Multiple water sector authorities in Ireland are finalising a process to review the Heavily Modified Water Body (HMWB) designation nationally in preparation for the Water Framework Directive (WFD) third cycle of River Basin Management Plan 2022-2027.
The largest grouping of waters which have being physically modified for a specified use are the national network of arterial drainage channels, comprising 11,500km of channel.
In compliance with the WFD, there is a prescribed process for the designation of water bodies as HMWB which embeds a series of requirements. OPW and EPA working collaboratively are executing this process and are moving to a position of designating arterial drainage a portion of channels as HMWB.
Hydromorphological pressures include physical alterations to channels and banks, alterations to the flow or water level regime, and the loss of connectivity within the adjoining floodplains. These pressures can include straightening, widening, deepening and dredging channels, removal of riparian vegetation, land drainage, abstraction, traditional flood protection structures and development adjacent to surface waters. In addition, structures such as culverts, locks, weirs and dams, act as barriers to the longitudinal continuity which can impact the migration of fish and eel and impede the natural siltation process i.e. downstream movement of riverine material from coarse gravels to fine silt.