During the botanical survey notes were taken on the hydrological status of the site.

The waters of Glenullin bog drain into either the Glenullin Water or the Agivey river. The confluence of these two streams is directly below the bog. The bog is a single hydrological unit of peatland, one single peat mass. Drainage or disturbance of any part of the bog will affect the overall phreatic level (ground water table). The phreatic level of a bog can be described by the use of mathematical equations. Most useful is the ground water mound theory (Bragg, 1988). This explains the existence of the raised water tables found in raised bogs and can be used to predict changes associated with disturbance.

The boundaries of the hydrological unit were located as:

1. The Glenullin Road. This road has been built on an embankment of peat and other foundation materials across what would have been the southern edge of Glenullin Bog. This can be clearly seen on the 1:10,000 Ordnance Survey map, the rough grazing symbols which indicate the presence of the bog are on both sides of the road. The road has had the effect of isolating the hydrology of the southern section of the bog (which has been cut-away and partially reclaimed) from the main part. The road now acts as a retaining dam for the southern edge of the bog. All water draining south from the bog collects in a drain cut along the northern side of the road. At three points along the road waters pass under the road and flow into the Agivey river.

2. The Glenulin Water. This runs along the northern edge of the bog. All the drains on the northern side of the bog discharge into the river. The river lies on mineral not a peat substrate. Immediately adjacent to the river, the peat deposit of the bog becomes increasingly thinner as the underlying boulder clay approaches the surface. In places the cover of peat reaches less than 50cm. It is suspected that a glacial terminal moraine is lying just under the surface of the bog, running adjacent to the Glenullin Water (Johnson, 1974). The bog would have once been contained by this structure, but as peat accumulated it grew ascertain the full extent of the ridge.

The drain and trackway along the eastern edge of the bog. This links the Glenullin Road drain and the Glenullin Water. There is some drainage from this side of the bog into this drain. Again the mineral deposit below the bog was found to be within a few centimetres of the surface adjacent to the drain. It is probable that this is a continuation of the moraine ridge located adjacent to the Flenullin Water.

In both cases the moraine is acting as a natural holding dam for the waters of the bog. It would be extremely difficult to drain the bog below this level without breaching the ridge. This would be a major undertaking, causing a large amount of disruption and sediment input into the Glenullin Water. The existence of the ridge possibly explains why the bog remains relatively wet despite all attemps to drain it.

3. The Western edge of the bog is less distinct due to the hand cutting in this area. A new hydrological boundary to the bog has been created by the drain which runs along the large bank on this edge. This again links the Glenullin Water and the Glenullin Road drain. Drains running west across the surface of the bog empty into the major drain. If this drain was not present there would probably be a net gain to the system of runoff water from the surrounding mineral land which is higher than the bog.

The site is a single self-contained hydrological unit with well defined boundaries.

Control of the water table level within these boundaries would be possible and easily achieved by the use of simple sluices.

The water table could be restored to its original position within the system, so that the surface of the bog is saturated at all times without any associated rise of the water table in adjacent agricultural areas.

There has been an effort by the illegal peat extractor to completely destroy the acrotelm, the ‘living’ bog surface of Glenullin bog. The acrotelm controls the hydrological functions of a raised bog system and has an essential role in the maintenance of a constantly high water table which is required for the survival of Sphagnum species.

Despite this Glenullin bog is not damaged beyond repair and a strong community effort is being made to save the bog with the aim of a full restoration.