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.

EPA Public Consultation on Heavily Modified Water Bodies

Heavily modified water bodies (HMWB) are surface waterbodies that have had their physical characteristics, or hydromorphological conditions, modified by engineering works for drainage or development.

Water bodies are modified for power generation, the creation of dams for water supply, flood defences, industrial activity, to improve drainage and for navigation. These modifications prevent the river or waterbody functioning in its natural state and may impact on the diversity of fish populations and invertebrates that can live there owing to impacts on the natural conditions. This means that these waterbodies cannot reach the good ecological status required for fish and invertebrates under the Water Framework Directive. These circumstances are recognised in the Water Framework Directive and such waterbodies are designated as heavily modified and required to achieve Good Ecological Potential rather than good ecological status that needs more natural conditions. Under Good Ecological Potential standards not impacted by the modification still needs to be achieved such as good chemical and nutrient status.

Recent EU guidance to help Member States designate water bodies that have been modified has resulted in Ireland re-designating many of its water bodies.

Using the 11 step process of the new guidelines that includes (a) waterbody characterisation tests, (b) designation tests and (c) the assessment of potential objectives, Ireland has designated a total of 466 waterbodies as heavily modified.   The largest contributor is the arterial drainage of rivers.

The EPA is holding a public consultation to seek views on the designation from which the EPA will make recommendations to the Department of Housing, Local Government and Heritage on the final designations for inclusion in the next River Basin Management Plan cycle

A total of 433 river, 20 lake and 13 transitional and coastal (TRAC) water bodies have been identified as Heavily Modified Water Body candidates

List is here: