Anybody know the answer?

[Al]

Badknees, there are also errors in measurement, that could a least partially account for your consternation. 

I still think you should be called PrettyDarnedGoodKne es, all things considered. 

Al

[jamesb]

sometimes the answer is very simple.

Its all the terrorist camps being set up on the other side of the river. why else would the national guard be fixin up the river road?


James

[SHANEA]

OY i just had a whole class on this 

the water can be flowing at the same rate, but if the cross-sectional area is different, then the CFS will be different.

Well, what are you waiting for...   

[Hoodoo]

One has to assume conservation of mass.

Al

P.S. Gravity rules!

Thanks, FYI below

http://www.srh.noaa.gov/wgrfc/stat_map/bigbendTXzm.shtml

Bad Knees
I have seen similar discrepancies with other gauges depending on the source of information. The link you posted also suggests an increase of  267 CFS between the Presidio gauge located below the Rio Conchos and Lajitas. 

The same source but a different page in their website shows the flow at Lajitas to be 0.0136 KFS or 13.6 CFS for a stage of 3 ft.

Lajitas Tabular Data

I don’t know if 13.6 CFS is any more accurate than 367 CFS but I am highly suspicious of 367 CFS being accurate for the current stage level. 

[01ACRViper]

Badknees, to the best of my knowledge, Manning's equation is what is used even to this day. What do you think is the right equation?

Al

Al,

Respectfully, I believe you are missing the point. I have no problem with the equation, actually, I agree with it.

The equation is used to estimate the flow rate by looking at the shape of the channel (gives cross sectional area), and the velocity which is measured by a mechanical flowmeter.

If you multiply the flowrate in ft./sec by the cross sectional area of the channel in sq. ft. you arrive at a flow rate in cu. ft./sec (CFS). This is adjusted by a drag coefficient because you can't practically measure the velocity at all points within the channel, ie. sides and bottom.

So flow rate Q, is a physical volume of water passing through the channel at a specific place in 1 sec.


Now....if there is 327 CFS passing through the channel in Lajitas, and some more coming in from Terlingua Creek, why is there only 32 CFS passing through the channel at Castolon? 

oh but you can measure the flow rates at all parts of the channel 

acoustic doppler velocimeter

[01ACRViper]

OY i just had a whole class on this 

the water can be flowing at the same rate, but if the cross-sectional area is different, then the CFS will be different.

Well, what are you waiting for...   

after all the work i did in there, i'm not eager to rip out my notes and work out the answer :o

[01ACRViper]

could it be as simple as the slope of the river has changed, causing it to flow less quickly? 

[badknees]

oh but you can measure the flow rates at all parts of the channel 

acoustic doppler velocimeter

Granted, however most of the gauging stations are stand alone remotes at a single point in the channel.

[01ACRViper]

oh but you can measure the flow rates at all parts of the channel 

acoustic doppler velocimeter

Granted, however most of the gauging stations are stand alone remotes at a single point in the channel.

when they first installed the station, they did a complete survey of the river using and ADV or another technique. they did this to get a velocity distribution. using this velocity distribution and manning's equation, they can computer discharge. They compute the discharge at several gauge heights to get a rating curve. this is just a graphical representation of the relationship between gauge height and discharge, it is different for every point along every river.

once they have this rating curve, all they need to do is find gauge height to computationally arrive at discharge. these stations most commonly use a bubbler, just a air pump and tube that forces air to the bottom of the river, and using known pressure constants calculates the depth. then they have the discharge. measure one thing, use that info to compute more things.

ok, now i'm just rambling. i really think infiltration into ground water and a greatly reduced slope is to blame for the loss in discharge. the water is still there, just flowing more slowly.

the rio grande is a losing river, that is, the water table is disconnected from it, and water from the river drains by gravity into the ground. this can lead to enormous drops in water volume.

[Al]

Exactly and the gaging stations are at a restriction such as a bridge.

Al

[01ACRViper]

sorry, i edited to be a little more thorough 

[SHANEA]

sorry, i edited to be a little more thorough 

You seem to be doing very good their w/o your notes.     What was the name of your professor, I'll email him and link him to the site to see how well you have done...   

[Hoodoo]

I agree with all of the above, however personal experience makes me suspicious of 367 cfs for a 3 ft.   gauge height at Lajitas.

Viper, your mission, should you choose to accept it, is to take an acoustic doppler velocimeter and perform a complete survey of the river gauge at Lajitas in order to determine the actual flow rate for a gauge height of 3 ft. Should any team member be caught or detained, any knowledge of your actions would be disavowed. Good luck, this message will self destruct in five seconds. 

[badknees]

I agree with all of the above, however personal experience makes me suspicious of 367 cfs for a 3 ft.   gauge height at Lajitas.

Viper, your mission, should you choose to accept it, is to take an acoustic doppler velocimeter and perform a complete survey of the river gauge at Lajitas in order to determine the actual flow rate for a gauge height of 3 ft. Should any team member be caught or detained, any knowledge of your actions would be disavowed. Good luck, this message will self destruct in five seconds. 

I think you are right to be suspect. The below comes from the BIBE daily report. Looks like somebody gerfingerpokened a decimal point!

River Levels
Flood Stage Today Yesterday
Presidio International Bridge 15.50 3.50ft/47 cfs 3.58ft/61 cfs
Lajitas 15.00 3.00 ft 3.00 ft
Castolon 15.00 2.63 ft/31 cfs 2.63ft/31 cfs
Johnson’s Ranch 15.50 2.55ft/26 cfs 2.57ft/30 cfs
Rio Grande Village 13.00 1.40ft/24 cfs 1.48ft/28 cfs
Dryden Crossing 59.00 2.90ft/97 cfs 2.93ft/101 cfs

[SHANEA]

I agree with all of the above, however personal experience makes me suspicious of 367 cfs for a 3 ft.   gauge height at Lajitas.

Viper, your mission, should you choose to accept it, is to take an acoustic doppler velocimeter and perform a complete survey of the river gauge at Lajitas in order to determine the actual flow rate for a gauge height of 3 ft. Should any team member be caught or detained, any knowledge of your actions would be disavowed. Good luck, this message will self destruct in five seconds. 

Could be your Doctoral Dissertation.  See, we've already got the hardest part done for you - what are you going to research - what's the topic going to be.  Some Nobel Prize Winning work titled "Flow Rates of the Rio Grande Between Lajitas and Castolon".

Dr. Viper.  Has a nice ring to it...