Monday 26 May 2014

Hill Lists – Cymru / Wales – 200m Twmpau updates – Mynydd Hiraethog



The first list to the Welsh 200m P30 hills was published on Geoff Crowder’s website v-g.me 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 seventh Group is Mynydd Hiraethog.


Mynydd Hiraethog 

South from Bae Penrhyn (Penrhyn Bay) at SH 829 815 to bwlch at SH 821 785 and continuing to the Afon Conwy at SH 802 766, and then east of the Afon Conwy to SH 856 511, and then north of the Afon Merddwr to bwlch at SH 928 499 and continuing north of the Afon Nug to SH 953 475, the Afon Ceirw to SJ 022 442 and the Afon Alwen to SJ 060425, continuing a short distance west of the Afon Dyfrdwy (River Dee) to SJ 066 429 and then south and west of the Afon Camddwr to the Fish Pond at Y Rug (SJ 056 438), continuing west of the Afon Camddwr to bwlch at SJ 069 477 and the Afon Clwyd at SJ 071 500 to the sea at SJ 997 808.  Bordering with the sea and Gogarth to the north, the Carneddau to the west, Arennig to the south and Bryniau Clwyd to the east.  


Twmpau - 200m updates

Ffridd y Mynydd    258m    SH 825 758

A promotion from the sub-list and summit relocation as this hill was originally listed as c 250m at SH 826 753 (SH 825 753).  There are eleven separate contour rings at c 250m in the vicinity of the high point of this hill, but only one has an uppermost c 255m ring contour on the Ordnance Survey enlarged mapping on the Geograph website.  The same ring contour has an old imperial height of 847ft (258.2m) on the Ordnance Survey Historical 1:25,000 map.  The bwlch contouring is between c 220m – c 225m and the critical bwlch is estimated as c 223m, giving this hill c 35m of drop. 



Gallt y Celyn    258m    SH 811 542

Since drop values were added to the list this hill has been listed with c 30m of prominence.  It appeared under an invented name of Bryn Graeanllyn but has now been amended to Gallt y Celyn which comes from the Tithe map.  It has a twin summit at SH 810 544, it is hoped that a Trimble survey can soon separate these summits.  The survey took place and de-twinned the two summits and a later bwlch survey confirmed this hill as a P30.



Dinas Mawr    254m    SH 808 539

This hill is adjacent to the twin summits at SH 811 542 and SH 810 544 and will soon be surveyed with the Trimble GeoXH 6000 to confirm (or otherwise) its inclusion in the Welsh 200m P30 list.  Until then it is promoted from the sub-list as bwlch contouring on current maps is between c 220m – c 230m and suggests a height of c 224m, giving this hill a drop of c 30m.  The Ordnance Survey enlarged mapping on the Geograph website has a 221m spot height on the area of the bwlch at SH 809 539 but as it is not centred on the hill to hill traverse it has not been used for drop evaluation.



Pt. 253m    253m    SH 940 639

Another promotion from the sub-list as the Ordnance Survey enlarged mapping on the Geograph website has a 253m spot height on the area of the summit and as bwlch contouring is between c 220m – c 225m and estimated as c 223m, it gives this hill c 30m of drop.  The hill was listed as Bryn Gwern-llifion which was an invented name; it has now converted to the Pt. notation.    

 

Pt. 211m    211m    SJ 060 618

This hill used to be listed in the sub-list with c 29m of drop under the name of Bryn Llewesog.  The summit contouring has been re-evaluated giving this hill c 30m of drop.  The Pt. notation has now been used for its name as the previously listed name was an invented one.  The name of Pen-y-cae appears on current Ordnance Survey maps and has been used in other P30 listings, but map study implies this name relates to the buildings at SJ 065 622 and not to the hill itself.  The name of Coed y Plas appears on the Ordnance Survey enlarged mapping on the Geograph website for the wood on this hill’s southern flank, this may be the locally known name of the hill, but as the wood does not reach the summit, the name has not been used until further investigation can take place.



Sub-Twmpau - 200m updates

Mynydd y Gyrt    298m    SH 967 693

The area of the bwlch has a 274m spot height at SH 969 690 on the large scale Ordnance Survey mapping on the Geograph website, this gives the hill 24m of drop.


Pt. c 216m    c 216m    SJ 009 646

The critical bwlch may well be situated in someone’s living room in the small community of Groes Fawr!  The summit is estimated as c 216m from an uppermost c 215m ring contour on the Ordnance Survey enlarged mapping on the Geograph website.  The bwlch contouring is between c 190m – c 195m and is estimated as c 192m, giving this hill c 24m of drop.


Coed y Fron    274m    SJ 051 446

The valley to valley contours are placed so close to one another the bwlch height is estimated to be c 251m, with the bwlch contouring between c 250m – c 260m.  With a spot height on the area of the summit of 274m it gives this hill c 23m of drop.  The name of Coed y Fron has been used as larger scale maps indicate that the wood just takes in the summit.


Pt. 265m    265m    SH 999 646

The summit height for this hill comes from the old imperial height of 868ft (264.6m) on the Ordnance Survey Historical 1:25,000 and the New Popular One-Inch maps.  The 868ft height also appears on a number of 1:10,560 maps.  The area of the bwlch has a 243m spot height at SH 996 647 on the large scale Ordnance Survey mapping on the Geograph website, giving this hill 22m of drop.


Pt. 213m    213m    SH 817 637

The bwlch contouring is between c 190m – c 195m with the critical bwlch estimated to be c 192m, giving this hill c 21m of drop.


Pt. 227m    227m    SJ 019 447

The area of the bwlch has a 207m spot height at SJ 020 448 on the large scale Ordnance Survey mapping on the Geograph website, this gives the hill 20m of drop.


Pt. 203m    203m    SH 821 740

The bwlch contouring has 5m intervals on the Ordnance Survey enlarged mapping on the Geograph website.  The contours are between c 180m – c 185m, with the critical bwlch estimated as c 183m, giving this hill c 20m of drop.



Next update due on the 2nd June 2014

No comments: