Riverfly sites in England and Wales now have two automatically generated values: the modelled trigger and the modelled target. This page explains how these are produced, and how they can be interpreted.

Where to find the Modelled Target and Trigger

Anyone can see the Modelled Target and Modelled Trigger for any registered Riverfly monitoring site on the database. On your home page, click on ‘Sites’ under ‘Riverfly Sites’ (if you don’t have a database account, you can sign up for one here). You can then search for the site you are interested in, and click on the listing.

If you are a co-ordinator, you will see the Modelled Target and Modelled Trigger appear automatically when you assign a location to a new site.

What these values mean

Modelled Trigger Level

The Modelled Trigger level produced when a site is set up can serve as an initial guide until the regional ecology contact sets the ‘Agreed Trigger Level’.

This allows monitors and co-ordinators to put results into perspective during this initial period of surveying. It can also be used by the ecology contact as a guide value when setting an Agreed Trigger Level.

Modelled Target Level

This is an indication of what RMI score would be expected at the site if the stream or river was in pristine condition. Different sites will have different maximum possible RMI scores, even in ideal conditions, because of differences in factors such as geology, latitude and altitude.

The Modelled Target Level provides a site-specific score to strive towards. It gives an idea of how high the RMI score could be at that site, if it was free from human influences.

How these values are generated

The Modelled Targets and Triggers are generated using the River Invertebrate Prediction and Classification System (RIVPACS). Specifically, RIVPACS Model 44 was used. This model predicts the expected composition of the freshwater invertebrate community at a site in the absence of significant anthropogenic stress. In other words, the RIVPACS model can tell you which riverflies, and in what quantities, you would expect to see at a particular site if it was free from the influences of humans, such as pollution. It bases this prediction on a series of geographic parameters, and the alkalinity of the stream.

The model was run at a 50 metre resolution across the English and Welsh river networks, meaning there is a dot every 50 metres along every river, allocated with a specific set of values. In the Riverfly database, when a site is registered, it pulls the Modelled Target and Modelled Trigger from the dot nearest to the site’s location on this hidden layer.

Important notes

Important notes

Ecology contacts at statutory bodies are under no obligation to follow up on surveys that get a score below the Modelled Trigger Level. It is only when a survey breaches the Agreed Trigger Level that the ecology contact should be notified.
RIVPACS assumes the entire cross-section of the river channel is being sampled. Therefore, for a sample’s RMI score to be correctly compared to these modelled scores, the monitor should have kicked at points that are spread all the way across the channel, from one bank to the other. If the river was too deep to cross all the way, a fully representative sample is not possible, so the modelled target and trigger are not applicable.
These values are currently only available for England and Wales because of the availability of the data required to generate the scores. We hope to expand this to Scotland and Northern Ireland if the relevant data can be obtained.
If no Modelled scores appear when you are setting up a site, check that you have located the pin in the correct place. The scores are drawn from the nearest point on our hidden map layer (which are every 50m along every river), but if the site co-ordinates are too far away from any of these points, no Modelled Trigger or Target will be generated.

The Riverfly Partnership is a network operating through the Freshwater Biological Association.
Registered charity number 214440

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