Geological Survey Ireland has been monitoring flood levels at Lough Funshinagh, Co Roscommon since 2016, and through a new collaborative project with I.T. Carlow, a preliminary analysis has been carried out into possible future flood behaviours at the Lough.

Water levels in Lough Funshinagh are currently exceptionally high. Thus far in 2021 the turlough has reached record levels, exceeding the previous known record in 2016 by approximately 0.8 m. The peak level was recorded on the 3rd of April when the turlough reached 69.04m (meters above sea level). Since then the turlough has dropped slightly, with levels of 68.75 m recorded as of the 20th of May. This data is available to view at: https://gwlevel.ie/

Figure1: Water level hydrograph for Lough Funshinagh, Co. Roscommon. June 2016- May 2021 (GSI datalogger is positioned at 63.5m AOD)

The potential future flood behaviour at Lough Funshinagh has been estimated by inputting 80 years of historic Met Éireann rainfall timeseries into a hydrological model of Lough Funshinagh. In this manner, the model can produce a statistical analysis of how flood patterns may evolve in Lough Funshinagh over the next 18 months based on current water levels coupled with historic rainfall trends.

The results of this analysis, carried out in April 2021, is presented in Figure 2. The probabilities of different flood levels over time are presented in the form of a heat map where yellow pixels indicate a greater probability and blue pixels of lower probability. In addition to the heatmap, frequency quantiles are presented as green lines (for the 5th, 25th, 50th, 75th and 95th quantiles). These lines indicate the proportion of model scenarios which indicate that Lough Funshinagh will be less than or equal to a given level. For instance, for each instant of time, 50% of the model runs suggest flood level below the 50th quantile (the thickest green line) and 50% of the model runs suggest flood level above the 50th quantile.

Figure 2: Probability analysis of potential future flooding scenarios in Lough Funshinagh based on historic rainfall trends.

Preliminary results indicate that:

• There is a 50% probability that water levels in Lough Funshinagh could reach approx. 68.4 m in 2022 (65 cm below the 2021 peak, and slightly higher than the 2016 peak).

• The probability of Lough Funshinagh reaching levels comparable with 2021 is between 5 and 25%

• There is a 50% probability that water levels in Lough Funshinagh will not drop below 67.4m during the remainder of 2021.

• The considered hydrological model can reproduce the observed flood levels at Lough Funshinagh between 2016 and 2021, which indicates that there has not been any relevant change in the hydrological functioning of Lough Funshinagh in the past 5 years.

It should be noted that work on the Lough Funshinagh model is ongoing. Results are subject to change and should be interpreted with caution. However, though preliminary, the results have been shared with Roscommon County Council to assist in the management of flooding at Lough Funshinagh. For more information on our groundwater flooding monitoring and mapping work, see here.