Nedd Fechan

The Nedd Fechan is a river almost wholly within the county of Brecknockshire, Wales, currently administered as part of the unitary authority of Powys. It rises on the eastern slopes of Fan Gyhirych in the Fforest Fawr section of the Brecon Beacons National Park and flows south for 7 miles (12 km) to join with the Afon Mellte at Pontneddfechan, their combined waters continuing as the River Neath (Welsh Afon Nedd) to the sea near Swansea. The only significant tributary of the Nedd Fechan is the Afon Pyrddin which joins it at Pwll Du ar Byrddin ('the black pool of the Pyrddin'). Downstream of this confluence it forms the boundary between Brecknockshire to its east and Glamorgan to its west.[1]

Geology

The headwaters of the river run over Old Red Sandstone as far as Blaen-nedd-isaf where they encounter the Carboniferous Limestone outcrop. The river then continues through a wooded gorge for the remainder of its course. The section downstream of Pont Rhyd-y-cnau is cut in sandstones and mudstones of the Millstone Grit series. The section between Pont Melin-fach and the confluence of the river with the Afon Pyrddin is perhaps the most dramatic as the river plunges over several falls of which Sgwd Ddwli and Sgwd Pedol are the most acclaimed. Each of the falls is associated with faults bringing harder sandstone beds into contact with the more readily eroded mudstones.[2]

Habitat protection

The entire gorge section of the Nedd Fechan valley is protected as part of a larger site of special scientific interest which also covers neighbouring river gorges. It also forms a part of a larger special area of conservation designated for its rare bryophyte flora.[3]

Archaeology

Downstream of the Pyrddin confluence is abundant evidence of the former silica rock mining industry. A number of adits are visible on both sides of the river, most of which were served by horse-drawn tramways. The former tramways now provide easy access along this lower section of the gorge.[4]

gollark: Yes.
gollark: @@@@@@<@236831708354314240><@&453380648611348500>@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@<@!330678593904443393>@@@@@@@@@@@@@@@@@@@@@@@@@''''
gollark: Okay, I managed to compress the WHYJIT compiler into a single discord message.
gollark: ```pythonimport argparse,subprocess,random,stringparser = argparse.ArgumentParser(description="Compile a WHY program using WHYJIT.")parser.add_argument("input",help="File containing WHY source code")parser.add_argument("-o","--output",help="Filename of the output executable to make",default="./a.why")parser.add_argument("-O","--optimize",help="Optimization level",type=int,default="0")#parser.add_argument("-d","--drawkcab",help=".sdrawkcab elif ecruos YHW eht ssecorP")args = parser.parse_args()def randomword(length): letters = string.ascii_lowercase return ''.join(random.choice(letters) for i in range(length))def which(program): proc = subprocess.run(["which",program],stdout=subprocess.PIPE) if proc.returncode == 0: return proc.stdout.replace(b"\n",b"") else: return Nonedef find_C_compiler(): compilers = ["gcc","clang","tcc","cc"] for compiler in compilers: path = which(compiler) if path != None: return pathdef build_output(code,max): #if args.drawkcab: code = code[::-1] C_code = f"""#define QUITELONG long long intconst QUITELONG max = {max};int main() {{ volatile QUITELONG i = 0; // disable some "optimizations" that RUIN OUR BEAUTIFUL CODE! while (i < max) {{ i++; }} {code}}} """ heredoc = randomword(100) devnull = "2>/dev/null" shell_script = f"""#!/bin/shTMP1=/tmp/ignore-meTMP2=/tmp/ignore-me-tooTMP3=/tmp/dont-look-here cat << {heredoc} > $TMP1{C_code}{heredoc}sed -e '1,/^exit \$?$/d' "$0" > $TMP3chmod +x $TMP3$TMP3 -x c -o $TMP2 $TMP1chmod +x $TMP2$TMP2exit $?""".encode("utf-8") with open(find_C_compiler(),"rb") as f: return shell_script + f.read()with open(args.input,"r") as f: contents = f.read() looplen = max(1000,(2 ** -args.optimize) * 1000000000) code = build_output( contents, looplen ) with open(args.output,"wb") as out: out.write(code)```
gollark: (and so, code gold was invented)

References
  1. Ordnance Survey Explorer sheet OL12 'Brecon Beacons National Park: western area'
  2. British Geological Survey 1:50,000 map sheet 231 'Merthyr Tydfil' & accompanying memoir
  3. Countryside Council for Wales website Archived 2013-10-13 at the Wayback Machine
  4. Brecon Beacons National Park website

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