Author Topic: formulae to ascertain paleao flow from the size of scallops  (Read 4073 times)

Offline exsumper

  • forum star
  • ****
  • Posts: 597
  • BEC , Caving Pleb!!
Sorry to intrude on your light hearted forum with something serious, but I have just started digging halloween rift again (and wish to conduct a scientific study of the cave )that could be an old resurgence of wookey hole. Andy Farrant has sent me a paper By R.Curl 1974 for ascertaining flow rates from the size of scallops. Not being an academic, (being a member of the bec, more shag your women and drink your beer type). I have laboured with the formulae for several days and have I hope come to an understanding. Could some of you more academic types, who might be familiar with the paper, answer whether or nor not the reynolds number Re*  and BL are constants, or not.
Could you also confirm whether the values I have are correct, R.Curl 1974 gives a value for Re* of 2200 and BL of 9.4.
"Despain and Stock" 2005 give a value for Re* of nearer 2250 and The same value of BL of 9.4. Is this correct or have I got things completely wrong and neither are constants.
I Would be a very grateful thickie for an explanation.
Regards.
Caving Pleb Power!!

Get a Life! throw your television into a skip

Offline Hels

  • regular
  • *
  • Posts: 67
Re: formulae to ascertain paleao flow from the size of scallops
« Reply #1 on: June 21, 2009, 09:45:27 am »
Hello

The Reynolds Number Re is not a constant it is a dimensionless number that gives a measure of the ratio of inertial forces to viscous forces.  It depends on the type of flow that is occurring.  For Example in a stream a Reynolds number of greater than 4000 would be turbulent flow, less than 2000 laminar flow and between the two would be transitional flow.  Therefore your Reynolds number is on the laminar / transitional boundary.

I hope this helps.

Hels

Offline exsumper

  • forum star
  • ****
  • Posts: 597
  • BEC , Caving Pleb!!
Re: formulae to ascertain paleao flow from the size of scallops
« Reply #2 on: June 21, 2009, 11:51:27 am »
Thanks for that hels,makes the murk abit clearer.
regards
exsumper.
Caving Pleb Power!!

Get a Life! throw your television into a skip

Offline Pitlamp

  • forum hero
  • *****
  • Posts: 5644
Re: formulae to ascertain paleao flow from the size of scallops
« Reply #3 on: June 28, 2009, 07:52:01 pm »
Ignore this if you feel it doesn't help . . . but . . .

scallop size is not just related to flow. In many active phreatic conduits in the Dales (i.e. sumps) there are huge (30 cm+ diameter) scallops in the roof and much smaller ones on the floor (say typically 5 cm across). These occur together where the flow rate is not the responsible variable. (The reason for this large difference is probably water layering in sumps when laminar flow occurs, resulting in layers of water with vastly different aggressiveness at different levels in the passage. There's a paper on it in Cave & Karst Science by Murphy et al, based on a study in Joint Hole - see index on BCRA website.) You need to interpret the scallops at Halloween rift very carefully.

At the end of the day you can argue the finer points of mathematical models as long as you like but it can all be eclipsed by a few simple direct observations of actively forming scallops. And you'll still have to do the work of digging to make your discovery anyway!

Incidentally another classic example of simple observations being more meaningful than a complex scientific project is the hydrology of the Malham district. People have been doing increasingly ambitious dye tracing experiments there for well over 100 years, which have given all sorts of wonderful results - and at times conflicting ones. Yet the fact is that in high flow there's only one big surface sink (the Tarn water in the Watlowes valley ) and one big spring (Malham Cove Rising). Don't miss the obvious by getting sidetracked up blind alleys resulting from overly complex "scientific" minutiae.

Best of luck with the dig anyway.


 

Main Menu

Forum Home Help Search
SimplePortal 2.3.5 © 2008-2012, SimplePortal