User Forum of Software BASEMENT

Alyssa

User

From: Aix-en-Provence, France

Registered: 2019-10-28

Posts: 41

How to choose number of grain classes?

Hi

I have a question regarding the decision of choosing the number of grain classes. I am using Wilcock & Crowe transport formula for 1D simulations.
When I run my simulation with 6 grain classes or 9 grain classes (both show the same grain size distribution) for the surface of the bed, the bedload transport is very different. I had the advice earlier from Basement developers that 9 classes is perhaps too much. Would that mean that the bedload transport for the 6 grain classes is more accurate? When I run with D50, again I get very different results.

Perhaps there has been studies on the impact of choosing grain class?
I have a gravel bed river (Rhône) with nearly no sand (98% > 8mm).

Any suggestions to get the fractional bedload transport as accurate as possible?

Thanks

Alyssa

Matteo Facchini

Developer

From: Trento

Registered: 2014-09-05

Posts: 284

Re: How to choose number of grain classes?

Hi Alyssa,
at the end of the day, the number of grain classes you choose defines different interpolations. I have done sometests during my PhD interpolating a grain size distribution with 2 or more grain classes and then calculate the statistics of each interpolated curve. They do change a bit, but the more classes you chosse the slightest the differences are.
From a morphodynamics point of view, single grain and multi grain are 2 different universes (think of the equations that are solved in the two cases...), but I remember that 3 to 5 grain classes are enough to properly describe 1D morphodyncamics.
In the end, you could always do a cost-benefit analysis based on the relation between the number of grain classes you use and the computational cost of your choice.
I hope this helps
Matteo