Monday, 14 July 2014

Hill Lists – Cymru / Wales – 200m Twmpau updates – Tarennydd

The first list to the Welsh 200m P30 hills was published on Geoff Crowder’s website in 2000; this list preceded the list of TuMPs by nine years, the list proved a very useful resource for the TuMP compilation for this category of hill.

The Welsh 200m P30 list documents all hills in Wales that are at or above 200m in height and are below 300m in height, to qualify for the main list each hill requires a minimum of 30m of prominence.

The hills listed below are updates to the Welsh 200m P30 list originally published on Geoff Crowder's website.  To see the original list click {here}

The original published list had a Sub-List which was entitled ‘Hills to Survey’.  This list consisted of all hills in Wales in the stipulated height band that have a minimum of 20m of prominence, but do not meet the minimum 30m of prominence to enter the main list, according to Ordnance Survey map spot heights and contours.  Nowadays the standard Sub-List takes in all hills that have a minimum of 20m of prominence.  However, the Hills to Survey Sub-List discounted hills whose map spot heights gave a drop value of less than 30m, but more than 20m.  By doing so, the only hills that were Sub-Listed were those that map values dictated stood a chance of entering the main list, for example; if a hill had a summit spot height of 250m and a bwlch spot height of 221m, it was not listed in the Hills to Survey Sub-List as with 29m of drop I thought it did not stand a chance of main list qualification.
When compiling the Sub-List I was measuring many hills for P30 status using a basic levelling technique, please click {here} for more information concerning this.  I now know that Ordnance Survey spot heights have a standard margin of uncertainty of + / - 3m associated with their accuracy.  Therefore many hills that were not listed in the original Sub-List may have sufficient drop to enter the main list.  Because of this the Sub-List has been altered to include all hills that have a minimum of 20m of drop but are not known to attain the minimum 30m of drop to enter the main list.

The hills listed below are those major amendments to the original Welsh 200m P30 list as it appears on Geoff’s website.  There are many hills that have been promoted from the Hills to Survey Sub-List to the main list, whilst there are many additions to the Sub-List now that it has been standardised to include all 20m minimum but below 30m drop hills.

When the 200m P30 list was first published it was the first to this category of hills and in some way it and its other 100m height band lists paved the way for Clem’s data that later appeared on the RHB file database and then for the TuMPs listing by Mark Jackson.

As well as the first P30 list to this height band the list is now the first to include a comprehensive Sub-List.

TuMP baggers beware; as the main list also includes P30’s not listed by Mark Jackson, so if you want to visit all P30’s you’ll have to include some non TuMPs to do so.

The list will be updated on a weekly basis and will be done so through each Group category, starting from the north and working south.  The fourteenth Group is the Tarennydd.


North of Bae Aberdyfi (Aberdovey Bay) at SN 592 945 and the Afon Dyfi (River Dovey) to SH 753 018, continuing west of the Afon Dulas to SH 757 077 and the Afon Deri to bwlch at SH 737 093 and then west and south of stream to SH 724 102 and Llyn Mwyngil (Tal y Llyn Lake), continuing south from SH 710 094 following the Afon Dysynni to Aber Dysynni and the sea at SH 560 030.  Bordering with Cadair Idris to the north, Bryniau Dyfi to the east, Pumlumon to the south and the sea to the west.

Sub-Twmpau - 200m updates

Foel Fach    c 277m    SH 674 060

A slightly contentious entry to the Sub list as it qualifies with an estimated drop of c 20m only because the summit height has been estimated as c 277m.  Judgments of such kind are rather dubious, but the best estimate from the size of the uppermost summit contour in relation to the other contours of the hill is that the high point is approximately 7m above the 270m contour.  The bwlch contouring is between c 250m – c 260m and has been estimated as c 257m at SH 673 058.  The Ordnance Survey enlarged Geograph map has three spot heights on the area of the bwlch, all of which have been assessed and considered not to be at the critical bwlch, these are; 251m at SH 676 059, 256m at SH 674 058 and 257m (also on the OS 1:25,000 map) at SH 675 059.

Next update due on the 21st July 2014

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