Flow rate - Discharge Vs Time/Distance

[Korrie]

You have the push and pull forces in the water, combined with the friction of the streambed, gradient etc.
There must be some physics guru's that can provide more light on the subject.

[saml]

This made my day!!!!

I hate weddings, but I love my wife. So I have to join her when she takes snaps at a wedding.
So at this one wedding from the script of "The Bride of Chucky" I was seated next to this lady that just has to know everything about everyone. So she kept asking questions about the photos and do we see a lot of weddings and do we this and do we that. I answered politely everytime. And then she asks "So what do you do for a living"? I knew I wasn't going to shake this lady, so I said " No one believes me if I tell them I am an Assassin, so I tell them that I am a Gynecologist. So what would you like me to do for you Today? Do you need someone taken out or do you want to book a Papsmeer? Took the lady a while to get her ducks in a row and then she asked " Are you serious, you just said that you put stickers on a boat". I replied "Yes I do work undercover from time to time".

So back to your question. The flow is 20m3/s, it increases to 70m3/s.
So 50km downstream the water is already flowing at 20m3/s. So to get to the 70m3/s, the floodgate actually adds 50m3/s. So how long will 50m3/s take to get down to the 50km mark?

There is a 1000m in one Kilometer
There is 60 seconds in a minute and 60 minutes in an hour.

So 50m3/s would have moved 3000 meter in one minute.(50m3/s x 60 seconds = 3000 meter/ minute)
And then 180 000 meter in one hour (3000 meter/min x 60 minutes = 180 000m/hour)
So 180 000 meter / 1000 = 180km is what that water would have traveled in just one hour.
So if I then go and break 180km up into 60 minute segments the water travels at 3km/minute.
50km devide by 3km/minute = 16.667 minutes for that water to reach you.

This is how I see it.

Koos Eckard - Assassin (aim small, miss small)

Woah Woah Woah, this is all wrong. The flow rate is measured in cubic meters per second. (volumetric flow rate) If that flow rate was passing through a small pipe the water would be bliksemming at breakneck speeds and then maybe it would travel 3km per minute (180km/hr!!!) , but since its passing through a nice wide and deep river the velocity of the water is much less.

Redhumpy you need to know the cross sectional area of the river at the barrage to work out the speed that the water is travelling at. Lets say (for arguments sake) at the barrage the river is 50m wide and 2m deep then the cross sectional area is 100m2. So divide flow rate (m3/s) by area (m2) and you will get velocity of water. so 70/100 = 0.7m/s which equals 2.5 km/hr so to go 50km it will take 20 hours.

This is assuming that the cross sectional area of the river stays at 100m2, which it obviously doesn't, but its a start for a rough estimate.
Plus its assuming that the barrage is 50m wide by 2m deep which it also isn't. but that's how you would work it out.

Without knowing the cross sectional area, if you only have the flow rate there is no way to work out water speed.

[Reveck Hariram]

The best guestimate would be looking at the graphs I have on the page one. The average speed works out 2.5km/hr (70km/28.2hrs)

[Andre]

Correct..absolutely. Cubic meters per second, is only the volume of water passing through a single location, in a second.. The wider the river, the slower the flow. It has nothing to do with speed. Its impossible to calculate the average speed of the water over a distance, unless there is a lot more information. If it is 20 cubic meters per second, or 200 cubic meters per second, it is still likely to flow at the same speed, due to the speed of the water flow being dependent on gravity. Its the Newton theory, where more water is heavier than less water, but a heavy object and a light object, fall to earth at the same rate. So therefore, lots of water, or a little bit of water, will flow at the same speed. My estimate of the speed of the flow on the Vaal, would be about 15km per day..give or take...just an estimate.

Woah Woah Woah, this is all wrong. The flow rate is measured in cubic meters per second. (volumetric flow rate) If that flow rate was passing through a small pipe the water would be bliksemming at breakneck speeds and then maybe it would travel 3km per minute (180km/hr!!!) , but since its passing through a nice wide and deep river the velocity of the water is much less.

Redhumpy you need to know the cross sectional area of the river at the barrage to work out the speed that the water is travelling at. Lets say (for arguments sake) at the barrage the river is 50m wide and 2m deep then the cross sectional area is 100m2. So divide flow rate (m3/s) by area (m2) and you will get velocity of water. so 70/100 = 0.7m/s which equals 2.5 km/hr so to go 50km it will take 20 hours.

This is assuming that the cross sectional area of the river stays at 100m2, which it obviously doesn't, but its a start for a rough estimate.
Plus its assuming that the barrage is 50m wide by 2m deep which it also isn't. but that's how you would work it out.

Without knowing the cross sectional area, if you only have the flow rate there is no way to work out water speed.

[smallstreams.co.za]

Kan iemand nie maar net 'n dobbertjie iewers ingooi en time hoe lank hy vat tot by die volgende punt waar jou mater hom uithaal nie???? Dis amper vakansie, ek is seker daar sal 'n paar dronk studente wees wat dit sal toets.

[E.T.]

Kan iemand nie maar net 'n dobbertjie iewers ingooi en time hoe lank hy vat tot by die volgende punt waar jou mater hom uithaal nie???? Dis amper vakansie, ek is seker daar sal 'n paar dronk studente wees wat dit sal toets.

En wie gaan die dronk studente uit die water red?

[smallstreams.co.za]

En wie gaan die dronk studente uit die water red?

Nie nodig - vra hom hoe ver hy gedryf het en hoe lank dit hom gevat het. Dan het jy dinamiese data en nie statiese data nie.

[E.T.]

Nie nodig - vra hom hoe ver hy gedryf het en hoe lank dit hom gevat het. Dan het jy dinamiese data en nie statiese data nie.

Drank, Studente, Data en Vaal......baie gevaarlik.
Elke jaar verdrink 'n lot van hulle op die Vaal.

[Scythe]

Duidelik nie genoeg nie ...

[Korrie]

Correct..absolutely. Cubic meters per second, is only the volume of water passing through a single location, in a second.. The wider the river, the slower the flow. It has nothing to do with speed. Its impossible to calculate the average speed of the water over a distance, unless there is a lot more information. If it is 20 cubic meters per second, or 200 cubic meters per second, it is still likely to flow at the same speed, due to the speed of the water flow being dependent on gravity. Its the Newton theory, where more water is heavier than less water, but a heavy object and a light object, fall to earth at the same rate. So therefore, lots of water, or a little bit of water, will flow at the same speed. My estimate of the speed of the flow on the Vaal, would be about 15km per day..give or take...just an estimate.

Andre
You also have the push factor of the water mass,