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# River Discharge. Rate/Velocity of the river? Watch

1. Hi there,

The definition of river discharge is stated as:

'The volume of water passing a measuring point or gauging station in a river in a given time. It is measured in cubic metres per second (cumecs).'

However, I am unable to get my head around it. Is it basically the velocity of a set volume of water?
As, as far as I am aware, when the discharge increases, the rate of flow increases.

Thanks for you time,

Xetter
2. (Original post by Xetter)
Hi there,

The definition of river discharge is stated as:

'The volume of water passing a measuring point or gauging station in a river in a given time. It is measured in cubic metres per second (cumecs).'

However, I am unable to get my head around it. Is it basically the velocity of a set volume of water?
As, as far as I am aware, when the discharge increases, the rate of flow increases.

Thanks for you time,

Xetter
Discharge simply, is the amount of water in the river at a given time.
3. (Original post by K-Fox)
Discharge simply, is the amount of water in the river at a given time.
But as it's units are ms-3 it has somthing to do with velocity right?
4. It's related to velocity, but not the same thing. The units for discharge - metres cubed per second - include the concept of volume. So the discharge is the volume of water passing a given point at any one time, standardised to be in cubic metres/second.

discharge increases with increased flow velocity, but that's not the only thing affecting discharge - the volume of water at the relevant point in the channel is also possitively correlated with discharge.
5. Don't know if I will help but this is how I view;

Discharge is the function of: Volume x Time

Now, we cannot measure the discharge of a river looking at the ENTIRE river. That would hard, as it would mean having to measure theoretically at EVERY POINT on the river.

The way us hydrologist calculate the DISCHARGE, is to use a CROSS-SECTION of the river. This is a singular points (normally before a confluence or before the sea) and split it up into metre2 areas.

Then we use the "Velocity-area cross-section plot" to calculate the volume (below)

V = Velocity (m/s)
A = Area (m2)

So, then the equation would be:

Q = (V1 * A1) + (V2 * A2) + (V3 * A3) + (V4 * A4) + (V5 * A5) + (V6 * A6)

Q = Discharge (m3/s)

Hope this helps...

Key points.

To answer you question: Discharge can increase because of 2 reasons;
- The velocity of the river has increased
or
-The area of the river has increased - HOWEVER, the area of the river will increase (widen) due to the increased discharge as it needs to accommodate for the increased volume of water.

Hope this helped!

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Updated: March 11, 2016
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