Mapping Mountains – Hill Reclassifications – 200m Twmpau

Dinas Mawr (SH 808 539) – 200m Sub-Twmpau reclassified to 200m Twmpau

There has been a confirmation of a reclassification to the 200m Twmpau (thirty welsh metre prominences and upward) ranks of hills due to a survey with the Trimble GeoXH 6000, with these details being retrospective as the survey that confirmed this reclassification was conducted on the 24^th December 2013.

The criteria for 200m Twmpau status is all Welsh hills at or above 200m and below 300m in height with 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. 

This hill was listed in the Hills to be surveyed sub list accompanying the original Welsh P30 lists on Geoff Crowder’s v-g.me website and was only reclassified to P30 status when the sub list was standardised and interpolated drop values were accepted for qualification to the main P30 list.

Prior to the survey with the Trimble GeoXH 6000 the hill was listed with 33m of drop based on the 254m summit spot height that appears on the Ordnance Survey 1:25,000 Explorer map and the 221m bwlch spot height that appears on the Ordnance Survey enlarged mapping hosted on the Geograph website.

The name of the hill is Dinas Mawr and it  is situated in the Mynydd Hiraethog range with its Cardinal Hill being Mwdwl Eithin (SH 917 540) and is positioned immediately above the A5 road which is to its south, and is placed between the small communities of Capel Garmon to the north north-east and Penmachno to the south south-west.

The upper section of the hill is a part of designated open access land and this can be accessed from public footpaths originating from the A5 road south-west of the summit or from a minor lane to the east of the summit.

The full details for the hill are:

Cardinal Hill:  Mwdwl Eithin

Summit Height:  254.0m (converted to OSGM15)

Name:  Dinas Mawr

OS 1:50,000 map:  116

Summit Grid Reference:  SH 80884 53931

Drop:  33.9m (converted to OSGM15)

Dinas Mawr (SH 808 539) this hill's reclassification to 200m Twmpau status is now confirmed by a survey with the Trimble GeoXH 6000

For details on the survey that confirmed the reclassification of this hill to 200m Twmpau status

Myrddyn Phillips (August 2017)

Mapping Mountains – Trimble Surveys – Mynydd Hiraethog

24.12.13  Dinas Mawr (SH 808 539), Gallt y Celyn (SH 811 542) and Gallt y Celyn (SH 810 544)

Dinas Mawr (SH 808 539)

One of the advantages of having the Trimble is being able to accurately survey hills such as the ones visited today.  With G&J Surveys prioritising English and Welsh marginal Marilyns and high prominence Sub-Marilyns, English and Welsh Nuttalls and continuing with our visits to Scotland, and with Alan Dawson concentrating on Scottish Marilyns, Sims and the occasional Hump, and with John Fitzgerald roaming around a multitude of Irish hills, it means that many parts of Wales and an occasional visit in to England with the Trimble can produce accurate data on hills that none of the above will visit.  Today was a prime example as I wanted to confirm the status of Dinas Mawr as it was originally listed as a Sub in the Welsh 200m P30 list, and was later promoted to P30 status through contour interpolation, this hill also has an adjacent P30 twin top, so I wanted to de-twin this hill as well.

The three summits are on open access land and are easily approached from a bridleway just above the A5.  The higher hills to the west and south were bathed under winter grey cloud, this heralded the heavy showers that were forecast and as I made my way through a gate toward the bwlch of Dinas Mawr the first of these hit me as a vicious hail shower.

The going under foot was problematical as small trees interspersed with bracken and copious amounts of bramble made for rather slow progress.  I assessed the point of the bwlch from various angles, chose my spot and gathered five minutes of data before heading up through the bracken and rock outcrops toward the summit of Dinas Mawr.

The top is crowned by a few quartz rocks and marks the highest point of a fine hill; I removed the quart cairn and set the Timble up to gather data.  I soon had to turn it off as the fierce wind was making it wobble, I re-started it after wedging a small quartz rock on the leeward side of the equipment.

 

The Trimble GeoHX on the summit of Dinas Mawr.

The route from this summit to the next proved torturous as I decided on a direct line that took me in to a forest of bramble.  After negotiating the slippery rock of a stone wall I headed up to the first of the 258m twin map height tops.  The high point consists of a long rock outcrop.

Looking back toward Dinas Mawr from Gallt y Celyn (SH 811 542).

By now more hail showers were massing and the next hit me as I was on the second 258m twin summit.  This consists of long grass on top of a large boulder.  The descent route was back on the inward track with the wind drying my clothes on the way.

The Trimble on the summit of the second of the 258m map heighted twin summits (SH 810 544)

Survey Result:


Dinas Mawr

Summit Height:  254.0m (converted to OSGM15)

Summit Grid Reference:  SH 80884 53931

Bwlch Height:  220.1m (converted to OSGM15)

Bwlch Grid Reference:  SH 80984 53980

Drop:  33.9m (200m Sub-Twmpau reclassified to 200m Twmpau)

Dominance:  13.35%

Gallt y Celyn (significant name change)

Summit Height:  257.6m (converted to OSGM15) 

Summit Grid Reference:  SH 81121 54259

Bwlch Height:  227.5m (converted to OSGM15, from subsequent Trimble GeoXH 6000 survey)

Bwlch Grid Reference:  SH 81548 54426 (from subsequent Trimble GeoXH 6000 survey)

Drop:  30.1m (converted to OSGM15) (200m Sub-Twmpau re-instated as 200m Twmpau after surveying the bwlch)

Dominance:  11.68%

Gallt y Celyn

Summit Height:  257.1m (converted to OSGM15)

Summit Grid Reference:  SH 81007 54476

Drop:  14m

Dominance:  5.45%

For the post detailing the bwlch survey of Gallt y Celyn please click {here}

For further details please consult the Trimble survey spreadsheet click {here}