COMHAIRLE CONTAE ÁTHA CLIATH THEAS
SOUTH DUBLIN COUNTY COUNCIL

MEETING OF RATHFARNHAM / TEMPLEOGUE / FIRHOUSE / BOHERNABREENA AREA COMMITTEE

Tuesday, May 09, 2023

QUESTION NO. 6

QUESTION: Councillor L. Hagin Meade

To ask the manager to detail the water quality results for the Dodder River in South County Dublin 2020-2023?

REPLY:

Water quality of rivers is determined using a combination of chemical, physical and ecological results along a river's length. The best summary description of the large water environmental data set for the R. Dodder is summarised by the EPA's ecological status description for all water bodies in Ireland. The ecological status range that can be assigned by the EPA are High status for pristine waters, proceeding through Good, Moderate, Poor and Bad status. The status of a river, or a length/segment of river, is calculated every three years by the EPA with the last national status calculation determined in 2021 which included information for the R. Dodder.

The R. Dodder is relatively long and is split into segments called waterbodies so each waterbody can be assigned a status. There are several waterbodies above the Glenasmole lakes which are assigned High and Good status. The water body from the Lower Glenasmole Lake to Old Bawn is assigned Good status and the remainder of the river length in South Dublin County is assigned Moderate status. The Upper Lake is assigned Good status which is a drinking water source and the Lower Lake is assigned Poor status - but is not a drinking water source.

The Council monitors phosphate and ammonia on a monthly basis in rivers which are two important nutrient chemicals and give a strong indication of the health of a river. The upper R. Dodder to Old Bawn showed phosphate and ammonia were consistently very low and ammonia concentrations have seen some further decreases since 2020 to 2023 which is welcomed. The lower the concentration of the nutrients the better the river status is likely to be. The same can be said of the length of river from Old Bawn to Balrothery Weir. As the river flows from Balrothery Weir to the Dublin City boundary there is a gradual increase in these nutrients, and this is reflected in a moderate decline in the ecological quality of the river.

The main source of pollution to the R. Dodder is that of domestic misconnections which is reflected in the status change as the river flows into and through the urban area. The Council is currently implementing the Dublin Urban Rivers LIFE project which aims to identify misconnection houses in a fast and efficient way. The outputs from that project will be applicable to the R. Dodder in the future.