Mapping Mountains – Hill Reclassifications – Y Pedwarau – The 400m Hills of Wales

 

Bryn Titli (SN 933 757) – 400m Sub-Pedwar addition

There has been an addition to the listing of the Y Pedwarau – The 400m Hills of Wales, with the summit height, bwlch height and their locations, the drop and status of the hill derived from a Trimble GeoXH 6000 survey conducted by Myrddyn Phillips and detail produced by Joe Nuttall in his surface analysis progamme, with subsequent LIDAR analysis conducted by the DoBIH team and independently by Myrddyn Phillips. 

Bryn Titli (SN 933 757)

The criteria for the list that this addition applies to are:

Y Pedwarau – The 400m Hills of Wales.  Welsh hills at or above 400m and below 500m in height that have 30m minimum drop, accompanying the main Y Pedwarau list are five categories of sub hills, with this hill being added to the 400m Sub-Pedwar category.  The criteria for this sub category being all Welsh hills at or above 400m and below 500m in height that have 20m or more and below 30m of drop.  The list is co-authored by Myrddyn Phillips and Aled Williams and is published on Mapping Mountains in Google Doc format.

Y Pedwarau - The 400m Hills of Wales by Myrddyn Phillips and Aled Williams

The name the hill is listed by is Bryn Titli and it is adjoined to the Hirddywel group of hills, which are situated in the north-easterly part of South Wales (Region B, Sub-Region B2), and it is positioned with the A470 road to its west and a minor road and the B4518 road to its east, and has the village of Llangurig towards the north north-west.

When the original 400m height band of Welsh P30 hills was published on Geoff Crowder’s v-g.me website, this hill was not included in the Hills to be surveyed sub list, as it was considered not to meet the criteria then used for this sub category. 

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

After the sub list was standardised, and interpolated heights and drop values also included the details for this hill were re-evaluated and it was listed with 19m of drop, based on the 493m summit spot height and the 474m bwlch spot height that appeared on the Ordnance Survey Vector Map Local hosted on Geograph website and which was entitled the Interactive Coverage Map. 

The Trimble GeoXH 6000 gathering data at the summit of Bryn Titli

Subsequently this hill was surveyed with the Trimble GeoXH 6000 on the 12.03.16, resulting in a 492.7m summit height positioned at SN 93383 75719 and a 472.7m bwlch height positioned at SN 93214 76009, with these values giving this hill 19.97m of drop. 

The Trimble GeoXH 6000 set-up position at the bwlch of Bryn Titli

However, it was not until LIDAR became available that the details for this hill relative to the data produced by the Trimble GeoXH 6000 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 analysis gives a 493.0m summit height positioned at SN 93382 75719 and a 473.0m bwlch height positioned at SN 93192 76017, with these values giving this hill 20.1m of drop. 

LIDAR image of Bryn Titli (SN 933 757)

Since the survey of these hills, the LIDAR (Light Detection & Ranging) technique is now being used to produce accurate height and position for hills.  Therefore, numerical data produced by surveying with the Trimble GeoXH 6000 is being updated.  However, each individual data set is analysed and as data produced by the Trimble GeoXH 6000 is considered more accurate it is this relative to the position produced by LIDAR that is prioritised.

Therefore, the addition of this hill to 400m Sub-Pedwar status is due to a Trimble GeoXH 6000 survey and LIDAR analysis, resulting in a 492.7m summit height and a 472.7m bwlch height, with these values giving this hill 20.0m of drop, which is sufficient for it to be classified as a 400m Sub-Pedwar. 

 

The full details for the hill are:

Group:  Hirddywel 

Name:  Bryn Titli 

OS 1:50,000 map:  136, 147

Summit Height:  492.7m (converted to OSGM15, Trimble GeoXH 6000) 

Summit Grid Reference:  SN 93383 75719 (Trimble GeoXH 6000) 

Bwlch Height:  472.7m (converted to OSGM15, height relative to Trimble GeoXH 6000) 

Bwlch Grid Reference:  SN 93192 76017 (LIDAR) 

Drop:  20.0m (Trimble GeoXH 6000 summit and LIDAR with height relative to Trimble GeoXH 6000 bwlch)

 

For the additions, reclassifications and deletions to Y Pedwarau – The 400m Hills of Wales reported on Mapping Mountains since the May 2013 publication of the list by Europeaklist please consult the following Change Registers:

 

Y Pedwarau

 

Y Pedwarau – 400m Sub-Pedwarau

 

Y Pedwarau – 390m Sub-Pedwarau

 

Y Pedwarau – 390m Double Sub-Pedwarau

 

Myrddyn Phillips and Aled Williams (August 2023)