User Forum of Software BASEMENT

Alyssa

User

From: Aix-en-Provence, France

Registered: 2019-10-28

Posts: 41

Sand franction (Fs) within Wilcock & Crowe formula

Hi

I notice a difference in manual calculations for bedload transport using Wilcock & Crowe compared to the Basement results. One reason could be the use of the non linear effect of Fs calculated in Basement (which was not used in the manual calculations).

Could anyone tell me how Fs is determined in Basement?
My GSD has not really sand (lowest grain class is D=2.8mm), would this mean it calculates Fs=0?

Any other processes I am missing that Basement incorporates that could affect the bedload transport as different from the manual calculations?

Thanks!
Alyssa

Matteo Facchini

Developer

From: Trento

Registered: 2014-09-05

Posts: 281

Re: Sand franction (Fs) within Wilcock & Crowe formula

Hi Alyssa,

if there is no sand the formula considers Fs=0. Refer to the manual (or to Parker's ebook) to see how the formula was implemented.

How did you test it? I think the best way would be to simulate uniform flow in a rectangular channel, otherwise the hydraulics is way to complicated to be approximated with manual calculations.

Cheers
Matteo

Alyssa

User

From: Aix-en-Provence, France

Registered: 2019-10-28

Posts: 41

Re: Sand franction (Fs) within Wilcock & Crowe formula

Hi Matteo

Thanks for the quick reply.
Yes I used a rectangular channel. I used first a hydrograph, but then confirmed with a uniform flow for each Q (which gives the same result as the hydrograph for each Q in the hydrograph).
If I count Fs=0, the difference becomes even larger between calculations/model.

cheers
Alyssa

Matteo Facchini

Developer

From: Trento

Registered: 2014-09-05

Posts: 281

Re: Sand franction (Fs) within Wilcock & Crowe formula

What I meant is that I would do the test using a single value of Q, check if uniform flow conditions are reached and in that conditions check the results against yout manual calculations.

Which basement output are you looking at?

Alyssa

User

From: Aix-en-Provence, France

Registered: 2019-10-28

Posts: 41

Re: Sand franction (Fs) within Wilcock & Crowe formula

Yes that's what I did. I tested with single values of Q until uniform flow is reached. I checked different flows, and I see that it is not really different from bedload simulated when using the hydrograph (which is good).
I'm looking at the out.dat file, total bedload flux, and fractional per grain size (6 classes). It's a rectangular reach, fixed slope- although it doesn't vary much over the reach, I take an average over all cross sections.
Is there a better way?

Matteo Facchini

Developer

From: Trento

Registered: 2014-09-05

Posts: 281

Re: Sand franction (Fs) within Wilcock & Crowe formula

Nope, what you do is correct. I am wondering what could be wrong. Do the results differ very much? If you want you can upload the file with your calculations somewhere, provide a link so I can have a look at your calculations

Alyssa

User

From: Aix-en-Provence, France

Registered: 2019-10-28

Posts: 41

Re: Sand franction (Fs) within Wilcock & Crowe formula

Hi
I found a silly mistake in my graph. With Fs=0 the results are basically the same now.
Thanks!

Matteo Facchini

Developer

From: Trento

Registered: 2014-09-05

Posts: 281

Re: Sand franction (Fs) within Wilcock & Crowe formula

Hey, that's actually good news
Cheers