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Irish Geological Association & International Association of Hydrogeologists, Irish Group: Day Excursion – Glen of the Downs SAC, Co. Wicklow

28 May All day

Credit: Alphonse Dousseau/Wikiwand

Leaders: Dr. Alison Orr & Dr Gerry Baker
(both of Arup)

TO REGISTER please fill in the form HERE 

Registration is on a first come, first served basis


Glen of the Downs, or Gleann dá Ghrua, means ‘The Valley of the Two Brows’. It is a 2 km long wooded glacial valley with steep sides rising to almost 250m. It contains a designated Nature Reserve comprising 59 ha, and is a Special Area of Conservation (SAC) based on the presence of Old Quercus petraea Sessile Oak woods with Ilex aquifolium (Holly) and Blechnum spicant (Hard Fern or Deer Fern). Bellevue was the name of the 19th Century Estate that included Glen of the Downs and there are some features, such as the Octagon on the eastern brow, from that time.
Tufa springs are located in the northern part of the forest, less than 1km along a forest path to the locations. The final part of the walk to the springs is across rough ground and access will require sturdy footwear. The excursion will focus on Tufa in Ireland and how it is considered within the planning process.

Credit: Alison Orr



The excursion will meet at Glen of the Downs car park just off the southbound lanes of the M11.
Latitude: 53.136 Longitude: -6.11624.
Great care is needed when entering and especially when exiting this Car park as there is usually lots of traffic on the N11 and it is all moving at c. 80km/hr or more.

For anyone coming by car from Dublin City Centre via the M50/N 11 this route takes up to 1 hour. Glen of the Downs is south of Kilmacanogue.
If you are travelling by car and you have spare places in your car that you would share, please let Stephen Carrington know. Ditto if you would like to take a car space that is offered.


Bus Éireann Route 133, Wicklow – Dublin Sunday service



This Bus runs with a good service on Sundays between Dublin and Wicklow. It leaves from Busáras and goes through Donnybrook by UCD and south. Alight at Glenview Hotel. The journey takes 1 hour with extra time to walk to the meeting place in the Car park. Take care when walking to the Car Park, again as traffic is usually rapid and plentiful.


Stop 1: Car Park of Glen of the Downs National Heritage Area

Stop 2: Tufa Springs in the Northern part of the woods approx. 1km away along the woodland path. Some of this walk is along rough ground.

Return to Car Park via woodland walks


Dr. Alison Orr

Alison is a hydrogeologist with nine years’ consultancy experience in hydrogeological assessment in Ireland and internationally. Alison completed a PhD in hydrogeology in Queen’s University Belfast in nutrient fate and transport. Alison’s area of expertise includes catchment science, water quality, environmental impact assessments, contaminant transport modelling, groundwater flood modelling, hydrogeology risk assessments, karst hydrogeology and groundwater resources.

Dr. Gerry Baker

Gerry is a hydrogeologist with over 20 years’ experience in Ireland and internationally throughout Europe and Africa. His main areas of expertise are in groundwater supply development and testing, groundwater modelling (conceptual, analytical, numerical, contaminant), baseline characterisation of hydrogeological environments, hydrogeological risk assessment, environmental impact assessment, water monitoring programme and implementation, soil monitoring and assessments, urban hydrogeology, dewatering design and implementation, karst hydrogeology, mine hydrogeology, groundwater flooding, discharges to groundwater, and oral hearing expert witness.

Outline Site Description (Wicklow Geological Site Report Excerpt) 


The Glen of the Downs comprises a deep channel that was formed by meltwater erosion on the northeastern flank of the Wicklow Mountains. The channel is oriented generally northwest–southeast, and extends for a distance of approximately 2 km.

Geological System/Age and Primary Rock Type

The feature is formed in an area of bedrock outcrop and subcrop and bedrock outcrops along the majority of the channel sides, giving the feature its’ ‘scalped’ appearance. The feature was etched out by meltwater during deglaciation at the end of the last Ice Age, about 12,000 years ago.

The bedrock in the locality is dominated by greywackes and quartzites of Cambrian age.

Main Geological or Geomorphological Interest

The Glen of the Downs is up to 100m deep and has a V-shaped profile. The base of the channel hosts a small stream, which seems tiny given the depth of the channel itself. Such streams, flowing through deep, relict glacial meltwater channels, are thus called ‘misfit’ streams.

The Glen of the Downs is considered to have formed completely in the Late-Glacial Period.

Initially the glen was a subglacial channel, formed under the ice, but later carried surface glacial outwash from Glacial Lake Enniskerry southwards. As well as this, the channel carried huge amounts of subglacial meltwater draining the ice sheet which extended into Wicklow from the Irish Sea Basin. This very high energy meltwater flow resulted in the Glen of the Downs’ unusual depth and size.

Much of the sides of the channel are very steep, and are nowadays covered in broadleaf forestry. The glen has an irregular long profile, which means that meltwater was under huge pressure from ice above, thus proving that the channel was initially subglacial in origin. The channel probably extended further southwards but its southern portion was blocked by ice marginal sediments which forced drainage from the later glacial lake to flow eastwards towards Delgany.

Site Importance – County Geological Site; recommended for Geological NHA

This is a site with excellent teaching potential on glacial meltwater erosion, as the feature is accessible, spectacular, and easily viewed from roads. The N11 passes through the feature and the glen is already an SAC and proposed NHA (Site Code 000719).