Velocity or discharge logging underwater caves

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Velocity or discharge logging underwater caves

Postby gulley.jason » Feb 28, 2013 12:09 pm

Does anyone have experience logging velocity and/or discharge in underwater caves? I'd like to measure changes in discharge in underwater conduits as deep as 100 m as they reverse flow, such as occurs over a tidal cycle. ADVs seem to do a good job making point measurements of velocity, but they are expensive and require particles in the water and some springs are too clear. Many of the cheaper (<$15k) instruments have shallow depth ratings are the loggers are not designed to be placed underwater. If anyone has any suggestions, I'd be keen to hear(read) them.

Thanks,

Jason
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Re: Velocity or discharge logging underwater caves

Postby John Lovaas » Feb 28, 2013 5:02 pm

Jason- if a change in temperature is good enough to indicate a change in flow, you could use temperature dataloggers as a proxy for flow/discharge measurement, which you could do for around $50/location. I've been using Onset HOBO Pendants for years with great success.

Even the cheapest kludged flow meter(flow meter head grafted to millivolt logger) I've ever thought about would be a couple of hundred dollars per location.
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Re: Velocity or discharge logging underwater caves

Postby gulley.jason » Mar 4, 2013 7:49 am

I've temperature logging to get timing of reversals, which only works in some circumstance. Where it does work, you only get velocity for the initial pulse of water, which is typically not peak velocity. I'm looking for a way to augment the temperature (and SpC) records that I'm getting from other sensors. Even a few thousand dollars a site would be preferable to some of the techniques I've looked into.
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Re: Velocity or discharge logging underwater caves

Postby chac » Mar 4, 2013 2:46 pm

Jason,

Ask Patricia Beddows about the loggers she had installed in the Dos Ojos Pit. Her study was done a number of years ago so there may be better flow and direction loggers available. I don't know the depth limitations for the brand of instrument she used. Her loggers were placed in the Wakulla Room as I recall (close to, but a bit shallower than 100 m).

You could also ask Pete Butt from KES, he may have some ideas. The good folks at Woods Hole Oceanographic Institution may also be able to help you. They have been doing some work in the QRoo area, but not at the depths you mention. As you probably know there are some Swiss companies that manufacture precision loggers. At the depth you mention, you may be into "a premium price" territory. :sadbanana:
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Re: Velocity or discharge logging underwater caves

Postby gulley.jason » Mar 5, 2013 8:35 am

Jim, thanks for the suggestions. With the exception of the WHOI, I've chatted with the other folks already. This was kind of a last ditch effort to see if anyone else knew of anything else out there.
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Re: Velocity or discharge logging underwater caves

Postby rchrds » Mar 24, 2013 11:30 pm

Jason, Tom Iliffe had a device with three little arms with optical sensors on the end that could calculate flow velocity and direction in multiple planes installed and logging for a year in a cave we mapped in Bermuda. I have no idea what the device cost, I gathered it wasn't cheap, but maybe I remember 15-18k being tossed around? I would ask him. Email me if you need contact info. (Rchrds.caver@gmail.com)
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Re: Velocity or discharge logging underwater caves

Postby rjack » Mar 25, 2013 3:38 pm

Are your springs really "too clear"? We use dopplers in streams with very low suspended solids (1-2 mg/L) successfully.
Here's a rather simple 100m depth rated (wired) one although they don't list a minimum TSS.
http://www.link-quest.com/html/FlowScout2000.pdf
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Re: Velocity or discharge logging underwater caves

Postby gulley.jason » Apr 3, 2013 8:27 am

Jason - thanks for the info. I've actually bought one of the sensors that Tom was using Bermuda. Your price estimate is pretty close, so it quickly becomes expensive to monitor multiple locations. Rjack, one of the locations I was intending to use an ADV is in the Yucatan. Other researchers have reported limited success due to lack of particles. Thanks for the link to the FlowScout, I was not aware of this product.
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Re: Velocity or discharge logging underwater caves

Postby rjack » Apr 3, 2013 12:00 pm

If its "too clear" for an ADV...
Does whatever you choose need to be off the shelf? Maybe you can make or have made something like a Price flow meter (the cupped propellor kind) with an adequate depth rating? (I only know about stream and river gauging and have no idea if the commercial ones would have a suitable depth rating off the shelf)

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Re: Velocity or discharge logging underwater caves

Postby gulley.jason » Apr 3, 2013 7:31 pm

I was mostly looking for off-the-shelf options as I lack the electronics skills to make or adapt sensors. The price meter idea is a good one and has been used to measure ocean current velocity and direction when combined with a fin and an electronic compass. Unfortunately, ADVs have largely replaced these older meters...
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Re: Velocity or discharge logging underwater caves

Postby rjack » Apr 4, 2013 10:49 am

Have you tried swoffer? I'm pretty sure their propellers can go either direction. Positive flow in the 'correct' orientation and negative in the inverse. You'd have to calibrate the propeller for both directions, but that could be a simple excel spreadsheet.
http://www.swoffer.com/ordering.htm

They might be able to make a cable extension for you and whalla budget (wired) flow meter.
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Re: Velocity or discharge logging underwater caves

Postby reece » May 27, 2013 3:52 pm

gulley.jason wrote:Does anyone have experience logging velocity and/or discharge in underwater caves? I'd like to measure changes in discharge in underwater conduits as deep as 100 m as they reverse flow, such as occurs over a tidal cycle. ADVs seem to do a good job making point measurements of velocity, but they are expensive and require particles in the water and some springs are too clear. Many of the cheaper (<$15k) instruments have shallow depth ratings are the loggers are not designed to be placed underwater. If anyone has any suggestions, I'd be keen to hear(read) them.

Thanks,

Jason


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