Emergence regime changes - local

Changes in water levels may reduce the intertidal zone (and the associated/dependent habitats) by changing either the spatial area and or duration of immersion/exposure during tidal cycles.  Changes in tidal flushing can change sediment dynamics that may lead to changing patterns of deposition and erosion and extent of tidal immersion. Impacts include reduced habitats, resources, and feeding times, exposure, desiccation.

A 1 hour change in the time covered or not covered by the sea for a period of 1 year.
Upstream and downstream of a tidal barrage may change the extent of tidal immersion (reduce or increase respectively), beach re-profiling could change gradients and therefore exposure times, capital dredging, managed realignment, and salt marsh creation may change the natural tidal range.
The benchmark is only relevant to the intertidal, excluding habitats below Chart Datum (CD). Excludes tidal 'turbines' but includes tidal barrage. Excludes wave devices as addressed in relation to habitat change (not effecting emergence regime per se). This excludes pressure from Climate Change sea level rise.

Outer Hebrides

The tables in this section reflect the output of the workshop (October 2019) when the pressures from human activities were assessed for the period 2014 to 2018 for the region. The summary text below the tables elaborates on some of the points that were made at the workshop.
This pressure assessment uses the FeAST classification which includes two abrasion pressures: surface abrasion & sub-surface abrasion. Some expert groups combined these as a single pressure "surface & sub-surface abrasion" whilst others focussed on using surface abrasion alone, hence there is a slight difference in handling for some regions.
The ranking of the pressures in terms of impact is a relative exercise within each region, and is not a statement of their absolute impact. Detailed comparison between regions on the basis of these relative pressure assessments is therefore not advisable.

Main pressures identified

Outer Hebrides