Mapping Mountains – Trimble Surveys – Mynydd Penlle’rcastell

01.08.18  Mynydd Penlle’rcastell (SN 664 095)

Mynydd Penlle'rcastell (SN 664 095)

The ruins of Penlle’rcastell stand atop a flattened mound of a hill overlooking the Afon Aman (River Amman) to its north; nowadays the whole hill is encircled by roads with the A474 following the course of this river hereabouts and the M4 toward the south, with a number of towns also encircling the hill, including Rhydaman (Ammanford), Pontarddulais, Pontardawe and Glanaman.

The old fortification atop the hill is thought to date from the late 13^th century and is associated with the Marcher Lords, today its earthwork system of ditches and embankments is still impressive, but where once its view would be unencumbered, today one looks out on the Mynydd y Betws Wind Farm which incorporates 15 turbines that are 110m (361ft) in height.

I’d often wondered what name would be most appropriate for this hill as those of Mynydd y Betws and Mynydd y Gwair have been presented on Ordnance Survey maps, with the position of the former consistently given on the upper northern part of the hill, and the latter on the upper southern part of the hill.  However, it is the Tithe map that delineates the land boundary of each and also names the central land taking in the summit of this hill as Mynydd Penlle’rcastell.

Today I was out on a bagging road trip with Suzanne, a good friend for many a year and who was house sitting for one of her friends in Caerfyrddin (Carmarthen) for the week.  If wanting easy access to the summit of Mynydd Penlle’rcastell a minor road crosses the hill in a north to south direction and at its high point there is sufficient space to park one or two cars, and with six hills planned for the day we opted for this easy access route.

Whilst heading east driving toward the hill dark shower clouds hung over it, and although the westerly breeze pushed these forever inland a darkened sky met us when we pulled up at the top of the minor road crossing the hill.

A narrow path led across the grassland toward the earthworks of Penlle’rcastell and this passed within a few metres of where LIDAR analysis places two points that vie for the summit position of this hill, and as Suzanne headed toward the ditches and embankments I used the Trimble as a hand-held device and zeroed in to the first of these two positions.

LIDAR image of the summit of Mynydd Penlle'rcastell

Suzanne heading toward the remains of Penlle'rcastell

Once the Trimble was gathering data I joined my bagging accomplice and investigated the ruined fortification.  During this an occasional light shower sped across the hill with the rain no more than spots brought on the breeze, and with a brightening forecast for late morning and afternoon it looked as if our timing on this hill was perfect.

Gathering data at one of two points surveyed for the summit position of Mynydd Penlle'rcastell

With one data set gathered and stored I positioned the Trimble at the second point that LIDAR indicates for the high point of this hill and gathered another data set.  Once data were stored I packed the equipment away and we turned toward my car and walked the short distance back to the minor road, next stop; Mynydd Sylen (SN 515 080).

Survey Result:

Mynydd Penlle’rcastell (significant name change)

Summit Height:  373.3m (converted to OSGM15)

Summit Grid Reference:  SN 66498 09531

Bwlch Height:  166.4m (LIDAR)

Bwlch Grid Reference:  SN 69945 09589 (LIDAR)

Drop:  206.9m

Dominance:  55.42%

For further details please consult the Trimble Survey Spreadsheet