Catchment News

Measuring how the Suir flows, from the mountains to the sea

‘Hydrometrics’ is the measurement of water levels and flow – how can it help us manage the Suir Catchment?

The River Suir drains a catchment of 3,542km². The headwaters of the Suir are located on the northern flanks of the Devil’s Bit Mountain in Co. Tipperary. The river flows east and then south through a wide limestone plain, past Thurles, where the Suir is joined by the River Drish flowing off the coal bearing Slieveardagh Hills on the eastern edge of the plain, and the Tipperary Clodiagh, which drains the hills to the south and west of the Devil’s Bit.

The Suir continues southward towards Cashel where it is joined by the Multeen River from the west and onwards to Cahir before which the Fidaghta, Ard and Aherlow Rivers flow into the Suir from the Golden Vale on the northern side of the Galtee Mountains. To the south of Cahir, the Suir enters the east – west aligned, limestone floored valleys which were formed by an ancient collision between the continental plates of Europe and America, and which characterise much of the landscape of southern Munster today.

Here the Suir is joined by the Thonoge and Tar Rivers which drain the karstified valley between the Galtee and Knockmealdown mountains. The Suir then turns north near the village of Newcastle, meeting the Nier River which drains the western side of the Comeragh Mountains. The Suir then turns east before reaching Clonmel, after which it is joined by the River Anner, flowing from the north and draining much of the central part of the Suir catchment and the slopes of Slievenaman. The Suir becomes tidal just before reaching Carrick-on-Suir, and is joined by a number of rivers between this point and Waterford city including the Lingaun, Portlaw Clodiagh (the only designated Freshwater Pearl Mussel subcatchment in the Suir catchment), Pil, and Kilmacow Blackwater and then makes its way to the confluence with the Nore and Barrow Rivers east of Waterford City. The Suir estuary then turns south, flowing out to sea through Waterford Harbour between Dunmore East and Hook Head.

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River levels and river flows are measured on the Suir and its tributaries by the Environmental Protection Agency (EPA) in conjunction with the Local Authorities for:

• drinking water supply resource assessment,
• waste water discharge assimilative capacity* calculations,
• environmental monitoring,
• conservation, and
• to enable planning and development proposals to be assessed.

*’Assimilative capacity’ refers to the ability of a body of water to cleanse itself; its capacity to receive waste waters or toxic substances without deleterious effects and without damage to aquatic life or humans who consume the water.’

The Office of Public Works also measures river levels and river flows in the catchment for drainage and flood management purposes. The hydrometric gauging station networks in the catchment are complimentary, with data shared between organisations to avoid duplication of effort. The EPA maintains the National Hydrometric Register and is a member of the National Hydrometric Working Group which provides national oversight of hydrometric operations to allow for efficient operation of hydrometric data collection.

Due to the historical development of the networks, the Office of Public Works network is focused on the main channel of the Suir from Templemore in the north to Waterford City in the southeast, with a small number of stations located on larger tributaries including the Drish, Tipperary Clodiagh, Multeen, Aherlow, Nier, and Anner Rivers. As this network is focused on drainage and flood management, it contains a high proportion of stations that are only measuring river levels as opposed to river flows (i.e. the amount of water flowing in the river). There is an extensive flood risk in the Suir catchment, which is reflected in the number of hydrometric stations maintained by the OPW here. In total they maintain 19 river level only stations and 16 river flow stations in the catchment.

The hydrometric stations maintained by the Local Authorities and the EPA conversely, are located where there is a need for river flow information relating to waste water discharge assimilation capacity, water resource assessment, environmental monitoring, and conservation objectives. Therefore, these stations tend to be located away from the main channel of the Suir at the location of waste water treatment or drinking water abstraction plants (Tipperary, Ballyporeen or Ballyshonnock for example), environmental sampling locations, or environmentally sensitive locations such as the Clodiagh Freshwater Pearl Mussel catchment at Portlaw. These types of assessments require river flow data which means this network is comprised exclusively of stations that measure river flow and not simply river level only. The EPA/Local Authority hydrometric network in the Suir catchment consists of 14 river flow stations. None of these stations are located on the main channel of the Suir, which is already covered to an adequate level by the Office of Public Work’s stations. Half of the EPA/Local Authority stations are located on tributaries of the Suir upstream of Carrick-on-Suir where there are specific abstraction or discharge pressures, and half of the EPA/Local Authority stations are located on rivers draining into the tidal estuarine part of the Suir, where the Office of Public Works does not maintain stations that measure river flow.

The combined network of 30 river flow monitoring stations and 19 river level only monitoring stations is one of the highest densities of any catchment in the country and provides a sound base for river flow related decision making in the Suir catchment. The EPA is currently undertaking a national review of the hydrometric network based on current and future river flow information needs. This review is based on an assessment of the known and possible pressures on the river and technological developments in river flow measurement, together with an understanding of the resource requirement relating to the collection of hydrometric data. In future, the existing, long-term strategic hydrometric network will be supplemented by a wider investigative hydrometric programme, including short-term project hydrometric stations that will provide tactical assistance to facilitate integrated catchment management on the ground in a practical manner. Combined with foreseen national developments in hydrometric modelling and estimation methods and applications, this will provide accurate river flow information for the Suir and its tributaries to inform decision making and effective management of the Suir catchment for all its residents.

Article by Conor Quinlan, EPA Hydrometric and Groundwater Section

All Hydrometric Data is available at http://www.epa.ie/hydronet/