Mapping Mountains – Summit Relocations – 200m Twmpau

 

Ffridd Cae Crydd (SN 749 976) 

There has been a Summit Relocation to a hill that is listed in the 200m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill confirmed by LIDAR analysis and a subsequent Trimble GeoXH 6000 survey conducted by Myrddyn Phillips. 

Ffridd Cae Crydd (SN 749 976) on centre left and Ffridd Eithaf (SN 745 977) on the right

The criteria for the list that this summit relocation applies to are: 

200m Twmpau – Welsh hills at or above 200m and below 300m in height that have 30m minimum drop, with an accompanying sub list entitled the 200m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 200m and below 300m in height with 20m or more and below 30m of drop, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward. 

The 200m Twmpau by Myrddyn Phillips

The name the hill is listed by is Ffridd Cae Crydd and it is adjoined to the Pumlumon group of hills, which are situated in the north-western part of Mid and West Wales (Region B, Sub-Region B2), and it is positioned with the A489 road to its north and minor roads to its west, south and east, and has the town of Machynlleth towards the north. 

When the original 200m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, the qualifying P30 hill was listed as Ffridd Eithaf (SN 745 977) with a summit height of 272m, based on the spot height that appears on the contemporary Ordnance Survey 1:25,000 Explorer map. 

Extract from the Ordnance Survey 1:25,000 Explorer map

When the listing that became known as The Welsh P15s was being compiled, Ffridd Cae Crydd was included in the P14 sub list with an estimated c 14m of drop, based on an estimated c 271m summit height and an estimated c 257m bwlch height, with both heights based on interpolation of 10m contouring that appear on the Ordnance Survey 1:25,000 Explorer map. 

However, it was not until LIDAR became available that the details for this hill could be accurately re-assessed.  The LIDAR (Light Detection & Ranging) technique produced highly accurate height data that is now freely available for much of England and Wales. 

LIDAR image of Ffridd Cae Crydd on right and Ffridd Eithaf on left

LIDAR analysis confirms Ffridd Cae Crydd as higher than Ffridd Eithaf and as the summit of both hills has now been surveyed with the Trimble GeoXH 6000, it is this result that is being prioritised for listing purposes. 

LIDAR summit image of Ffridd Cae Crydd on right and Ffridd Eithaf on left

The Trimble GeoXH 6000 survey result for each summit is given below: 

 

Ffridd Cae Crydd:  272.289m at SN 74910 97692 

Ffridd Eithaf:  272.175m at SN 74578 97750 

 

As LIDAR analysis confirms Ffridd Cae Crydd as higher than Ffridd Eithaf, and as this has now been substantiated by the Trimble GeoXH 6000 survey, this comes within the Summit Relocations used within this page heading, these parameters are: 

The term Summit Relocations applies to when the high point is positioned in a different field, to a different feature such as a conifer plantation, within a different map contour, a different point where a number of potential summit positions are within close proximity, when natural ground or the natural and intact summit is confirmed compared to a higher point such as a raised field boundary or covered reservoir that is considered a relatively recent man-made construct, or a relocation of approximately 100 metres or more in distance from either the position of a map spot height or from where the summit of the hill was previously thought to exist. 

The Trimble GeoXH 6000 gathering data at the summit Ffridd Cae Crydd

The Trimble GeoXH 6000 gathering data at the summit of Ffridd Eithaf

Therefore, the summit height produced by the Trimble GeoXH 6000 survey is 272.3m and this is positioned at SN 74910 97692, this position is not given a spot height on the contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map, and is approximately 330 metres eastward from where the previously listed summit is positioned.

 

ills of Wales, and are reproduced below@

The full details for the hill are:

Group:  Pumlumon

Name:  Ffridd Cae Crydd 

OS 1:50,000 map:  135

Summit Height:  272.3m (converted to OSGM15, Trimble GeoXH 6000)  

Summit Grid Reference (New Position):  SN 74910 97692 (Trimble GeoXH 6000) 

Bwlch Height:  232.8m (LIDAR) 

Bwlch Grid Reference:  SN 75107 97628 (LIDAR) 

Drop:  39.4m (Trimble GeoXH 6000 summit and LIDAR bwlch) 

Myrddyn Phillips (October 2021)