Anybody know the answer?

[badknees]

I was looking at river flows and found the following:

 
Rio Grande at Lajitas
DATE AND TIME        HEIGHT (ft)    FLOW (cfs)
06/04/2008 13:00 GMT          3.00          367
06/03/2008 13:00 GMT          3.00          367
06/02/2008 13:00 GMT          3.20          403

Terlingua Creek near Terlingua
  DATE AND TIME        HEIGHT (ft)    FLOW (cfs)
06/05/2008 00:15 GMT          3.09           46
06/05/2008 00:00 GMT          3.09           46
06/04/2008 23:45 GMT          3.09           46

Rio Grande at Castolon
 DATE AND TIME        HEIGHT (ft)    FLOW (cfs)
06/05/2008 00:00 GMT          2.64           32
06/04/2008 23:45 GMT          2.64           32
06/04/2008 23:30 GMT          2.64           32


So... my question is, where does all the water go between Lajitas and Castolon Stations? - Golf course?

[SHANEA]

Would it be accounted for by the difference in the width, depth, and elevation of the river?   Each place will have a different flood stage based on factors such as these.  Plus, how long does it take for water measured at Lajitas to actually reach Castolon.  If it is measured at Lajitas on X day, when does it "arrive" at Terlingua - call it Y, then onto Castolon - call it Z. 

Thus, the function of this has to be something along the lines of: River Viscosity

I bet our own VIPER could explain it...    

[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.

[Al]

Study Manning's equation:

http://www.fsl.orst.edu/geowater/FX3/help/8_Hydraulic_Reference/Manning_s_Equation.htm

Al

[badknees]

Study Manning's equation:

http://www.fsl.orst.edu/geowater/FX3/help/8_Hydraulic_Reference/Manning_s_Equation.htm

Al

I looked at it and it still does not explain my question. The equation is used to determine flow rate in CFS if one knows the other variables in the equation, including velocity. I suspect the the roughness factor(frictional drag) is the most difficult variable to input accurately. Flow rate (CFS)  does not change in a channel as a result of cross sectional area. Velocity changes. My question still stands..... the only way to change the flow rate (Q) is to add or subtract volume from the channel. So.... where did the water go?

[Al]

It's all about selecting the right roughness coefficient.  Chow is a God-like figure.

http://www.fsl.orst.edu/geowater/FX3/help/8_Hydraulic_Reference/Mannings_n_Tables.htm

Al

[Al]

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

[badknees]

It's all about selecting the right roughness coefficient.  Chow is a God-like figure.

http://www.fsl.orst.edu/geowater/FX3/help/8_Hydraulic_Reference/Mannings_n_Tables.htm

Al

OK, but question still stands, where did the other 300+ CFS go?

[Al]

Conservation of mass is even a more basic equation.  What goes in must come out.  With regard to open channel flow the only two other variables, I am aware of, is the amount that infiltrates into the ground and the amount of evaporation. When determining the water level in a ditch or river one identifies an up channel restriction such as a narrow portion of the open channel, culvert pipes, a bridge, etc. and then determines how water backs up from there.

Al

[badknees]

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?  

[badknees]

Conservation of mass is even a more basic equation.  What goes in must come out.  With regard to open channel flow the only two other variables, I am aware of, is the amount that infiltrates into the ground and the amount of evaporation. When determining the water level in a ditch or river one identifies an up channel restriction such as a narrow portion of the open channel, culvert pipes, a bridge, etc. and then determines how water backs up from there.

Al

I can buy evaporation,and infiltration, however if there was a significant amount backing up, Santa Elena Canyon would fill up. The difference between Lajitas and Castolon is more than 300 CFS. That is equal to about 193,894,560 gals/day. That is a lot of evaporation and infiltration. Is there something about Santa Elena that would allow that much loss.

I also checked the difference between Castolon and Johnson Ranch and it is only about 6 CFS difference.

[Al]

Based on my limited observations in the desert, water doesn't just flow above the ground.  Fractured or eroded rocks and soil with high permeabilities can allow water to flow in fair abundance beneath ground's surface.  Then a relatively impermeable layer of soil or rock can cause this very same water, that you can't see standing on the ground, to be forced back to up ground's surface where it is observed. 

Al

[badknees]

Based on my limited observations in the desert, water doesn't just flow above the ground.  Fractured or eroded rocks and soil with high permeabilities can allow water to flow in fair abundance beneath ground's surface.  Then a relatively impermeable layer or soil or rock can cause this very same water, that you can't see standing on the ground, to be forced back to up ground's surface where it is observed. 

Al

Good point. That may be the answer. Could Santa Elena drive the flow underground?

[Al]

One has to assume conservation of mass.

Al

P.S. Gravity rules!

[badknees]

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