be snapped to the river network.

• Your network must have be run through RivEX and processed for catchment ID and distance to mouth.  You will have also run your network through the segment identifier process.  Please refer to the appropriate sections of this manual for how to calculate these values.

• Site spacing is calculated by looking at the differences in distance to network mouth.  It is not a route finding tool such as network tracing and thus does not encode the network with inter-site differences.

• To use the site spacing tool you must complete the parameters section of the main interface and press the Build button.

• Click on the Site Spacing tab.

• In the select point layer frame, identify the point layer that represents the sites and the unique ID field as shown below.  This point layer must be loaded into the map document before you open the main RivEX interface.

• You will asked to confirm that the point layer is a layer with points snapped to the network. Go here to find out about using RivEX for snapping points to the network.

• You must now identify the catchment ID field and distance to mouth fields fields.  These are RivEX generated fields and must have been created before you use the site spacing tool.

• When you tick the check box you will be confronted with the following message box.  This is simply to ensure that you have computed the important segment identification tables and stored them as Geodatabase tables in C:\RivEX\Output.

• You must not have changed the name of your network since you built the segment ID tables as RivEX searches the C:\RivEX\Output directory.  For example your network was called MyRivers.shp and consisted of 2 catchments numbered 1 and 2.  When running site spacing, RivEX searches the network and will determine there are 2 catchments numbered 1 and 2.  With this knowledge RivEX builds a path name to the segment table, for example C:\RivEX\Output\MyRivers_Tables.mdb . If you had renamed the dataset to MyRiversx2.shp then RivEX would try and find MyRiversx2_Tables.mdb which obviously does not exist!

• There are three final optional settings that can be set: use selection, include source and build distance matrix, as shown below.

• Tick the use selection if your point layer has an existing selection you wish to use.  This is useful for sub-setting sites from a dataset which may be distributed through various sub-catchments.  By selecting the sites that follow a single channel then RivEX will ignore all the other sites.  If you do not check this tick box then all sites are processed.  The image below demonstrates an example situation.

• Use Include source when you need to determine the distance between the source and the most upstream site.  The source is defined as the furthest point away from the network mouth that is upstream of the last site, see below image.

• RivEX can build a matrix of distances in a separate Excel worksheet. Simply tick this checkbox and all combination of distances will be written, see example screen shot below.  The matrix is limited to 254 sites as MS Excel can only store 255 columns.

• Click on Go! and the tool will run and and when finished, announce that it will send the data directly to MS Excel.  The tool will terminate early if any of the sites do not have a unique ID or identify a single starting polyline (i.e. not snapped to the network).

• The Excel file will contain at least two worksheets. The first lists all the sites, the catchment ID they fall within (they should always be the same) and their distance from the network mouth.  The second worksheet lists the sites as pairs  of ID's and the distance between them (see image below).  A third worksheet will exist if you have asked for the distance matrix.