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Hi There,

I am very new to modelling and I have some question on depth average velocity.

I have a set of field measurement current data measured in 6 layers, which are surface layer, 0.2H, 0.4H, 0.6H, 0.8H and bottom layer. The field measurement is used to calibrate the model. The question is, how could I find the depth average current of my field measurement in order to calibrate the depth average velocity produced by TELEMAC2D? Is it average out the current measurement at 6 layers?

Thanks for the reply.
Have a nice day!

Hi Angie,

If you cannot have more measurements over the water column, the arithmetic average of you 6 values is a correct estimator for depth average velocity. But are you sure you have measurement at the bottom layer, or a little bit higher? Same question for the surface layer (a little bit deeper?).

Regards,

Chi-Tuan

Hi Chi-Tuan,

Thanks for your reply.

I take the measurement slightly higher than the bottom bed and slightly lower than the water surface.

Another questions, if I have more current data along the water column, what kind of method I can used to get a more accurate depth-average velocity? Is it by using the vertical velocity graph?

Really thanks for the help.

Have a nice day!

Hi Angie

You could integrate the velocity along the vertical axis and then divide the result by the water height.

Hope this helps

Sorry coulet... Can you explain further? Integrate the function of V to Y?

You wrote you know the velocity in various level between 0 and free surface.
If you integrate this velocity between 0and the free surface and then you devide by the water height you obtain an average velocity.
It's just a mathematical point of view on how to compute an average.

Regards

Oh I See!
Has been thinking too deep on it already. Thanks for reminding me...
Appreciate..
Thanks! =)

Hi,
you can use too a logarithmic profile to interpolate your data and get an averaged velocity from it.

Emile

Thank you all the suggestions.

Is it the same method to find the depth average direction? (Sum up all the layer's current direction and divide it by the number of data?

Hi Angie,

To calculate depth averaged direction (or depth averaged magnitude), you have to first calculate depth averaged components of velocity u and v (with one methodology described before), and then calculate magnitude as square root of u^2+v^2 (scalar velocity in TELEMAC) or direction as atan2(v,u). Depth averaged direction is not the average of directions over the vertical.

Regards,

Chi-Tuan