Hydrogeothermal Conditions in Éire - Geological Survey of Ireland

- 11 -It might be possible to go back over old records and the limitedpublications, to see if there have been significant changes in temperatureover tQe past 200 years or so. But the only old reliable data appears tolie is that given by Rutty for the period about 1757. He notes Mallow spawater as issuing at 68 0 F (20 0 C), as compared with 20.7 0 e measured on 15 Nov.1979 (Table 36. Rutty also notes that st. Margarets (NO. 1009)registered 51 F (lO.SoC) or 5S o F C12.8 0 C) on 20 July, 1752; this wouldcompare with 17.2 0 C on the morning of 7 December 1979. In a study of thebiology of the Enfield spring, Fahy (1975) gave some temperature figures,based apparently on a recording thermometer placed in the spring; hereports in his Table I a range from 6 0 to 22.5 0 C. He also states that thespring has a day-degree quota of 6,606, as against 3,835 for an Irishisothermic spring. Fahy (1975, p. 112) mentions but three thermal springsrecorded in Ireland, and introduces the supposedly warm spring at Dunlavinin Co. Wicklow, with the footnote "The area was visited by me; the springwas not located".From the periodic temperature measurements made on the mainLeinster group of springs (Fig. 2), those for the Enfield (NO. 1005) andst. Gormans (No. 1007) have been selected for presentation here, Fig. 3.During the eight years to end-1978, Enfield water temperature was recorded62 times and that of St. Gormans 64 times. No self-registering or min-maxthermometers were used. Periods when the springs had dried-up or becomestagnant were noted; such low/nil flows tended to occur from August toNovember. Figure 3 shows water temperature for Enfield and for st.Gormans over the calander years 1976 and 1978. These were years for whichgood records were available, and which come after the 1974-76 drought.The plottings show how temperatures reach a peak in the spring,and then fall quite sharply from May'to October, to rise again during thewinter. The discharges also increase in spring and fall in autumn. So,as flow increases, so does temperature; as flow decreases, so do temperaturesfall. It is considered that this relationship is of considerablesignificance. The source of the heat which warms the water must be muchgreater than the amount of heat taken away by the water. It suggests thatthe larger the volume of water moving underground, the more it is broughtinto contact with zones of more heat or higher temperatures. This mayindicate a deeper circulation in the ground when winter infiltration hasrecharged the aquifers and the water is moving strongly towards itsdischarge point.The degree-days for the two springs have also been calculated,due to irregularity of measurement and that fact that st. Gormans was dryfor part of the year, degree-days are only approximate. Enfield showed7820 degree-days (21.3S o C average) in 1976 and 7380 degree-days (20.22 0 Caverage) in 1978. St. Gormans showed_6230 degree-days in 1976 (17.06 0 eaverage) and 6790 degree-days (18.61 0 C average) in 1978. The differencesin average and from year to year may have significance, but certainlyneed to be related to volumes of water discharged if the data is to beused as an analytical tool./ ...