Driminidy Lough - Palaeoecology of a Lowland Lake and bog

The Interactive map

This interactive map is built in layers which can individually be switched on and off. The map can be zoomed in and out by use of the + and – buttons in the top left, or by the use of a mouse wheel.

The measure icon (under the '+' and '-') will activate when clicked. Left click to start a line of measuring, double click to stop that line of measuring; and click again on the icon to turn off measuring. Lengths are displayed in metric units.

The legend for all layers is found by moving the mouse pointer over the icon in the top right. The map is displayed within its own frame and can be moved by dragging with the mouse left button.

Clicking anywhere on the map will raise a popup box that describes the layers active at that point.

When the map first opens the hillshade layer, and some other selected layers, are switched on. Other available layers include -

  • Townlands – a lot of townland borders follow streams and rivers so if 'rivers' are switched on some townland boundaries (black lines) will be covered by blue lines. There are two Townland layers available - one is just borders and the other includes townland name labels.
  • 50 m contours - these accentuate the relief and are best. These have been generated and so their accuracy is dependent upon the data they are based on - in this case the 30 m grid of the ALOS satellite. 10 m contours have been included on this map. Some editing of the generated contours may have been necessary.
  • Ringforts are displayed - they may be Raths (red dots), Cashels (yellow dots) and unclassified (UC - white dots).
  • Deglaciation landforms, Glacial features, Quaternary Sediments and Bedrock Geology are all available and complement each other but can also mask each other.
  • Roads are available, principally as a means for identifying the locations on the map.

Included on this map is a high resolution digital surface model (DSM) obtained from BlueSky, a company that has flown aerial surveys over the whole of Ireland. The accuracy of the elevation data is the best that is currently available. However, being a DSM the surfaces include houses, trees and bushes; generating contour lines from the DSM therefore includes these features. So there are two areas within the DSM to take note of - whether using the 2m contours or the 1m - the bog surface around the lake is clearly very uneven and tussocky, and this is very clear in the contours; and to the south east of the lake and bog is an area of woodland. The DSM shows us the surface of the treetops, so heights will portray this.

The difference in accuracy between the satellite data and the aerial survey data means that there is a discrepancy between the 50 m and 10 m contours of the whole map and the 2m and 1m contours of the DSM. If you are looking closely at the area of the DSM it is probably best to switch off the other contour layers.

The lower accuracy of the satellite data does mean some generated contours are in error - the Dromduvane stream is actually portrayed at one point as flowing uphill between two very steep and high hills. This is clearly wrong.

Bear in mind the satellite images were taken from 700 km altitude.

Click here to go to the Interactive Map

The Area of the Map

This map shows an area of about 4.2 km by 2.2 km centred on the small lake of Driminidy Lough. This lake and surrounding bog is probably of early post glacial origin, but this has yet to be confirmed. This will be done by ascertaining the full depth of the sediment and obtaining radiocarbon dates for some samples of organic matter, most crucially from the bottom of the deposit. A core will be taken, either from the bog or from the lake bed sediment, and this will be sampled, processed and analysed.

Of particular interest is the outlet from the bog / lake depression that leaves from the south west corner and flows down along the course of the bog road until it meets the other outlet, which it joins and they both flow into the Dromduvane stream. This drainage channel is now dry, being at a slightly higher level - 1 m or less - than the active drainage channel in the NW corner. The townland boundary between Kilscohanagh in the north and Driminidy North to the south follows this dry drainage channel, including that part of the first drainage channel after this one joins it. The Dromduvane stream is also followed by various townland boundaries.

That the townland boundary - townlands are supposed generally to have been created in antiquity - should follow this southern channel suggests that this channel may have been the active and flowing channel at that time. The current drainage channel was therefore possibly created later. We can conjecture why this would have been done - possibly when the road was established and a causeway constructed across the original channel. This may have blocked the channel, making the lake level rise until the current channel started to flow, and this then eroded down until it reached its current level below the original channel.

The bog road appears to be a relatively recent addition to the landscape - it does not appear on the 1st edition OS 6 inch map of about 1840, but it does on the 25 inch OS map of about 1880 (this can be checked on the OSI website here). Possibly this road across the low lying poorly drained land was built as part of a famine relief scheme. No townland boundaries follow this road - except where the bog road follows stream courses. This does raise the interesting possibility that townland boundaries - supposedly of great antiquity, but in reality we do not know for sure - may be indicators of the antiquity of the features they follow. It is noticeable that the road from Bredagh Cross north over the hills to Drimoleague - prior to the bog road the main route between the two - is followed all along its route by townland boundaries.

Other points of interest -

  • The lake lies in a band designated as flat alluvial glaciofluvial plain - this refers to the action of meltwater coming from the ice. It may carry a heavy load of sediment and so can be very abrasive, and also potentially deposits a lot of sediment. In addition the flow can fluctuate enormously as melting and freezing cycles change. Thus the smoothing and levelling effect of such systems can be extreme, eroding protruding features of the landscape and filling hollows with sediment. We must imagine this happening in a landscape with ice present to at least some degree, and probably a complete absence of plant life. The land surface will have been very unstable and easily moved around.
  • The same band of land is also marked as a deglaciation landform, as a glaciofluvial terrace. The action of glacial meltwater carrying substantial amounts of sediment continued as the ice melted at the end of the ice age. It would be hard to determine when the lake was formed or the glacial sediments deposited since the only practical opportunity for dating will be radiocarbon dating organic sediments - and these obviously would not have been deposited until the climate had improved and land surface became more amenable to organisms. Possibly the first organisms to get established would be diatoms and other microorganisms such as algae in the lakes and stream. These may be found in sediments below any organic sediment such as peat, and will be one of the focal points of the ongoing investigation.

How this map was made

The map has been generated, using a program called QGIS2Web, from an Open Source GIS called QGIS. This software is constantly being improved and, like all open source products, is highly efficient and free. The layers have all originated from data made freely available to the public domain. There are some inconsistencies in the map, arising partly through the different sources the data came from not being in alignment either with accuracy, completeness or definition.

Read more about how these maps are made and where the data comes from.

Click here to centre the map in the screen

Click here to centre the map in the screen