Scenario

You are a fish biologist studying the location of salmon spawning sites (redds). Are the locations of redds influence by the proximity of weirs? To answer that question a key metric is distance to weir. Weirs could be upstream or downstream of a redd. You can use the link sites tool to answer this question, the output being a polyline for each pair of redd-weirs that can be connected. 


WarningThe following guide is using a fictitious set of points and is in no way representing known barriers or redds...


Workflow


Step

Processing Task

1

You have prepared your river network and added the required attribution to the network so you can use the Link sites tool.  How do you know which attributes you need to add to the network so this tool will function? The answer is in the help file, under the usage section. You need to have attributed your river network with Catchment ID.

2

It is highly likely that your redds data was collected using a GPS. You need to convert that data into a spatial dataset such as File GeoDatabase point Feature Class. It must:

    • Be in the same coordinate system as your river network layer, you will need to project it.
    • Contain a numeric ID field with unique values. ObjectID and text fields are not allowed.
    • Snapped to the network, you can use the RivEX snap sites tool.


Avoid using shapefiles these are an old data format with limitations.

3

Your barrier data will likely come from another organisation such as your local\national government agency or even from an  organisation that collects such data such as amber in the EU. Like the redd sites, your barrier dataset will require some initial setup. It must:

    • Be in the same coordinate system as your river network layer, you will need to project it.
    • Contain a numeric ID field with unique values. ObjectID and text fields are not allowed.
    • Snapped to the network, you can use the RivEX snap sites tool.


Avoid using shapefiles these are an old data format with limitations.

4

Your input data would look as below, 4 redds sites (green) and 5 weirs (orange). Both site layers should have been snapped to the network and are in the same coordinate system as the river network.

Redds and weirs

5

With the network and datasets prepared you can run the link sites tool. Below we are searching FROM the redds TO the weirs and transferring useful site information to the links.

Link sites tool

6

The output is shown below.


The link from redd site #8 to weir #10 has been selected. Note there are no links coming from redd site #6, this is because the input dataset was NOT properly quality controlled and snapped to the network. Non-intersecting sites drop out of analysis.

Linked sites

The attribute table with the highlighted row. Note all fields that came from the FROM sites (redds) are prefixed with F_ and all fields from the TO sites (weirs) are prefixed with T_. This naming convention is used to avoid field name conflicts when both FROM and TO layers have fields with the same name. For redd site #8 we can say it is not an active spawning site and #10 weir is 2.9Km away, 1m high and without a fish pass. If source ID had been transfered to both site layers then these fields would be in the link dataset and we would be able to compare ID's and establish that weir #10 was not on the same main stem as redd site #8.

Links attribute table

Idea

The output of this tool not only provides you the distance between sites but also a geometry that you could use in further analysis. You could use the polyline in further spatial analysis (e.g. buffering and selecting up riparian habitat) or simply to visualise the route taken between two locations.


In this worked example we looked at fish vs barriers but these points could represent invertebrate sampling locations, infrastructure, geomorphological features, pollution events, invasive species, woody debris to name but a few!


Return to top of page