EPA - Ireland's Environment, An Integrated Assessment - 2020

Chapter 7: Water Quality Hydromorphological Alterations and Their Impacts on Surface Water Barriers, such as weirs and dams, can prevent the movement of fish and can be severely detrimental to migratory fish species. Other modifications, such as land drainage and channelisation can also impact surface water ecology. Hydromorphological alterations (i.e. physical changes) associated with agricultural drainage, land reclamation, channelisation, flood protection work and navigational dredging, among others, can damage the morphology and hydrology of surface water bodies and can prevent waters from reaching good ecological status. For example, the presence of physical barriers, such as weirs, dams and channel diversions, can damage river habitats and prevent the movement of fish and can be extremely detrimental to migratory fish species such as salmon, sea trout and lamprey (see Topic Box 7.3). Changes in hydrological flow as a result of physical morphological changes can also increase sedimentation rates and alter the composition of river and lake substrates, which in turn can affect bottom- dwelling organisms. For example, increased sedimentation is known to be one of the main environmental factors affecting the critically endangered freshwater pearl mussel in Irish rivers (Moorkens, 1999). Furthermore, over-abstraction of water can reduce river flows and lake levels to an extent that can damage their ecology. In general, abstractions in Ireland are not considered to be a widespread significant pressure on surface water or groundwater resources. During drier periods, however, such as the 2018 drought (see Topic Box 7.4), some abstractions require active management to ensure that they do not have a negative impact on waters. In early June 2020 Irish Water brought into effect a national hosepipe ban lasting until 21 July 2020. This was legally backed up by a National Water Conservation Order. The reason for the order was an increased demand for water and widespread drought conditions. In bringing in the ban, the utility company noted that Met Éireann had confirmed that May 2020 had been the driest May since 1850. Irish Water reported that 27 of its drinking water schemes were in drought and 50 were at risk of going into drought (Irish Water, 2020). River Clodiagh (Portlaw), an example of good hydromorphological conditions. 175