Mapping Mountains – Hill Reclassifications – Humps

Twyn y Waun (SO 082 070) – Recommended Subhump addition

This is the thirty first in a series of Hill Reclassification posts that detail hills whose status has either been altered in the listing of the Humps (HUndred Metre Prominences) through map study and / or surveys that I have instigated, or it is the recommendation that their status is altered.

The artificial summit of Twyn y Waun (SO 082 070)

Many preceding posts detailing these alterations to the Humps are retrospective as these hill reclassifications were either initiated from studying the Ordnance Survey Interactive Coverage Map that is hosted on the Geograph website, or initiated from a survey with the Trimble GeoXH 6000, and for the recommended addition that affects the Humps the survey of this hill took place on the 01.12.17.

The listing of Humps was published in book format by Lulu in 2009 and entitled More Relative Hills of Britain, its author; Mark Jackson gives credit to a number of people who contributed toward the formation of this list, these include; Eric Yeaman, Alan Dawson, Clem Clements, Rob Woodall, Bernie Hughes, Pete Ridges and others.  When the list was published in book format there were 2987 Humps listed with their criteria being any British hill that has 100m or more of drop, accompanying the main list is a sub category entitled Subhumps, with the criteria being any British hill that has 90m or more and below 100m of drop.

More Relative Hills of Britain by Mark Jackson

The details for the recommended reclassification appear below:

There has been a recommended reclassification to the listing of the Humps (HUndred Metre Prominences) instigated by a survey with the Trimble GeoXH 6000 which took place on the 01.12.17.

This hill has an intact natural summit and an artificial summit that now overshadows it and Mark Jackson lists this hill with 63m of drop based on an estimated c 451m height for the natural summit which has an uppermost 450m contour on the Ordnance Survey 1:50,000 Landranger map and the Interactive Coverage Map hosted on the Geograph website, and an estimated bwlch height of 388m based on bwlch contouring at 10m intervals and between 380m – 390m on the 1:25,000 Explorer map.  However, OS Maps which is the recent replacement for OS Get-a-map gives bwlch contouring at 5m intervals and between 375m – 380m, with the latter height taking in the width of a road and indicating an estimated bwlch height of c 380m, which if the artificial summit was taken for that of the hill gives this hill c 96m of drop.

However, it was not until LIDAR became available that the bwlch 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. 

The natural summit of Twyn y Waun is now overshadowed by its artificial summit

Twyn y Waun is adjoined to the Y Cymoedd – dwyreiniol group of hills and is positioned between the town of Merthyr Tudful (Merthyr Tydfil) to its west and Rhymni (Rhymney) to its east and has the A 465 Heads of the Valleys Road to its north-west.

Therefore, if the artificial summit is taken as that for the hill it is recommended that its status is amended to that of Subhump.

The full details for the hill are:

Name:  Twn y Waun (as listed in the Tumps)

Summit Height:  451m (as listed in the Tumps) (476.0m [converted to OSGM15] artificial summit)

OS 1:50,000 map:  160

OS 1:25,000 map:  12, 166

Summit Grid Reference:  SO 08457 07348 (as listed in the Tumps) (artificial summit at SO 08209 07041)

Drop:  63m (as listed in the Tumps) (96.0m Trimble GeoXH 6000 summit and LIDAR bwlch, artificial summit)

Myrddyn Phillips (January 2018)