Sunday, 9 April 2017

Mapping Mountains – Hill Reclassifications – Y Trichant

Garreg Ddu (SH 701 462) - Trichant reclassified to Sub-Trichant

There has been a reclassification to the listing of Y Trichant, this is the draft title for the hills in the 300m height band of the Twmpau (thirty welsh metre prominences and upward) due to analysis of LIDAR data by Aled Williams.  The hill was listed in the sub category that accompanied the original Welsh P30 lists when published on Geoff Crowder’s website, with the criteria for Y Trichant being all Welsh hills 300m or more and below 400m in height with 30m minimum drop and the now standardised Sub-Trichant being all Welsh hills 300m or more and below 400m in height with 20m or more and below 30m of drop.

When drop values were added to the Welsh P30 Master Lists this hill was given an estimated c 29m of drop, however this was re-evaluated and the hill was reclassified to Trichant status with c 30m of drop, this was based on the 348m summit spot height that appears on Ordnance Survey 1:25,000 Explorer maps and an estimated bwlch height of c 318m.  

The hill is adjoined to the Arenig group of hills with its Cardinal Hill being Manod Mawr (SH 724 446) and is placed in the Region of North Wales (Region A, Sub-Region A3).  The hill is situated between the town of Blaenau Ffestiniog to its immediate south and the Llechwedd Slate Mines to its immediate north.

The hill forms the southern barrier to the extensive slate mines that pre-dominate the landscape above and to the north of Blaenau Ffestiniog, and is situated on open access land, and can be accessed from the backstreets of the town leading to an old incline to the open hillside above.

The name of the hill is Garreg Ddu and its reclassification to Sub-Trichant status is due to analysis of LIDAR data by Aled Williams.  LIDAR (Light Detection & Ranging) is highly accurate height data that is now freely available for much of England and Wales.

Aled’s analysis of LIDAR data gives the hill the following details:

Garreg Ddu

Summit Height:  348.0m

Summit Grid Reference:  SH 70186 46223

Bwlch Height:  319.6m

Bwlch Grid Reference:  SH 70178 46356

Drop:  28.4m

Therefore, the 348.0m LIDAR data produced for the summit position at SH 70186 46223 and the 319.6m LIDAR data produced for the bwlch position at SH 70178 46356 gives this hill 28.4m of drop, which is insufficient for its retention as a Trichant, therefore this hill is listed as a Sub-Trichant and the total in the Y Trichant and the Twmpau which will be updated accordingly.

The full details for the hill are:

Cardinal Hill:  Manod Mawr

Summit Height:  348.0m (LIDAR data)

Name:  Garreg Ddu

OS 1:50,000 map:  115

Summit Grid Reference:  SH 70186 46223 
Drop:  28.4m (LIDAR data)

Garreg Ddu (SH 701 462) now reclassified to a Sub-Trichant

My thanks to Aled Williams for sending the details of this hill to me.

Myrddyn Phillips (April 2017)

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