Geological experts working for Neath Port Talbot Council have produced the most comprehensive assessment so far of risk to people and properties in the Pantteg Landslide area in Ystalyfera in the Swansea Valley which has encountered ground instability since at least 1897.
During late 2017, a specialised aerial drone survey of Pantteg was carried out.
This comprised what is known as ‘LiDAR’ (Light Detection and Ranging) - a method using a laser to measure distances to the surface.
The measurements have been used to develop a very accurate map of Pantteg (known as a point-cloud) and have provided the information needed, such as slope angles and elevations, to produce a draft plan showing the risk to life and property from identified landslide hazards.
The LiDAR information is much more accurate than, for example, Google Earth and has provided data with a millimetre scale accuracy.
The LiDAR measurements have also been used to create a 3D visual output of how the slopes, properties and infrastructure relate to each other and a supplementary aerial survey has enabled images to be referenced to locations within the LiDAR/point-cloud (known as photogrammetry).
This is very useful as it demonstrates the topography using a visual interaction as opposed to the abstract LiDAR data.
Risk categories range from Very High to Very Low and the assessment includes different types of hazard from large scale landslides to debris avalanches, boulder and rock falls.
ESP experts say the central Pantteg area is the zone with the highest hazard and risk of landslides.
ESP have identified the Pantteg landslide as “very active” and further instability is likely to occur on a frequent basis in the future. The detailed risk assessment will be collectively reviewed once complete, as per normal practice.
Since a fresh landslip in February 2017, the cost to the council has been £440,000 with expenditure expected to reach more than £850,000 by March this year.
The land in the area is largely privately owned.
Extensive work completed and ongoing in the Pantteg area includes:
- Cyfyng Rd slope analysis (ongoing)
- Updated hazard/risk map (completed)
- Tree survey report (completed)
- Tree felling work (due for completion end of February 2018)
- Quarry inspections at Cwar Pen-y-Graig (One competed in August 2017 another due in January 2018) and Cwar Pen-y-Graig arw (One carried out on 20th November 2017 the next due in March 2018).
- Drainage – (1) Godre’r graig system (vegetation completed, survey completed, refurbishment 100% complete) (2) Church Rd system (vegetation completed, survey work finished, refurbishment 80% complete), (3) Pantteg system (Vegetation 90% complete, survey 90% complete, refurbishment work ongoing).
- Retaining wall 2 (wall construction completed)
- Retaining wall 3 (strengthening work started 22/1/18)
- Protecting bund enhancement opposite the chapel (work due to start 26/2/18).
On Monday, January 29 at Ysgol Gyfun Ystalyfera School (doors open 6pm, meeting starts 7pm) a 3D fly-through model showing the landslip area and other detailed information including an updated hazard/risk map of the area will be on show at a public meeting where council officials and Members will be available to answer residents’ questions.
The leader of Neath Port Talbot Council, Councillor Rob Jones said: “Earth Science Partnership is now providing residents in the Pantteg area with the most detailed information they possibly can about the risks posed by landslides which have plagued this area going back at least to the 1890s.
“We are making the information available on our website so people can digest the information ready for the public meeting in Ystalyfera on Monday evening when senior council officers and Members will be on hand to answer questions and inevitable concerns.
“We have used huge resources and a large amount of public money and have engaged trusted geological experts – whose detailed work will be peer reviewed – to give residents in the Pantteg area a greater understanding of the land that surrounds them and which they live on.”