Water flow (tidal current) changes - local

Changes in water movement associated with tidal streams (the rise and fall of the tide, riverine flows), prevailing winds and ocean currents. The pressure extremes are a shift from a high to a low energy environment (or vice versa), which can alter the biota, substratum, sediment transport and seabed elevation.  The potential exists for profound changes (e.g. coastal erosion/deposition) to occur at long distances from responsible activity, with complex interactions.

Peak mean spring tide flow change of greater than 0.1m/s over an area >1km2 or 50% of width of water body for > 1 year
Activities that have the potential to modify hydrological energy flows, e.g. tidal energy generation devices remove (convert) energy and such pressures could be manifested leeward of the device, capital dredging may deepen and widen a channel and therefore decrease the water flow, canalisation &/or structures may alter flow speed and direction; managed realignment (e.g. Nigg Bay, Moray Firth), aquaculture nets or other structures may also alter water flow around the coast. The pressure will be spatially delineated.
The Marine Habitat Classification for Britain and Ireland (https://mhc.jncc.gov.uk/) uses tidal flow to help describe biotopes (e.g. the categories for tides are: very strong: >3m/sec; strong: 1.5-3; Moderately strong: 0.5-1.5; weak: <0.5; very weak - negligible – see https://mhc.jncc.gov.uk/media/1027/04_05_introduction.pdf). These may help with assessing habitat features against the benchmark.


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