Water table movements

Beside a small road, and adjacent to the bogs which fringe Lough Gara, and attached to the top of metal casing, is a small green box.

Borehole at grid reference 167580 295295, distant Callow bog, Monasteraden village and Mullaghathee hill.

Within the box is a clockwork-driven rotating drum which records the water level in this borehole over a period of a month.

David Drew, Donal Daly & Caoimhe Hickey examining the chart recorder

A gearing mechanism reduces the scale of the ups and downs so that they fit on the chart. We can see that over the last few days there has been a regular up and down oscillation, with a periodicity of slightly over 24 hours, and an amplitude of between 2 and 3cm. The levels appear independent of rainfall (see next chart), and are a result of earth tides.
Gravitational forces affecting the aquifer are causing the rock to periodically expand and contract, thereby reducing and expanding the water-containing fissures with a corresponding rise and fall of the water level in them.

water levels in borehole from 07/08/2000 to 15/08/2000

A borehole 3.5km to the southwest, by the Old Lung Bridge, shows a completely different graph over the same period. The rises match periods of rain, the major peak corresponding with a fall of 17mm recorded nearby at Coolavin house, a dry period of two days, a fall of 5mm, and another dry day.

water levels in borehole, Lissian Townland, grid reference 165200 292850, from 07/08/2000 to 15/08/2000

300m south of the main road a rising (grid reference 165080 292660) occurs just south of the narrow road. The water's temperature and conductivity were measured — a temperature of 10oC and a high conductivity (high content of ions) confirming a groundwater rather than a surface origin for the water. This conclusion is confirmed by the presence in the field just to the south of collapse features, one with a linear alignment, suggesting till collapse into a cave system.

Caoimhe Hickey, watched by Monica Lee, working on the Roscommon Groundwater Protection Scheme