OpenStreetMap

Dyke?

Posted by Gerhardus Geldenhuis on 20 December 2012 in English (English)

Found what looks like a dyke in the river...

Noting it down for future interest.

Location: Emfuleni Ward 25, Emfuleni Local Municipality, Sedibeng District Municipality, Gauteng, RSA

Comment from z-dude on 21 December 2012 at 06:34

zooming into the river, there seems to be an old road or disused railway bed ruins stretching across the landscape. it may be the foundations of an old railway that is now gone.

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Comment from Gerhardus Geldenhuis on 21 December 2012 at 10:54

Hmmm, I gave your suggestions serious consideration. I compared the Google Maps images, the South Africa CD:NGI Aerial and the Bing imagery to be sure. What convinces me that it is geological rather than the remains of a road or railway is the following: * It's only visible in the vicinity of the river, if it were a road or railway I would have expected it to be visible a lot further away from the river.

  • It forms a prominent ridge and casts a shadow in some places in the Bing imagery which would support it being a natural ridge rather than a old road.

  • The vegetation is more dense and differently coloured on these features which would suggest a difference in soil and thus underlying geology. If it is such an old road then it is unlikely that there were money or equipment to bring in "foreign" rock and material from other areas to build the road/railway which could account for the difference in vegetation.

  • The "lines" cross the river twice in short succession. By moving the it slightly north you could have build only one bridge. I am generally fairly optimistic about the level of intelligence of railway engineers that build South African railways and I don't think they would have made such a mistake.

All that being said I would still be open to convincing otherwise. I do think it is rather academic at this stage as it is not worth mapping for OSM and would require a site visit to be sure. I will try and visit the location when I am in South Africa in January.

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Comment from z-dude on 22 December 2012 at 03:03

I traced out what I think is the ruins that I think you're talking about. http://www.openstreetmap.org/browse/way/197607043

Google books finds 'The Surveyor' page 70, published 1897. http://books.google.ca/books?id=zplVAAAAYAAJ&q=vaal+river+barrage&dq=vaal+river+barrage&hl=en&sa=X&ei=4hbVUNKtO4K1iwLjqIHYDw&ved=0CDQQ6AEwAA

Searching google books for 'vaal river barrage' shows that they were adding weirs and features to the river before the 1922 Vaal River Barrage listed by wikipedia. http://en.wikipedia.org/wiki/Vaal_Barrage

These features could be old dams.

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Comment from z-dude on 22 December 2012 at 03:16

There's another pair of features west of parys, so it might be geological instead of a weir.

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Comment from z-dude on 22 December 2012 at 03:21

zooming out with opencyclemap, it looks like parys is at the north northeast end of a crater, so maybe the geology is that these are crater ridges from an old impact.

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Comment from Gerhardus Geldenhuis on 22 December 2012 at 11:30

Hi Alexz, The Vaal Barrage is still very much standing and is further east from the location we are discussing. It has 9m high sluice gates that can be lifted completely out of the water to let water through. 1996 was the only year that I saw all of the gates completely lifted out of the water. Normally if you lift one of the gates 2m it causes significant rise downstream and the police drive from resort to resort warning the fishermen. If you are lucky and get permission to go on the Barrage while they open a sluice gate you might sometimes see very big catfish swimming in the stream of water gushing out from underneath the sluice gate. They hover there to catch smaller fish that got sucked in.

Your comment about the impact crater reminded me that one of my friends has spend several weeks mapping parts of the crater close to the town of Parys. She is much more familiar with the geology and I have asked her for an expert opinion.

I have extended your trace slightly to the south east and added two more traces to the north east and south west of your trace for illustration purposes of other similar features.

Regards

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