Water flow direction and sediment patterns.

[Jon]

Someone was explaining how to interpret sediment patterns with relation to water flow in a sand filled passage today whilst on a dig. Does anyone know if there is any info about this online?

 

[gus horsley]

I haven't seen anything online but, unless the passage is completely blocked with sand, sediment patterns will be similar to those found in gorges so it might be worth looking in your local library for a book on geomorphology.  The angle and shape of the passage, amount of fill, grain size, amount of water flow, etc are all going to be very variable and will produce different effects in different digs.

 

[Jon]

Cheers. It is completely blocked with sand actually, and Richard did a good job of explaining the basics in the limited time we had but I'd like a few diagrams to refer to. I'll follow up your advice, thanks.

 

[Pitlamp]

Cave divers learn to interpret sediments in sumps because they greatly help laying line in the right direction - and because they offer directional information if the line is ever lost. I'm thinking of ripple marks, imbrication, fans of finer sediment in the lee of boulders etc. I think (but I'm not certain, without checking) that there is some advice on this in the Cave Diving Group Manual, if you can find a copy. (Can't get to mine at the moment due to it being buried whilst decorating.)

Isn't there something elsewhere on this forum about using sediments to interpret which way the water flowed in one of the digs in Notts 2? That may be relevant to what you're trying to sort out; you could try a search?

 

[Jon]

Inlet 8, where I was today. I was hoping I could find some reference material to read. I'm planning on getting Art Palmer's book, maybe it's in there.

 

[Pitlamp]

Off the top of my head, try Googling on "sedimentary structures" which should bring up geological sources. Geologists make use of the sort of thing you're interested in to work out flow directions at the time sedimentary rocks were deposited. Your situation is exactly the same except your sediments haven't gone hard yet. (At least I hope not, otherwise your dig might take longer!)

 

[Andy Farrant]

Look up cross bedding or ripple lamination. The direction of water flow in sands is often indicated by a set of inclined sand laminae. Bear in mind though that in a sump, sand can bank up in corners and eddys, so the direction of water flow recorded by the sediment is specific to that location, and may not be representative of the whole passage. Aslo bear in mind that although the sediment fill flow direction is normally is the same as the present water flow, that need not always be the case (eg relict sand deposited during the last glacial for example).

 

[Jon]

Thanks.