Mapping Mountains – Trimble Surveys – Carnedd Wen

 

02.07.21  Y Gaer (SJ 204 155) 

Y Gaer (SJ 204 155)

As its name implies this hill has the remains of an ancient hill fort on its summit area, however nowadays these remains are barely discernible to the untrained eye.  Whereas many such remains are prominent with their embankments and ditches still on grand display, this particular Y Gaer just has the last vestiges of a slight rise still on view.  This is no more than a little bump that is easily bi-passed in favour of the higher ground near-by. 

This higher ground is positioned at a small covered reservoir which is circular and sits atop a raised grass slope.  The ground leading up to the base of the raised grass slope is natural, whereas the raised grass slope and the covered reservoir are man-made, with the line between the natural ground as its base and the artificially raised ground relatively easy to pinpoint. 

I’d visited this hill once before in August 2015 in the company of Alex Cameron during a hill bagging day.  On that day I placed the Trimble on the highest ground at the top of the raised grass slope at the immediate base of the bricked section of the covered reservoir.  This was at the top of the artificially raised ground and not at natural ground at its base.  Today I wanted to rectify this and gather data from the highest remaining natural ground. 

Gathering data during the first summit survey of Y Gaer with the Trimble GeoXH 6000 placed on the top of the artificially raised ground leading to the exposed part of the covered reservoir

Since originally surveying this hill LIDAR has become available and gives coverage for this hill’s summit and bwlch, and prior to my re-visit I analysed LIDAR and built contours up for where the natural ground became man-made.  By doing so the position and height of the remaining natural ground can be found, this exercise also showed where the high point of the ancient hill fort is positioned.  During the re-survey I planned to gather data at these two points, the highest of which would then be listed as the summit of this hill. 

LIDAR image of Y Gaer (SJ 204 155)

If wanting a quick visit to the summit of Y Gaer this is easily accomplished from its east.  This is the approach Alex and I took six years ago.  This eastern approach is from the top of a narrow lane where a car can be safely left.  A gate then gives access to the field where the summit of the hill is situated. 

From this point it is only a short walk to the top of the hill, and once there I assessed the lay of land at the immediate base of the steep rising grassed slope leading to the top of the covered reservoir.  Having decided the highest remaining natural ground I soon positioned the Trimble to gather data and sat on the other side of the covered reservoir as the equipment quietly beeped away collecting individual datum points. 

Gathering data during the second summit summit of Y Gaer with the Trimble GeoXH 6000 placed at the highest remaining natural ground at the base of the artificially raised ground leading to the exposed part of the covered reservoir

Once allotted data were gathered and stored I re-positioned the equipment at the high point of what remains of the ancient hill fort, this is a few metres from the base of the covered reservoir and is now no more than a slight undulation. 

Gathering data at the high point of the ancient hill fort

The Trimble GeoXH 6000 set-up position at the high point of the ancient hill fort

During data collection I stood below the equipment and watched as an occasional vehicle appeared on the narrow lane below, otherwise all was quiet.  This was the fourth of ten hills visited with Alex six years ago, today it was the last of five as afternoon commitments and a forecast of potential heavy rain and thunder dictated that I now needed to head back home, and once the Trimble was closed down and packed away I retraced my route back to the car and did just that. 

 

Survey Result: 

 

Y Gaer

Summit Height:  129.3m (converted to OSGM15, Trimble GeoXH 6000)

Summit Grid Reference:  SJ 20417 15566 (Trimble GeoXH 6000) (summit relocation confirmed) 

Bwlch Height:  91.2m (LIDAR)

Bwlch Grid Reference:  SJ 21177 15977 (LIDAR)

Drop:  38.2m (Trimble GeoXH 6000 summit and LIDAR bwlch)

Dominance: 29.51% (Trimble GeoXH 6000 summit and LIDAR bwlch)

 

 

For details on the 1^st survey of Y Gaer

 

For further details please consult the Trimble Survey Spreadsheet