8. Spatial standards for fish barriers
We are proposing to apply the spatial standards used in the classification of other parameters to the fish barrier classification method in Scotland. The current fish barrier method consists of a GIS based tool to assess the proportion of suitable habitat in a waterbody from which migratory fish are excluded by artificial impassable barrier. It is described in detail in the UKTAG method statement 'Barrier to fish migration method (Scotland)'. The current method downgrades some waterbodies where the total affected length is actually relatively short and therefore of limited significance in terms of available fish habitat.
The spatial standards introduced by the Scottish Government in 2014 require at least a specified minimum total length of habitat to be impacted in order for a classification downgrade to apply. They are designed to avoid a disproportionate downgrade where the total length of impacted habitat is relatively insignificant when considering the total length of that waterbody. Hydrology, hydro-morphology, water quality and biological tools all currently follow this approach, but to date the fish barrier tool has not included this spatial element.
The existing fish barrier assessment method will continue to be used to generate an initial classification result. The spatial standards would then be applied, and only those results which breach the minimum habitat length would be treated as downgraded. These proposals will ensure that the effect of barriers on classification better reflects their actual impact on fish habitat This will better support assessment of ecological status, regulatory decisions and help target the implementation of programmes of measures aimed at achieving improvements in ecological status in rivers. It also means that the barrier tool will be better aligned to the approaches taken to classify other elements.
The spatial standards are summarised below; this is a simplified version, and the full version in Schedule 4 of the Scotland River Basin District (Standards) Directions 2014 should be consulted for caveats and exceptions.
- If a barrier is affecting >1.5km of contiguous habitat, then spatial standards are breached. If not then:
- If a barrier is blocking >15% of the total waterbody length, then the spatial standards are breached. If not then:
- If a barrier is blocking a significant length of tributary and the length of tributaries is >25% of the total length of all watercourses in the waterbody catchment (from GIS analysis), then the spatial standards are breached. If not then the spatial standards are not breached, and the fish barrier result should be applied.
Applying the extra spatial standards test will remove the influence of some barriers from classification, if they are only blocking access to a short stretch of habitat. This will have the effect of upgrading the barrier classification on a small proportion of waterbodies and remove the need for an improvement measure.
Implications of the proposal
A comparison between the current classification and one incorporating the spatial standards is summarised in Table 8.1.
|Class||Existing fish barrier classification||New proposed fish barrier classification||Net change|
This shows that of the 2717 waterbodies classified for fish barriers, the application of spatial standards would mean 81 being upgraded in status. As well as the 80 waterbodies moving to High status one waterbody improves to moderate status. This would result in overall classification status for 14 waterbodies being upgraded to good or above.